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Attempts to Induce Conception in Lactating Sows

U. S. Department of Agriculture, Beltsville, MD 20705

Abstract

Three experiments were conducted to determine whether conception could be induced in lactating sows with physical contact with a boar or in lactating sows artificially inseminated after hormone treatment to induce ovulation. In experiment 1, 44 primiparous Yorkshire crossbred sows and their litters were grouped two or three to a pen on either day 14 or 21 postpartum (pp) with or without a boar until weaning on day 42 pp. Estrus was not observed in sows before weaning, and plasma progesterone concentrations showed that only two of 23 sows with a boar had ovulated. These two sows had, on days 60 and 75 of the induced pregnancy, 25 and 22 corpora lutea (CL) and 24 and 13 normal appearing fetuses.

In experiment 2, 18 sows were injected once during the interval from day 14 to 17 pp with a combination of 400 IU of pregnant mare serum gonadotropin (PMSG) and 200 IU of human chorionic gonadotropin (HCG). Each sow was injected 72 hr later with gonadotropin-releasing hormone (GnRH) analog (AY-25205) to induce ovulation. Sows were artificially inseminated 30 hr after the GnRH treatment. Their reproductive tracts were recovered 42 to 45 hr after insemination, and ovulation response and fertilization rate were determined. The number of sows treated with 0, 125, 250 or 500 ug of GnRH analog, number of sows ovulating and number of sows with fertilized ova, respectively, were: 3, 0 and 0; 4, 1 and 0; 4, 1 and 0; 7, 6 and 5.

In experiment 3, sows were treated on day 7, 14 or 21 pp with either 1,500 IU of PMSG followed 80 hr later by 750 IU of HCG or with a 600 IU of PMSG: 300 IU of HCG combination followed 80 hr later by 500 ug of GnRH analog. Sows were artificially inseminated 24 and 40 hr after the second hormone injection. Blood plasma samples were assayed for progesterone to monitor luteal function, and the sows were allowed to farrow. Only 20 of 53 treated sows appeared to have a normal luteal phase. Of 20 sows with luteal function, on day 18 of the induced cycle, only 12 farrowed.

¹ Reproduction Laboratory, Animal Physiology and Genetics Institute, Science and Education Administration.

² Non-Ruminant Laboratory, Nutirition Institute, Science and Education Administration.

³ Mention of specific products or equipment does not constitute a guarantee or endorsement by the USDA and does not imply its approval to the exclusion of other products that may be suitable.

⁴ ACKNOWLEDGMENTS. The authors express appreciation to Dr. M. L. Givner, Ayerst Research Laboratories, Montreal, Canada, for supplying the GnRH analog AY 25205 and to Dr. B. J. A. Furr, Imperial Chemical Industries, Ltd., England, for providing the antiserum 465/5 for the progesterone radioimmunoassay. The assistance of Kathy Ogle and Dan Deaver is gratefully acknowledged.