Deaths and disposals in lines selected for milk yield and control lines of Jersey cattle.

Deaths and disposals of Jerseys from birth to 120 d of first lactation during a selection experiment were summarized. Cows were randomly assigned to the high milk yield and young sire lines. Service sires were bulls with the highest estimated breeding value for milk for the high milk line and a collection of all young unproven bulls available in AI in 1967. Cattle that were unsuitable for conditions of normal herd management were candidates for culling. Culling of uncalved heifers and of lactating cows was also permitted to maintain group sizes. Culling for herd reduction was random. Culling for low milk yield was permitted after cows reached 120 d of first lactation. Death and disposal data were analyzed through 120 d of first lactation. By 120 d of first lactation, 29.6% of females born to the young sire line had died or been involuntarily removed compared with 29.8% born to the high milk yield line. Deaths were 54.8% of total losses for the high milk yield line compared with 58.4% for the young sire line. Stillbirths were a larger proportion of total losses for animals in the high milk yield line (21.4%) than for those in the young sire line (15.3%). The most frequent cause of death was scours and pneumonia during 1st mo of life for animals in both lines. Selection of sires for high milk yield does not decrease total survival rates through the early first lactation.

Correlated responses in reproduction accompanying selection for milk yield in Jerseys.

Reproductive traits of heifers and primiparous cows from a long-term selection project were analyzed to determine correlated response to single-trait selection for milk yield. Data were from 1056 daughters (765 selection, 291 control) of 37 bulls (17 selection, 20 control). Traits in heifers were ages at first observed estrus and at first breeding, services to conception, interval from first service to conception, and length of first gestation. Traits in primiparous cows were ages at first calving and at first breeding, after calving; services to conception; length of second gestation; and intervals from calving to first observed estrus, to first breeding, and to conception, from first service to conception, and from first to second calving. Analyses for services to conception in heifers and primiparous cows were categorical using models containing genetic group and generation. Analyses of other traits were by linear mixed models using fixed effects of genetic group, generation within group, and year-season of birth. Sires were assumed random and nested within genetic group. The mean square for sires within group was used to test for group differences. No significant differences were found between genetic groups in traits measured in heifers; however, the interval from first service to conception approached significance (control superior). In primiparous cows, differences between genetic groups were significant for the intervals of calving to first breeding and calving to conception and for length of second gestation (control superior). For other traits, reproductive performance of the control was better but not significantly different from that of the selected group. Reproductive performance should be monitored during selection for high milk yield.

Correlated response in growth and body measurements accompanying selection for milk yield in Jerseys.

Growth and body measurements from a long-term selection project were analyzed to determine correlated responses to single-trait selection for milk yield. Data were from 1056 daughters (765 selection, 291 control) of 37 bulls (17 selection, 20 control) of 37 bulls (17 selection, 20 control) and included BW and measures of heart girth, chest depth, wither height, and length from withers to pins and from withers to hooks taken at 6 mo, 15 mo, first calving, end of first lactation, and maturity. Other data were birth weight, change in measurements and weights from first calving to end of first lactation, monthly rate of gain from 1 to 13 mo of age, and age reaching breeding weight (250 kg). Principal component scores were calculated from standardized measurements at each age. The first three principal components has meaning (size, length vs. girth, and height vs. girth). All analyses used linear mixed models with fixed effects of genetic group, generation within group, year-season of birth or calving, parity of dam, and birth status (multiple or single birth). Sires were assumed to be random and nested within genetic group. Mean squares for sires was used to test for group differences. Generation did not differ in any analysis and was removed from all models. Selection cows were heavier, larger in some measurements, and had greater overall size at 6 mo of age. Selection cows had greater monthly rate of gain and attained breeding weight at an earlier age. Genetic groups did not differ for any other measurement or weight. Control cows gained more weight and increased more in some measurements between first calving and end of first lactation. Selection for milk yield did not result in an undesirable correlated response in an growth or body measurement.

Direct response in yield and correlated response in components accompanying selection for milk yield in Jerseys.

In 1967, the Jersey herd at the Dairy Experiment Station, Lewisburg, TN was divided into two groups on the basis of ancestry, type, and breeding value for milk as part of a project to determine effects of single trait selection for high milk yield on yield and correlated traits. Control group was mated randomly to 20 unproven young sires selected randomly from those available from breeding studs in 1967. Selection group was mated to sires selected solely on the basis of their high transmitting ability for milk. Selection sires were selected at intervals and used for 4 yr. By the end of the project (1984), lactation information was available on 672 daughters (520 selection and 152 control) of 37 bulls (17 selection and 20 control). Differences in breeding values for milk, fat, and fat test as calculated from the PTA reported in the July 1989 USDA genetic evaluations and differences in first lactation mature equivalent production of milk, fat, fat test, and 4% FCM were examined. Linear mixed models were used for all analyses and contained the fixed effects group, generation within group, and year. Sires were random, nested within group, and used to test for group differences. Groups differed for all traits. Selection was superior to control in breeding value for milk and fat (828 and 31 kg) and for production of milk, fat, and 4% FCM (1066, 42, and 1061 kg). Control was superior to selection in breeding value and production fat test (.15 and .12%). Group differences existed within generation class for all yield traits but not for fat percentage. Realized response closely matched or exceeded expected response as estimated from pedigree information.

Inbreeding of and relationship among registered Holsteins.

Holstein-Friesian Herdbooks (Holstein-Friesian Association of America, Brattleboro, VT) were used to draw random samples of 600 registered females born during each of the yr 1970, 1976, and 1982. A two-line pedigree, one random line of ancestry tracing from the sire and another tracing from the dam to the beginning of the Holstein-Friesian Herdbook, was tabulated for each of these 1800 females. These were used to estimate inbreeding and inter se relationship for the Holstein breed. Estimates of inbreeding were 4.7, 3.8, and 4.3% for 1970, 1976, and 1982. These estimates were not different from one another or from 1928 and 1931 estimates. Estimates of inter se relationship were 5.2, 7.3, and 9.8% for 1970, 1976, and 1982. These estimates were different from one another and from an estimate of 3.4% for 1931. The increase in inter se relationship without corresponding increase in inbreeding indicates that a change in mating strategies has evolved over time. The majority of breeders now apparently mate animals that are less related than if mating was random, whereas in the past there was more of a tendency to mate within the same line. Despite these attempts to avoid inbreeding, it may be only a matter of time until increasing inter se relationship causes an increase in inbreeding. Because of detrimental effects associated with inbreeding, it is important that the Holstein breed be monitored on a regular basis for these parameters. Ancestors that occurred most frequently in the 1982 sample were identified and their direct relationships to the breed tabulated for the years studied.