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 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.

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.

Selection in Hereford cattle. I. Selection intensity, generation interval and indexes in retrospect.

Selection intensity and generation interval were evaluated in a Hereford cattle herd made up of 14 inbred lines and 14 linecross groups corresponding to the lines of inbred sires at the Suan Juan Basin Research Center, Hesperus, Colorado. Selection indexes practiced were calculated in retrospect. Analyses of the records collected from 1946 through 1973 involved weaning weight (WW) and postweaning traits in males and females. Analyses by line were performed for the inbreds, while pooled analyses were done on the inbred and linecross populations. From records of 1,239 calves weaned, age of sire averaged 3.75 yr compared with 4.52 yr for age of dam, showing faster generation turnover for sires than for dams. Generation interval determined as actual age of midparent was 4.13 yr. Selection applied for WW, evaluated as annual selection differentials within inbred lines and then pooled over all lines, averaged .55 standard deviations (sigma)/generation for sires. For females, selection was much less intense. Midparent selection differential amounted to .33 sigma/generation. For sires, pooled standardized selection differentials per generation over all lines during the postweaning gain period were .49 sigma, .46 sigma, .40 sigma, -.20 sigma, -.10 sigma and .69 sigma, respectively, for initial weight, final weight, feed consumed, feed efficiency (FE, unadjusted and adjusted) and average daily gain (ADG). Selection of females for postweaning traits was not intense. Selection index actually practiced in retrospect for sires was: IS = .4461 (WW) - .0092 (FE) + .6126 (ADG). The indexes for dams included WW, 12-mo weight (12W), 18-mo weight (18W), mature spring weight (SPW) and mature fall weight (FAW) and were: for inbred dams, ID = .1824 (WW) - .0284 (12W) + .0736 (18W) - .1097 (SPW) - .1097 (FAW); for linecross dams, ID = .2693 (WW) - .2960 (12W) + .0147 (18W) + .1185 (SPW) - .0354 (FAW). The corresponding index selection differentials were .818, .203 and .209. Sire index selection differentials represent about 79% of the total selection differentials.

Selection in Hereford cattle. II. Expected and realized response.

Data from 14 inbred lines and 14 linecross groups of Hereford cattle at the San Juan Basin Research Center, Hesperus, were used to evaluate expected and realized response in birth and weaning traits and postweaning traits in males and females over a 28-yr period. There were large differences in the means and variances of the performance traits among the inbreds and linecrosses, with the inbreds showing inbreeding depression and greater variability among lines, while the linecrosses manifested within-breed heterosis. Except for gain from weaning to 12 mo, in females, genetic progress was expected in all traits studied, mainly due to sire selection. Regressions of annual trait means on years indicated positive phenotypic trends in the inbreds for heart girth circumference at birth, adjusted weaning weight (adjusted for inbreeding), weaning score, final weight, feed consumption and the yearling weights and gains in females. Changes were negative for other traits. In the linecross group phenotypic trends were positive in all traits except heart girth circumference, weaning age, initial test weight and feed efficiency. Estimated genetic progress per generation due to within-line selection was negative in most of the traits in the inbreds but was considerably positive for the linecrosses for most of the traits. As expected, between-line selection yielded greater genetic improvement in the inbred than in the linecross population. The different patterns of response in the two populations are attributed to high rates and levels of inbreeding. Although variable, the actual progress was below prediction in most of the traits studied.

A comparison of crossbred and straightbred cow-calf pairs. I. Heterosis effects on total feed efficiency.

Records of 104 crossbred and 33 straightbred individually fed cow-calf units were used to study the effects of heterosis on total cow-calf feed efficiency in the production of weight of calf at weaning, 168 d postweaning, slaughter and in the carcass. The cows were Angus, Hereford, Charolais and reciprocal crosses of these breeds. The calves were straightbred and all possible two-breed backcrosses and three-breed crosses produced from first cross cows. The efficiency of the cow-calf unit was defined as kg of calf produced per kg of total TDN (total digestible nutrients) consumed by the cow-calf pair. Total feed consumed by the cows was for an average period of 315 d, from approximately November 21 to October 2. Total calf TDN consisted of creep to weaning and feed during the postweaning fattening period to slaughter. For all measures of cow-calf unit efficiency studied, the heterosis estimates were small but generally positive, ranging from -.8 to 2.1%. The average advantage of all crosses over the straightbred parents for the conversion of total feed consumed by cow-calf pair to calf weight at weaning was 2%. Heterosis effects, individual and maternal combined, on the average, among two-breed backcrosses and the three-breed crosses were essentially the same. Among the three groups of first-cross cows compared, the study indicated that a slight advantage in total cow-calf efficiency was exhibited by the Angus X Hereford cross.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in genetic variances with increased inbreeding of beef cattle.

Data on performance traits from a herd of Hereford cattle composed of inbred lines and linecross groups were analyzed to estimate within- and among-line genetic variances and to evaluate how these variances changed with increased inbreeding. Within-line variances were highly erratic while among-line variances tended to be somewhat more consistent. Changes in variances with increased inbreeding did not generally follow the theoretical expectations for the redistribution of genetic variances.

Comparison of two- and three-way rotational crossing and synthetic variety production involving inbred lines of Hereford cattle: postweaning traits.

Data for this linecrossing study were the postweaning growth and weight records of calves born from 1967 through 1975. The records consisted of 264 bull (M) and 263 heifer (F) straightline (SL) calves; 108 M and 100 F two-line rotational cross (2W) calves; 130 M and 102 F three-line rotational cross (3W) calves and 58 M and 51 F synthetic variety (SV) calves, all in the Hereford breed. Average inbreeding percentages of calves and dams in Lines 1, 4, 6 and 10 were 24, 28, 34 and 28; respectively. The M calves were fed a growing-fattening diet for 196 d after a 14-d period of adjustment to postweaning environment. The F calves were fed to gain approximately .5 kg daily during winter from weaning to about 12 mo of age and were then grazed on native pasture until about 18 mo of age. For M, average percentage increases over SL by 2W, 3W and SV combined over three generations were respectively, 9.0, 11.0, 11.6 for initial weight; 5.9, 8.1, 8.8 for 140-d weight; 4.8, 7.2, 7.7 for final 196-d weight and 1.5, 4.2, 4.7 for 196-d gain. All above estimates of increased weight or gain over SL were significant except for 196-d gain in 2W. For F, average percentage increases over SL by 2W, 3W and SV, respectively, were 9.0, 10.9, 11.3 for initial weight; 8.2, 9.2, 8.4 for 12-mo weight; 7.5, 7.7, 9.1 for 18-mo weight; 5.2, 5.3, 5.7 for 18-mo score. All these estimated increases over SL were significant.(ABSTRACT TRUNCATED AT 250 WORDS)

Genotype X environment interaction in Hereford cattle: III. Postweaning trait of heifers.

The postweaning performance of heifers from contrasting lines of Hereford cattle was compared simultaneously at Miles City, Montana and at Brooksville, Florida in an experiment designed to evaluate the importance of genotype X environment interactions in beef cattle. During Phase 1 of the study (1964 to 1973), the performance of two unrelated lines, M1 and F6, was compared at the two locations. During Phase 2 (1967 to 1974), two related lines, M1 of Montana origin and F4 derived from M1 by selection in Florida, were compared at each of the two locations. The line X location interaction term was highly significant in either Phase 1, Phase 2 or both for weaning weight, daily gain from weaning to spring, spring yearling weight, daily gain from weaning to fall, fall yearling weight, yearling condition score, conformation score, wither height, body depth, body length, shoulder width, hook width and forecannon circumference. Daily gain of yearlings from spring to fall was the only objective measurement for which the interaction term was nonsignificant in both phases. These results, consistent with the results on performance to weaning age reported previously, indicate the existence of highly significant genotype X environment interactions in beef cattle. The results indicate that genetic adaptation to the local environment is important in beef cattle production and should be considered in designing breeding programs or performance testing procedures and in interregional transfer of breeding stock.

Preweaning and weaning heterosis for maternal effects of beef x beef and beef x dairy crosses.

Effects of maternal heterosis were estimated from preweaning and weaning data on 178 three-breed cross progeny of straight Hereford, Angus and Charolais heifers (beef) and contemporary reciprocal cross heifers. In addition, 27 three-breed cross calves produced by beef x Brown swiss females were used for a comparison of beef x beef with beff x Brown Swiss crossbred dams. Statistical analyses were performed with and without the data from the 27 beef x Brown Swiss calves. Only first-calf records, obtained from 1965 through 1967, were used to evaluate maternal qualities of straightbred and crossbred dams. Breed of sire of sow was a source of variation (P less than .01) in all progeny traits, and breed of dam of cow was a source of variation (P less than .05 to P less than .01) in all of these traits except birth weight. Interaction effects of breed of sire of cow x breed of dam of cow were consistenetly nonsignificant. Estimated maternal heterosis percentages were 1.4, 1.0, 1.1 and .4 (.02 of one grade) for birth weight, average daily gain from birth to weaning, 205-day weaning weight and weaning conformation score of progeny, respectively. Comparison of beef x Brown Swiss dams with beef cross dams showed that beef x Brown Swiss dams had calves with higher average birth weight, higher preweaning average daily gain, higher average 205-day weaning weight and higher average weaning score (P less than .05 to P less than .01).