Ultrasonic Backfat Depth Research Articles

Castration methods in crossbred cattle raised on tropical pasture

The aim of this study was to evaluate the effects of castration methods (surgical or immunological – GnRH vaccine) on performance and carcass traits of beef cattle raised until slaughter on tropical pasture. On Day 0, 30 crossbred beef bulls (50% Aberdeen Angus × 50% Nellore) with a bodyweight (BW) of 233 ± 38 kg and age of 8 months were randomly divided into three groups: intact males (INT) – Control, surgically castrated (SUC; Day 1), and immunocastrated (IMC; Days 1, 84 and 237). Serum testosterone concentrations, scrotal circumference, average daily gain, and ultrasonic backfat depth were evaluated at 42-day intervals (eight evaluations). All animals were slaughtered for the evaluation of carcass traits on Day 336. The GnRH vaccine was efficient in suppressing serum testosterone concentrations (P = 0.02) and scrotal circumference (P < 0.01). No difference in performance was observed between IMC and SUC animals, in which average daily gain was reduced by 14% (P < 0.01) and final BW by 7% (P < 0.01) compared with the INT group. Regardless of the method used, castration improved carcass traits by reducing carcass drip loss during cooling (P = 0.02), by increasing hindquarter percentage (P < 0.01), and by tending to increase the proportion of noble cuts (P = 0.05) compared with the INT group. However, the surgical method was more efficient than the other treatments by increasing fat deposition in the carcass (P < 0.01). Anti-GnRH immunisation in beef cattle raised on tropical pasture can replace surgical castration, but both methods reduce performance. However, in this production system, castration could be an efficient method to add value to the carcass by increasing the hindquarter proportion and fat deposition.

Evaluation of growth, deposition of back fat, and loin muscle for purebred Berkshire pigs housed in bedded hoop buildings.

This study was conducted to evaluate the accretion of BW, back fat, and loin muscle from purebred Berkshire pigs raised in bedded hoop barns in Iowa. The growth of a total of 144 purebred Berkshire pigs (18 barrows and 18 gilts per trial) was evaluated from 4 trials (2 winter and 2 summer trials). Pigs were fed ad libitum utilizing a 5-phase standard corn-soybean meal feeding program that met or exceeded NRC nutrient requirements. Pigs were housed in bedded hoop barns (unheated) to approximate common niche market requirements. At 21-d intervals, pigs were serially weighed, and ultrasonic back fat depth and loin muscle area (LMA) measurements were taken. Live BW measurements began at the trial initiation at approximately 18 to 32 kg, but ultrasonic scans for 10th-rib back fat depth and LMA began at between 36 and 45 kg until market weight of about 122 ± 2.5 kg. The rate (µ) of live body growth (weight) and ultrasonic back fat depth were influenced ( < 0.01) by trial and sex, with no significant interactions between trial and sex. Both live BW and back fat deposition were significantly greater in trial 1 than all other trials (2, 3, and 4). The rate of accretion and maximum growth of LMA depth were not affected ( > 0.05) by trial and sex. Overall, barrows averaged 31 mm of back fat at 125 kg, whereas gilts had an average of about 23 mm at 121 kg of market weight. Results suggest that because of the sex differences in growth and back fat deposition between Berkshire barrows and gilts, it may be important to formulate their diets differently in commercial pork production systems.

TECHNICAL NOTE: Use of mixed model nonlinear functions to adjust pig growth and measurement data

<h2>ABSTRACT</h2> Current methods to adjust pig performance data to a constant BW or age assume linear relationships between the growth of the measurement and either age or BW. Serial BW and ultrasonic measurements from a set of gilts were used to provide an example of the development of alternative methods to adjust pig performance data. Each pig was weighed at approximately 125, 138 153, 167, and 174 d of age. Ultrasonic backfat depth and loin depth measurements were collected at each weigh day on approximately one-half of the gilts. The BW data were fitted to a mixed model generalized Michaelis-Menten (GMM) function with one pig-specific random effect for mature BW. By including each pig's random effect, the pig's predicted age to achieve target BW was estimated. An allometric equation Y=(1 + a_i) A BW^Bwith a pig-specific random effect (a_i) provided the best fit of the ultrasonic data to BW. An alternative approach to adjust pig growth or measurement data using mixed model nonlinear equations was suggested. The pig's actual data were used to solve for its specific random effect. Then, using the nonlinear equation and the pig's random effect, the pig's measurement at the target age or BW can be estimated. This alternative approach may better predict the mean and variances of each pig's growth and better adjust pig performance data.

Evaluation of the Growth of Backfat Depth, Loin Depth, and Carcass Weight for Different Sire and Dam Lines

<h2>ABSTRACT</h2> The growth of 1,990 barrows and gilts of 3 sire and 2 dam lines was evaluated over 2 replicates. Pigs were weighed and ultrasonic backfat and loin depth measurements were taken at approximate 28-d intervals from 37kg BW to target BW of 113, 127, or 141kg. Carcass backfat and loin depths were measured with an optical probe. An exponential equation Y=exp(b₀ + b₁X + b₂X²) + a_i[exp(b₀ + b₁BW + b₂BW²)]^D (where Y is the value of the measurement; b₀, b₁, and b₂ are regression coefficients; and D is a parameter) with a pig-specific random effect (a_i) provided the best fit of the ultrasonic data to BW. The ultrasonic backfat depths were affected (<i>P</i> < 0.01) by replicate, dam line, and the interactions of replicate × BW and dam line × BW. The ultrasonic backfat depths of the gilts increased at a rate of 0.0077cm/kg BW gain at 40kg BW to 0.0115 cm/kg BW gain at 135kg BW. Barrows had backfat growth rates of 0.0110 cm/kg BW gain at 40kg BW, which increased to 0.0149 cm/kg BW gain at 115 to 125kg BW. The ultrasonic loin depths were affected (<i>P</i> < 0.05) by replicate, sire line, and replicate × BW and sire line × BW interactions. Carcass backfat and loin depths were affected (<i>P</i> < 0.01) by replicate, sire line, dam line, target BW, sex, and the sire line × sex interaction. Pigs of different sire and dam lines have different rates of backfat and muscle growth, indicating differences in compositional growth.

Detection of single nucleotide polymorphisms associated with ultrasonic backfat depth in a segregating Meishan × White Composite population1,2

Multiple genomic scans have identified QTL for backfat deposition across the porcine genome. The objective of this study was to detect SNP and genomic regions associated with ultrasonic backfat. A total of 74 SNP across 5 chromosomes (SSC 1, 3, 7, 8, and 10) were selected based on their proximity to backfat QTL or to QTL for other traits of interest in the experimental population. Gilts were also genotyped for a SNP thought to influence backfat in the thyroxine-binding globulin gene (TBG) on SSC X. Genotypic data were collected on 298 gilts, divided between the F8 and F10 generations of the US Meat Animal Research Center Meishan resource population (composition, one-quarter Meishan). Backfat depths were recorded by ultrasound from 3 locations along the back at approximately 210 and 235 d of age in the F8 and F10 generations, respectively. Ultrasound measures were averaged for association analyses. Regressors for additive, dominant, and parent-of-origin effects of each SNP were calculated using genotypic probabilities computed by allelic peeling algorithms in GenoProb. The association model included the fixed effects of scan date and TBG genotype, the covariates of weight and SNP regressors, and random additive polygenic effects to account for genetic similarities between animals not explained by known genotypes. Variance components for polygenic effects and error were estimated using MTDFREML. Initially, each SNP was fitted (once with and once without parent-of-origin effects) separately due to potential multi-collinearity between regressions of closely linked markers. To form a final model, all significant SNP across chromosomes were included in a common model and were individually removed in successive iterations based on their significance. Across all analyses, TBG was significant, with an additive effect of approximately 1.2 to 1.6 mm of backfat. Three SNP on SSC3 remained in the final model even though few studies have identified QTL for backfat on this chromosome. Two of these SNP exhibited irregular parent-of-origin effects and may not have been detected in other genome scans. One significant SNP on SSC7 remained in the final, backward-selected model; the estimated effect of this marker was similar in magnitude and direction to previously identified QTL. This SNP can potentially be used to introgress the leaner Meishan allele into commercial swine populations.

The relationship between body dimensions of living pigs and their carcass composition

Recent analysis pointed towards visual imaging analysis (VIA), which yields pig body size measures and shape indices from two-dimensional visual images of living pigs, as a potential technique for estimating fat and lean content in pig carcasses (Doeschl et al., 2004). The present analysis further explored the potential of using VIA body size and shape indices as indicators of the proportion of lean and fat in various carcass joints, either alone or in combination with ultrasonic backfat depth of the live animal. Due to increasing interest in the shape of retail cuts in the meat industry, the association between VIA size measures and the dimensions of the longissimus dorsi and gluteobiceps muscles is also assessed.

The effect of litter size and sward height on ewe and lamb performance

This study compared ewe and lamb performance in twin‐ and triplet‐bearing/rearing ewes offered varying sward heights from day 64 (P64) of pregnancy until weaning at day 87 (L87) of lactation. Ninety‐six twin‐ and 90 triplet‐bearing Romney ewes were randomly assigned on P64 to four replicated sward height treatments (2, 4, 6, and 8 cm sward height). Within 24–36 h of parturition (L1) the ewes were reassigned to two (4 and 8 cm) replicated sward heights until weaning at L87. Ewes grazing the 2 cm sward height during pregnancy were significantly (P < 0.01) lighter at P99 and P132 and at L1 than ewes grazing 4, 6 or 8 cm swards. These ewes also had significantly (P < 0.01) lower dry matter intakes, condition scores, and ultrasonic backfat depths. Litter size had no effect on ewe intake, ewe liveweight or condition score throughout pregnancy and lactation. Ewes grazing the 2 cm sward height had significantly (P < 0.05) lower dry matter intakes during pregnancy than ewes on the 4, 6, and 8 cm treatments. Estimated herbage dry matter intakes measured using n‐alkanes were similar to calculated energy requirements. Lambs born to ewes grazing the 2 cm swards during pregnancy were lightest at birth (P < 0.01), but sward height during pregnancy or lactation had no effect on lamb weaning weight or lamb survival rate to weaning. Triplet‐born lambs were 0.9 kg lighter (P < 0.05) than twins at birth, with the difference increasing in those lambs reared as a full triplet set to 4.7 kg at L87. Lamb losses were 14% in twin‐born lambs and 32% in triplet‐born lambs. There was no sward height by litter size interaction for ewe liveweight, intake or lamb birth and weaning weight or survival, therefore the results suggest ewes rearing either twins or triplets should be fed sward height allowances of 4 cm or better during pregnancy. However, there is no need to feed above 4 cm in pregnancy or lactation to optimise lamb weaning weight, lamb survival or ewe liveweight and condition score gain.

Dietary Conjugated Linoleic Acid Can Decrease Backfat in Pigs Housed under Commercial Conditions

Conjugated linoleic acids (CLA) have been shown to decrease body fat content of individually-housed pigs but little is known about the responses under commercial conditions. Two studies were conducted to evaluate the effect of CLA under commercial conditions using contemporary genotypes. The experimental designs were Similar between the two sites. Briefly, the studies were 2x2 factorial designs with the respective factors being sex (boar and gilt) and supplemental dietary CLA (0 and 4 g/kg). The studies involved 16-20 pens of pigs with 4-5 pens of each sexxCLA group. The first study was conducted with 144 pigs in 16 pens consuming a pelleted feed for 6 weeks at Bunge Meat Industries, Corowa, NSW. In the second study, 160 pigs were obtained from a commercial source and put into 20 pens in simulated commercial conditions and fed a mash diet for 7 weeks at Medina Research Station, WA. In Study 2 some aspects of meat quality were also investigated. Data from Study 1 showed that, although CLA had no significant effect upon feed intake and daily gain, the small changes in both resulted in a reduction in (-0.10 g/g, p=0.10) feed conversion ratio (FCR). While there was no significant effect of CLA on ultrasonic backfat depths, there was a significant decrease in carcass P2 (-1.0 mm, p=0.014) and estimated carcass fat (-7 g/kg, p=0.049). In the study conducted at Medina CLA had no significant effect upon feed intake, feed:gain or most measures of back fat. The exception was that dietary CLA decreased the rate of accumulation of fat at the shoulder, particularly in gilts, resulting in a significantly lower amount of shoulder fat at slaughter (-1.3 mm, p=0.044). CLA tended to increase dressing percentage although this was not significant (+0.5%, p=0.14). Meat from CLA treated pigs tended to be darker (p=0.12) and had a higher ultimate pH (p=0.06). These data suggest that under commercial conditions dietary CLA can improve growth performance and decrease P2 in pigs of an improved genotype, particularly gilts.

Effect of Wagyu genetics on marbling, backfat and circulating hormones in cattle

Backfat depths, marbling scores, and concentrations of plasma insulin, cortisol, triiodothyronine (T3), and thyroxine (T4) were determined in 394 calves with and without Wagyu genetics. Hormone concentrations were determined three to five times for hormones between weaning and slaughter. Calves were weighed and backfat was ultrasonically determined at 28-d intervals, and assigned for slaughter when ultrasonic backfat depths approached 12 mm. Heifers weighed less (P &lt; 0.001) and had more backfat (P &lt; 0.05) and more marbling (P &lt; 0.05) than steers at slaughter. Breed influenced slaughter weight (P &lt; 0.001) and average backfat depth (P &lt; 0. 001), with Wagyu/Angus and Wagyu/Hereford crosses and Angus purebreds generally having greater backfat depths and lower slaughter weights than other crosses and purebreds. Marbling scores were not affected by breed (P &gt; 0.1), although Wagyu crosses had more marbling (P &lt; 0.05) compared with purebreds when variability in marbling due to differences in backfat depth was removed. Plasma cortisol, T3 and T4 were affected by calf breed, although there were no clear patterns for groups of breeds or breed crosses. There was a slight trend (P &lt; 0.2) towards higher insulin levels and lower cortisol, T3 and T4 levels in some groups of calves with more backfat. Higher mean levels (P &lt; 0.05) of T3 and T4 were found in all but one group of animals with more marbling. Thus, thyroid hormones may have a role to play in enhancing marbling in cattle. Key words: Wagyu cattle, marbling, backfat, insulin, cortisol, thyroid hormones

Genetic and nutritional effects on age at first oestrus of gilts selected for components of efficient lean growth rate

Genetic and nutritional effects on age at first oestrus of gilts selected for components of efficient lean growth rate

Patterns of change with growth for muscularity and other composition characteristics of Southdown rams selected for high and low backfat depth

Male Southdown sheep ranging in age from birth to near maturity (c. 28 mo) from genetic lines selected for about five generations for increased (n = 40) and decreased (n = 40) weight‐adjusted ultrasonic backfat depth were used to investigate patterns of change in muscularity and other composition characteristics. Measures of muscularity in terms of muscle depth relative to bone length were greater for the high‐backfat line in anatomical areas around or beside the femur, tibia, total pelvic limb, humerus, and scapula, but not the radius/ulna. Levels of muscularity increased at a decreasing rate with increasing carcass weight from about 1 to 36 kg in all areas. Where there was a genetic line effect on muscularity, this tended to be greater at higher carcass weights, with minimal differences at birth. Muscle to bone ratios corresponding to these measures of muscularity showed similar patterns of change and line differences. Leg bone weight was higher for the low‐backfat line; for the same femur length, a number of femur dimensions were greater for that line. Carcass length at a set weight was greater for the low‐backfat line, and the allometric growth ratio (AGR) for length declined with increasing carcass weight. Greater measures of fatness for the high‐backfat line only became apparent at carcass weights above about 10 kg and AGRs for measures of fatness increased with increasing carcass weight. Some non‐carcass offal components (liver, spleen, heart) were heavier in rams of the low‐backfat line at the same carcass weight, and AGRs for liver and spleen decreased with increasing carcass weight. It is concluded that, in addition to decreases in fatness, selection for lower backfat depths in these Southdown rams has led to a number of other undesirable composition changes including lower levels of muscularity and muscle to bone ratios, changes in the shape of the femur, and greater weights of some non‐carcass components. Generally these changes were more apparent at higher liveweights.

Individual animal model estimates of genetic correlations between performance test and reproduction traits of landrace pigs performance tested in a commercial nucleus herd

AbstractBivariate individual animal model estimates of genetic and environmental correlations between reproduction traits (number born alive and average piglet weight) and performance test traits (ultrasonic backfat depth, average daily food intake, average daily gain and food conversion ratio) of Landrace pigs were calculated. The estimates were produced using a derivative-free restricted maximum likelihood algorithm to calculate likelihoods for different combinations of covariance parameters. A quadratic approximation to the likelihood surface was used to estimate the maximum likelihood values with respect to the covariance parameters. For all combinations of performance test traits with reproduction traits the resulting genetic and residual correlation estimates were low, with a maximum absolute value of 0·233 for the genetic correlation between food conversion ratio and number born alive. Standard errors of genetic correlation estimates were between 0·11 and 0·15. There is expected to have been little effect upon reproduction traits from the rigorous selection carried out upon performance test traits over the years. When incorporating reproduction data into best linear unbiased prediction analysis procedures it should be possible to analyse performance test and reproduction traits from this population separately, thereby making savings on computer resources and time required for the analysis of all traits.

Individual animal model estimates of genetic parameters for performance test traits of male and female landrace pigs tested in a commercial nucleus herd

AbstractEstimates of heritabilities, common litter of birth effects and additive maternal genetic effects were produced for ultrasonic backfat depth, average daily food intake, average daily gain and food conversion ratio of Landrace boars and gilts. Boars and gilts were performance tested under different regimes. A bivariate derivative-free restricted maximum likelihood procedure was used to estimate genetic correlations between the performance test traits as recorded in the two sexes.Heritability estimates from the analysis including the common litter of birth effect tended to be towards the low end of the range of recently published estimates. This may reflect either population specific effects, such as effects of long-term selection, or the use of an individual animal model.Estimates of the common litter of birth effect were around 0·05, and generally had a significant effect upon the fit of the model, while additive maternal genetic effect estimates were negligible. Therefore, it is expected that omission of maternal effects from models for evaluation by best linear unbiased prediction will not hinder genetic progress. Inclusion of common litter of birth effects would be recommended, although this result may not hold for populations given food ad libitum.The estimates of genetic correlations between performance test traits of boars and gilts indicate that the levels of genotype-environment interaction (G × E) and genotype-sex interaction were low across most traits and data sets, with all genetic correlation estimates lying between 0·8 and 1·0. The lowest estimates of the genetic correlations, which were observed in data sets where the environments appeared to differ most, indicate that G × E interactions may be a problem in populations where males and females are subject to test regimes with greater differences than those seen here.

Selection for high or low backfat depth in Coopworth sheep: juvenile traits

AbstractA selection experiment was established in Coopworth sheep in 1981 to breed for increased or reduced ultrasonic backfat depth (scan C). Foundation females came from four flocks recorded for scan C and live weight, with weight-adjusted scan C data within flock being used for initial screening and subsequent selection. Three groups of animals per source flock, comprising proportionally the fattest 0·12, a random sample, and the leanest 0·12, were used to establish the F, control and L lines, respectively. Ewe flock numbers from 1981 to 1992 averaged 51 per line. Foundation rams were selected in the same manner from four different farms (two sources each in 1981 and 1982) to provide F line (proportionally the fattest 0·04), control line and L line (leanest 0·04) rams for use in 1981 and 1982, with four mated per line per year. Thereafter homebred rams were selected, with 41 or 42 homebred rams being used per line until 1992. Average generation intervals were 2·13 years and annual inbreeding rates per line 0·004. Bivariate heritability estimates for log scan C and log live weight, and a univariate estimate for log scan C using restricted maximum likelihood with an animal model, were 0·28, 0·22 and 0·38, respectively (all with s.e. 0·03). There was a suggestion of lower heritabilities in the L line for log scan C after adjustment for live weight. Realized heritabilities in the F and L lines were 0·34 (s.e. 0·07) and 0·26 (s.e. 0·03), respectively. Deviations of back-transformed weight-adjusted scan C in the last 2 years ofF and L data analysed (1991 and 1992 birth years) from the control flocks were 2·08 and −0·85 mm, which corresponded to responses of +2·50 and −1·03 phenotypic standard deviations, respectively. In addition there were relatively large responses in live weight taken at scanning, with F and L lines averaging 34·0 and 40·2 kg, compared with 38·0 kg for controls in the 1991 and 1992 birth years. The genetic and phenotypic correlations between log scan C and log live weight at scanning were 0·16 (s.e. 0·07) and 0·46 (s.e. 0·01) respectively.

Genetic relationships between predicted and dissected carcass composition in Scottish Blackface sheep

Carcass composition was measured on 133 Blackface ram lambs from a flock divergently selected for predicted carcass lean proportion. Prediction equations for different carcass components were developed using combinations of live weight and ultrasonic backfat and muscle depth. Both carcass lean and carcass fat proportion were best predicted using only live weight and fat depth, and a genetic transformation of the equation predicting carcass lean proportion was highly correlated (genetic correlation = 0·97) with the index on which the sheep were selected. Weights of carcass tissues were more accurately predicted than proportions. Lean weight was best predicted using live weight and muscle depth, and the weights of different fat components were best estimated using live weight, muscle depth and fat depth.The equations predicting carcass lean proportion, carcass fat proportion, lean mass and fat mass had heritabilities of 0·29, 0·27 0·20 and 0·23, respectively. Heritabilities for carcass lean and carcass fat proportions, and the subcutaneous and intermuscular fat components were 0·43, 0·48, 0·24 and 0·49, respectively. Genetic correlations of the equation predicting carcass lean proportion with lean and fat proportions were 0·52 (s.e. 0·21) and –0·45 (s.e. 0·22), respectively. The same correlations for the equation predicting carcass fat proportion were –0·47 (s.e. 0·22) and 0·57 (s.e. 0·21). The equations predicting carcass lean and fat proportions were strongly correlated with subcutaneous fat proportion but weakly genetically correlated with intermuscular fat proportion.

Grassland performance of Hereford cattle selected for rate and efficiency of lean gain on a concentrate diet

AbstractThe performance of 273 Hereford calves from lines previously selected for lean growth rate (LGR) or lean food conversion efficiency (LFCR), on a concentrate diet, was evaluated on a grassland diet over a period of 3 years. Both bull and heifer calves were tested, and each year the performance test ran from the 1st week of May (average age of 233 days) until the 1st week of October. Carcass lean content was predicted from body weight and ultrasonic backfat depth, and lean gain was calculated from the product of live-weight gain and predicted carcass lean content. The LGR line was superior to the control (C) line for live-weight gain on test, lean gain on test and lean gain from birth until the end of test. The LFCR line performed similarly to the C line for live-weight gain on test and lean gain on test, but was inferior for total lean gain. For lean gain on test, the proportional differences between the lines were similar to those predicted from parental breeding values for LGR, but they were smaller for total lean gain. The lines did not differ significantly for either fat depth or predicted carcass lean content.Heritabilities were high for all growth traits, e.g. 0·52 (s.e. 0·17), 0·54 (s.e. 0·17) and 0·59 (s.e. 0·17) for live-weight gain on test, lean gain on test and total lean gain, but lower for fat depth and carcass lean content, 0·25 (s.e. 0·17) and 0·14 (s.e. 0·16), respectively. Genetic correlations with LGR, measured on a concentrate diet, were 0·57 for lean gain on test and 0·56 for total lean gain. If only males were considered, these correlations rose to 0·80 and 0·70, respectively. Coheritabilities between the two environments for lean growth were close to 0·3. It is concluded that although there is some evidence for genotype × environment and genotype × sex interactions, selection for lean growth on a concentrate regimen will still be effective in improving grassland performance.

Selection for predicted carcass lean content in Scottish Blackface sheep

AbstractScottish Blackface sheep have been selected for either increased or decreased predicted carcass lean content at 20 weeks of age, using an index combining ultrasonic backfat depth and body weight. The index was designed to alter carcass lean content without changing body weight. After 4 years there have been large responses in the index and fat depth, the proportional difference between the divergent lines in fat depth is 0·28, but body weight and ultrasonic muscle depth have not changed between the lines. The realized heritability for the index is 0·45. Heritabilities for the index, ultrasonic fat depth, body weight and ultrasonic muscle depth, calculated using multivariate restricted maximum likelihood, are 0·47 (s.e. = 0·14), 0·39 (s.e. 0·13), 0·23 (s.e. 0·12) and 0·36 (s.e. 0·14), respectively. The selected lines will be used to investigate relationships between carcass lean content, viability and maternal performance under the harsh environmental conditions encountered in the Scottish hill environment.

Selection for carcass lean content in a terminal sire breed of sheep

AbstractA divergent selection experiment for carcass leanness in Texel-Oxford sheep was established to examine the differences between genetically lean and fat animals derived from the same base population. The selection criterion was designed to change body composition without a corresponding change in live weight, using an index of ultrasonic backfat depth and live weight at 20 weeks of age. The index was constructed using estimates of genetic and phenotypic parameters, which were available at the start of the experiment in 1985. The difference between the high and low lines, after 3 years of selection, for the selection index, live weight at 20 weeks of age, ultrasonic backfat and muscle depths was 0·59,1·30 kg, -0·76 mm and 0·88 mm respectively. The estimated difference for carcass lean and fat weight was 0·72 kg and -0·04 kg respectively with 13·5 g/kg and -13·8 g/kg for carcass lean and fat proportion. The realized heritability for the selection index, estimated from the regression of cumulative response on cumulative selection differential was 0·42, with a standard error of 0·25, after taking account of genetic drift. The selection index heritability, estimated with residual maximum likelihood (REML) methodology, was 0·46 (s.e. 0·14). REML heritability estimates for live weight at 20 weeks of age, ultrasonic backfat and muscle depths were 0·20 (s.e. 0·13), 0·35 (s.e. 0·14) and 0·43 (s.e. 0·14) respectively.

Correlated responses in slaughter and carcass traits of crossbred progeny to selection for carcass lean content in sheep

AbstractCorrelated responses in slaughter and carcass traits to divergent selection for high or low carcass lean content in Texel-Oxford sheep were measured in the crossbred progeny of 23 rams. Rams were selected using the selection index: -0·995 FATD + 0·206 WT20, where FATD and WT20 are the ultrasonic backfat depth and live weight at 20 weeks of age, with both traits standardized to have zero mean and unit phenotypic variance. A total of 329 crossbred lambs were slaughtered at 16 weeks of age and 250 lambs were slaughtered at fixed weight, 38 to 40 kg for castrated males and 36 to 38 kg for ewe lambs. Progeny from high-line rams grew faster, as indicated by the heavier slaughter weight of lambs slaughtered at fixed age (04 (s.e.d. 0·5) kg) and the lower age at slaughter for lambs slaughtered at fixed weight (-5 (s.e.d. 3) days). Subcutaneous and internal fat scores and the Meat and Livestock Commission carcass appraisal and conformation scores were all lower in the high line than in the low line and the magnitude of the selection line differences for lambs slaughtered at fixed weight was essentially double that of lambs slaughtered at fixed age (0·8 v. 0·5 score units).Shoulder joints of 254 lambs, slaughtered at fixed age, were dissected and half carcasses were dissected on 66 of the lambs. Carcass and shoulder joint information was combined with double-sampling methodology, using multiple regression equations to predict carcass composition. For each tissue type, viz. lean, subcutaneous fat, internal fat and bone, the correlations between carcass content and shoulder joint content were at least 0·90 and the proportions of variation in carcass tissue content accounted for by the prediction equations were also at least 0·90. Progeny of high-line rams had higher carcass lean weight, (402 (s.e.d. 140) g) than progeny from the low line, with no difference in carcass fat weight, such that carcass lean content was higher, (10 (s.e.d. 5) g/kg), and carcass fat content was lower, (-10 (s.e.d. 7) g/kg). Based on the slaughter and carcass traits of these crossbred progeny, divergent selection for high and low carcass lean content has established lines of animals with different rates of lean growth but similar rates offat deposition.

Correlated responses in slaughter and carcass traits of crossbred progeny to selection for carcass lean content in sheep

A divergent selection experiment in a terminal sire breed of sheep was started in 1985 to examine the differences between genetically lean and fat animals, which were derived from the same population. Responses in performance and physiological traits measured on the selection lines were reported at the BSAP 1991 Winter Meeting. Responses In slaughter and carcass traits, measured on crossbred progeny of the terminal sires, are presented in this study.The ram selection index was -0.995 FATD + 0.206 WT20, where FATD and WT20 are the ultrasonic backfat depth and liveweight at 20 weeks of age, with both traits standardised to have zero mean and unit phenotyplc variance. A total of 32 and 34 rams from the high (lean) and low (fat) selection lines were performance tested in 1988, and 11 rams were selected from the high line and 12 rams from the low line for mating to crossbred ewes for the progeny test, with a selection differential of 0.85 Index units. There were 8 and 11 rams from the high and low lines with progeny slaughtered at fixed weight, such that the selection differential was 1.0 Index units. A total of 329 crossbred lambs were slaughtered at 16 weeks of age and 250 lambs were slaughtered at fixed weight, 39±1 kg for castrates and 37±1 kg for ewe lambs.