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Altrenogest and Fat for Summer Breeding of Primiparous Sows¹

Kansas State University⁴, Manhattan 66506

Abstract

Delaying the onset of estrus after weaning and adding fat to the postweaning diet were studied for their effects on estrus and fertility in 232 crossbred primiparous sows on a commercial swine farm. Sows were assigned randomly to the following treatments after weaning in June, July, August, or September, 1983; 1) altrenogest (20 mg/d) was fed for 7 d after weaning (n=76), 2) altrenogest was fed for 7 d plus .5 3 kg dried animal and vegetable fat product (.45 kg actual fat/d) for 14 d after weaning (n=78), or 3) no treatment (controls, n=78). While a similar proportion of sows came into heat after weaning (lactation length = 4 wk), sows fed altrenogest (14.4 ± .2 d) returned to estrus about 9 d later (P<.01) than controls (5.6 ± .2 d). Serum progesterone concentration was assayed in blood samples collected from a subgroup (74%) of the cows not observed in estrus by 3 wk after weaning to determine possible causes of anestrus. If serum progesterone (>5 ng/ml) was elevated, we assumed that sows had ovulated without expressing estrus (behavioral anestrus) or ovulated with undetected estrus (less overt estrus or error in estrous detection), whereas low progesterone (<5 ng/ml) indicated that sows were anovulatory. About 53% of the sows not observed in estrus across all treatments had luteal function, probably resulting from postweaning ovulation. Incidence of anovulation without estrus was 47%. Farrowing rate was higher (P<.05) for sows fed only altrenogest (64%) compared with controls (46%), but similar to fat supplemented, altrenogest-treated sows (52%). Average number of total pigs born was similar among treatments. However, there was a tendency for altrenogest-fed sows to have more (P=.06) litters with 11 or more pigs (44%) than control sows (24%). These results suggest that feeding altrenogest or altrenogest plus fat after weaning did not increase the percentage of primiparous sows in estrus following summer weanings, but delaying the onset of estrus after weaning by feeding altrenogest may have improved fertility and fecundity of sows bred after weaning their first litter.

¹ Contribution No. 85-233-J, Kansas Agr. Exp. Sta., Manhattan 66506. The authors acknowledge Mark Acock for allowing this study to be conducted at Morrison Pork, Smolan, KS. We acknowledge Better Nutrients, Inc., Memphis, TN, for providing the fat product (Fatso® 8-85 Meal) and Dr. Stephen K. Webel and Roussel-UCLAF for donating the altrenogest (Regu-mate®) and financial assistance for this study. Gratitude also is expressed to Susan Durham, Robert Erickson, Mark Johnston and Ed Kluber for their help in laboratory analyses and data collection and to Cindy Barrett for typing this manuscript.

² Address reprint requests to this author.

³ Present address: Central Soya Feed Research, Decatur, IN 46733.

⁴ Dept. of Anim. Sci. and Ind.

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