NO EFFECTS OF BULL EXPOSURE ON EXPRESSION OF ESTROUS BEHAVIOR IN HIGH-PRODUCING DAIRY-COWS

Bull exposure has been shown to hasten the onset of estrous cyclicity in postpartum beef cows, but has not been examined in high-producing, postpartum dairy cows. This investigation examines the effects of bull presence on postpartum reproductive behavior in dairy cattle. Forty-f ive multiparous dairy cattle (9764 +/- 140 kg milk/lactation) were ran domly allocated into three groups at the time of calving. Treatments c onsisted of no bull exposure (NBE), twice daily exposure (2 x dBE), an d continuous exposure (CBE). Estrus detection was carried out for all groups for a period of 1/2 h 2 x daily following milking. Blood sample s were collected every other day from day 10 postpartum until the time of the first artificial insemination (AI) service or until day 100 po stpartum, whichever occurred first. Systemic progesterone concentratio ns were used to determine ovulation occurring without associated estro us behavior. Intensity of estrous behavior was scored on a scale of 0 to 4, where 0 indicated no estrous behavior associated with ovulation and 4 indicated primary signs of estrus for at least two consecutive o bservation periods, Bull exposure had no effect on time to first behav ioral estrus (P = 0.31), behavior score at first ovulation (P = 0.62), or score at first behavioral estrus (P = 0.82). Energy status was sim ilar in all treatment groups (P = 0.59), Bull exposure did not affect long-term reproductive outcome in these dairy cattle. (C) 1998 Elsevie r Science B.V.