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.

Growth patterns of cows sired by British and Continental beef and American dairy bulls and out of Hereford dams.

Growth patterns from birth to maturity were compared for 92 straightbred Herefords (H) and 299 Hereford crossbred (XB) cows. Crossbred cows were out of Hereford dams and were sired by bulls of two British [Angus (A) and Shorthorn (Sh)], two Continental [Charolais (C) and Simmental (S)] and two American dairy breeds [Brown Swiss (B) and Holstein (F)]. British XB and H cows differed only slightly in weight but both weighed less than Continental and dairy XB cows. Body condition also differed significantly among breed types; dairy XB were thinnest. Among XB individuals SH calves were heaviest (34 kg) and AH calves were lightest (30 kg) at birth. Birth weights of Continental XB were 2.6 kg more than those of British XB and 1.7 kg more than those of dairy XB. At weaning, all XB calves were heavier than straightbred H calves, but differences among XB types were not significant. However, on the average, Continental XB and dairy XB calves were heavier (28 kg) than British XB at 19 mo. At 32 mo, Continental and dairy XB weighed 41 and 23 kg more, respectively, than British XB. Although differences between the British XB and the Continental and dairy XB at some ages were not significant, no case existed where the latter two groups weighed less than British XB. Adjusting weight to a common condition score reduced phenotypic variance at all ages and changed the ranking of some breed types for weight, primarily by increasing predicted weights of dairy XB. Differences in growth curves were reflected by differences in mature weight and maturing rate. Asymptotic weights of Continental XB were highest, followed by those of dairy XB. British XB and H weighed least at maturity (average of 509 kg). The CH cows matured more slowly but grew to a heavier mature weight (592 kg) than SH cows (552 kg). Generally animals reached 95% of their mature weight between 68 and 80 mo of age.

Growth patterns of Angus, Charolais, Charolais X Angus and Holstein X Angus cows from birth to maturity.

Growth patterns of 182 cows [73 Angus (AA), 31 Charolais (CC), 38 Charolais X Angus (CA) and 40 Holstein X Angus (FA)] were studied from birth to maturity. Breed type significantly affected weight and condition at all ages. Crossbred cows were heavier than AA and lighter in weight than CC cows (P less than .01) at all periods. Differences between CA and FA cows were small. The CA cows were somewhat heavier than FA cows, but when weight was adjusted for condition, these two groups reversed rank at 56 and 68 mo. Differences in weight among breed types increased from birth to 44 mo and stabilized thereafter. Weights at early ages were influenced more by environmental effects than were weights at later ages. Adjustment for condition significantly reduced phenotypic variation in weight at all ages. Two growth models (Brody and Richards) were fitted to the weight-age data for each breed type. Differences in growth were expressed in terms of differences in mature weight and maturing rate. The AA cows were smallest at maturity and matured most rapidly; CC cows were largest and matured least rapidly. The FA and CA cows were intermediate and similar in mature size and maturing rate. Crossbreeding may have increased maturing rate somewhat when weights were not adjusted for condition. The four-parameter Richards model did not provide an appreciably better fit to the data than the three-parameter Brody model, and both models described early growth less adequately than later growth.

Sire breed effects in matings with Angus cows: I. Fertility, calf survival and performance to 18 months.

Over six calf crops, 524 exposures of Angus cows to three sire breeds resulted in 432 weaned calves for an 82.4% calf crop. Least-squares means for weaning rate by sire breed were 81.8, 80.5 and 83.9% for Angus, Charolais and Holsteins, respectively. Sire breed effect was not significant for calving rate, calf mortality or overall weaning rate, but was significant for all growth traits from birth to 18 mo. Angus-sired calves were smallest at birth, grew at a slower rate and were lightest in weight at all ages. Charolais-sired calves were heaviest at all weigh periods and Holstein-sired calves were intermediate. Holstein-sired calves scored significantly lower for both grade and condition than did Angus- and Charolais-sired calves. Charolais-sired calves had the highest grade. Calving rate tended to be influenced by the effect of cow (P less than .10) and sire breed X year (P less than .001). Calving rate was highest for 3-yr-old and for 6- to 10-yr-old cows and was also 1.5 percentage units higher for crossbred matings. Cow productivity (kg of calf weaned/cow exposed) is a combined measure of fertility, calf survival and weaning weight. Although sire breed did not significantly affect cow productivity (P less than .20), actual values favored cows producing crossbred calves by 14 and 9 kg for Charolais and Holstein crosses, respectively. Likewise, weight differences at 18 mo favored these crosses by 50 and 32 kg for heifers and 72 and 62 kg for steers. Among the two crossbred types, Charolais X Angus heifers were 28 kg heavier (P less than .05) than Holstein X Angus heifers at 18 mo but the 10 kg difference in steers was not significant. The fact that the large sire breeds produced calves with heavier weaning weights without demonstrating significant increases in overall productivity points out the importance of high weaning rates.

Heritability and repeatability of speed for 2- and 3-year-old standardbred racehorses.

Repeatabilities (t) and heritabilities (h2) of racing time were estimated from data on 7,206 2- and 3-yr-old Standardbred pacers and trotters competing in 1-mile (1.6 km) charted races at six tracks between 1975 and 1978. A total of 38,487 records representing 2,387 sire progeny groups were divided into subsets by gait, age and track. Initially, the designation "class of race" was recognized as a subjective categorization that reflected nonrandom assignments of horses to races. After extensive investigation, we concluded that racing times should be adjusted by linear regression for the time of the winning horse (defined at the "pace" of the race). Residual regression coefficients of time on pace ranged from .61 +/- .08 to .79 +/- .05 s/s and appeared to adequately account for the environmental effects of class. Repeatabilities of adjusted times ranged from .32 +/- .08 to .55 +/- .04 and heritabilities ranged from -.25 +/- .22 to .66 +/- .16. Overall estimates of t and h2 (pooled over gaits, ages and tracks) were .44 +/- .01 and .29 +/- .03, respectively. When data were not adjusted for pace, the sire, horse and error variance component estimates were inflated by environmental effects (pooled t = .62; pooled h2 = .36). Racing time adjusted for pace is recommended for use as a selection criterion in Standardbred horses.