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Postpartum Reproductive Performance of Finnsheep-crossbred Ewes¹

Roman L. Hruska U. S. Meat Animal Research Center, U. S. Department of Agriculture^,3, Clay Center, NE 68933

Abstract

Postpartum reproductive potential was evaluated in Finnsheep-crossbred ewes. Luteinizing hormone (LH) concentrations in serum were determined on days 10 and 30 postpartum in lactating and nonlactating ewes that were ovariectomized on day 2 postpartum. The increase in LH secretion after ovariectomy was not affected by the number of lambs (0, 1 or 2) that each ewe nursed, but LH concentrations were higher on day 10 for ewes that lambed in the fall than for ewes that lambed in the spring. Bromocriptine reduced prolactin concentrations in postpartum ewes but had no effect on LH secretion in ewes that were ovariectomized on day 2. Treatment of ovariectomized ewes with estradiol-17β on day 11 postpartum produced increased LH concentrations that were maximal 18 hr after treatment. The magnitude of this effect of estrogen was reduced in lactating ewes, but was not affected significantly by bromocriptine treatment.

Estrous activity was not increased in intact lactating ewes by bromocriptine treatment from days 15 to 29 postpartum. The interval from parturition to estrus in ewes that lambed in the fall was longer for lactating than for nonlactating ewes, and this interval was shortened in lactating ewes by a single treatment with estradiol between days 2 to 5 postpartum followed by 15 days of progesterone implantation. Results of the present studies indicate that poor reproductive performance before day 40 postpartum in Finnsheep-crossbred ewes that lamb in the fall is not due to impairment of gonadotropin secretion or ovulation. Rather, the main limitation appears to be the absence of estrous behavior and possibly the ability to maintain pregnancy.

¹ Cooperation of the Nebraska Agr. Exp. Sta. Univ. of Nebraska, Lincoln, is acknowledged. The author expresses appreciation to Dr. G. Niswender for LH antisera, Dr. D. Bolt for prolactin antisera, Dr. L. Reichart, Jr., for purified prolactin (LER-860-2), Abbott Laboratories for progesterone implants, Sandoz Pharmacueticals for bromocriptine (CB-154), and NIAMDD, National Institutes of Health, for LH S-18 and prolactin S-ll reference preparations and purified LH for iodination. The technical assistance of Ms. Ann Hultine and Mr. George McMillan is acknowledged.

² Science and Education Administration, Agricultural Research.

³ Mention of a trade name, proprietary product, or specific equipment does not constitute a guarantee or warranty by the US Department of Agriculture and does not imply its approval to the exclusion of other products that may be suitable.