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Relation of Number of Embryos in Domestic Sows to Sex Steroid Hormone Changes during the First 28 Days of Pregnancy^{1, 2,}

Purdue University, Lafayette, Indiana

Abstract

DAILY administration of estrogen and progesterone to sows at a ratio of 1:2,000 from days 14 to 24 of pregnancy significantly reduced embryo death (Reddy, Lasley and Mayer, 1958). Pregnancy was maintained after ovariectomy on day 15 until day 25 with estradiol benzoate and progesterone (Day et al., 1959). Also, a positive relationship has been reported between levels of metabolites of progesterone in urine and embryonic viability (Mayer, Glasgow and Gawienowski, 1961). A luteotropic effect of the conceptus in rabbits has been proposed by Stormshak and Casida (1966) who found that the effect of LH on CL regression was greater for animals with two conceptuses as compared to those with six conceptuses. More recently, Tillson, Erb and Niswender (1970) have shown significant differences between pregnant and nonpregnant sows in levels of progesterone and LH in peripheral blood plasma and rate of excretion of metabolites of progesterone in urine. Excretion rates of metabolites in urine were higher as early as 4 to 8 days after breeding in the pregnant sows.

¹ Journal Paper No. 4034. Purdue University Agricultural Experiment Station, Lafayette, Indiana 47907. A contribution from the Department of Animal Sciences.

² The author are indebted to Dr. G. D. Niswender, Department of Pathology, University of Michigan, Ann Arbor, for LH hormone assays.

³ Present address: ALZA Corporation, Palo Alto, California.