Estimates of genetic parameters for kyphosis in two crossbred swine populations

Genetic parameters for degree of kyphosis were estimated from a Duroc-Landrace F(2) population (n = 316) and from a composite population (line C) composed of Duroc, Large White, and 2 sources of Landrace (n = 1,552). Live presentation did not indicate kyphosis in pigs or sows. Degree of kyphosis was measured by scoring the shape of the vertebral column of split carcasses on a scale from 0 (normal) to 3 (severe). Of the animals slaughtered, 75.6 and 68.9% were normal, 11.1 and 23.3% were mild, 11.1 and 6.2% were moderate, and 2.2 and 1.5% were severe in F(2) and line C, respectively. Fixed effects of age, sex, number of ribs, number of lumbar vertebrae, number of nipples, carcass length, and HCW were not significantly associated (P > 0.10) with kyphosis score when using linear models. Estimated heritabilities for kyphosis score were 0.30 and 0.32 in F(2) and line C, respectively, when using an animal model. Estimated genetic correlations between kyphosis score and number of ribs, number of lumbar vertebrae, number of nipples, carcass length, and HCW were 0.05, -0.13, 0.00, 0.05, and 0.03, respectively. Selection to decrease kyphosis should be effective and would not be expected to affect the number of ribs, lumbar vertebrae, nipples, or carcass length. In addition, selection for growth should not affect the incidence of kyphosis.     

Estimates of non-genetic effects and genetic parameters for body measures and subjectively scored traits in Finnhorse trotters

This study examined non-genetic effects and genetic parameters of body measures and subjectively scored traits in the Finnhorse trotter population. The data was based on studbook inspections from 1971 to 2004 covering observations on 6381 horses. There were five body measures – height at withers, height at croup, circumference of girth, length of body and circumference of cannon bone – and six subjectively scored traits – character, body conformation, leg stances, quality of legs, hooves and movements – included in the analyses. Multivariate mixed models were applied with year–sex and age as fixed effects and animal as a random effect. The year–sex effect had a significant influence on body measures and scored traits. Age at judging had a significant influence on all traits but height at withers and body conformation. Heritability estimates were from 0.53 to 0.78 for body measures and 0.10 to 0.19 for scored traits. Genetic correlations between body measures were highly positive, from 0.75 to 0.98, whilst genetic correlations between scored traits varied between − 0.20 and 0.51. Genetic correlations between body measures and scored traits were mainly negative, from − 0.38 to 0.09. Our results indicate that additive genetic effects are relevant determinants for body measures of Finnhorse trotters. The scored traits were of low to moderate heritability and were relevantly influenced by environmental effects.     

Estimates of genetic parameters for live animal ultrasound, actual carcass data, and growth traits in beef cattle

Growth and carcass measurements were made on 2,411 Hereford steers slaughtered at a constant weight from a designed reference sire program involving 137 sires. A second data set consisted of ultrasound measures of backfat (USFAT) and longissimus muscle area (USREA) from 3,482 yearling Hereford cattle representing 441 sires. Restricted maximum likelihood procedures were used to estimate genetic parameters among carcass traits and live animal weight traits from these two separate data sets. Heritability estimates for the slaughter weight constant steer carcass backfat (FAT) and longissimus muscle area (REA) were .49 and .46, respectively. In addition, FAT had a negative genetic correlation with REA (-.37), weaning weight (-.28), and yearling weight (-.13) but positive with marbling (.19) and carcass weight (.36). Marbling was moderately heritable (.35) and highly correlated with total postweaning average daily gain (.54) and feedlot relative growth rate (.62). Heritability estimates for weight constant USFAT and USREA were .26 and .25, respectively. The genetic correlation between weight constant USFAT and USREA was positive (.39), indicating that in these young animals USFAT does not seem to be an indication of maturity. Mean USFAT measures and variability were small (.48 +/- .17 cm, n = 3,482). Results indicate that carcass fat on slaughter steers and ultrasound measures of backfat on young breeding animals may have different relationships with growth and muscling. These relationships need to be explored before wide scale selection based on ultrasound is implemented.     

Estimates of genetic parameters for growth traits in Kermani sheep

Birth weight (BW), weaning weight (WW), 6-month weight (W6), 9-month weight (W9) and yearling weight (YW) of Kermani lambs were used to estimate genetic parameters. The data were collected from Shahrbabak Sheep Breeding Research Station in Iran during the period of 1993-1998. The fixed effects in the model were lambing year, sex, type of birth and age of dam. Number of days between birth date and the date of obtaining measurement of each record was used as a covariate. Estimates of (co)variance components and genetic parameters were obtained by restricted maximum likelihood, using single and two-trait animal models. Based on the most appropriate fitted model, direct and maternal heritabilities of BW, WW, W6, W9 and YW were estimated to be 0.10 +/- 0.06 and 0.27 +/- 0.04, 0.22 +/- 0.09 and 0.19 +/- 0.05, 0.09 +/- 0.06 and 0.25 +/- 0.04, 0.13 +/- 0.08 and 0.18 +/- 0.05, and 0.14 +/- 0.08 and 0.14 +/- 0.06 respectively. Direct and maternal genetic correlations between the lamb weights varied between 0.66 and 0.99, and 0.11 and 0.99. The results showed that the maternal influence on lamb weights decreased with age at measurement. Ignoring maternal effects in the model caused overestimation of direct heritability. Maternal effects are significant sources of variation for growth traits and ignoring maternal effects in the model would cause inaccurate genetic evaluation of lambs.     

Estimates of genetic parameters for conformation measures and scores in Finnhorse and Standardbred foals

The aim of this study was to estimate genetic parameters for conformation measures and scores in the Finnhorse and the Standardbred foals presented in foal shows. Studied traits included height at withers and at croup, six subjectively evaluated conformation traits and overall grade. Data were from 10‐year period (1995–2004) and consisted of 5821 Finnhorse foals (1–3 years old) with 7644 records and 2570 Standardbred foals (1–2 years old) with 2864 records. Variance components were estimated with REML – animal model using VCE4 program. The model included age class, year of judging, sex and region as fixed effects, and additive genetic, permanent environmental and residual as random effects. Estimates of heritability for measured traits were very high in both breeds (0.88–0.90). Estimates of heritability for conformation traits varied from 0.13 to 0.32 in the Finnhorse and from 0.06 to 0.47 in the Standardbred. In both breeds, estimates of heritability were lowest for hooves and movements at walk, and highest for type and body conformation among scored traits. Estimate of heritability for overall grade was in the Finnhorse 0.32 and in the Standardbred 0.34. Genetic correlations between overall grade and different conformation traits were 0.35–0.84 in the Finnhorse and 0.31–0.88 in the Standardbred. Thus, selection based on the overall grade would improve all studied characteristics.     

Estimates of genetic parameters for direct and maternal effects on embryonic survival in swine.

Survival of 16,838 potential embryos was determined by counting corpora lutea and fetuses at 50 d of gestation for 1,081 litters by 225 sires. These data, coded as 1 or 0 depending on whether an ovulation was represented by a fetus, were used to estimate direct and maternal additive genetic variances and their covariance for embryonic survival. Data were from first-parity gilts of a Large White-Landrace composite population subdivided into two lines, one selected for an index of ovulation rate and embryonic survival for seven generations and a contemporary control line. Variance components were obtained by ANOVA and expectations of covariances among relatives and by derivative-free restricted maximum likelihood (DFREML) in an animal model. As a trait of the embryo, heritability of direct effects obtained with ANOVA was 3.8%, heritability of maternal effects was 1.5%, and the genetic correlation between them was -.51. After adjustment of embryonic survival for ovulation rate, lower estimates of each parameter were obtained with ANOVA. Heritability of embryonic survival as a trait of the dam was 9 to 10%. Estimates of heritability of both direct and maternal effects obtained with DFREML were less than 1% and the genetic correlation between them was -.64. When survival of embryos from only those dams with 15 or more ovulations was analyzed, heritability of maternal effects was 4.4%. Estimates of common environmental effects on embryonic survival ranged from 5 to 7%.     

Estimates of parameters between direct and maternal genetic effects for weaning weight and direct genetic effects for carcass traits in crossbred cattle

Estimates of heritabilities and genetic correlations were obtained for weaning weight records of 23,681 crossbred steers and heifers and carcass records from 4,094 crossbred steers using animal models. Carcass traits included hot carcass weight; retail product percentage; fat percentage; bone percentage; ribeye area; adjusted fat thickness; marbling score, Warner-Bratzler shear force and kidney, pelvic and heart fat percentage. Weaning weight was modeled with fixed effects of age of dam, sex, breed combination, and birth year, with calendar birth day as a covariate and random direct and maternal genetic and maternal permanent environmental effects. The models for carcass traits included fixed effects of age of dam, line, and birth year, with covariates for weaning and slaughter ages and random direct and maternal effects. Direct and maternal heritabilities for weaning weight were 0.4 +/- 0.02 and 0.19 +/- 0.02, respectively. The estimate of direct-maternal genetic correlation for weaning weight was negative (-0.18 +/- 0.08). Heritabilities for carcass traits of steers were moderate to high (0.34 to 0.60). Estimates of genetic correlations between direct genetic effects for weaning weight and carcass traits were small except with hot carcass weight (0.70), ribeye area (0.29), and adjusted fat thickness (0.26). The largest estimates of genetic correlations between maternal genetic effects for weaning weight and direct genetic effects for carcass traits were found for hot carcass weight (0.61), retail product percentage (-0.33), fat percentage (0.33), ribeye area (0.29), marbling score (0.28) and adjusted fat thickness (0.25), indicating that maternal effects for weaning weight may be correlated with genotype for propensity to fatten in steers.     

Prediction of swine carcass composition by total body electrical conductivity (TOBEC)

An experiment was conducted to determine prediction equations that used readings for total body electrical conductivity (TOBEC) in the model for estimation of total fat-free lean and total fat weight in the pork carcass. Ultrasound measurements of live hogs were used to select 32 gilts that represented a range in weight, muscling, and fatness. The TOBEC readings were recorded on warm carcass sides, chilled carcass sides, and the untrimmed ham from the left carcass side. Physical dissection and chemical analyses determined fat-free lean and fat weight of the carcass. All of the ham tissues were analyzed separately from the remainder of the carcass tissues to incorporate ham measurements for prediction of total fat-free lean and total fat weight in the entire carcass. Prediction equations were developed using stepwise regression procedures. An equation that used a warm carcass TOBEC reading in the model was determined to be the best warm TOBEC equation (R2 = 0.91; root mean square error = 0.81). A three-variable equation that used chilled carcass TOBEC reading, chilled carcass temperature, and carcass length in the model was determined to be the best chilled TOBEC equation (R2 = 0.93; root mean square error = 0.73). A four-variable equation that included chilled carcass side weight, untrimmed ham TOBEC reading, ham temperature, and fat thickness beneath the butt face of the ham in the model was determined to be the best equation overall (R2 = 0.95; root mean square error = 0.65). The TOBEC and the fat-free lean weight of the ham are excellent predictors of total carcass fat-free lean weight.     

Growth, development and body composition in three genetic stocks of swine

Differences in growth, chemical body composition and visceral organ development were evaluated in three genetic stocks: Beltsville Highfat (HF) and Lowfat (LF) Duroc-Yorkshire composites and a Hampshire X Large White cross (CX). Ten sets of littermate barrows were used from each stock. One pig from each set was slaughtered at 10, 17 and 24 wk of age. After slaughter, each pig was dissected into three fractions: carcass, head and feet, viscera and blood. Backfat was measured at three locations and visceral organs were weighed separately. Each fraction was frozen, ground, sampled and analyzed in duplicate for protein, fat, water and ash. The CX pigs were heaviest at all ages and contained the most fat-free mass (FFM). The HF pigs were smallest and contained the most fat, while LF pigs tended to be intermediate. The LF pigs deposited a greater proportion of weight in head and feet and a greater proportion of total FFM in the carcass than HF and CX pigs. Estimated allometric growth coefficients for non-fat chemical components relative to empty body weight (EBWT) were lower for HF than LF and CX, which were similar. Coefficients for fat were similar among stocks yet intercepts differed widely. Relative to total FFM, water increased at a faster rate and ash a slower rate in CX pigs compared to HF and LF. Growth coefficients were calculated for internal organs relative to EBWT. Coefficients for organs of the digestive tract were not different among stocks. However, significant differences among stocks were found for heart, lung, spleen and liver that were not explained by differences in body composition.     

Failure of photoperiod to alter body growth and carcass composition in beef steers

In each of two experiments, 70 crossbred steers were blocked by BW and assigned to initial slaughter groups or to treatments in a 2 x 2 design. In Exp. 1, treatments were 168 d of photoperiod (8 h of light [L]:16 h of dark [D] or 16L:8D) and plane of nutrition (high energy [HPN] or low energy [LPN]). On d -22, 67 and 155, blood was sampled every 20 min for 8 h. Relative to LPN, HPN increased (P less than .01) ADG by 28%, carcass weight by 26% and accretion of carcass fat by 109% and carcass protein by 20%. On d 155, compared with LPN, HPN increased (P less than .01) serum insulin (INS; 1.09 vs .64 ng/ml) and lowered (P less than .05) growth hormone (GH; 2.14 vs 3.70 ng/ml), but prolactin was not affected. Photoperiod did not affect BW gains, carcass composition or serum hormones. In Exp. 2, treatments were 113 d of photoperiod (8L:16D or 16L:8D) and Synovex-S implant (presence [IMP] or absence [NONIMP]). On d 93, blood was sampled every 30 min for 10 h. Relative to NONIMP, IMP increased (P less than .01) ADG by 12% and accretion of carcass protein by 16%. Implants did not affect carcass weight or accretion of fat. Compared with NONIMP, IMP increased (P less than .05) GH (3.16 vs 2.39 ng/ml) and INS (.68 vs .46 ng/ml) but did not affect PRL. Photoperiod did not affect BW gain, carcass composition or serum hormones. We conclude that photoperiod fails to influence growth and carcass composition of steers.     

Estimates of genetic parameters associated with lactation feed intake and growth and composition traits measured during a performance test

Days to reach 113.4 kg, adjusted backfat depth and adjusted loin muscle area to 113.4 kg were evaluated on pure‐bred Landrace (n = 15 660) and Yorkshire (n = 14 808) boars and gilts. Daily lactation feed intake (LFI) was recorded within parity records from pure‐bred Yorkshire (n = 1587) and Landrace (n = 2197) females during day 1–22 of lactation, and LFI curves were predicted using a mixed model. Evaluation of feed intake differences between 2 consecutive days of lactation resulted in the following periods: day 1–6 (PB1), day 7–10 (PB2) and day 11–18 (PB3). Average rate of change in intake (ARC), average daily intake (ADI) and variation from predicted daily LFI values (VAR) metrics were computed for each period of lactation. Gibbs sampling was used to estimate the genetic covariance between LFI metrics and grow‐finish traits. Genetic correlations were strongest between grow‐finish traits, and LFI metrics in first parity sows and were generally favourable, but correlations with LFI metrics during parity 2 or greater were low and not different from 0 (p > 0.05). Genetic correlations between LFI metrics in parity 1 sows with growth and composition traits varied greatly in strength and direction. Selection for leaner, heavier muscled gilts had a limited effect on LFI metrics. However, selection for increased growth rate was associated with higher ARC and ADI and smaller VAR values.     

Conjugated linoleic acid changes swine performance and carcass composition

Conjugated linoleic acid (CLA) is a collective term for positional and geometric isomers of linoleic acid. Dietary CLA has been shown to improve feed efficiency, decrease body fat, and increase lean tissue in laboratory animals. We hypothesized that CLA would improve performance and carcass composition and would be deposited in pork tissues. Diets of 40 crossbred pigs were supplemented with CLA to determine its effects on performance and carcass composition. Eight replications of five littermate barrows with an initial average weight of 26.3 kg were allotted at random to individual pens. Within replication dietary treatments containing 0, 0.12, 0.25, 0.5, or 1.0% CLA were assigned at random. Pigs were weighed and feed disappearance was determined at 14-d intervals. Average daily gain increased linearly as the level of CLA increased in the diet (P < 0.05). Average daily feed intake was not affected by the concentration of CLA in the diet. Therefore, a linear increase in gain:feed ratio (P < 0.05) was observed. Carcasses from animals fed control diets had greater 10th rib backfat than carcasses from animals fed CLA (P < 0.05). Ultrasound measurement and carcass measurements showed less fat depth over the loin eye at the 10th rib of pigs fed doses of CLA (P < 0.05) than that observed for control pigs. Belly hardness (firmness) increased linearly as the concentration of CLA in the diet increased when bellies were measured for firmness either lean side up (P < 0.001) or lean side down (P < 0.05). Loin dissection data demonstrated that CLA produced a quadratic treatment effect both for less intermuscular fat (P < 0.001) and less subcutaneous fat (P < 0.05) and a linear increase for bone (P < 0.05), although finished loin weight only tended to increase (P = 0.08). The CLA concentration increased in a linear relationship in both subcutaneous fat (P < 0.001) and lean tissue (P < 0.001). Dietary CLA was incorporated into pig tissues and had positive effects on performance and body composition.     

Estimates of environmental effects and genetic parameters for body measurements and weight in Brahman cattle raised in Mexico

A Derivative Free Restricted Maximum Likelihood (DFREML) algorithm was used with single trait and two traits animal models to estimate the variance and covariance components and thus, heritabilities and phenotypic, genetic and environmental correlations among nine different body measurements and weights of Brahman cattle raised in Mexico. The following measurements were considered: hip width, pin width, hip‐pin width, anterior height, posterior height, body length, thorax perimeter, scrotal circumference and weight. The analysis was based on a total of 1018 animals, born between 1992 and 1995, from 17 herds in the Mexican States of Chiapas, San Luis Potosi, Tabasco, Tamaulipas and Veracruz. The model included the following fixed effects: herd, year‐season of birth, sex, age of the animal and feed management. The only random effect was the direct additive genetic contribution of each animal. All fixed effects in the model were significant for all traits (p < 0.05). Estimated heritabilities for the traits were: hip width 0.57, pin width 0.32, hip‐pin width 0.41, anterior height 0.56, posterior height 0.54, body length 0.32, thorax perimeter 0.49, scrotal circumference 0.02 and weight 0.66. The magnitude of the heritabilities was medium to high, with the exception of scrotal circumference. The genetic correlations among all body measurements were consistently positive and high, ranging from 0.64 to 1.00. Although other measures showed higher genetic correlations with weight, thorax perimeter combines a high value (0.70) with ease and repeatability, making it a useful field measurement to estimate body weight when scales are not available.     

Analysis of body composition changes of swine during growth and development.

This study was conducted to model the growth of carcass, viscera, and empty body components and component composition of pigs. Quantitative tissue and chemical composition of 319 swine, representative of barrows and gilts from five commercial genetic populations, was determined at eight stages of growth between 25 and 152 kg. After whole body grinding and carcass dissection, proximate analyses were performed to calculate concentrations of protein, lipid, moisture, and ash of carcass, viscera, empty body, carcass lean, and carcass fat. Linear and nonlinear equations were developed to investigate the growth patterns of each component. Nonlinear growth functions accounted for the greatest amount of variation in empty body protein, lipid, moisture, and ash mass. Differences (P < .05) existed between barrows and gilts for nearly all components investigated. Carcass lean and fat tissues significantly increased in lipid percentage and decreased in moisture percentage as live weight increased. There were significant changes in the ratio and composition of the tissues of barrows and gilts during growth. Nonlinear models fitted the data better than allometric equations for nearly all of the components investigated.     

Estimates of (co)variance components and genetic parameters for growth traits in Sirohi goat

Data were collected over a period of 21 years (1988–2008) to estimate (co)variance components for birth weight (BWT), weaning weight (WWT), 6-month weight (6WT), 9-month weight (9WT), 12-month weight (12WT), average daily gain from birth to weaning (ADG1), weaning to 6WT (ADG2), and from 6WT to 12WT (ADG3) in Sirohi goats maintained at the Central Sheep and Wool Research Institute, Avikanagar, Rajasthan, India. Analyses were carried out by restricted maximum likelihood, fitting six animal models with various combinations of direct and maternal effects. The best model was chosen after testing the improvement of the log-likelihood values. Heritability estimates for BWT, WWT, 6WT, 9WT, 12WT, ADG1, ADG2, and ADG3 were 0.39 ± 0.05, 0.09 ± 0.03, 0.06 ± 0.02, 0.09 ± 0.03, 0.11 ± 0.03, 0.10 ± 0.3, 0.04 ± 0.02, and 0.01 ± 0.01, respectively. For BWT and ADG1, only direct effects were significant. Estimate of maternal permanent environmental effect were important for body weights from weaning to 12WT and also for ADG2 and ADG3. However, direct maternal effects were not significant throughout. Estimate of c ² were 0.06 ± 0.02, 0.03 ± 0.02, 0.06 ± 0.02, 0.05 ± 0.02, 0.02 ± 0.02, and 0.02 ± 0.02 for 3WT, 6WT, 9WT, 12WT, ADG2, and ADG3, respectively. The estimated repeatabilities across years of ewe effects on kid body weights were 0.10, 0.08, 0.05, 0.08, and 0.08 at birth, weaning, 6, 9, and 12 months of age, respectively. Results suggest possibility of modest rate of genetic progress for body weight traits and ADG1 through selection, whereas only slow progress will be possible for post-weaning gain. Genetic and phenotypic correlations between body weight traits were high and positive. High genetic correlation between 6WT and 9WT suggests that selection of animals at 6 months can be carried out instead of present practice of selection at 9 months.     

Serum concentrations of leptin in six genetic lines of swine and relationship with growth and carcass characteristics

The objective of this study was to evaluate the relationship between serum concentrations of the hormone leptin with growth and carcass traits insix distinct breeds of pigs entered into the 2000 National Barrow Show Sire Progeny Test. Breeds evaluated were Berkshire (n = 131), Chester White (n = 33), Duroc (n = 40), Landrace (n = 23), Poland China (n = 26), and Yorkshire (n = 41). Serum samples were collected and assayed for concentrations of leptin at entry into test (On-Test Leptin) at 34 +/- 6.7 kg of live weight and again 24 h prior to harvest (Off-Test Leptin) at 111 +/- 3.1 kg of live weight. Carcass measurements taken included hot carcass weight, carcass length, backfat, longissimus muscle area (LMA), longissimus pH, Hunter L-value, chemically determined intramuscular fat (IMF), and subjective color, marbling, and firmness scores. Average daily gain, IMF percentages, and water-holding capacity (WHC) were also determined. On-Test Leptin concentrations were not different (P > 0.10) between swine breeds; however, Off-Test Leptin concentrations did differ (P < 0.001) across genotype. Berkshire had the greatest Off-Test Leptin concentrations (6.58 +/- 0.43 ng/mL), and Duroc and Yorkshire had the lowest (3.49 and 3.96 +/- 0.68 ng/mL; respectively). In addition, Off-Test Leptin concentrations were correlated with average daily gain (r = 0.29; P < 0.001), last-rib fat thickness (r = 0.48; P < 0.001), 10th rib backfat (r = 0.52; P < 0.001), LMA (r = -0.33; P < 0.001), percent fat-free carcass lean (r = -0.51; P < 0.001), and WHC (r = 0.15; P < 0.05). Off-Test Leptin concentrations also differed by gender, with barrows having greater (P < 0.001) serum concentrations of leptin than gilts (6.55 +/- 0.48 vs 3.35 +/- 0.44). Differences exist between breeds of pigs in a manner consistent with breed-specific traits for growth, leanness, and quality; thus, leptin may serve as a useful marker for selection or identification of specific growth and carcass traits.     

Estimated genetic parameters for carcass traits of Brahman cattle

Heritabilities and genetic and phenotypic correlations were estimated from feedlot and carcass data collected from Brahman calves (n = 504) in central Florida from 1996 to 2000. Data were analyzed using animal models in MTDFREML. Models included contemporary group (n = 44; groups of calves of the same sex, fed in the same pen, slaughtered on the same day) as a fixed effect and calf age in days at slaughter as a continuous variable. Estimated feedlot trait heritabilities were 0.64, 0.67, 0.47, and 0.26 for ADG, hip height at slaughter, slaughter weight, and shrink. The USDA yield grade estimated heritability was 0.71; heritabilities for component traits of yield grade, including hot carcass weight, adjusted 12th rib backfat thickness, loin muscle area, and percentage kidney, pelvic, and heart fat were 0.55, 0.63, 0.44, and 0.46, respectively. Heritability estimates for dressing percentage, marbling score, USDA quality grade, cutability, retail yield, and carcass hump height were 0.77, 0.44, 0.47, 0.71, 0.5, and 0.54, respectively. Estimated genetic correlations of adjusted 12th rib backfat thickness with ADG, slaughter weight, marbling score, percentage kidney, pelvic, and heart fat, and yield grade (0.49, 0.46, 0.56, 0.63, and 0.93, respectively) were generally larger than most literature estimates. Estimated genetic correlations of marbling score with ADG, percentage shrink, loin muscle area, percentage kidney, pelvic, and heart fat, USDA yield grade, cutability, retail yield, and carcass hump height were 0.28, 0.49, 0.44, 0.27, 0.45, -0.43, 0.27, and 0.43, respectively. Results indicate that sufficient genetic variation exists within the Brahman breed for design and implementation of effective selection programs for important carcass quality and yield traits.     

Estimates of genetic parameters and predicted selection responses for growth, fat and lean traits in mice

Heritabilities (?2) and genetic correlations (rG) were estimated by regression of offspring on sire in two replicate, unselected lines of mice. Traits were associated with growth, feed efficiency, fat deposition and lean tissue. The ?2 for growth traits ranged from .34 to .42, except for 3-wk body weight, which was only .05. The ?2 for feed efficiency was .28. Ranges in ?2 were .45 to .50 for fat deposition traits and .36 to .42 for lean tissue traits. The rG involving 3-wk to 6-wk feed efficiency with hind carcass and fat measurements at 12 wk were small. Antagonisms were found between the sign of rG and the direction of usual breeding goals for pairs of traits (e.g., rG greater than 0 between fat deposition and hind carcass weight and rG less than 0 between hind carcass as a percentage of body weight and body weight). Selection indexes were developed to counteract these antagonisms. Modified selection indexes were compared where responses in individual traits rather than the aggregate breeding value were of major importance. The aggregate breeding values and selection indexes included: 1) epididymal fat pad weight and body weight, 2) hind carcass weight and body weight, or 3) all three traits. Economic weights in retrospect were calculated for the modified selection indexes. In some cases, expected correlated responses in component traits were not influenced greatly over a wide range of ratios of economic weights, but in other cases the component traits changed sharply over a narrow range of ratios.