J. Anim Sci.
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J. Anim Sci. 1987. 65:1585-1594.
© 1987 American Society of Animal Science
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Hormonal, Estrual, Ovulatory and Milk Traits in Postpartum Dairy Cows Following Multiple Daily Injections of Oxytocin

Robert E. Stewart and Jeffrey S. Stevenson1

Kansas State University,2, Manhattan 66506

Abstract

Release of oxytocin at suckling or milking may delay onset of estrous cycles in postpartum cows. Twenty lactating Holsteins of mixed parity were given 100 mU oxytocin iv (n=10) or 2 ml saline (control; n=10) via jugular catheters at 0530, 0930, 1730 and 2130 daily from calving (d 0) until 28 d postpartum. All cows were milked twice daily at 0130 and 13 30. Blood was collected thrice weekly (Monday, Wednesday, Friday at 0530) for 12 wk and analyzed by radioimmuno-assay for progesterone and 13,14-dihydro-15-keto-prostaglandin F2{alpha} (PGFM) in serum. On d 12, blood was collected every 15 min for 6 h via jugular catheters and concentrations of luteinizing hormone (LH), cortisol and PGFM were determined. Rate of involution of the reproductive tract was estimated twice weekly by palpation per rectum. Overall mean, baseline concentrations, number of pulses/6 h, and pulse duration of LH on d 12 were similar among treatment groups. However, oxytocin seemed to reduce (P<.10) pulse amplitude of LH in multiparous cows (.4 ± .2 vs .8 ± .1 ng/ml), but not in primiparous cows. Concentrations of cortisol and PGFM in serum on d 12 were unaffected by treatment. The average intervals from calving to first ovulation, based on changes of progesterone in serum and the intervals to first estrus, were similar between treatment groups. Rates of involution of the cervix and uterus also were similar between treatments. Milk yield, percent protein in milk and somatic cell counts did not differ between treatment groups. However, percent fat in milk tended to be higher (P<.10) in cows given oxytocin than in controls (3.99 ± .22 vs 3.68 ± .21). These data indicate that multiple daily injections of oxytocin did not affect: 1) length of anestrus and anovulation in postpartum dairy cows, 2) LH release and 3) rates of cervical and uterine involution.

Footnotes

1 Contribution no. 87-303-J, Kansas Agric. Exp. Sta., Manhattan, KS 66506. The authors express appreciation to E. M. Carpenter for her assistance in the laboratory and to K. Minneman for typing this manuscript. We thank Dr. G. D. Niswender, Colorado State Univ., for donation of LH antiserum, Dr. K. Kirton, The Upjohn Co., Kalamazoo, MI, for donation of antiserum to 13,14-dihydro-15-keto-prostaglandin F2{alpha}, Dr. L. E. Reichert, Jr., Albany Medical School, for donation of purified LH (LER 1716-2) for iodination, and the Hormone Distribution Office, NIAMDD, Bethesda, MD for donating reference LH (NIH-LH-B4).

2 Dept. of Anim. Sci. and Ind.






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Copyright © 1987 by the American Society of Animal Science.