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Body Growth and Testicular Characteristics of Boars Fed a Synthetic Progestogen, Altrenogest^1,2,

Kansas State University^,5, Manhattan 66506

Abstract

A synthetic progestogen (altrenogest) was fed to 24 Yorkshire x Duroc boars to determine effects on body growth, serum testosterone, and testicular characteristics. Boars from six litters (blocks) were allotted randomly to one of four treatment groups at 12 wk of age. Treatment groups were: (1) controls, (2) altrenogest fed for 3 wk, (3) altrenogest fed for 6 wk and (4) altrenogest fed for 9 wk. Treatment began at 15 wk of age at a daily dose of 20 mg·boar^–1. Although there were no differences among treatment groups for gain and feed intake, boars fed altrenogest for 6 and 9 wk tended to consume more feed and were less (P<.05) efficient than boars fed altrenogest for 3 wk or controls. Boars fed altrenogest for 3, 6 and 9 wk maintained lower (P<.05) peripheral serum testosterone concentrations than controls from 15 to 24 wk of age. However, serum testosterone increased after altrenogest withdrawal in the 3- and 6-wk treatment groups but did not reach control concentrations by 24 wk. Boars fed altrenogest for 9 wk maintained serum testosterone below 1 ng/ml during the treatment period. Despite lower concentrations of serum testosterone in altrenogest-treated boars, backfat thickness was similar to controls, perhaps suggesting a slight anabolic effect of altrenogest on nutrient partitioning. Testicular weights and volumes at 24 wk decreased (P<.001) linearly with increased duration of altrenogest feeding. Serum testosterone and estradiol in testicular venous effluent at castration were lower (P<.01) in altrenogest-treated boars than in controls. These data demonstrate that feeding altrenogest inhibits both testicular growth and steroidogenesis of boars without altering body growth or backfat thickness.

¹ Contribution No. 85-337-J, Kansas Agr. Exp. Sta., Manhattan 66506.

² The authors appreciate the generous donation of the progestogen (altrenogest or Regu-mate®) used in this study from Dr. Stephen K. Webel and Roussel-UCLAF. Gratitude is expressed to Susan Durham for her assistance with laboratory analyses and to Cindy Barrett for typing this manuscript.

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

⁴ Reprint requests.

⁵ Dept. of Anim. Sci. and Ind.