Date of Award:

5-1-1996

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Committee Chair(s)

LeGrande C. Ellis

Committee

LeGrande C. Ellis

Committee

Dana K. Vaughan

Committee

Carl D. Cheney

Committee

Michael L. Wolfe

Committee

James A. Gessaman

Abstract

Bull exposure has been shown to hasten the onset of estrous cyclicity in postpartum beef cattle but has not been examined in high producing dairy cattle. This investigation was carried out to examine effects of bull presence on postpartum reproductive characteristics in dairy cattle. Forty-five multiparous dairy cattle were randomly allocated into three groups at the time of calving. Treatments consisted of no bull exposure (NBE), twice daily bull exposure (2xdBE), and continuous bull exposure (CBE). Estrus detection was carried out for all groups for one-half hour twice daily following milking. Systemic progesterone (P4) was determined from blood samples collected every other day from day 10 postpartum until first artificial insemination (AI) or day 100, whichever occurred first. P4 was used to determine reproductive function and ovulation occurring without estrous behavior. Intensity of estrous behavior was scored on a scale of 0 to 4, where 0 indicated no estrous behaviour associated with ovulation and 4 indicated primary signs of estrus for at least two consecutive observation periods. Occurrence of first sustained rise in P4 was significantly later during the postpartum period in both bull-exposed (BE) groups compared to the NBE group (31.3 ± 2.5 d vs 21.9 ± 2.3 d; F1,43 = 5.53; P = 0.02). Length of first ovarian cycle, as measured by P4 concentrations, was not significantly different between treatments (x̄ = 13.7 ± 0.71 d; F2,39 = 1.13; P = 0.33). Length of postpartum period until first ovulation tended to be shorter in NBE cows compared to BE cows (36.8 ± 2.2 d vs 43.9 ± 2.5 d; F1,40 = 3.33; P = 0.08). There was no significant difference in peak P4 concentrations prior to the first ovulation or time interval from first ovulation to second ovulation between groups. Peak P4 concentrations were higher in NBE cows compared to BE cows prior to the second postpartum ovulation (9.1 ± 0.9 ng/ml vs 7.0 ± 0.46 ng/ml; F1,36 = 4.09; P = 0.05). Bull exposure had no effect on time to first behavioral estrus (F2,42 = 1.21; P = 0.31), behavior score at first ovulation (F2,39 = 0.49; P > 0.62), or score at first behavioral estrus (F2,38 = 0.20; P = 0.82). Energy status was similar across treatment groups (F2,44 = 0.54; P = 0.59). Bull exposure did not affect long-term reproductive outcome in these dairy cattle.

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