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Some Factors Influencing Semen Characteristics in Range Bulls¹

New Mexico State University, Las Cruces 88003

Abstract

Semen characteristics of 41 beef bulls maintained under range conditions during 1972, 1973 and January 1974 were studied to determine the effects of age, body weight, season and winter supplementation. As has been demonstrated in bulls of dairy breeding, semen volume increased in beef bulls as their weights increased. However, this relationship was not found when bulls were compared within age groups. Bulls of 3 to 4 years of age had larger semen volumes than heavier and older bulls 8 to 9 years of age (P<.05). Older bulls had significantly (P<.01) more sperm cells per milliliter of semen and more total cells per ejaculate. No significant differences in percent motile cells were found due to age effects. Season influenced volume of ejaculates, with larger semen volumes collected in the spring of the year and lowest volumes in the winter. Highest density was observed in fall semen samples. Summer samples were consistently poorest in all characteristics. Energy level of winter supplementation had some pronounced effects on semen characteristics. Bulls receiving a 10% protein pellet and more total dietary energy, had significantly (P<.01) more cells per milliliter of semen, a higher percentage of motile cells and a better rate of forward movement score than the bulls receiving a 41% protein pellet. However, a supplement x age interaction revealed that among older bulls, density and total cells per ejaculate was greatest in bulls receiving a higher energy supplement, while in younger bulls, a higher protein supplement resulted in significantly (P<.05) more cells per ejaculate. No significant differences (P<.05) were found in percent abnormal cells due to age, body weight, season or supplementation.

¹ Journal Article Number 631, New Mexico State University Agricultural Experiment Station.

² Professor, Department of Animal, Range and Wildlife Sciences.

³ Former Graduate Assistants, Department of Animal, Range and Wildlife Sciences.