Relationships of first lactation milk and type traits to cow survival and a sire index for discounted total milk.
The probability of cow survival during each of six consecutive 13-mo periods after first calving was regressed on lactation milk yield and 15 type traits, each recorded during the first lactation. Adjusted coefficients of determination were small (.028 to .081). The ratio of variance in predicted cow survival probabilities due to milk only with that due to the 15 type traits was 12.6:1, 4.7:1, 2.5:1, .5:1, 0:1, and .02:1 for respective herdlife periods. Maximum effect of type traits on herdlife ranged from 11 to 109 d. Prediction equations for cow survival were incorporated into a sire index for discounted total milk yield of progeny. Type traits affected the sire index by their influence on the six predicted survival rates. Milk yield affected the discounted total milk index directly as well as through the survival rates. Simulated variation from milk estimated transmitting abilities for sires accounted for 99.9% of the total variation in the discounted total milk index. Since the effect of the type traits on cow survival rates was greatest during the later herdlife periods, too few animals would have survived to these later periods to reveal any significant effect from type on the discounted total milk index.
Keller
D S
DS
Department of Dairy Science, Ohio State University, Columbus 43210.
Allaire
F R
FR
D000818:Animals; D002417:Cattle / Q000235:genetics*; D005260:Female; D007774:Lactation / Q000502:physiology*; D008297:Male; D009026:Mortality; D011247:Pregnancy; D011336:Probability; D012044:Regression Analysis