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Reproductive Capacity of Dairy Bulls. XI. Puberal Characteristics and Postpuberal Changes in Production of Semen and Sexual Activity of Holstein Bulls Ejaculated Frequently^{1 ,2,}

Dairy Breeding Research Center, Department of Dairy and Animal Science, The Pennsylvania State University, University Park 16802

ABSTRACT

Twenty Holstein bulls attained puberty (50 x 10⁶ sperm/ejaculate; 10% motile sperm) at 39 ± 1 wk of age and 295 ± 4 kg body weight. Starting at puberty, 10 bulls were ejaculated biweekly to 1 yr and then weekly (1x) to 2 yr of age, and 10 bulls were ejaculated three times weekly (3x) to 1 yr and then six times weekly (6x ) to 2 yr of age. All characteristics of semen increased through 77 to 88 wk of age. Between 77 to 88 wk and 89 to 104 wk of age, only volume of ejaculate and total sperm per week increased. Motility of sperm increased only during the first 12 wk after puberty. All seminal traits except motility of sperm differed between lx and 6x bulls. Frequency of ejaculation did not affect the percentage of ejaculates acceptable for freezing or body growth rate. Between 1 and 2 yr of age, 6x bulls yielded 3.3 times more sperm per week and 3.5 times more motile sperm per week than lx bulls. Within frequency of ejaculation, time of reaction to ejaculation did not change between 1 and 2 yr of age, but an average of 40% more time was needed to obtain an ejaculation on 6x than lx (9.4 versus 6.7 min). By 13 to 24 wk after puberty, 83% of ejaculates were acceptable for freezing. Thus, Holstein bulls could be sampled in a progeny testing program by 15 mo of age.

¹ Authorized for publication as Paper No. 4953 in the journal series of The Pennsylvania Agricultural Experiment Station on October 16, 1975.

² Supported in part by Atlantic Breeders Cooperative, Lancaster, PA, Sire Power, Inc., and NEBA, Tunkhannock, PA.

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