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Estrous and Litter Traits in Gilts Altered by Altrenogest, Flushing and Pubertal Status^1,2,

Kansas State University⁵, Manhattan 66506

Abstract

Influences of estrous synchronization with altrenogest and flushing on reproductive traits in guts were evaluated in three experiments on two farms. Crossbred gilts were fed altrenogest or altrenogest and an additional 1.55 kg ground sorghum grain for at least 10 d before breeding (flushing), or served as controls. Additional grain for the flushing treatment was provided to guts from the eighth day of altrenogest treatment until they were detected in estrus. The combination of altrenogest and flushing (On Farm A) increased (P<.05) litter size when compared with gilts treated only with altrenogest and controls that received neither altrenogest nor flushing. This response was entirely among gilts inseminated at their pubertal estrus. For pubertal gilts fed altrenogest and the flushing treatment, litter traits were similar to other treated or control gilts inseminated at a postpubertal estrus. No treatment effects on litter size were detected for gilts inseminated at a postpubertal estrus. Gilts on Farm B responded differently, with larger litter sizes (P=.08) for those treated with altrenogest and flushing plus altrenogest than for control gilts. Reasons for farm differences might be unidentified genetic or management factors or different seasons of the year when gilts were treated on Farm B (summer) vs Farm A (fall, winter and spring). Our results indicate a marked potential for increasing litter size in gilts mated at their pubertal estrus because their unstimulated ovulation rate (no altrenogest or flushing) did not challenge adequately the biological capacity of their uteri.

¹ Contribution No. 86-444-J, Kansas Agr. Exp. Sta., Manhattan, 66506.

² The authors appreciate the generous donation of altrenogest and partial support of this project by Dr. Stephen K. Webel and Roussel-UCLAF. We also acknowledge gratefully the cooperation of Mark Acock and Morrison Pork, Smolan, KS, where a portion of this research was conducted. Gratitude is expressed to R. Ericson, K. Johnston, Mike Johnston, Mark Johnston, E. Kluber, R. LaForge, W. Schmidt and S. Durham for their excellent technical assistance and to J. Gieber for typing the manuscript. A portion of this work was reported previously at the 18th Annu. Meet. of the Midwest. Sec. Amer. Soc. of Anim. Sci., Chicago, IL, March 1985.

³ Reprint requests.

⁴ Present address: Central Soya Feed Research, Decatur, IN 46733.

⁵ Dept. of Anim. Sci. and Ind.