Estimation of genetic parameters among reproductive and growth traits in yearling heifers

Growth and reproductive data were obtained on 779 beef heifers at the San Juan Basin Research Center, Hesperus, Co. Genetic parameters were estimated for age of puberty (AOP), age of first calving (AOC), julian day of first calving (DOC), julian day of second calving (DOSC), birth weight, weaning weight, yearling weight, and average daily gain from weaning to yearling and to cycling weights. The least squares model included birth year, age of dam and breed as fixed effects, sire/breed as a random variable, and day of birth and percent inbreeding as covariates. Day of birth was not included in the analyses of AOC, DOC or DOSC. Paternal half-sib estimates of heritability were: AOP, .10 +/- .17; AOC, .01 +/- .12; DOC, .09 +/- .13 and DOSC, .36 +/- .18. Genetic and phenotypic correlations were generally favorable, but genetic correlations were variable with large standard errors. Inbreeding had a detrimental effect on reproductive traits, and a seasonal effect was present for AOP.     

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.     

Genetic, phenotypic and environmental relationships between sow body weight and sow productivity traits

Yorkshire and Duroc litter records were used to estimate genetic, phenotypic and environmental relationships between sow body weight and sow productivity traits. Two data sets with two subsets each were used to complete this study; 663 and 460 records included litter traits only, while 522 and 359 records also contained sow body weight for Yorkshires and Durocs, respectively. Heritability estimates for number born (NB), number born alive (NBA), total birth weight of live pigs (BWLIT), litter weight at 3 wk (WT3WK), sow weight at parturition (WTDAMPAR) and sow weight at weaning (WTDAMWN) were .24 +/- .14, .21 +/- .14, .42 +/- .16, .19 +/- .14, .72 +/- .21 and .42 +/- .18, respectively, for Yorkshires and .05 +/- .10, .04 +/- .10, .21 +/- .14, .25 +/- .15, .85 +/- .25 and .87 +/- .26, respectively, for the Durocs. Repeatability estimates for NB, NBA, BWLIT, WT3WK, WTDAMPAR and WTDAMWN were .13 +/- .06, .17 +/- .06, .27 +/- .06, .13 +/- .06, .64 +/- .05 and .54 +/- .05, respectively, for Yorkshires and .17 +/- .06, .21 +/- .06, .14 +/- .06, .17 +/- .06, .28 +/- .07 and .39 +/- .07, respectively, for Durocs. Genetic correlations among litter traits were high and positive in the Yorkshire data. Genetic correlations between NBA and WTDAMPAR, NBA and WTDAMWN, WT3WK and WTDAMPAR, and WT3WK and WTDAMWN were .37 +/- .25, .18 +/- .34, .60 +/- .29 and .29 +/- .45, respectively, in the Yorkshire data. Genetic correlations among litter traits in the Duroc analysis had large standard errors but were generally similar to the estimates obtained from the Yorkshire data. The genetic correlation between WTDAMPAR and WTDAMWN was .93 +/- .09 for Yorkshire sows. The primary conclusion from this study is that as selection increases sow productivity traits, there will be a positive correlated response in sow body weight.     

Relationships of sire scrotal circumference to offspring reproduction and growth

Reproductive and growth data were obtained on 779 and 564 yearling beef heifers and bulls, respectively, that had sires with yearling scrotal circumference data at the San Juan Basin Research Center, Hesperus, CO. Partial regression coefficients of reproductive and growth traits on inbreeding (FXC) and age of the individual and adjusted scrotal circumference of sire (SCSI) were obtained. Growth and reproductive traits of heifers and growth and breeding soundness traits of bulls were analyzed. Separate analyses for each sex were performed, but least squares models were similar. Models included fixed effects of breed, birth year (BY), age of dam (AOD) and the covariates FXC, age (day of birth in heifer analyses) and SCSI. Scrotal circumference of sire was adjusted for age, FXC, AOD and BY using values obtained in a separate analysis. Seminal traits improved as age increased, and there was a seasonal effect present for age of puberty. Inbreeding had a detrimental effect on reproductive traits. Partial regression coefficients for the reproductive traits on SCSI were: age of puberty, -.796 d/cm; age of first calving, -.826 d/cm; julian day of first calving, -.667 d/cm; julian day of second calving, .597 d/cm; most probable producing ability, .132 %/cm; percent sperm motility, -.74 %/cm; percent primary sperm abnormalities, .08 %/cm; percent secondary sperm abnormalities, .92 %/cm; percent normal sperm, -1.28 %/cm; total breeding soundness examination score, .28 units/cm and scrotal circumference, .306 cm/cm. A heritability of .39 was obtained for scrotal circumference.     

Estimation of genetic parameters and effects of cytoplasmic line on scrotal circumference and semen quality traits in Angus bulls

The purpose of this study was to estimate the heritability of scrotal circumference (SC) and semen traits, genetic correlations between SC and semen quality traits, and the effect of cytoplasmic line on SC and semen traits. Breeding soundness exam (BSE) data were collected on registered Angus bulls at 4 ranches over 7 yr. The American Angus Association provided historical pedigree information to estimate the effect of cytoplasmic line on SC and semen quality traits. After editing, the evaluated data set contained 1,281 bulls with breeding soundness exam data that traced back to 100 founder dams. Data were analyzed using a 2-trait animal model to obtain heritability, genetic correlation between SC and semen quality traits, as well as the effect of cytoplasmic line as a random effect for SC, percent motility (MOT), percent primary abnormalities (PRIM), percent secondary abnormalities (SEC), and percent total abnormalities (TOT) using multiple-trait derivative-free REML. Fixed effects included source ranch and collection year, and test age was used as a covariate. Estimates of heritability for SC, MOT, PRIM, SEC, and TOT were 0.46, 0.05, 0.27, 0.23, and 0.25, respectively. Genetic correlations between SC and MOT, PRIM, SEC, and TOT were 0.36, -0.19, -0.11, and -0.23, respectively. The proportions of phenotypic variance accounted for by cytoplasmic line for SC, MOT, PRIM, SEC, and TOT were <0.001, 0.013, 0.023, 0.002, and <0.001, respectively. Genetic correlations between SC and semen quality traits were low to moderate and favorable. Cytoplasmic line may have a marginal effect on MOT and PRIM, but is likely not a significant source of variation for SC, SEC, or TOT.     

Genetic relationships between scrotal circumference and female reproductive traits

Records for yearling scrotal circumference (SC; n = 7,580), age at puberty in heifers (AP; n = 5,292), age at first calving (AFC; n = 4,835), and pregnancy, calving, or weaning status following the first breeding season (PR1, CR1, or WR1, respectively; n = 7,003) from 12 Bos taurus breeds collected at the Meat Animal Research Center (USDA) between 1978 and 1991 were used to estimate genetic parameters. Age at puberty (AP) was defined as age in days at first detected ovulatory estrus. Pregnancy (calving or weaning) status was scored as one for females conceiving (calving or weaning) given exposure during the breeding season and as zero otherwise. The final model for SC included fixed effects of age of dam at breeding (AD), year of breeding (Y), and breed (B) and age in days at measurement as a covariate. Fixed effects in models for AP and AFC were AD, Y, B, and month of birth. Fixed effects in models for PR1, CR1, and WR1 included AD, Y, and B. For all traits, random effects in the model were direct genetic, maternal genetic, maternal permanent environmental, and residual. Analyses for a three-trait animal model were carried out with SC, AP, and a third trait (the third trait was AFC, PR1, CR1, or WR1). A derivative-free restricted maximum likelihood algorithm was used to estimate the (co)variance components. Direct and maternal heritability estimates were 0.41 and 0.05 for SC; 0.16 and 0.03 for AP; 0.08 and 0.00 for AFC; 0.14 and 0.02 for PR1; 0.14 and 0.03 for CR1; and 0.12 and 0.01 for WR1. Genetic correlations between direct and maternal genetic effects within trait were -0.26, -0.63, -0.91, -0.79, -0.66, and -0.85 for SC, AP, AFC, PR1, CR1, and WR1, respectively. Direct genetic correlations between SC and AP and between those traits and AFC, PR1, CR1, and WR1 ranged from -0.15 (between SC and AP) to 0.23 (between AP and WR1). Estimates of heritability indicate that yearling SC should respond to direct selection better than AP, AFC, PR1, CR1, and WR1. Variation due to maternal genetic effects was small for all traits. No strong genetic correlations were detected between SC and female reproductive traits or between AP and the other female traits. These results suggest that genetic response in female reproductive traits through sire selection on yearling SC is not expected to be effective.     

Characteristics of Line 1 Hereford females resulting from selection by independent culling levels for below-average birth weight and high yearling weight or by mass selection for high yearling weight

Simultaneous selection for low birth weight and high yearling weight has been advocated to improve efficiency of beef production. Two sublines of Line 1 Hereford cattle were established by selection either for below-average birth weight and high yearling weight (YB) or for high yearling weight alone (YW). Direct effects on birth weight and yearling weight diverged between sublines with approximately four generations of selection. The objective of this study was to estimate genetic trends for traits of the cows. A three-parameter growth curve [Wt = A(1 - b0e(-kt))] was fitted to age (t, d)-weight (W, kg) data for cows surviving past 4.5 yr of age (n = 738). The resulting parameter estimates were analyzed simultaneously with birth weight and yearling weight using multiple-trait restricted maximum likelihood methods. To estimate maternal additive effects on calf gain from birth to weaning (MILK) the two-trait model previously used to analyze birth weight and yearling weight was transformed to the equivalent three-trait model with birth weight, gain from birth to weaning, and gain from weaning to yearling as dependent variables. Heritability estimates were 0.32, 0.27, 0.10, and 0.20 for A, b0, k, and MILK, respectively. Genetic correlations with direct effects on birth weight were 0.34, -0.11, and 0.55 and with direct effects on yearling weight were 0.65, -0.17, and 0.11 for A, b0, and k, respectively. Genetic trends for YB and YW, respectively, were as follows: A (kg/generation), 8.0+/-0.2 and 10.1+/-0.2; b0 (x 1,000), -1.34+/-0.07 and -1.16+/-0.07; k (x 1,000), -14.3+/-0.1 and 4.3+/-0.1; and MILK (kg), 1.25+/-0.05 and 1.89+/-0.05. Beef cows resulting from simultaneous selection for below-average birth weight and increased yearling weight had different growth curves and reduced genetic trend in maternal gain from birth to weaning relative to cows resulting from selection for increased yearling weight.     

Yearling trait comparisons among inbred lines and selected noninbred and randomly bred control groups of Rambouillet, Targhee and Columbia ewes

Inbreeding with concurrent selection was used to develop 26 Rambouillet, 20 Targhee and 10 Columbia inbred lines of sheep. Inbreeding coefficients averaged 30, 29 and 30% for the three breeds, respectively, at the conclusion of the study. A selected noninbred control group and a randomly bred unselected control group were maintained for each breed. Yearling traits were evaluated for 545 Rambouillet, 572 Targhee and 411 Columbia yearling ewes, each belonging to one of the inbred lines or control groups. In each breed, the selected controls were generally of greatest overall merit, the unselected controls intermediate and the inbred lines of least merit. Only a few yearling traits of only a few inbred lines were superior (P less than .05) to those of their appropriate selected control groups. Selection within inbred lines was generally ineffective in offsetting inbreeding depression. However, single trait selection for traits of high heritability, notably yearling weight, clean fleece weight and staple length, appeared to compensate for inbreeding effects on those traits. Deleterious consequences of inbreeding were particularly apparent in yearling weight, average daily gain, type and condition scores, grease and clean fleece weights and index of overall merit. Inbreeding also resulted in fewer neck folds among inbreds of all three breeds. Correlations between the rankings of inbred lines at weaning and yearling ages were high for traits of higher heritability. Superiority of the selected controls in most traits was of about the same magnitude at weaning and yearling ages. In no case did the final overall merit (index value) of an inbred line of any of the three breeds significantly exceed the overall merit of its respective selected control group.     

Relationship between a bull's parental genetic merit difference and subsequent progeny trait variability in Angus, Gelbvieh, and Limousin cattle

Data from the American Angus Association, American Gelbvieh Association, and the North American Limousin Foundation were analyzed to determine whether parental genetic differences are associated with Mendelian sampling of their bull progeny or with Mendelian sampling variances and weight variances of their bull progeny's offspring. Parental differences were measured as the difference between the parents' EPD for birth weight (DIF(BW)), weaning weight direct (DIF(WW)), and yearling weight (DIF(YW)). A bull's data were used if both parents had calculated EPD and the bull had at least 25 progeny with records for the specific trait. Traits calculated for each bull were his Mendelian sampling (MS(Bull)), progeny Mendelian sampling variance (MSsigma2progeny), progeny weight variance (WTsigma2), and progeny corrected weight variance (CWTsigma2 = adjusted weight minus appropriate dam EPD) for birth, weaning, and yearling weights. Pearson correlations were computed between DIF(BW), DIF(WW), and DIF(YW) and MS(Bull), MSsigma2progeny, WTsigma2, and CWTsigma2 for each trait, within each breed. Across breeds, the correlations ranged from -.07 to .11 for MS(Bull) .01 to .14 for MSsigma2progeny, -.06 to .09 for WTsigma2, and -.06 to .08 for CWTsigma2. Although some of the correlations were significantly different from zero their relatively small magnitude indicates little relationship between parental differences in genetic merit and subsequent offspring variability for each of the three breeds.     

Genetic associations between flight speed and growth traits in Nellore cattle

The aim of the present study was to estimate genetic parameters for flight speed and its association with growth traits in Nellore beef cattle. The flight speed (FS) of 7,402 yearling animals was measured, using a device composed of a pair of photoelectric cells. Time interval data (s) were converted to speed (m/s) and faster animals were regarded as more reactive. The growth traits analyzed were weaning weight (WW), ADG from weaning to yearling age, and yearling scrotal circumference (SC). The (co)variance components were estimated using REML in a multitrait analysis applying an animal model. The model included random direct additive genetic and residual effects, fixed effects of contemporary groups, age of dam (classes), and age of animal as covariable. For WW, the model also included maternal genetic and permanent environmental random effects. The direct heritability estimate for FS was 0.26 ± 0.05 and direct heritability estimates for WW, SC, and ADG were 0.30 ± 0.01, 0.48 ± 0.02, and 0.19 ± 0.01, respectively. Estimates of the genetic correlation between FS and the growth traits were -0.12 ± 0.07 (WW), -0.13 ± 0.08 (ADG), and -0.11 ± 0.07 (SC). Although the values were low, these correlations showed that animals with better temperaments (slower FS) tended to present better performance. It is possible to infer that longterm selection for weight and scrotal circumference can promote a positive genetic response in the temperament of animals. Nevertheless, to obtain faster genetic progress in temperament, it would be necessary to perform direct selection for such trait. Flight speed is an easily measured indicator of temperament and can be included as a selection criterion in breeding programs for Nellore cattle.     

Age adjustment factors, heritabilities and genetic correlations for scrotal circumference and related growth traits in Hereford and Brangus bulls

Field data records on 10,511 Hereford and 2,522 Brangus bulls between 330 and 430 d of age were analyzed to find age of calf and age of dam adjustment factors for yearling scrotal circumference. Age of calf adjustment factors were .024 cm/d for Hereford bulls and .041 cm/d for Brangus bulls. Sons of Hereford dams were adjusted to a 6- to 8-yr dam age basis by adding .7, .3, .2, .2 or .3 cm for dams 2, 3, 4, 5 or 8 or more years old, respectively. Age of dam adjustment factors for Brangus bulls were .8, .4, .3 and .2 for dams 2, 3, 4 or 8 or more years old, respectively. Variance and covariance components for yearling scrotal circumference and several growth traits were estimated within breed using multiple-trait models and pseudo expectations involving the solutions and the right-hand sides of the mixed-model equations. Additive heritability estimates for yearling scrotal circumference of .53 and .16 were found for Hereford and Brangus bulls, respectively. Maternal heritability estimates of .12 and .10 were found for Hereford and Brangus bulls, respectively. Genetic correlations between yearling scrotal circumference and other growth traits were positive for both sets of data indicating that selection for yearling scrotal circumference should not adversely affect other growth traits in either breed. Environmental correlation estimates between yearling scrotal circumference and adjusted birth weight and between yearling scrotal circumference and adjusted 205-d weight and adjusted 365-d height were positive and moderate in magnitude for both breeds.     

Effect of preweaning nutritional management on yearling weight response in an open-herd selection program

Records on 276 progeny were collected in the final 2 yr (1984 and 1985) of an 8-yr Hereford cattle selection project. Selection was practiced using the top sires from the American Hereford Association's National Cattle Evaluation based on yearling weight expected progeny difference. An unselected control line was maintained to monitor environmental change. One-half of each line was creep-fed during the preweaning period for the last 2 yr to evaluate genotype x environment interactions. Direct response to yearling weight selection averaged 28 +/- 8 kg. Correlated response to selection amounted to .057 +/- .028 kg/d in preweaning ADG, 14 +/- 6 kg in weaning weight, .085 +/- .033 kg/d in postweaning ADG, 4.6 +/- 1.5 cm in yearling hip height and 11.2 +/- 3.0 cm2 in yearling pelvic area. Yearling fat thickness and scrotal circumference were not significantly affected by selection. Significant effects of creep feeding were observed for yearling weight (15 +/- 3 kg), preweaning ADG (.067 +/- .012 kg/d), weaning weight (13 +/- 2 kg), yearling hip height (1.2 +/- .5 cm) and yearling fat thickness (.07 +/- .03 cm). Postweaning ADG, yearling pelvic area and yearling scrotal circumference were not affected by creep feeding. No significant genetic group x creep feeding effects were found for any of the traits analyzed, indicating calves genetically superior for growth did not gain any additional advantage from creep feeding.     

Population parameter estimates for performance and reproductive traits in Polish Large White nucleus herds

Performance test records from on-farm tests of young Polish Large White boars and reproductive records of Polish Large White sows from 94 nucleus farms during 1978 to 1987 were used to estimate population parameters for the measured traits. The number of boar performance records after editing was 114,347 from 3,932 sires, 21,543 dams, 44,493 litters and 1,075 herd-year-seasons. Reproductive performance records of sows involved 41,080 litters from 2,348 sires, 18,683 dams and 1,520 herd-year-seasons. Both data sets were analyzed by using restricted maximum-likelihood programs. The model used for the performance records included fixed herd-year-seasons, random sires, dams and error effects, and covariances for the year of birth of sire and year of birth of dam. The model used for the reproduction data set was the same as the performance data with parity as an additional fixed effect. Estimated heritabilities were .27, .29, .26, .07, .06, .06 for average daily gain standardized to 180 d (ADG), backfat thickness standardized to 110 kg BW (BF), days to 110 kg (DAYS), litter size at birth born alive (NBA), litter size at 21 d (N21) and litter weight at 21 d (W21), respectively. Estimated common environmental effects for the same traits were .09, .10, .09, .06, .07 and .08, respectively. Genetic correlations were .25 (ADG and BF), -.99 (ADG and DAYS), -.21 (BF and DAYS), .91 (NBA and N21), .68 (NBA and W21) and .80 (N21 and W21). The respective phenotypic correlations were .23, -.99, -.20, .88, .75, .86. These population parameters for Polish Large White pigs are similar to those for breeds in other countries.     

Genetic parameters for carcass traits and their live animal indicators in Simmental cattle

The objective of this study was to estimate parameters required for genetic evaluation of Simmental carcass merit using carcass and live animal data. Carcass weight, fat thickness, longissimus muscle area, and marbling score were available from 5,750 steers and 1,504 heifers sired by Simmental bulls. Additionally, yearling ultrasound measurements of fat thickness, longissimus muscle area, and estimated percentage of intramuscular fat were available on Simmental bulls (n = 3,409) and heifers (n = 1,503). An extended pedigree was used to construct the relationship matrix (n = 23,968) linking bulls and heifers with ultrasound data to steers and heifers with carcass data. All data were obtained from the American Simmental Association. No animal had both ultrasound and carcass data. Using an animal model and treating corresponding ultrasound and carcass traits separately, genetic parameters were estimated using restricted maximum likelihood. Heritability estimates for carcass traits were 0.48 +/- 0.06, 0.35 +/- 0.05, 0.46 +/- 0.05, and 0.54 +/- 0.05 for carcass weight, fat thickness, longissimus muscle area, and marbling score, respectively. Heritability estimates for bull (heifer) ultrasound traits were 0.53 +/- 0.07 (0.69 +/- 0.09), 0.37 +/- 0.06 (0.51 +/- 0.09), and 0.47 +/- 0.06 (0.52 +/- 0.09) for fat thickness, longissimus muscle area, and intramuscular fat percentage, respectively. Heritability of weight at scan was 0.47 +/- 0.05. Using a bivariate weight model including scan weight of bulls and heifers with carcass weight of slaughter animals, a genetic correlation of 0.77 +/- 0.10 was obtained. Models for fat thickness, longissimus muscle area, and marbling score were each trivariate, including ultrasound measurements on yearling bulls and heifers, and corresponding carcass traits of slaughter animals. Genetic correlations of carcass fat thickness with bull and heifer ultrasound fat were 0.79 +/- 0.13 and 0.83 +/- 0.12, respectively. Genetic correlations of carcass longissimus muscle area with bull and heifer ultrasound longissimus muscle area were 0.80 +/- 0.11 and 0.54 +/- 0.12, respectively. Genetic correlations of carcass marbling score with bull and heifer ultrasound intramuscular fat percentage were 0.74 +/- 0.11 and 0.69 +/- 0.13, respectively. These results provide the parameter estimates necessary for genetic evaluation of Simmental carcass merit using both data from steer and heifer carcasses, and their ultrasound indicators on yearling bulls and heifers.     

Quantitative analysis of birth, weaning, and yearling weights and calving difficulty in Piedmontese crossbreds segregating an inactive myostatin allele.

The Piedmontese breed has a high frequency of double-muscling. Animals tested in this breed are homozygous for a guanine to adenine transition in exon 3 (C313Y) of the myostatin (MSTN) gene. This transition seems to be responsible for the double-muscling phenotype. The objective of this study was to compare effects of alternative MSTN genotypes on proportion of assisted calving and weights at birth, weaning, and 1 yr of age. Reciprocal backcross and F2 calves out of Piedmontese-Angus (PA) and Piedmontese-Hereford (PH) dams born in 1995 (n = 82), 1996 (n = 75), and 1997 (n = 144) were evaluated for birth (BWT, kg), adjusted weaning (W200, kg), and yearling (W365, kg) weights and calving difficulty expressed as a proportion of assisted calving (CD). The number of copies of C313Y was assessed in each calf. Data were analyzed with a model that included effects of year, sex, subclasses of proportion Piedmontese (.25, .5, .75) by number of C313Y copies (0 = +/+, 1 = mh/+, 2 = mh/mh), and age of dam as covariate. For BWT, heterozygous mh/+ animals were 3.2 +/- .8 kg heavier than +/+ animals. Homozygous mh/mh animals increased .19 +/- .06 in proportion of CD compared with mh/+ animals. Differences between homozygous animals (mh/mh - +/+) were 5.2 +/- 1 kg for BWT and .21 +/- .06 for CD. Heterozygous mh/+ animals were 9.1 +/- 4 kg heavier at W200 than homozygous +/+ animals. Homozygous +/+ and heterozygous animals were 20 +/- 8 and 24.5 +/- 8 kg, respectively, heavier at W365 than mh/mh animals. Differences between mh/+ and the mean of mh/mh and +/+ genotypes for W200 and W365 were 8.8 +/- 3 and 18 +/- 5 kg, respectively, suggesting dominance effects on postnatal growth. Production of heterozygous animals, to take advantage of the positive impact of one copy of C313Y on carcass traits, may be a viable option when the value of increased retail product yield is greater than the increased cost associated with calving difficulty.     

Scrotal circumference in yearling Hereford bulls: adjustment factors, heritabilities and genetic, environmental and phenotypic relationships with growth traits

Field data on 4,233 yearling Hereford bulls were analyzed using fixed and mixed model least-squares procedures to examine factors affecting scrotal circumference; determine appropriate adjustment factors; and study genetic, environmental and phenotypic relationships among scrotal circumference and growth traits. Scrotal circumference was affected by postweaning feed level; contemporary group/feed level; age of dam; and covariates age, weight and height. Of the three covariates, weight had the greatest effect, and any factor which caused an increase in weight tended to increase scrotal circumference. Quadratic effects of age, weight, height and age X age of dam interaction effects were significant or approached significance, but were of minor importance. Large contemporary group effects suggested the need for expressing scrotal circumferences as trait ratios or as deviations from contemporary group means. Scrotal circumference adjustment factors recommended for yearling Hereford bulls were .026 cm X d-1 of age and .8, .2 and .1 for sons of 2-, 3- and 4-yr old dams, respectively. Heritability of weight-adjusted scrotal circumference was .46 +/- .06 compared with .49 +/- .06 for age-adjusted scrotal circumference, indicating considerable additive genetic variation for relative scrotal size. Correlations between scrotal circumference and growth traits were moderate to high. The genetic correlation between scrotal circumference and yearling weight was the highest of these at .44 +/- .16. Potential implications of this relationship are discussed.     

Genetic study of embryonic mortality in White Leghorn lines selected for egg production traits

The present study compares embryonic mortality between lines selected for different production traits, assesses the effects of inbreeding of the hen and embryo on embryonic mortality, and estimates genetic parameters of embryonic mortality. The experiment covered 10 generations of selection for increased egg number (EN), egg weight (EW), egg mass (EM) and a control line (C). The data included age at 1st egg, egg number and egg weight. Percent fertile eggs (PF), percent hatched of fertile eggs (PHF) and percent dead chick at hatch (PDH) were also recorded for the selected parents. PDH was higher in the selected lines than in the control line. Among the selected lines, the EW line had the highest embryonic mortality. Inbreeding of the hen and embryo had no significant effect on PDH in any of the lines. Estimates of heritability for PDH were 0.10+/-0.05, 0.02+/-0.02, 0.03+/-0.02 and 0.02+/-0.02 for lines EN, EW, EM and C, respectively. There was a positive genetic correlation between egg weight and PDH in line EW indicating that selection for increased egg weight was associated with high embryonic mortality. A negative genetic correlation between PDH and reproductive traits in line EN was observed, which is favourable.     

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)     

Genetic analysis of growth,visual scores,height, and carcass traits in Nelore cattle

Covariance components were estimated for growth traits (BW, birth weight; WW, weaning weight; YW, yearling weight), visual scores (BQ, breed quality; CS, conformation; MS, muscling; NS, navel; PS, finishing precocity), hip height (HH), and carcass traits (BF, backfat thickness; LMA, longissimus muscle area) measured at yearling. Genetic gains were obtained and validation models on direct and maternal effects for BW and WW were fitted. Genetic correlations of growth traits with CS, PS, MS, and HH ranged from 0.20 ± 0.01 to 0.94 ± 0.01 and were positive and low with NS (0.11 ± 0.01 to 0.20 ± 0.01) and favorable with BQ (0.14 ± 0.02 to 0.37 ± 0.02). Null to moderate genetic correlations were obtained between growth and carcass traits. Genetic gains were positive and significant, except for BW. An increase of 0.76 and 0.72 kg is expected for BW and WW, respectively, per unit increase in estimated breeding value (EBV) for direct effect and an additional 0.74 and 1.43, respectively, kg per unit increase in EBV for the maternal effect. Monitoring genetic gains for HH and NS is relevant to maintain an adequate body size and a navel morphological correction, if necessary. Simultaneous selection for growth, morphological, and carcass traits in line with improve maternal performance is a feasible strategy to increase herd productivity.     

Inbreeding and inbreeding depression on reproduction and production traits of White Leghorn lines selected for egg production traits.

1. The rate of inbreeding and its effect on reproduction and egg production traits were studied in White Leghorn lines selected for egg production traits. The experiment was carried out for 10 generations in a control line (C) and in lines selected for increased egg number (EN), egg weight (EW) and egg mass (EM). 2. Data were available on reproduction traits, such as percent fertile eggs (PF), percent hatched of fertile eggs (PHF) and percent hatched of total eggs set (PHT), and on egg production traits such as age at 1st egg (AFE), egg number and egg weight. 3. The rate of increase in average inbreeding per generation was 1.50, 1.24, 1.14 and 0.18% for the line EN, EW, EM and C, respectively. The effect of inbreeding on reproduction and production traits was estimated by including the inbreeding coefficient of the hen (Fh), embryo (Fe) and mate (Fs) as a partial linear regression in the model. 4. There was a significant effect of inbreeding on reproduction traits in line EW attributable to the inbreeding of the hen, embryo and mate. No such effect was observed in the other lines. 5. In all lines inbreeding tended to reduce egg number and delay sexual maturity. In general, all lines reacted differently to inbreeding.