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Variables associated with peripartum traits in dairy cows. VII. Hormones, calf traits and subsequent milk yield.

Independent effects of certain partum and peripartum traits on subsequent milk yields (Y) during days 1 to 27 (Y27), 28 to 60 (Y60) and 1 to 200 (Y200) of lactation were estimated from data on 167 Holstein cows and first-calf heifers. The variables were health status, calf sex and covariates (linear, quadratic and cubic) of calf birth weight (CBW), cow age (CA), month of calving code (season) and the peripartum blood plasma concentrations (means of three samples taken from 48 hr prepartum to within 2 hr postpartum) of prolactin (PRL), progesterone (P4), estrone (E1), estradiol-17 beta (E beta) and estradiol-17 alpha (E alpha). Except for Y200 values, the measures of milk yield were positively correlated (P < .01) with each other and with CA, CBW, plasma PRL and plasma E beta. Plasma PRL, E beta and E1 were positively correlated with each other and with CA (PRL and E beta) and CBW (E1 and E beta). Covariates prominently and independently related to increases in Y were CA, CBW and plasma PRL (P < .01). Predicted Y27, Y60 and Y200, calculated with equations of the cubic model, increased by 12.4, 6.5 and 3.7%, respectively, between CBW of 37 and 50 kg, and by 16.6, 15.9 and 14.8% between plasma PRL concentrations of 50 and 195 ng/ml. Season of calving, calf sex and health status were associated with changes in Y27 but not Y60 or Y200. Within the health status group, only infectious disorders (metritis or mastitis) decreased (P < .025) milk yield adjusted for CA and cow weight (adjusted Y60 and Y200). Among all other cows, including those with dystocia alone, adjusted yields were increased by heavier calves (P < .07, Y60), high plasma PRL (P < .025, Y60) and below average plasma E1 (P < .025, Y200). It may be practical to increase milk yield by providing supplemental light prepartum to increase plasma PRL and by selecting sires to maintain CBW above average.