Effect of including relationships in the estimation of genetic parameters of beef calves.

Variances and covariances for birth weight, gain from birth to weaning (ADG), and 205-d weight were obtained from a sire-dam model and a sire-maternal grandsire model for a herd of Angus and a herd of Hereford cattle. Estimates of direct additive genetic variance (sigma 2A), maternal additive genetic variance (sigma 2M), covariance between direct and maternal additive genetic effects (sigma AM), permanent environmental variance (sigma 2PE), and residual variance (sigma 2e) were obtained both with and without the inverse of the numerator relationship matrix (A-1) included. Estimates of heritability for direct genetic effects (h2A), maternal genetic effects (h2M), and the correlation between direct and maternal effects (rAM) for birth weight were .37, .18, and -.01 in Angus and .53, .23, and -.19 in Herefords, respectively, for the analyses without A-1. For the analyses with A-1, estimates of h2A, h2M, and rAM were .42, .22, and -.12 for Angus and .58, .22, and -.13 for Herefords, respectively. Estimates of h2A, h2M, and rAM for ADG were .43, .15, and -.44 in Angus and .52, .38, and -.03 in Herefords, respectively, without A-1. With A-1, estimates of h2A, h2M, and rAM were .57, .15, and -.32 for Angus and .58, .39, and -.05 for Herefords, respectively. Estimates of h2A, h2M, and rAM for 205-d weight were .49, .15, and -.46 for Angus and .58, .43, and -.06 for Herefords, respectively, without A-1. With A-1, estimates of h2A, h2M, and rAM were .63, .16, and -.36 for Angus and .66, .43, and -.08 for Herefords, respectively. Estimates of h2A were higher with A-1 than without A-1, but estimates of h2M were similar. Using variances and covariances obtained from analyses including A-1 generally gave higher estimates of direct breeding values than using variances and covariances obtained from analyses not including A-1. Both Pearson product-moment and Spearman rank correlations were high (.99) between estimates of breeding values from the two analyses, although some changes in rank did occur.     

Relationships among absolute growth rate, relative growth rate and feed conversion during postweaning feedlot performance tests

Knowledge of the relationships between absolute growth rate (AGR), relative growth rate (RGR) and feed conversion (FCONV) of bulls in postweaning feedlot performance tests can give cattle producers important information for selecting superior sires. Weight gain and FCONV data that were collected during 16 yr were analyzed from 393 Angus and 340 Hereford bulls by 26 and 27 sires, respectively, that were individually fed in 140-d tests. Sire variance and covariance components were used to obtain heritability (h2) estimates for AGR, RGR and FCONV and the genetic correlations (rg) and phenotypic correlations (rp) among these traits. Respective mean AGR, RGR and FCONV were 1.27 +/- .14 kg/d, .4378 +/- .0395%/d and 7.32 +/- .58 kg/kg for the Angus and 1.28 +/- .12 kg/d, .4552 +/- .0388%/d and 6.56 +/- .46 kg/kg for the Hereford bulls. Estimates of h2 were similar for AGR and RGR in both Angus (.36 +/- .11 and .22 +/- .09) and Hereford (.33 +/- .11 and .20 +/- .09) bulls. The h2 estimates for FCONV were .14 +/- .07 for Angus and .13 +/- .08 for Herefords. For the Angus and Hereford bulls, respectively, rg were .86 +/- .09 and .86 +/- .13 between AGR and RGR, -.84 +/- .38 and -.74 +/- .49 between AGR and FCONV and -.84 +/- .49 and -.61 +/- .64 between RGR and FCONV. The rp were .80 +/- .03 and .68 +/- .04 between AGR and RGR, -.58 +/- .05 and -.51 +/- .05 between AGR and FCONV and -.71 +/- .04 and -.73 +/- .04 between RGR and FCONV for the Angus and Hereford bulls, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Postweaning growth of unselected Hereford and Angus cattle fed two different diets

Two unselected herds of purebred Hereford and Angus cattle were created and their progeny evaluated during a 4-yr period (1964 to 1967) for 168-d postweaning gain when they were fed either a high- or medium-energy diet. Birth weight and 200-d adjusted weaning weight also were measured and the importance of sire x diet interactions for postweaning gain examined. Year effects were significant (P less than .001) for all traits in Herefords and for postweaning gain in Angus. Postweaning gain of both breeds increased in successive years, but no trend was observed for birth and 200-d weights. Bulls were heavier than heifers (P less than .05) for all three traits in both breeds. Hereford and Angus calves receiving the high-energy diet gained more (P less than .001) than their contemporaries fed the medium-energy diet. Sire differences were significant for birth weight in Herefords and for all three traits in Angus. Sire x diet interactions were not significant for postweaning gain in either breed. Genetic correlations were calculated by two methods: the two-way ANOVA approach using sire and sire x diet interaction variance components and the one-way ANOVA approach in which gains by progeny of each sire on each diet were considered to be two distinct traits. The genetic correlations for gain in Herefords could not be estimated by either method because of negative sire variance component estimates. The genetic correlations for gain in Angus were 1.08 for the two-way ANOVA method and 1.43 +/- .64 for the one-way ANOVA method. These results indicate that sires ranked the same based on progeny performance when fed either diet.     

Genetic parameter estimates for postweaning traits of beef cattle in a stressful environment

Postweaning growth data, collected from a Hereford herd located in the Southwest, were used to estimate genetic parameters for weights and gains. The herd was maintained on unsupplemented range forage, and average weight losses from weaning to yearling age were 9% for bulls and 12% for heifers. Data were grouped into years with poor and good environments based on contemporary group means for gain from 8 to 12 mo. Postweaning growth data (12- and 20-mo weights, 8- to 12-mo gain and 12- to 20-mo gain) were analyzed by least squares methods with a model that included year of birth, sire within year of birth, age of dam and a covariate of age for 12- and 20-mo weights. Heritability estimates of 12- and 20-mo weights for bulls were .58 +/- .15 and .55 +/- .22 in good environments vs .32 +/- .11 and 1.09 +/- .15 in poor environments; for heifers these estimates were .19 +/- .08 and .35 +/- .12 in good environments vs .38 +/- .07 and .47 +/- .09 in poor environments. Heritability estimates of 8- to 12-mo and 12- to 20-mo gain for bulls were .32 +/- .14 and .51 +/- .24 in good environments vs .16 +/- .11 and .09 +/- .14 in poor environments; for heifers these estimates were .21 +/- .08 and .14 +/- .10 in good environments vs .10 +/- .06 and .44 +/- .10 in poor environments. Genetic correlations among the preweaning traits of birth and weaning weight and postweaning weight traits were positive and of a moderate to large magnitude, with the exception of birth and 12-mo weight in a poor environment (-.06 +/- .49). Genetic correlations between 8- to 12-mo gain and birth weight in poor environment and weaning weight in all environments were negative (range from -.06 +/- .33 to -.53 +/- .41). Genetic correlations among 12- and 20-mo weights were large and positive in all environments. Relationships among gains were more variable.     

Heritability estimates of pregnancy rate in beef cows under natural mating

Observations of 3,029 matings over 17 yr on an Ozark upland range were used to estimate heritability of pregnancy rate in Angus, Hereford and Polled Hereford cows. Pregnancy rate, the percentage of cows exposed that produced a live calf in the spring, was transformed using the empirical logit transformation and then analyzed for each breed separately by weighted least squares using a mixed model procedure. A numerator relationship matrix for sires of cows was incorporated into the sire model to account for relationships among sires. Variation among years significantly affected pregnancy rate in all three breeds. Age of dam significantly affected pregnancy rate in the Angus and Hereford groups. Paternal half-sib estimates of heritability from the observed binary data (h2b) for pregnancy rate were calculated on first-calf heifers and mature cows for each breed. Respective h2b estimates for heifers and mature cows were .17 and .09 in the Angus group, .04 and .01 in the Hereford group and .05 and .05 in the Polled Hereford group. The heritability estimates when binary records were transformed to the probit scale (h2) were .04 +/- .003 and .02 +/- .001 for Angus, .01 +/- .002 and 0 for Hereford and .01 +/- .001 and .02 +/- .001 for Polled Hereford for heifers and mature cows, respectively. Heritability estimates in this study are in agreement with the literature, indicating little opportunity for improvement in pregnancy rate by selection within a breed.     

Evaluation of phenotypic and genetic trends in weaning weight in Angus and Hereford populations in Virginia

Weaning weight records of 27,774 Angus calves in 13 herds and 14,738 Hereford calves in 11 herds born during 1953 through 1983 in Virginia were analyzed using regression techniques and maximum likelihood (ML) procedures to estimate phenotypic and genetic trends for adjusted weaning weight (AWWT), weaning weight ratio (WWR) and deviations of AWWT from the mean AWWT of the contemporary group (DEV). Phenotypic trends for AWWT in the Angus and Herefords were .96 plus or minus .02 and .82 plus or minus .03 kg/yr, respectively. In the Angus breed, estimates of one-half of the sire genetic trend obtained from the ML procedure for WWR and DEV were .40 plus or minus .04 ratio units/yr and .72 plus or minus .07 kg/yr, respectively; corresponding values for Herefords were .25 plus or minus .06 ratio units/yr and .45 plus or minus .12 kg/yr. Estimates of one-half of the dam trends for the respective traits were .32 plus or minus .02 ratio units/yr and .55 plus or minus .04 kg/yr for Angus and .21 plus or minus .03 ratio units/yr and .30 plus or minus .07 kg/yr for Herefords. Estimates of sire and dam genetic trends from the regression analyses were slightly higher than estimates from the ML procedure, but adjustments to eliminate bias due to non-random mating and culling from the regression analyses increased the similarity of the results from the two procedures. Average annual genetic trends over the entire study period from the ML procedure for AWWT were 1.27 kg/yr for Angus and .75 kg/yr for Herefords. Genetic trends were not linear over the entire period. Total genetic trends in AWWT for Angus and Hereford, respectively, were .30 and -.61 kg/yr before 1971 and 2.18 and 1.98 kg/yr after 1970.     

Estimates of covariances between reproduction and growth in Australian beef cattle

Estimates of covariance components between scrotal circumference, serving capacity, days to calving, and yearling and final weight were obtained for Hereford, Angus, and Zebu cross cattle in temperate and tropical Australia. Analyses were carried out by REML employing a derivative-free algorithm and fitting bivariate animal models. Aspects of modeling and computational requirements related to the use of this method are discussed. Estimates of heritabilities agreed closely with those from univariate analyses, being low for female reproductive performance and moderate to high for male reproduction and growth. Estimates of genetic correlation between male and female fertility traits were low but favorable, being -.25, -.28, and -.41 between scrotal circumference and days to calving for Herefords, Angus, and Zebu crosses, respectively. Genetic correlations between male reproductive traits and weights ranged from .24 to .52 for the temperate breeds and were higher (.65 to .69) for Zebu crosses. Phenotypic correlations between scrotal circumference and weights were similar for all breeds, ranging from .32 to .47, whereas serving capacity and weights were phenotypically unrelated. Estimates of correlations between days to calving and weights were less consistent. Phenotypically, there was little association between the two traits. Genetic correlations for Zebu crosses were negative and low to moderate (-.36 to -.66) and estimates for Angus were close to zero.     

An evaluation of bias in estimated breeding values for weaning weight in Angus beef cattle field records. I. Estimates of within herd genetic trend

Genetic trends for weaning weight were evaluated in 15 purebred herds in the United States participating in the Angus Herd Improvement. Records production testing program. Regression techniques were used for separate estimates of sire and dam contributions that were summed to estimate total herd trend. Sire contributions, calculated as the pooled within sire regression of weaning weight ratio on year of calf birth, ranged from .01 +/- .23 to 1.30 +/- .24 across the herds and average .51 ratio units/yr. Dam contributions, estimated as the pooled within dam regression of offspring weaning weight ratio, deviated from the contemporary paternal half-sib average ratio, on year of calf birth, ranged from .06 +/- .06 to .68 +/- .11 and averaged .34 ratio units/yr. A positive trend in direct effects was associated with a possible negative trend in maternal effects. The annual trend within herds ranged from .21 to 1.50 ratio units and averaged .85 units over all herds, representing 1.8 kg annual genetic gain in weaning weight.     

Life span of beef-type Bos taurus and Bos indicus x Bos taurus females in a dry, temperate climate

Females representing Hereford, Red Poll, F1 Hereford x Red Poll, F1 Red Poll x Hereford, F1 Angus x Hereford, F1 Angus x Charolais, F1 Brahman x Hereford, and F1 Brahman x Angus breed types were evaluated from birth until 10 yr of age. Of 308 females born alive, 35.7% died or were culled because of injury, serious illness, or reproductive failure. Breed types differed (P less than .01) in total number of mating seasons per cow and total number of progeny born and weaned. Values for lifetime total number of calves weaned were as follows: Hereford, 4.54; Red Poll, 5.45; Hereford x Red Poll, 4.45; Red Poll x Hereford, 5.49; Angus x Hereford, 5.98; Angus x Charolais, 5.57; Brahman x Hereford, 6.96; and Brahman x Angus, 6.22. Brahman crosses (P less than .01) and Angus x Charolais (P less than .10) exceeded Hereford dams in lifetime total number of calves weaned but did not differ from Angus x Herefords. Analysis of the Hereford-Red Poll diallel showed no evidence of heterosis in life span traits. Results indicate that breed type was a major source of variation in reproductive life span of beef-type females. F1 Bos indicus crosses and Angus x Herefords were outstanding in longevity.     

Correlated responses to selection for yearling or18-month weight in Angus and Hereford cattle

Correlated responses to selection for yearling (AS1 herd) or 18-month weight (AS2 herd) wereevaluated against a control (AC0 herd) in a progeny test herd using 2294 calves born in 1975–1988. A sample of privately-owned Angus bulls, available by artificial insemination (AI), were compared with them for eight liveweight or gain traits up to 18 months, with four carcass traits on steers. Cows of known pedigree in the progeny test herd were also evaluated for seven maternal traits. Other correlated responses were evaluated directly in the ACO and selection herds (three puberty traits, daily food intake, cow weight, and survival and reproduction traits).Realised genetic correlations to selection for yearling weight (AS1 herd) averaged 6% higher (forgrowth and carcass traits) than published paternal half-sib estimates, whilst those with 18-month weight (AS2 herd) were about 10% lower than with yearling weight. The sign of maternal genetic effects for live weights up to weaning varied among selection herds. Realised genetic correlations with selection weight averaged 0.51 (carcass fat depth), 0.93 (food intake), 0.16 (scrotal circumference in bulls), 0. 18 (age at puberty) and 0.37 (weight at puberty in heifers), 0.38 (cow weight, AS I herd) and 0.92 (cow weight, AS2 herd). The selection herd differences from control were not significant for cow or calf mortality or reproductive traits (6501 mating records), but tended to be negative for cow and calf death rates, and variable for overall reproductive rate.     

Maternal characteristics of young dams representing Bos taurus and Bos indicus x Bos taurus breed types

Reproductive traits and preweaning growth of progeny from young Hereford, Red Poll, Hereford X Red Poll, Red Poll X Hereford, Angus X Hereford, Angus X Charolais, Brahman X Hereford and Brahman X Angus dams were evaluated. First-calf heifers were mated with Red Angus bulls; Santa Gertrudis sires were used for each cow's second and third breeding season. Herefords, Red Polls and Hereford-Red Poll crosses were below average in percentage of calves weaned, whereas Angus-sired and Brahman-sired dams exceeded the overall mean. Angus X Charolais (P less than .10), Brahman X Hereford (P less than .01) and Brahman X Angus (P less than .10) dams weaned a higher percentage of calves than straightbred Herefords. None of these breed types differed from young Angus X Hereford females in reproductive performance. Angus X Charolais calves ranked highest in 180-d calf weight, exceeding progeny from both Hereford (P less than .01) and Angus X Hereford (P less than .10) dams. Brahman X Hereford dams weaned heavier (P less than .05) calves than Herefords, but their progeny did not differ at weaning from those reared by Angus X Herefords. Calves from Brahman X Angus dams weighed 12.7 kg less (P less than .01) than Angus X Hereford progeny. Analysis of the Hereford-Red Poll diallel showed evidence of (P less than .10) maternal heterosis in 180-d calf weight.(ABSTRACT TRUNCATED AT 250 WORDS)     

Life-cycle evaluation of Bos taurus and Bos indicus X Bos taurus breed types in a dry, temperate climate: performance of mature dams

Mature dams representing Hereford, Red Poll, F1 Hereford x Red Poll, F1 Red Poll x Hereford, F1 Angus x Hereford, F1 Angus x Charolais, F1 Brahman x Hereford and F1 Brahman x Angus breed types were evaluated. All cows were bred to Limousin sires to produce two-way or three-way-cross progeny. Mature Brahman x Hereford dams produced a higher (P less than .05) percentage of live calves than Herefords, but dam breed differences in percentage of calves weaned relative to the number of cows exposed for mating were not statistically significant. Progeny of Angus x Charolais and Red Poll dams were outstanding in weaning weight, but Hereford and Brahman-cross calves were below average. Planned comparisons showed that Angus x Charolais calves were heavier (P less than .01) at weaning than Hereford (23.0 +/- 3.8 kg) or Angus x Hereford (9.6 +/- 3.2 kg) progeny. Mature Angus x Hereford mothers weaned heavier calves than did Brahman x Herefords (7.4 +/- 3.2 kg, P less than .05) or Brahman x Angus (10.9 +/- 3.0 kg, P less than .01). Analysis of the Hereford-Red Poll diallel showed evidence of maternal heterosis in calf weaning weight (4.0 +/- 2.6 kg, P less than .05), but there was no difference in the percentage of calves weaned by crossbred vs straightbred dams.(ABSTRACT TRUNCATED AT 250 WORDS)     

Heritabilities and genetic correlations of growth and reproductive measurements in Hereford bulls

Weight, hip height, heart girth, pelvic height, pelvic width and scrotal circumference were measured at 403 and 490 d on 427 Hereford bulls. The bulls were members of a random-selection herd so estimates of genetic parameters should have a minimum of bias due to selection. Heritabilities and genetic correlations were estimated by normal paternal half-sib (PHS) correlation procedures. In addition, 256 son-sire pairs (RSS) were used to estimate heritabilities and genetic correlations by regression and covariance methods. The PHS method produced heritability estimates in the range of .41 to .58 for all measures at both ages, with the exceptions of hip height at 403 d (.24) and pelvic height at 490 d (.23). The estimates derived in the RSS method ranged from .10 to .60. The RSS relationship would contain a portion of any maternal X direct covariance effects. A difference in heritability estimated by the two methods could be a reflection of this covariance. Genetic correlations tended to be larger than phenotypic and, in several cases, were negative. The difference in the correlation between two measurements taken at 403 d vs the same correlation estimated at 490 d was not readily explainable but may be evidence for differences in maturation rates or maternal effects. Scrotal circumference had a positive genetic correlation with weight and heart girth and near 0 or negative genetic correlations with pelvic measures. Hip height had positive genetic correlations with weight and heart girth at 403 and 490 d and with pelvic measurements at 403 d, but the correlations were not as large at 490 d.(ABSTRACT TRUNCATED AT 250 WORDS)     

Inbreeding and immunoglobulin G1 concentrations in cattle

Immunoglobulin G1 concentration (IgG1) was measured in presuckle colostrum and calf serum obtained at 36 h and at weaning from inbred and straightbred Angus, Brangus, Hereford, Red Angus and Simmental cattle. Sources of variation considered as dam traits examined for IgG1 in colostrum and 36-h calf serum included line of sire, sire within line, age, and linear regression of IgG1 on inbreeding of dam. Only line of sire and inbreeding of dam were significant in the analysis of 36-h calf serum. Sources of variation considered as calf traits examined for IgG1 in calf serum at 36 h and at weaning included line of sire, sire within line, sex of calf, age of dam, and regressions of calf serum IgG1 on inbreeding of the calf and on dam's colostral IgG1. Only sire within line and the regression on dam's colostral IgG1 were significant for calf serum IgG1 at 36 h. Large differences existed in 36-h calf serum IgG1 between sires both within lines and when lines were ignored. Calves with 36-h serum IgG1 of less than 10 mg/ml were two to four times more likely to die before weaning than calves with higher IgG1 levels. The heritability estimates of IgG1 by paternal half-sib analysis were .41 +/- .30 for colostrum measured as a trait of the dam and .56 +/- .25 for 36-h. calf serum and .05 +/- .17 for calf serum at weaning considered as a trait of the calf. These estimates indicate that IgG1 in colostrum and 36-h calf serum could be increased by selection.(ABSTRACT TRUNCATED AT 250 WORDS)     

Genetic parameter estimates for preweaning traits of beef cattle in a stressful environment

Data collected from 1957 through 1985 from a Hereford herd located in the Southwest were analyzed separately for each sex to evaluate the heritabilities of and genetic correlations among preweaning growth traits within groups of environmentally similar years. Data were grouped into years with poor, moderate and good environments based on contemporary group means for male calves' weaning weight. A total of 7,690 records were analyzed for birth weight, weaning weight and preweaning daily gain with a model that included year of birth, sire within year of birth, age of dam and a covariate of day of birth for birth weight or age at weaning for the weaning traits. Year of birth was a significant source of variation in all environments for all traits, accounting for more of the variation in the good and poor years than in moderate years. Heritability estimates for all traits were greater in good and moderate years than in poor years for bull calves. For heifers, however, estimates for weaning weight and preweaning daily gain were greater in the poor environment. Genetic correlations among birth weight and preweaning gain increased from the good environment to the poor environment (-.49 +/- .26 to .82 +/- .56 for male calves and -.09 +/- 2.6 to .46 +/- .25 for female calves) but phenotypic correlations were near zero in all environments.(ABSTRACT TRUNCATED AT 250 WORDS)     

Estimation of genetic parameters for wool fiber diameter measures.

Genetic and phenotypic correlations and heritability estimates of side, britch, and core diameters; side and britch CV; side and britch diameter difference; and clean fleece weight were investigated using 385 western white-faced ewes produced by 50 sires and maintained at two locations on a selection study. Data were analyzed using analysis of variance procedures, and effects in the final model included breed of sire-selection line combination, sire within breed-selection line, and location. Heritabilities were estimated by paternal half-sib analysis. Sires within breed-selection line represented a significant source of variation for all traits studied. Location had a significant effect on side diameter, side and britch diameter difference, and clean fleece weight. Age of ewe only affected clean fleece weight. Phenotypic and genetic correlations among side, britch, and core diameter measures were high and positive. Phenotypic correlations ranged from .68 to .75 and genetic correlations ranged from .74 to .89. The genetic correlations between side and britch diameter difference and side diameter or core diameter were small (-.16 and .28, respectively). However, there was a stronger genetic correlation between side and britch diameter difference and britch diameter (.55). Heritability of the difference between side and britch diameter was high (.46 +/- .16) and similar to heritability estimates reported for other wool traits. Results of this study indicate that relatively rapid genetic progress through selection for fiber diameter should be possible. In addition, increased uniformity in fiber diameter should be possible through selection for either side and britch diameter difference or side or britch CV.     

Estimation of genetic parameters among breeding soundness examination components and growth traits in yearling bulls

Data on breeding soundness examinations (BSE) and performance traits were obtained on 549 yearling beef bulls at the San Juan Basin Research Center, Hesperus, Co from 1976 to 1984. Genetic parameters estimated for components of BSE included percent motility (PMOT), percent primary abnormalities (PPRIM), percent secondary abnormalities (PSEC), percent normal sperm (PNOR), scrotal circumference (SC) and BSE score (BSESC). Performance traits included birth weight, weaning weight, yearling weight and average daily gain. The least squares model included birth year, age of dam and breed as fixed effects, sire/breed as a random variable, and age and percent inbreeding as covariates. Paternal half-sib estimates of heritability were PMOT, .08 +/- .07; PPRIM, .31 +/- .09; PSEC, .02 +/- .05; PNOR, .07 +/- .06; BSESC, .10 +/- .06 and SC, .40 +/- .09. Phenotypic correlations among BSE components and growth traits were generally favorable. Genetic correlations involving percent secondary abnormalities were highly variable with large standard errors. Seminal traits improved as age increased and became poorer as inbreeding increased.     

Genetic parameters for carcass and meat quality traits and their relationships to liveweight and wool production in hogget Merino rams.

Genetic parameters for carcass and meat quality traits of about 18-month-old Merino rams (n = 5870), the progeny of 543 sires from three research resource flocks, were estimated. The estimates of heritability for hot carcass weight (HCW) and the various fat and muscle dimension measurements were moderate and ranged from 0.20 to 0.37. The brightness of meat (colour L*, 0.18 +/- 0.03 standard error) and meat pH (0.22 +/- 0.03) also had moderate estimates of heritability, although meat relative redness (colour a*, 0.10 +/- 0.03) and relative yellowness (colour b*, 0.10 +/- 0.03) were lower. Heritability estimates for live weights were moderate and ranged from 0.29 to 0.41 with significant permanent maternal environmental effects (0.13 to 0.10). The heritability estimates for the hogget wool traits were moderate to high and ranged from 0.27 to 0.60. The ultrasound measurements of fat depth (FATUS) and eye muscle depth (EMDUS) on live animals were highly genetically correlated with the corresponding carcass measurements (0.69 +/- 0.09 FATC and 0.77 +/- 0.07 EMD). Carcass tissue depth (FATGR) had moderate to low genetic correlations with carcass muscle measurements [0.18 +/- 0.10 EMD and 0.05 +/- 0.10 eye muscle area (EMA)], while those with FATC were negative. The genetic correlation between EMD and eye muscle width (EMW) was 0.41 +/- 0.08, while EMA was highly correlated with EMD (0.89 +/- 0.0) and EMW (0.78 +/- 0.04). The genetic correlations for muscle colour with muscle measurements were moderately negative, while those with fat measurements were close to zero. Meat pH was positively correlated with muscle measurements (0.14 to 0.17) and negatively correlated with fat measurements (-0.06 to -0.18). EMDUS also showed a similar pattern of correlations to EMD with meat quality indicator traits, although FATUS had positive correlations with these traits which were generally smaller than their standard error. The genetic correlations among the meat colour traits were high and positive while those with meat pH were high and negative, which were all in the favourable direction. Generally, phenotypic correlations were similar or slightly lower than the corresponding genetic correlations. There were generally small to moderate negative genetic correlations between clean fleece weight (CFW) and carcass fat traits while those with muscle traits were close to zero. As the Merino is already a relatively lean breed, this implies that particular attention should be given to this relationship in Merino breeding programmes to prevent the reduction of fat reserves as a correlated response to selection for increased fleece weight. The ultrasound scan traits generally showed a similar pattern to the corresponding carcass fat and muscle traits. There was a small unfavourable genetic correlation between CFW and meat pH (0.19 +/- 0.07).     

Genetic analyses of live-animal ultrasound and abattoir carcass traits in Australian Angus and Hereford cattle

In order to estimate genetic parameters, abattoir carcass data on 1,713 Angus and 1,007 Hereford steers and heifers were combined with yearling live-animal ultrasound measurements on 8,196 Angus and 3,405 Hereford individuals from seedstock herds. Abattoir measures included carcass weight (CWT), percentage of retail beefyield (RBY), near-infrared measured intramuscular fat percentage (CIMF), preslaughter scanned eye muscle area (CEMA), and subcutaneous fat depth at the 12th rib (CRIB) and at the P8 site (CP8). Ultrasound scans on yearling animals included 12th-rib fat depth (SRIB), rump fat depth at the P8 site (SP8), eye muscle area (SEMA), and percentage of intramuscular fat (SIMF). Records on CWT were adjusted to 650-d slaughter age, and the remaining abattoir traits were adjusted to 300-kg CWT. Scan data were analyzed treating records on males and females as different traits. Multivariate analyses were performed on a variety of trait combinations using animal model and REML algorithm. Heritability (h2) estimates for CWT, RBY, CIMF, CP8, CRIB, and CEMA were .31, .68, .43, .44, .28, and .26, respectively, for Angus and .54, .36, .36, .08, .27, .38, respectively, for Hereford. Pooled across sexes, h2 estimates for SIMF, SP8, SRIB, and SEMA were .33, .55, .51, and .42, respectively, for Angus and .20, .31, .18, and .38, respectively, for Hereford. Genetic correlations (r(g)) between the same pair of carcass traits measured at yearling through scanning and directly at the abattoir were moderate to strongly positive, suggesting that selection using yearling ultrasound measurements of seedstock cattle should result in predictable genetic improvement for abattoir carcass characteristics. Estimates of r(g) between the scanned fat measurements and RBY were negative, ranging from -.85 for Angus heifers to -.05 for Hereford heifers. Also, the estimates of r(g) between SEMA and the fat records measured at the abattoir were negative and ranged from -.94 in Hereford heifers to -.02 in Angus heifers.     

Genetic effects for reproductive traits in beef cattle and predicted performance

Reproductive data were collected on 4,595 cow exposures and subsequent calvings over four generations in a rotational crossbreeding study involving Angus, Brahman, Charolais and Hereford breeds. Direct and maternal additive (Ig and Mg) and nonadditive (Ih and Mh) genetic effects were estimated for calving rate, calf survival, weaning rate, calving assistance and calf birth date. Genetic effects were estimated by regressing individual animal response on the proportion of genes from breed of origin and gene combinations expected for the four breeds in offspring and in dams. Breed direct and maternal additive and nonadditive genetic effects were expressed as a deviation from the least squares mean. Brahman Ig effects decreased calving and weaning rate (-9.5 +/- 4.0 and -11.8 +/- 4.4%) but Mh effects for weaning rate that included Brahman were positive, ranging from 16.5 +/- 6.7% for Angus-Brahman to 27.8 +/- 6.9% for Brahman-Hereford. The Brahman Ig effect delayed calf birth date (9.8 +/- 2.1 d; P less than .01), whereas Angus and Hereford Ig effects influenced earlier calf birth dates (-4.3 +/- 1.9 and -4.1 +/- 1.9 d; P less than .05). Brahman combination Mh effects also influenced earlier calf birth dates (P less than .01). The Charolais Ig effect for calving assistance was positive (4.3 +/- 1.9%; P less than .05), whereas Angus-Brahman and Brahman-Charolais Mh effects for calving assistance were negative (-6.5 +/- 3.2 and -7.0 +/- 3.2%; P less than .05) and more desirable. Predicted reproductive traits for rotational mating systems were intermediate between predicted reproductive traits for two- and three-breed terminal crosses. Predicted calving and weaning rates were maximized when Brahaman first-cross and Charolais-Hereford cows were used in three-breed cross mating systems.