Carcass Characteristics

The importance of carcass characteristics and meat quality were recognized as a priority for improvement,27 and several breeds followed the lead of the American Angus Association and began collecting carcass data as early as 1974.

From: Animal Agriculture , 2020

Pasture-finished beef production in the south

Matt Poore , ... Sarah Blacklin , in Management Strategies for Sustainable Cattle Production in Southern Pastures, 2020

Carcass characteristics of steers from different breed types

Carcass characteristics and rib section parameters of the same steers harvested at the end of the winter grazing periods are shown in Table 10.5. In general, the data demonstrated the expected differences between the beef breeds, a dairy breed, and a nontraditional beef breed: the beef breeds had more fat, greater ribeyes, smaller KPH (kidney, pelvic and heart fat), and less bone.

Table 10.5. Carcass characteristics from steers of different breed types at the end of winter grazing (April/May).

Breed type Live BW (lb) Carcass Wt. (lb) Dressing (%) Skeletal maturity Lean maturity Marbling score Fat thickness, in. REA (sq in.) KPH (%)
Angus 974 510 52.4 A50 A50 307 0.19 9.2 0.92
Brangus 938 502 53.5 A50 A50 283 0.16 9.4 0.89
Holstein 1098 547 49.7 A60 A60 293 0.07 8.0 1.17
Pineywoods 670 352 52.5 A60 A60 293 0.07 8.1 1.75

REA, ribeye area; KPH, kidney, pelvic and heart fat.

We are unaware of any other published carcass data with regard to Pineywood (Criollo) cattle. Of these cattle harvested at the end of the winter grazing period, Pineywoods had the greater KPH as a percent of the 9–11 rib section than any other breed type. They also had a lean percent that was greater than the beef breeds and similar to Holstein. Their percent fat was intermediate, and percent bone was similar to Angus and Brangus.

Carcass data obtained at the end of the summer grazing period after a yearlong finishing period followed a similar pattern as the data obtained after the winter grazing season (Table 10.6). As expected, greater carcass weight, marbling scores, ribeye area, and KPH were observed as an effect of increased maturity (18–19 months of age). Even greater carcass weight, ribeye area, and marbling score would be expected if the steers had remained for another winter grazing season. However, many small producers in the Gulf Coast region cannot retain steers for a second winter, as they already have a new group of steers starting the yearlong finishing period after weaning (October).

Table 10.6. Carcass characteristics from steers of different breed types at the end of summer grazing (September/October).

Breed type Live BW (lb) Carcass Wt. (lb) Dressing (%) Skeletal maturity Lean maturity Marbling score Fat thickness (in.) REA (sq in.) KPH (%)
Angus 1145 621 54.2 A50 A50 372 0.27 10.4 1.30
Brangus 1137 646 56.9 A50 A50 420 0.31 10.6 2.50
Holstein 1200 635 53.0 A50 A60 350 0.04 8.7 1.75
Pineywoods 754 421 55.8 A60 A60 360 0.10 9.8 3.00

REA, ribeye area; KPH, kidney, pelvic and heart fat.

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Biology and regulation of carcass composition

P.L. Greenwood , F.R. Dunshea , in Improving the Sensory and Nutritional Quality of Fresh Meat, 2009

2.6 Genotypic influences on carcass composition

Domesticated ruminants and pigs have been selected for traits including survival and reproductive capacity, growth rate, muscularity, yield of meat, and eating quality characteristics including intramuscular fat content. In this section we provide a brief overview of effects of breed, quantitative selection, single genes with large effects, and of gene markers, on carcass characteristics in livestock. We also refer to recent research in sheep that has used estimated breeding values for growth, muscling and fatness to assess genotypic effects within differing production environments. More specific details of genotypic effects are provided in Part II ( Chapters 9 to 13 Chapter 9 Chapter 10 Chapter 11 Chapter 12 Chapter 13 ) of this book, and the reader is also referred to earlier reviews of the genetics of carcass and quality traits of pork (Sellier, 1998; Rohrer, 2001), sheep meat (Banks, 1997; Thompson and Ball, 1997) and beef (Marshall, 1999; Cundiff, 2006).

Highly selected livestock, such as European cattle breeds, display productive advantages in more temperate climates within highly managed systems, whereas tropically adapted animals such as Bos indicus cattle and various sheep and goat breeds have the capacity to survive and produce in hotter and/or more humid environments in which other types perform poorly. For example, Bos indicus breeds survive well in the tropics and produce a high proportion of lean beef from their carcass, although they do produce somewhat tougher meat than Bos taurus cattle (Thompson, 2002).

Substantial genotypic advantage conferred by using specific breeds of livestock may be captured by the use of pure-bred herds or flocks (for example, Dorset v Suffolk sheep: Beermann et al., 1995), terminal sires (for example, Piedmontesev Wagyu-sired cattle: Greenwood et al., 2006a), or within composite herds comprising animals with defined proportions of genetic material from specific breeds or genotypes. Industry-based breeding and selection programs within and across improved breeds of livestock utilise quantitative selection techniques and progeny testing to improve traits of interest such as growth, muscling, fatness, marbling, survival and reproduction. Increasingly, these programs are looking to incorporate effects of gene markers into their data bases (Nicholas, 2006).

Examples of breeds or genotypes of livestock with more extreme carcass characteristics include:

•

European breeds of cattle that are late-maturing and display high degrees of muscling, in some cases associated with mutations resulting in non-functional myostatin and extreme levels of muscling, for example, Belgian Blue and Piedmontese cattle (Bellinge et al., 2004);

•

Wagyu and Hanwoo cattle from Japan and Korea, respectively, that produce highly marbled beef (Pethick et al., 2004);

•

Texel sheep which have a mutation in the myostatin gene that causes translational inhibition of the mRNA into myostatin, resulting in high muscling (Laville et al., 2004; Clop et al., 2006);

•

Callipyge sheep, which have a mutation which, when present in heterozygous offspring that inherit the mutation from their sire, produces extreme muscling, particularly of the hindquarters, but which is associated with extremely tough meat (Freking et al., 2004);

•

Pietran pigs that have high levels of muscling (Sellier, 1998).

The most extreme effects of specific genes on carcass characteristics result in double muscled cattle and the Callipyge sheep phenotypes. Although mutations for these genes result in increased muscularity, their specific causes and effects differ substantially, as summarised in Table 2.5.

Table 2.5. Comparison of characteristics of Callipyge sheep and double-muscled cattle

Callipyge sheep Double-muscled cattle
Specific cause Uncertain (DLK-1 involved) Myostatin (GDF8) mutation (non-functional myostatin)
Location of single nucleotide polymorphism(s) Ovine Chromosome 18 Bovine chromosome 2 (Ovine chromosome 2) 1
Genotype resulting in mutant phenotype Heterozygote with mutant allele inherited from sire (polar overdominance) Homozygous for mutant allele (heterozygote has intermediate phenotype)
Phenotypic expression Primarily postnatal Prenatal and postnatal
Location of muscle hypertrophy Hindquarter and loin More generalised
Myofibres of affected muscles (cf. normal) No hyperplasia Hyperplasia
More type 2X More type 2X
Far less type 2A Less type 2A
Less type 1 in some affected muscles
Type 2 hypertrophy May have type 2
Hyperplasia hypertrophy depending on mutation and genetic background of cattle
More glycolytic More glycolytic
Predominant mechanism in enhanced muscle growth Reduced protein degradation (more calpastatin) Increased protein synthesis
Meat quality (cf. normal) Much tougher, pale Similar or more tender, pale
1
Mutation in Texel breed of sheep which affects translation into myostatin protein.

Recent studies have assessed the use of sires with a range of Australian sheep breeding values (ASBVs) for muscling (eye muscle depth), fatness (subcutaneous fat depth) and growth (post-weaning weight) on a broad range of commercial, cellular, and biochemical measures (Table 2.6). Furthermore, associations of ASBVs with factors including age, live weight, carcass weight, gender of offspring, and nutrition have also been assessed (Hegarty et al., 2006; Warner et al., 2007). This approach to understanding influences of quantitative selection for traits differs from previous single-trait selection line studies by assessing effects across a continuum of breeding values for a trait (for example, muscling), while accounting for effects of breeding values for other associated traits (for example, growth and fatness). Among the numerous experimental, single-trait selection lines are those for growth rate or weaning weight (Thompson et al., 1985a,b,c; Parnell et al., 1986; Oddy and Sainz, 2002), fatness (Abdullah et al., 1998), muscularity (Cafe et al., 2006c) and net feed efficiency (Arthur et al., 2004).

Table 2.6. Effects of increasing the estimated breeding values of sires for post-weaning eye-muscle depth (PEMD) on major growth and carcass characteristics of lambs

Unaffected Positively affected Negatively affected
Post-weaning LWG A Slaughter weight (0.59 kg) A
Carcass EMD (0.61 mm) A Carcass C-fat depth (–0.136 mm) A
Conformation score (0.03–0.85) A B
Carcass protein (0.037 kg) B
Four hindquarter muscles (0.021 kg) B
Radius, ulna lengths C Proportion of lean in carcass (0.015) C Proportion of bone in carcass (–0.022) C
Bone mid-shaft width C Carcass muscle to bone ratio (0.20) C
RNA:DNA in muscle (0.351) D DNA concentration in muscle (–10.2 μg/g) D
Protein:DNA in muscle (24.9) D
Total protein in muscle (1.29 g, semimembranosus) (3.17 g, longissimus) D
% type 2X myofibres (0 to 2.14) E % type 2A myofibres (0 to −1.29) E
Cooking loss Connective tissue seam thickness (219 μm) F Muscle fascicle width (–0.27 mm) F
Longissimus shear force G Longissimus IMF% (–0.11) G
Meat colour (L,a,b∼) G Overall consumer liking (–1.32) G
A
Hegarty et al. (2006a);
B
Hegarty et al. (2006b);
C
Cake et al. (2006);
D
Greenwood et al. (2006c);
E
Greenwood et al. (2006b), range indicates muscle × EBV interaction;
F
Allingham et al. (2006);
G
Hopkins et al. (2005). ∼ Colour assessed approximately 24h after slaughter and 30–40 min after cutting.

(adapted from Hegarty et al., 2006c). Regression coefficients are provided for each trait significantly affected (P<0.05) by PEMD within multifactor analyses

Copyright © 2006

Use of sires with greater ASBVs for muscling (eye muscle depth) increased slaughter weight and proportion of lean while reducing subcutaneous fat depth and the proportion of bone in the carcass (Table 2.6). This results in an increase in carcass conformation score and the muscle-to-bone ratio (Cake et al., 2006), which is consistent across ages ranging from 4 to 22 months (Warner et al., 2007). This advantage of high muscling breeding value and the growth advantages due to high sire ASBV for post-weaning weight were maintained within low and high nutritional systems. In contrast to increased muscularity at any given weight that is generally associated with large mature size within breeds and strains of sheep (Black, 1983; Beermann et al., 1995), offspring of sires selected using ASBVs for eye muscle depth had reduced mature weight, which was particularly associated with the skeleton (Warner et al., 2007).

Increasing sire breeding values for muscling also increased the percentage of type 2X (fast glycolytic) myofibres (Greenwood et al., 2006b) and connective tissue seam thickness (Allingham et al., 2006), and reduced the percentage of type 2A (fast oxidative–glycolytic) myofibres (Greenwood et al., 2006b). Furthermore, the intramuscular fat content (Hopkins et al., 2005) declined, and there was a reduction in consumer acceptance of meat (Hopkins et al., 2005) with increased breeding value for muscularity. These latter findings are consistent with those for pigs genetically selected for greater eye muscle area, which also has adverse consequences for eating quality associated with an increasing proportion of fast glycolytic myofibres (Rehfeldt et al., 2000; Fiedler et al., 2004). They suggest that continued genetic selection for muscling should incorporate eating quality characteristics and may also need to include myofibre characteristics within indexbased genetic selection programs if acceptable eating quality is to be maintained while increasing meat yield. It was also evident that site-specific genetic selection for increased muscling has differing affects across different muscles (Greenwood et al., 2006b,c), with implications for compositional and eating quality characteristics (Hegarty et al., 2006).

Marker-assisted selection has been made possible through the development of molecular technologies that allow identification of specific gene markers or single nucleotide polymorphisms (SNPs) for commercially important traits. A detailed history of developments in the search for DNA markers is provided by Nicholas (2006). The search for SNPs in ruminants was enhanced by development of the bovine gene map, which was made possible through the identification of quantitative trait loci (QTL) using microsatellite markers on specific chromosomal regions, the development of linkage and radiation-hybrid maps covering a large proportion of the genome coupled with loci physically mapped using in situ hybridisation, and the use of Location Database (LDB) to integrate this information. Identification of markers in or near specific genes has been possible using fine-mapping of QTL, although identification of the causative quantitative trait nucleotide (QTN) has occurred infrequently due to difficulties in their identification, as detailed by Nicholas (2006).

DNA sequencing of the bovine genome and the advent of large-scale, high throughput detection and SNP genotyping now allows for genome-wide studies to determine the association of SNPs with commercially important traits (Hawkin et al., 2004). Differential expression of genes using, in particular, microarrays containing many thousands of genes, is also used as a means of identifying important genes (Lehnert et al., 2006a,b, 2007) and gene networks (Reverter et al., 2006) that regulate development of carcass tissue traits and their response to the environment. More recently, these developments have allowed for expression QTL (eQTL) studies to be undertaken in which microarray profiling is integrated with high throughput SNP genotyping to allow for a detailed molecular phenotype to be rapidly linked to a genome region responsible for a specific trait (Lehnert et al., 2006b).

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Quality Evaluation of Meat Cuts

Liyun Zheng , ... Jinglu Tan , in Computer Vision Technology for Food Quality Evaluation, 2008

1 Introduction

Currently meat quality is evaluated through visual appraisal of certain carcass characteristics, such as marbling (intramuscular fat), muscle color, and skeletal maturity. Although the visual appraisal method has been serving the meat industry for many years, the subjective evaluation leads to some major intrinsic drawbacks, namely inconsistencies and variations of the results in spite of the fact that the graders are professionally trained ( Cross et al., 1983). This has seriously limited the ability of the meat industry to provide consumers with products of consistent quality, and subsequently its competitiveness.

As there is always a desire from the meat industry for objective measurement methods, many research efforts have been devoted to developing instruments or devices. One obvious and popular approach is to measure the mechanical properties of meat as indicators of tenderness, with the most well known perhaps being the Warner-Bratzler shear-force instrument. For cooked meat, the shear strength correlates well with sensory tenderness scores (Shackelford et al., 1995); however, such a method is not practical for commercial fresh-meat grading.

To overcome this problem, one of the most promising methods for objective assessment of meat quality from fresh-meat characteristics is to use computer vision (Brosman and Sun, 2002; Sun, 2004). Recently, applications of computer vision for food quality evaluation have been extended to food in many areas, such as pizza (Sun, 2000; Sun and Brosnan, 2003a, 2003b; Sun and Du, 2004; Du and Sun, 2005a), cheese (Wang and Sun, 2002a, 2002b, 2004), and cooked meats (Zheng et al., 2006a; Du and Sun, 2005b, 2006a, 2006b). However, for fresh meats, research began in the early 1980s. For example, Lenhert and Gilliland (1985) designed a black-and-white (B/W) imaging system for lean-yield estimation, and the application results were reported by Cross et al. (1983) and Wassenberg et al. (1986). Beef quality assessment by image processing started with the work by Chen et al. (1989) to quantify the marbling area percentage in six standard USDA marbling photographs, and later on McDonald and Chen (1990a, 1990b) used morphological operations to separate connected muscle tissues from the longissimus dorsi (LD) muscle. For quality evaluation of other fresh meat, such as pork and lamb, early studies were performed by Kuchida et al. (1991) and Stanford (1998). The composition (fat and protein %) of pork were analyzed based on color video images (Kuchida et al., 1991) and video-image analysis was also used for on-line classification of lamb carcasses (Stanford, 1998). Since then, research has been progressing well in this area.

To develop a computer vision system (CVS) for objective grading of meat quality, several steps are essential. Although the existing human grading system has many intrinsic drawbacks, any new systems designed as a replacement must still be compared with the human system before they can be accepted. Furthermore, the existing human grading system is qualitative, whereas the quantitative characteristics that contribute to the human grading are not always obvious. Therefore, it is necessary to search for image features that are related to human scores for marbling abundance, muscle color, and maturity – and, eventually, official grades such as USDA grades. Moreover, to improve the usefulness of the grading system, new instrumentally-measurable characteristics are needed to enhance the power of the grades in predicting eating quality, such as tenderness.

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Nutrition and Feeding Management to Alter Carcass Composition of Pigs and Cattle

Virgil W. Hays , Rodney L. Preston , in Low-Fat Meats, 1994

II Impact of Energy Level

The most common and readily demonstrated effects of nutrition on carcass characteristics relate to biologically available energy (e.g., metabolizable energy) intake relative to intake of other essential nutrients. In pigs the metabolizable energy intake, the protein (essential amino acids) intake, and protein-to-energy ratio in the diet have marked effects on carcass composition at a standardized body weight. The related effects of protein and energy are not simple. Excess protein may be utilized almost as efficiently as carbohydrates for energy purposes. This is apparent from the estimated energy values of feedstuffs (National Research Council, 1984, 1988b; Ewan, 1991) and the rates of body weight gain and fat deposition on high protein diets as reported by Wagner et al. (1963). The metabolizable energy values of the high protein ingredient soybean meal are very similar to those of the high-carbohydrate ingredient corn (3.15 vs 3.25 and 3.76 vs 3.84 Mcal/kg for cattle and pigs, respectively). The differences are somewhat greater in terms of net energy values. For beef cattle the net energy values (Mcal/kg) for gain are 1.48 and 1. 55 for soybean meal and corn, respectively; and for pigs the respective net energy values are 1.96 and 2.58.

If adequate energy in the form of carbohydrates or fat is not provided, the animal will utilize protein for energy purposes at the expense of protein accretion. These interrelationships are exemplified in pigs by studies of Cunningham et al. (1962) as summarized in Table I. The low level of feeding (1.60   kg/day) of the low protein diet was inadequate in protein or energy for maximum protein retention. At this level of feeding, protein was being used for energy purposes. Additional protein resulted in some increase in total protein deposition, but a lesser increase in protein intake in combination with increased energy intake (higher feeding level) resulted in an even greater increase in protein retention.

Table I. Effects of Diet Restriction and Protein Intake on Energy and Protein Utilization in Pigs

Protein level:
Feeding level:		 Low
Low		 High
Low		 Low
High
Trial 1
  Feed intake/day (g) 1600 1600 2450
  N intake/day (g) 31.2 53.1 47.8
  Dig. Energy/day (cal.) 4836 4698 7311
  N retention/day (g) 10.3 14.3 16.6
  N retention (%) 33.0 26.9 34.4
Trial 2
  Feed intake/day (g) 1630 1640 3220
  Daily gain (g) 284 243 755
  Feed/gain 5.82 6.95 4.40
  Loin eye area (sq. in.) 4.33 4.24 4.14
  Carcass protein (%) 15.2 15.6 14.6
  Carcass fat (%) 38.4 37.7 40.0

Adapted from Cunningham et al. (1962).

In pigs, the effects of energy intake on performance and carcass composition may be illustrated by varying the total feed intake (restricted vs ad libitum feeding) or by varying the metabolizable energy density of the diet (by substituting fat for carbohydrate or highly digestible carbohydrates for more fibrous materials). In cattle, this is accomplished primarily by varying the ratios of forage and concentrate feeds. Either method of varying energy intake will influence body composition.

Examples of the effects of feed restriction on performance and body composition in pigs are presented in Tables II and III (Braude et al., 1958; Greer et al., 1965). Moderate restriction of feed intake results in a relatively small but significant improvement in feed efficiency but a rather marked reduction in rate of gain. Fat in the carcass is reduced substantially as measured by thickness of backfat or percent intramuscular fat in the longissimus muscle. Note that intramuscular fat is reduced to a much greater extent, on a percentage basis, than is external fat cover (backfat). It is well established, as illustrated in these two tables, that restriction of feed intake will result in a higher ratio of lean to fat in the carcass. In barrows fed ad libitum, 92.5% or 85% of ad libitum intake, Leymaster and Mersmann (1991) also found that fat deposition was decreased; whereas protein intake even on the lowest feeding level was near adequate and rate of protein deposition was minimally affected. To limit fat deposition, the diets should be formulated so as to limit only the energy intake, and energy should not be limited to less than that required for maximum lean tissue deposition. The added cost of labor and/or automated feeding devices involved in restricting total feed intake, the added costs associated with slower rates of gain, and the low premiums paid for the improved carcasses do not encourage restricted feeding in the U.S. In some countries, however, it is rather common to restrict the feed intake. In those countries practicing restricted feeding, either labor costs are relatively lower, feed costs are relatively higher, or the premiums for leaner carcasses are relatively greater than in the U.S.

Table II. Effects of food Restriction on performance and carcass Characteristic of Pigs

Body weight (kg)
14.5 to 54.5
54.5to 90.8		 Ad lib
Ad lib 		Feeding level
Ad lib.
2.95   kg		 To scale a
To scale
Feed intake (kg/day) 2.65 2.47 2.14
Daily gain (g/day) 676 640 563
Feed/gain 3.92 3.86 3.81
Backfat (cm) 3.92 3.71 3.50
Depth of longissimus (cm) 4.41 4.52 4.43
Width of longissimus (cm) 7.51 7.75 7.64
a
908 g/day initially plus 45 for each 1.36   kg increase in body weight to a maximum of 2.95   kg.

Adapted from Braude et al. (1958).

Table III. Effects of Restricting Corn Base Diets on Performance and Carcass Characteristics of Pigs

Feeding level
Percent of ad libitum 		100 85 70
Trial 1
  Feed intake (kg/day) 3.15 2.44 2.06
  Avg. daily gain (kg) 0.77 0.61 0.51
  Feed/gain 4.09 4.00 4.04
  Ham and loin (% of carcass) 35.9 38.0 38.4
  Backfat (cm) 3.78 3.40 3.22
  Fat in 1. dorsi (% of D.M.) 20.7 14.3 15.3
Trial 2
  Feed intake (kg/day) 2.61 2.11 1.80
  Avg. daily gain (kg) 0.70 0.55 0.45
  Feed/gain 3.73 3.84 4.00
  Ham and loin (% of carcass) 37.1 38.6 39.4
  Backfat (cm) 3.73 3.61 3.28
  Fat in 1. dorsi (% of D.M.) 16.4 13.0 11.4

Adapted from Greer et al. (1965).

Energy intake by pigs may be altered either by adding fibrous feeds to the diet to reduce energy density or adding fat to the diet to increase energy density. Animals tend to voluntarily adjust feed intake to satisfy energy needs. Pigs consume more feed per day if the dietary energy density is diluted (added fiber) and consume less feed when fat is added to the diet. However, the adjustment often is not of sufficient magnitude to totally compensate. The data in Table IV (Wagner et al., 1963) show that pigs fed the lower energy diets consumed 14.6% more feed than did those fed the higher energy diets, and this was sufficient to almost compensate for the difference in energy density (17.5%). Pigs on the high energy diet consumed only 3.6% more energy per day. Within the same protein level, substituting fat (10%) for soybean hulls resulted in a 9 to 11% increase in backfat thickness and a 32 to 34% increase in intramuscular fat.

Table IV. Effect of Dietary Energy and Protein Levels on Performance and Carcass Characteristics in Pigs

Energy (Mcal ME/kg)
Protein (%)		 3.12 a
25		 2.93 a
13		 3.59 b
25		 3.52 b
13
Feed intake (kg/day) 2.08 2.52 1.82 3.11
Energy intake (Mcal ME/day) 6.50 7.39 6.54 7.43
Protein intake (g/day) 520 327 458 285
Average daily gain (g) 929 929 754 835
Feed/gain 3.23 3.41 2.63 2.72
Backfat (cm) 3.15 3.30 3.43 3.67
Longissimus fat (%) c 7.9 12.6 10.4 16.9
a
Diets formulated to contain 0.950 Mcal productive energy per kg.
b
Diets formulated to contain 1.15 Mcal productive energy kg.
c
Percent of dry matter.

Adapted from Wagner et al. (1963).

The effects of restricting energy intake by adding fibrous feeds to the diet are illustrated in Table V (Merkel et al., 1958a,b). Ground corn cobs or alfalfa meal were used to dilute the metabolizable energy content of the diet. Diluting with corn cobs resulted in a 6.5 and 34.4% reduction in backfat thickness and intramuscular fat in the longissimus, respectively; but, it also resulted in a 10% reduction in rate of gain and a 44.9% increase in feed required for unit of gain. The same amount (3.90 vs 3.85   kg) of the non-cob fraction of the diet was required per unit of gain; however, the composition of the gain was altered. Reducing energy intake by reducing level of fat, by increasing level of fiber, or by restricting total feed intake will increase the lean-to-fat ratio as measured by backfat thickness, intramuscular fat levels, lean cut yield, or chemical analysis of the total carcass.

Table V. Effect of High Fiber Diets on Performance and Carcass Characteristics of Pigs

Item Diet
High concentrate High fiber
Corn cobs 30% Alfalfa 53%
Average daily gain (g) 645 581 399
Feed/gain 3.85 5.58 6.98
Backfat (cm) 4.29 4.01 2.97
Fat in longissimus (% of D.M.) 15.1 9.9 10.9

Adapted from Merkel et al (1985a.b).

Altering weight gain and body composition during the growing phase can be more practical in cattle than in pigs because of their efficient utilization of fibrous feedstuffs. Energy intake can be restricted to a level below that required for a high rate of fat synthesis, while at the same time maintaining adequate intakes of protein, minerals, and vitamins to assure maximum muscle growth. This is accomplished by feeding a diet consisting of a high forage-to-concentrate ratio or allowing animals to graze on pasture forages with only mineral supplementation.

Reid (1971), Preston (1971), Marchello and Hale (1976), Thonney et al. (1981), Nour et al. (1983a,b), and Old and Garrett (1987) concluded that in cattle fed to usual market grades (22–30% fat), plane of nutrition did not affect the final carcass fat level if compared at equal body or preferably carcass weights. Preston (1990) concluded that the major impact of increasing plane of nutrition on growth of cattle, large or small mature size, is to increase rate of gain and improve feed efficiency. While apparent carcass fat and marbling (intramuscular fat) increase and retail yield decrease in cattle fed diets high in grain (high plane of nutrition), when adjusted for greater carcass weight, these differences become very small or nonexistent. Large-frame cattle need to be fed for maximum rate of gain (high grain diets) to heavier weights to achieve a similar degree of marbling as small-frame cattle before reaching an age that negatively impacts tenderness and overall consumer acceptability. When interest on investment, yardage, and other fixed costs are considered, there is little to be gained in "growing" large-frame cattle on roughage-type diets especially when the energy cost of these diets is near equal to or higher than in high grain diets (Amer et al., 1994).

There is not universal agreement on the influence or lack thereof of plane of nutrition on carcass composition of cattle (Byers, 1982; Williams et al.,1983). This indicates that factors other than plane of nutrition are interacting to produce variable results. Limit feeding of a concentrated diet from 243 to 342   kg body weight followed by ad libitum feeding of a concentrated diet to 505   kg resulted in steers with less fat thickness but somewhat more marbling as compared to steers continuously fed the concentrated diet ad libitum to the same final body weight (de la Torre et al., 1993). These authors concluded that "programmed" feeding can be used to alter carcass composition but at the expense of reduced feed lot performance (rate of gain and efficiency of gain). Keele et al. (1993) reported that decreases in fat content of the carcass and increases in the days required to reach a given carcass weight were increased as dietary energy was decreased. Obviously these two factors, energy content of diet and rate of gain, are related. Together, however, they accounted for only 20% of the variation in carcass fat; whereas, carcass weight accounted for 55% of the difference in carcass fat.

Marbling can be influenced by plane of nutrition or systems of feeding (Lofgreen, 1968; Hedrick et al., 1982; Bennett, 1988). However, plane of nutrition and cattle type (mature size) also alter feed lot performance and final carcass weight. Owens et al. (1993) postulated that plane of nutrition may alter mature size of cattle. Thus as concluded by Preston (1971), there is little relationship between plane of nutrition and marbling independent of carcass weight.

As with pigs, carcass composition of cattle can be influenced by energy concentration of the diet, but the difference in energy level must be of such magnitude that rate of gain and efficiency of feed conversion will be affected to such an extent that it may be economically impractical under present grading and pricing conditions. If high roughage feeds are sufficiently less costly, their use in cattle may justify the reduced performance, particularly when much of the body weight gain may be acquired on pasture or other low cost forages.

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DOUBLE-MUSCLED ANIMALS

S. De Smet , in Encyclopedia of Meat Sciences (Second Edition), 2014

Carcass and Meat Quality

The largest merit of double-muscled animals lies in their superior carcass characteristics ( Table 1). Because of the slower rate of fat deposition, slaughter maturity is delayed. Inversely, animals of this genotype can be finished to higher slaughter weights. Dressing proportion is significantly increased (approximately 5%) compared to normal animals because of the reduced digestive tract and the lower weight of skin and organs. At similar age or weight, carcasses of double-muscled animals have higher proportions of lean meat and lower proportions of fat and bone. Although prominence is generally given to the muscle hypertrophy in describing the double-muscled condition, the reduced development of the fat tissues is relatively much more distinct. The size but not the number of the fat cells is decreased. The reduction in bone proportion is more moderate. The muscle hypertrophy and the fat and bone hypotrophy are general but not uniform throughout the body. Especially superficial muscles and the hindlimbs compared to the forelimbs are most affected, but differences between studies as to the relative muscle hypertrophy are noticed. Bones of the limbs are shorter and thinner according to the same gradients observed for the muscles. The muscle to bone ratio is maximal at the level of the shoulders and the thigh where the hypertrophy is also most visible. At a comparable level of subcutaneous fat cover, a lower overall carcass fat content is found for double-muscled compared to normal animals. The nonuniform muscle hypertrophy and greater conformation in general results in a different size and shape of most meat cuts and in a higher proportion of more expensive cuts. In commercial practice, this effect of conformation and carcass cutability may add substantially to the difference in carcass value of double-muscled animals, irrespective of the difference in lean meat content. The combination of increases in dressing proportion, carcass lean content, and upgrading of some cuts may yield a difference in the proportion of high value cuts on a live weight basis that amounts to more than a quarter for pure-bred double-muscled compared to normal cattle.

As mentioned above on the genetic determination, the myostatin-deficient condition leads to an increase in muscle fiber number (Table 1). The contractile differentiation during the first two-thirds of gestation and the metabolic differentiation of aerobic oxidative metabolism during the last third of fetal growth are delayed in double-muscled fetuses. A higher proportion of glycolytic muscle fibers at the expense of oxidative and oxido-glycolytic fibers are thus found at birth and throughout life in double-muscled cattle. Most reports indicate no major changes in the muscle fiber dimensions, and slightly lower as well as higher fiber sizes have been reported. Hence, the relative area of type IIB fibers is increased and the overall muscle metabolism is more glycolytic.

The more glycolytic muscle fiber type results in a faster muscle pH fall postmortem in double-muscled animals, whereas ultimate pH values are generally not different. Concomitantly, the meat is paler, illustrated by higher CIE L? values (Table 1). A lower ratio of CIE a?/b? values corresponds to a less red color tint in line with reduced levels of myoglobin. The higher rate of glycolysis early postmortem, in combination with the increased muscle mass, also leads to slightly higher muscle temperatures postmortem, and consequently an increased degree of protein denaturation. This is expected to affect water-holding capacity unfavorably. However, data on several measures of water-holding capacity have been variable. Slightly higher drip and purge losses are generally found, but lower, unchanged as well as higher cooking losses have been reported. Differences in color and water-holding capacity in comparison with changes in other traits are relatively moderate.

With respect to meat tenderness and palatability in general, literature concerning double-muscled cattle are coherent on most but not all points (Table 1). Meat tenderness and tenderisation are complex phenomena determined by a number of factors. The content and nature of connective tissue content together with the postmortem weakening of the myofibrillar and cytoskeletal network are considered the most important factors, provided that no extreme muscle shortening occurs during rigor development. No difference in sarcomere length in meat of double-muscled animals is observed under normal slaughtering conditions. A large reduction (approximately 25%) in muscle collagen content in double-muscled animals is reported in almost all studies. The perimysial connective tissue network is thinner, but the nature of the perimysial collagen in terms of solubility and crosslink concentrations on a collagen molar basis is not affected. The much lower content of connective tissue explains the upgrading of lower quality cuts to more expensive cuts, allowing for a larger and more homogenous distribution of high quality meat throughout the carcass. In muscles with a low content of connective tissue, like the Longissimus, the positive effect of double muscling on tenderness may be mitigated by reduced myofibrillar and cytoskeletal protein degradation that normally occurs during the tenderisation process. Double-muscled cattle have consistently lower µ-calpain, calpastatin, and cathepsin levels in the Longissimus, associated with changes in protein breakdown and in line with the reduced in vivo protein turnover. Total proteolysis and tenderization during full ageing seem to be lower in double-muscled animals. However, observations in the Longissimus indicate that proteolysis occurs at a faster rate early postmortem in double-muscled beef animals, consistent with the more glycolytic muscle fiber type and the earlier rigor development. Data for other muscles on enzyme activities and postmortem proteolysis are very scarce. The overall effect on shear force values is variable, depending on the muscle studied and on the time/temperature treatment of the meat. Across studies and muscles, shear force values of raw meat have always been lower due to the lower collagen content. The literature shows that cooking meat for 1   h at 75   °C, the recommended standard preparation method for shear force determinations, yielded higher values for double-muscled animals, but not in all studies. Because of extensive solubilization of collagen, this procedure of shear force determination can be regarded as a measure of myofibrillar toughness, but is not necessarily a good indication of overall tenderness. The higher myofibrillar toughness of double-muscled animals as a result of reduced proteolysis is apparently only reflected in higher shear force values in heated low-collagen muscles in some studies. Indeed, taste panel tenderness evaluations on cooked meat do always show higher tenderness ratings, although the benefit may be lower for muscles low in connective tissue. Hence, in general meat from double-muscled animals is more tender. Meat of double-muscled animals is particularly suited for raw consumption or after short time heating only, culinary preparation methods prevalent mainly in Western and Southern Europe. Regarding other taste panel parameters, lower juiciness, and beef flavor ratings have been reported, in line with the lower intramuscular fat content.

The meat composition in double-muscled animals is changed according to the altered carcass composition. The meat protein content is higher and, because of the lower collagen content, protein quality in terms of essential amino acids content is improved. The intramuscular fat content is approximately 25% lower when compared to normal counterparts. Differences in fatty acid composition in different fat depots have also been reported. In intramuscular fat, the triacylglycerol content is greatly reduced as a result of the lower fat deposition, whereas the phospholipid content is only slightly lower in line with the lesser amount of cell membranes of the more glycolytic muscles. Accordingly, the contents of saturated and monounsaturated fatty acids are significantly reduced, whereas the contents of polyunsaturated fatty acids are similar or slightly reduced. Consequently, the molar proportions of polyunsaturated fatty acids are significantly higher and those of saturated and especially monounsaturated fatty acids are lower. The ratio of intramuscular polyunsaturated to saturated fatty acids is thus higher in meat from double-muscled animals. Similar but less marked changes are to be expected in other fat depots. There are also indications for alterations in the n-6 and n-3 polyunsaturated fatty acid metabolism, based on differences in the proportions of the long chain fatty acids resulting from elongation and desaturation of linoleic and linolenic acid. The content of conjugated linoleic acids is similar relative to the sum of fatty acids, but is lower on muscle weight basis. Meat oxidative stability of double-muscled and normal animals has not been properly compared at present, but there are no indications for large differences.

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DOUBLE-MUSCLED ANIMALS

S. De Smet , in Encyclopedia of Meat Sciences, 2004

Carcass and Meat Quality

The greatest merit of double-muscled animals lies in their superior carcass characteristics. Because of the slower rate of fat deposition, slaughter maturity is delayed. Conversely, animals of this genotype can be finished to higher slaughter weights. Dressing yield is significantly increased compared to normal animals because of the reduced digestive tract and the lower weight of skin and organs. At similar age or weight, carcasses of double-muscled animals have higher proportions of meat and lower proportions of fat and bone. Although prominence is generally given to the muscle hypertrophy in describing the double-muscled condition, the reduced development of the fat tissues is relatively much more distinct. The size, but not the number, of the fat cells is decreased. The reduction in bone proportion is more moderate. The muscle hypertrophy, and the fat and bone hypotrophy, are general but not uniform throughout the body. In particular, superficial muscles and the hind limbs, compared to the fore limbs, are most affected, but differences between studies regarding the relative muscle hypertrophy are noted. The bones of the limbs are shorter and thinner according to the same gradients observed for the muscles. The muscle-to-bone ratio is maximal at the level of the shoulders and the thigh, where the hypertrophy is also most visible. At a comparable level of subcutaneous fat cover, a lower overall carcass fat content is found for double-muscled compared to normal animals. The nonuniform muscle hypertrophy, and the more blocked conformation in general, results in a different size and shape of most meat cuts and in a higher proportion of more expensive cuts. In commercial practice, this effect of conformation and carcass cutability may add substantially to the difference in carcass value of double-muscled animals, irrespective of the difference in lean meat content. The combination of increases in dressing yield and carcass lean content, and upgrading of some cuts, may yield a difference in the proportion of high-value cuts on a live weight basis that amounts to more than 25% for pure-bred double-muscled cattle compared to normal cattle.

As already mentioned regarding the genetic determination, the myostatin-deficient condition leads to an increase in muscle fibre number. The contractile differentiation during the first two-thirds of gestation, and the metabolic differentiation of aerobic oxidative metabolism during the last third of fetal growth, are delayed in double-muscled fetuses. A higher proportion of glycolytic muscle fibres, at the expense of oxidative and oxido-glycolytic fibres, is thus found at birth and throughout life in double-muscled cattle. Most reports indicate no major changes in the muscle fibre dimensions, and slightly lower as well as higher fibre sizes have been reported. Hence, the relative area of type IIB fibres is increased and the overall muscle metabolism is more glycolytic.

The more glycolytic muscle fibre type results in a faster muscle pH fall post-mortem in double-muscled animals, whereas ultimate pH values are generally not different. Concomitantly, the meat is paler, as illustrated by higher CIE L* values. A lower ratio of CIE a*/b* values corresponds to a less red colour, in line with reduced levels of myoglobin. The higher rate of glycolysis early post-mortem, in combination with the increased muscle mass, also leads to slightly higher muscle temperatures post-mortem, and consequently an increased degree of protein denaturation. This is expected to affect water-holding capacity unfavourably. However, data on several measurements of water-holding capacity have been variable. Slightly higher drip losses are generally found, but lower, or unchanged, as well as higher cooking losses have been reported. Differences in colour and water-holding capacity in comparison with changes in other traits are relatively moderate.

With respect to meat tenderness and palatability in general, literature data concerning double-muscled cattle are coherent on most but not all points. Meat tenderness and tenderization are complex phenomena determined by a number of factors. The content and nature of connective tissue, together with the post-mortem weakening of the myofibrillar and cytoskeletal network, are considered the most important factors, provided no extreme muscle shortening occurs during rigor development. No difference in sarcomere length in meat of double-muscled animals is to be expected under normal slaughtering conditions. A large reduction in muscle collagen content in double-muscled animals is seen in almost all studies. The perimysial connective-tissue network is thinner, but the nature of the perimysial collagen in terms of solubility and crosslink concentrations on a collagen molar basis seems little affected. The much lower content of connective tissue explains the upgrading of lower-quality cuts to more expensive cuts, allowing for a larger and more homogenous distribution of high-quality meat throughout the carcass. In muscles with a low content of connective tissue, such as the longissimus, the positive effect of double muscling on tenderness may be absent owing to a relatively more important contribution of myofibrillar and cytoskeletal protein degradation during the ageing process. Double-muscled cattle have consistently lower μ-calpain, calpastatin and cathepsin levels in the longissimus, associated with changes in protein breakdown and in line with the reduced in vivo protein turnover. Data for other muscles on enzyme activities and post-mortem proteolysis are very scarce. Both the changes in enzyme activities and protein concentrations during tenderization observed in the longissimus indicate that proteolysis occurs at a faster rate early post-mortem in double-muscled beef animals, consistent with the more glycolytic muscle fibre type and the earlier rigor development. Total proteolysis and tenderization during full ageing seem to be lower in double-muscled animals. The overall effect on shear force values is variable, depending on the muscle studied and on the time/temperature treatment of the meat. Across studies and muscles, shear force values of raw meat have always been lower, in view of the lower collagen content. The literature shows that cooking meat for 1 hour at 75 °C – the recommended standard preparation method for shear force determinations – yielded higher values for double-muscled animals, but not in all studies. Because of extensive solubilization of collagen, this procedure of shear force determination can be regarded as a measure of myofibrillar toughness, but it is not necessarily a good indication of overall tenderness. The higher myofibrillar toughness of double-muscled animals, as a result of reduced proteolysis, is apparently reflected in higher shear force values only in heated low-collagen muscles in some studies. On the other hand, taste panel tenderness assessment on cooked meat always show higher tenderness ratings, although the benefit may be lower for muscles low in connective tissue. Hence, in general, meat from double-muscled animals is more tender. Meat of double-muscled animals is particularly suited for consumption raw or after only short-time heating – culinary preparation methods prevalent mainly in western and southern Europe. Regarding other taste panel parameters, lower juiciness and beef flavour ratings have been reported, in line with the lower intramuscular fat content.

The meat composition is changed according to the altered carcass composition. The meat protein content is higher in double-muscled animals and, because of the lower collagen content, protein quality in terms of essential amino acids content is improved. The low intramuscular fat content has already been mentioned. Differences in fatty acid composition in different fat depots have also been reported. In intramuscular fat, the triacylglycerol content is greatly reduced as a result of the lower fat deposition, whereas the phospholipid content is only slightly lower, in line with the smaller amount of cell membranes in the more glycolytic muscles. Accordingly, the content of saturated and monounsaturated fatty acids is significantly reduced, whereas the content of polyunsaturated fatty acids is smaller or slightly reduced. Consequently, the molar proportion of polyunsaturated fatty acids is significantly higher and that of saturated and especially monounsaturated fatty acids is lower. The ratio of intramuscular polyunsaturated to saturated fatty acids is thus higher in meat from double-muscled animals. Similar but less marked changes are to be expected in other fat depots. There are also indications of alterations in n-6 and n-3 polyunsaturated fatty acid metabolism, based on differences in the proportions of the long-chain fatty acids resulting from elongation and desaturation of linoleic and linolenic acid. The content of conjugated linoleic acids is similar relative to the sum of fatty acids, but is lower on a muscle weight basis. Meat oxidative stability of double-muscled and normal animals has not been properly compared at present, but there are no indications of large differences.

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Historical perspectives of the meat and animal industry and their relationship to animal growth, body composition, and meat technology

Steven M. Lonergan , ... Dennis N. Marple , in The Science of Animal Growth and Meat Technology (Second Edition), 2019

Introduction

There are significant relationships between the regulation of animal growth and body composition and meat quality traits of domestic animals. Animal growth traits and carcass characteristics have great influences on the value of the live animal for both breeding value and retail meat value. Therefore it is important to understand growth and development concepts when management decisions are made for livestock production systems.

This book will provide fundamental science-based concepts as well as applied and practical concepts from prenatal growth to postnatal growth of cattle, sheep, and pigs. This book is unique, as information is also presented that relates growth and development traits to the carcass value, meat retail characteristics, meat processing, and meat storage traits that are important at the wholesale and retail markets.

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Innovative uses of aromatic plants as natural supplements in nutrition

E. Christaki , ... P. Florou-Paneri , in Feed Additives, 2020

Biological properties of aromatic plants (functional foods) nutrigenomics

The addition of aromatic plants and their derivatives to livestock nutrition is an interesting tool for providing supplements with biologically active compounds. These reveal considerable properties such as antimicrobial, antiviral, antifungus, antioxidant, antiinflammatory, and immunostimulatory (Diaz-Sanchez et al., 2015; Adaszynska-Skwirzynska and Szczerbinska, 2017; Ribeiro dos Santos et al., 2017). Subsequently, the use of aromatic plants due to their valuable compounds is fundamental for successful development of novel, healthy foods, the functional foods. These foods beyond their nutritional effects have demonstrated benefits to the human organism by improving the state of health or well-being. They may reduce the risk of chronic diseases such as cardiovascular, neurodegenerative, bone metabolism, cancer and may find application for the treatment of respiratory and inflammatory disorders, allergies and diabetes (Prescott and Saffery, 2011; Ismail and Imam, 2014). Accordingly, the interest of the dietary use of the compounds of aromatic plants as functional ingredients or nutraceuticals has been enhanced by the recent advances in genetics. In relevant studies, an interaction between dietary components and the genome has been highlighted, which is mandatory to affect metabolic pathways and homeostasis in the human body. Hence, a new concept the "nutrigenomics" has been revealed. The nutrigenomic actions exerted by the aromatic plants could be a preventive approach for optimizing health, delaying chronic disorders or minimizing their intensity or severity, since many diseases have a genetic predisposition (Simopoulos, 2010; Ismail and Imam, 2014; Carrasco Lopez, 2015; Pavlidis et al., 2015; Elsamanoudy et al., 2016).

Modes of action

Although the precise modes of action of the phytogenics are not elucidated yet, studies have shown their beneficial effects on productive animals, concerning growth performance, carcass characteristics, and meat quality. Generally, the benefits of aromatic plants and their essential oils depend greatly on the diversity and number of aromatic compounds responsible for their biological activities, their synergistic effect, the origin of the plants, the inclusion level in the diet and their pharmacokinetics ( Franz et al., 2010; Diaz-Sanchez et al., 2015; Gadde et al., 2017; Sanchez-Vidana et al., 2017).

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ELECTRICAL STIMULATION

C.E. Devine , ... I. Richards , in Encyclopedia of Meat Sciences (Second Edition), 2014

Electrical Stimulation Parameters

Any electric current above a certain threshold will stimulate muscles, and for this reason stunning or immobilization currents can have a beneficial effect on tenderness by also accelerating glycolysis. The current flow is dictated by the applied voltage and carcass characteristics such as pelt cover, animal size (determining resistance) and fatness (potential insulation), and contact area (in particular reduced contact with shin). However, in commercial situations where high voltage ES is used, large peak current flows occur (e.g., in excess of 2  A peak per carcass). In situations where many carcasses are stimulated simultaneously on the same electrode system, very sophisticated power supplies, delivering up to 60   A total, are needed for the pulsed currents and currents are not necessarily shared equally between carcasses. Development of new systems for sheep/lambs and beef in Australia using short pulse widths and moderate voltages use segmented electrodes to ensure that each electrode only contacts one carcass at a time. This allows computer-controlled electronics to give a precise, but adjustable current to each carcass to match the requirements of a particular carcass type (Figures 2 and 3a,b). The current pulses in these systems use very rapid rise times that appear to provide a greater stimulation effect with lower peak current to give very effective results (Box 2).

Box 2

Meat characteristics following ES. Color (redness (a*), color stability at 630/580   nm, shear force (N), pH, predicted temperature at pH 6.0 (°C), for the m. longissimus of electrically stimulated (800   mA, pulse width 0.5   ms, peak voltage of 300   V, 15   Hz, for 60   s) and nonstimulated lamb carcasses (40 per treatment). Chilled at 4.2   °C. All values are predicted means (s.e.d.)

Trait Stimulated a Nonstimulated s.e.d.
Initial loin pH 6.34a 6.79b 0.04
Predicted temperature at pH 6.0 24.8b 13.9a 1.50
Shear force (N) at 1-day aging 36.0a 44.0b 2.40
Redness (a*) 7.70a 7.00a 0.32
Color stability (630/580   nm) 3.20a 3.00a 0.14

Source: Adapted from Toohey, E.S., Hopkins, D.L., Stanley, D.F., Nielsen, S.G., 2008. The impact of new generation pre-dressing medium-voltage electrical stimulation on tenderness and colour stability in lamb meat. Meat Science 79, 683–691.

a
Stimulation treatment was at a current of 800   mA with a pulse width of 0.5   ms for duration required. Means followed by the same letter in a row are not significantly different (P=.05).

Voltages used vary from 32 to 3600   V (historically). The value specified might be that of the peak or the rms (root mean square) voltage, or in some cases the average over the total time. The rms voltage is the effective value or heating capacity of a waveform. For a sine wave, the rms value is the peak voltage divided by v2. For 1130   V peak, 50   Hz, the rms voltage is 800   V. However, for many derived (nonsinusoidal) waveforms the rms may be quite different and ineffective. For one version, termed the Meat Industry Research Institute of New Zealand (MIRINZ) waveform, every seventh half-sine wave of a 50   Hz sine wave is used and the rms voltage is the peak voltage divided by v14. Figure 5 illustrates the meaning of the different terms used to describe voltages and waveforms. Defining a waveform with a frequency (expressed in Hz) is likely to lead to confusion unless the waveform is also defined in terms of shape, duration, and pulse spacing. Square waves also can be used and may be unipolar or bipolar and applied as discrete pulses or even as pulse trains.

Figure 5. Terms used to describe pulses and waveforms illustrated by sinusoidal (a and c), half sinusoidal (b) and square wave pulses (d). In (a) there are 50 sinusoidal cycles per second (100 half sine wave pulses); peak and rms voltages are indicated. The pulses in (b) are obtained by cutting out half-sinusoidal pulses, which in this case gives 10   ms duration pulses, 14.28 pulses per second, with the same peak voltage. The pulse width (mark) and space between pulses give the mark-to-space ratio used to specify a single repetitive cycle, with the polarity of pulses and the number of cycles per second required to complete the description. The waveforms (b) and (c) both have the same period (inverse of frequency) and peak amplitude, but have different shape characteristics. Square wave pulses (d) can have variable widths depending on the characteristics desirable, and only a particular stimulation waveform is shown here.

Extensive research in Australia particularly in sheep and lambs has demonstrated that ES systems must be validated and optimized to ensure effective operation – in other words mere application of electricity does not guarantee a satisfactory result. In instances where this does not happen or system monitoring is not employed ES can be relatively ineffective. In some situations with multielectrode systems, lights are used to indicate when each electrode is operating, to limit ineffective ES. Although any stimulation increases dpH/dt, it is only optimum parameters (duration, peak voltage, and pulse characteristics) that increase the fall ?pH significantly. It is likely where ES is not regarded as effective or useful the resultant ?pH has not been sufficient.

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Artificial Insemination and Embryo Transfer in Sheep

C.F.B. SHIPLEY, , ... J.R. HUNTON , in Current Therapy in Large Animal Theriogenology (Second Edition), 2007

Marker-Assisted Selection

The use of genetic markers for the identification of animals carrying a specific gene is known as marker-assisted selection. Economically important major qualitative genes such as those for fecundity (Booroola-FecB; Thoka), health (scrapie resistance), growth and carcass characteristics (Callipyge), and sex have all been recently identified in sheep. The Booroola, Callipyge and male-specific genes have additionally been isolated after identification by molecular techniques. Genetic markers allow individuals to be screened for specific genes that may not be expressed (fecundity genes in males) or before phenotypic expression is normally observed in expressing animals. This advantage is most pronounced if marker-assisted selection is combined with ET and manipulation, and embryos can be screened for the presence of specific genes before they are transferred. Future developments should include the evolution of screening methods by which an embryo's genetic makeup could be determined through noninvasive methods. Marker-assisted selection will play an increasingly important role in livestock selection as more genes and gene markers are identified.

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