Date of Award
Doctor of Philosophy
Breeding information and records of yield for dairy cows from the northeast part of the United States were evaluated. Nine measures of yield were age adjusted by multiplicative factors. Ten measures of fertility were defined. Records for first parity (41,710), second parity (31,162), third parity (22,389), and virgin heifers (15,357) were analyzed;Repeatabilities for pairwise combinations of first three lactations were .32 to .61 for measures of yield and .01 to .16 for measures of fertility. Repeatabilities of virgin heifer fertility with first parity fertility were .01 to .03;Heritabilities of yield were .10 to .18 for first parity by Henderson's Method 3, but estimates from restricted maximum likelihood were .23 for 305-day milk both fat-corrected and on a mature equivalent basis. Heritabilities of fertility were zero to .03 for all parities. Virgin heifer heritabilities of fertility were slightly higher;Phenotypic correlations of yield and fertility were small and antagonistic for measures of yield early in lactation, but became more antagonistic with advancing gestation for measures of yield later in lactation. Yield and fertility for first parity were distinctly antagonistic, genetically. Genetic correlations tended to moderate for second parity, and the genetic relations between measures of yield and fertility for third parity were not conclusive and had large standard errors;Phenotypic correlations of virgin heifer fertility and first parity yield were near zero; genetic correlations tended to be complementary. Virgin heifer fertility and first parity fertility had opposite genetic relationships with first parity yield. Comparing fertility for virgin heifers and first parity cows, phenotypic correlations were near zero, and genetic correlations usually were not significantly different from zero and showed little indication of being consistent in sign;Index selection of sire progeny was applied to 305-day milk which was fat corrected and days open. Considerable economic weight had to be assigned to days open for days open to influence the index to a meaningful extent due to the low heritability of days open.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Leslie Bennett Hansen
Hansen, Leslie Bennett, "Genetic relationship of yield and fertility in dairy cattle " (1981). Retrospective Theses and Dissertations. 6913.