Sire Of Cow Research Articles

Effects of Sire of Fetus upon Subsequent Production and Days Open of the Dam

To quantify effects of the fetal-placental unit upon postpartum performance of the dairy cow, Dairy Herd Improvement Association records from Florida, Georgia, North Carolina, and South Carolina (27,200 lactations of 11,935 Holsteins and 3,731 of 1788 Jerseys) were studied by method of least squares. The final model included herd-year-season, sire of fetus, and sire of cow. Sire of fetus accounted for 8.2 and 11.8% of the total variability in mature equivalent milk yield (Holsteins and Jerseys), 9.8 and 14.3% in fat yield, and 1.9 to 3.2% in days open. Interactions of sire of fetus with sire of cow accounted for none of the variability in yields (negative estimates of variance) but 4.4 and 4.8% of the variability in days open. Correlations between effects of sire of fetus on milk and fat yields were .96; for yields and days open they were .02 and −.02 for Jerseys and −.12 and −.13 for Holsteins. Correlation between sire of fetus constants and estimated breeding values for milk yield in a sample of 50 Jersey sires was −.04. Future consideration of sire of fetus effects could lead to increased repeatability of sire proofs and rate of genetic change. Hypothesized mechanism is that effects of the fetal-placental unit, possibly hormonal and at least partly genetically determined, influence development of the dam's mammary gland and its subsequent performance.

Estimating Heritability of Hereford Cow Weights2

Estimates were calculated from both adjusted and unadjusted weights of 1,584 cows in 17 representative Virginia Hereford herds. Adjusted weights were adjusted for year, herd, flesh condition, sire of cow, age, days postpartum and the interactions of year × age and year × condition. Variations of this basic model were used to analyze several subsets of the data, however, because the sires of some cows were unknown, there were repeat observations on some cows in two herds, some cows did not wean calves the years weights were taken or because of computer inability to handle the large number of sire groups. Heritability estimates ranged from 0.52±.16 to 1.00±.16. The lowest h2 was obtained from an indirect method (Harvey, 1970 as modified by Bailey et al., 1971) based on the sire component of variance calculated from data set 3 consisting of 854 cows by 210 sires. This low estimate probably resulted from a poor estimate of the sire component of variance.

Heterosis in Preweaning Maternal Traits among Lines of Hereford Cattle

Birth and weaning data on 259 three-way cross calves produced by inbred and two-way linecross Hereford cows were used to estimate the amount of heterosis in maternal traits. The data were collected at the United States Range Livestock Experiment Station, Miles City, Montana, during the years 1965 through 1967. Inbred cows from five lines (Lines 1, 4, 6, 9 and 10) and cows representing all possible two-way combinations of these lines produced in Phase 1 of the experiment were bred to produce two calf crops to evaluate maternal heterosis. Records on calf birth weight, pre-weaning daily gain, 205-day weaning weight and weaning score were considered as characteristics of the cows and were analyzed by least-squares procedures. The effects studied were: Line of sire of cow (LS), line of dam of cow (LD), LS × LD, sex of calf, year-age of dam groups, and sires within year-age of dam groups. Differences among the lines for maternal ability were evident from the analysis of variance and line of sire or dam least-squares means. However, the LS × LD interaction effects were small and nonsignificant. Heterosis estimates for maternal effects on birth weight, preweaning daily gain, 205-day weaning weight and weaning score were: 1.5, 5.4, 4.7 and 0.4%. These estimates for heterosis in maternal ability are consistently less than heterosis estimates for the same traits in Phase 1 of the experiment where comparisons were based on the performance of inbred vs. line-cross calves and all dams were inbred.

Misidentification in Estimating the Paternal Sib Correlation

Misidentification of sires of cows in paternal half-sib analyses of variance biases the estimate of heritability downward. Four models of misidentification yield approximately the same reductions in estimated heritability. The reduced estimates are approximately p2 of the actual heritability where p is the fraction of cows whose sire is correctly identified. The reduction in heritability estimates from daughter-dam regression would be to a fraction, p, of the actual heritability where p is the fraction of dams correctly identified. Empirical paternal sib analyses of New York Dairy Herd Improvement Holstein records suggest that misidentification is more common among grade cows with registered dams and grade cows having grade dams which are not identified than among registered cows with registered dams.

Cow-Indexing Procedure and Culling Levels for Potential Dams of Dairy Bulls

A procedure to index dairy cows on milk production is described. First records of cows were compared to first records of contemporaries, and second and later records of cows to second and later contemporary records. The index combined this information with the proof of the cow's sire. Of 5,704 Guernsey cows, 144 had indices two or more standard deviations above the average index. Restrictions on the milk fat percentage of these “potential” dams of bulls caused the numbers to drop rapidly. Restrictions on type classification decreased numbers to a lesser degree. Mean indies suggested that cows classified “Excellent” received preferential treatment.