Blood samples collected from 25 heifers at 100, 130, 160 and 190 days of age were analyzed for progesterone, androstenedione, testosterone, estrone and estradiol. The relation between steroid levels at each age and first lactation milk yield was assessed by linear regression analysis which showed day-130 androstenedione level to be the most highly correlated variable. Subsequently day-130 serum steroid levels in 99 heifers were studied and the relation to milk yield analyzed by multiple regression procedures, including breed as a variable. Although the data set was found to account for 22% (R2) of the variation in 308- day 1st lactation mature equivalent, 18% was due to breed alone. Thus the reported usefulness of prepubertal steroid levels for predictina lactation oer- formance was not confirmed.

G. J Marcus, A. J McAllister, A. J Hackett

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume XI. Genetics of reproduction, lactation, growth, adaptation, disease, and parasite resistance., , 119–123, 1986
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