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Effect of Energy Intake after Weaning on the Sexual Development of Beef Bulls. I. Semen Characteristics and Serving Capacity^1,2,

Kansas State University, Manhattan 66506

Abstract

Simmental and Hereford bulls were individually fed varying levels of the same diet to determine the effects of energy intake after weaning, degree of fatness, and short-term weight change on reproductive characteristics of yearling beef bulls. For 200 d (ending in May), 29 Simmentals were fed an average of 14.6, 19.2 or 23.8 Mcal and 27 Herefords were fed 13.4, 17.5 or 22.2 Mcal metabolizable energy per bull daily. Bulls then were adjusted to a roughage diet for 10 d before grazing brome pasture for 38 d (ending in June). Energy level did not affect motility or sperm morphology of semen collected with an artificial vagina in May and June. High energy levels were not detrimental to bull performance during a 30-min serving-capacity test in May or June. Backfat thickness was not related to semen characteristics or serving capacity. Amount of weight lost from May to June did not affect the semen quality or serving capacity of Herefords. Those Simmental bulls that had a more positive weight change from May to June had a more favorable change in semen quality from May to June (P<.05) due to lower semen quality in May (P<.05). The high level of energy was not detrimental to semen characteristics or serving capacity. Some of the Simmental bulls may have been underfed for maximum semen quality at the beginning of the pasture period. Within the normal range of energy fed to beef bulls from weaning to the beginning of the breeding season as yearlings, it may be more likely to underfeed breeds of large mature size than to overfeed British breeds.

¹ Contribution 85-106-J, Dept. of Anim. Sci. and Ind., Kansas Agr. Exp. Sta., Manhattan 66506.

² The authors wish to thank Margo Heekin, research assistant, for help in data collection and Glassel Flaherty, Paul Rimple and Colleen Coughlin for help in semen collection and evaluation.

³ Present address: Dept. of Anim. and Range Sci. South Dakota State Univ., Brookings 57007.