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Reproductive Capacity of Beef Bulls. II. Postpuberal Relations among Ejaculation Frequency, Sperm Freezability and Breeding Potential^{1, 2,}

The Pennsylvania State University, University Park³

Abstract

Sperm freezability and breeding potential were determined from puberty to 2 years of age on 17 Angus and Hereford bulls. Seven were ejaculated biweekly to 1 year and weekly to 2 years of age (1x group), five were ejaculated three times weekly to 2 years of age (3x group) and five were ejaculated at 3x to 1 year and six times weekly to 2 years of age (6x group).

A total of 2822 ejaculates, or 98% of the specified number of 2880, were collected by artificial vagina and 1402 of those ejaculates, or 50%, were acceptable for freezing (at least 396x10⁶ sperm/ml., 40% progressively motile sperm and 840x10⁸ total motile sperm). An average of 79%, or 730 of 924 samples representing 1176 ejaculates, froze satisfac- torily (minimum of 10x10⁶ motile sperm per ampule after storage for 3 weeks at –196° C).

The percent of acceptable ejaculates collected during the first 60 weeks after puberty ranged from 25 to 75 for individual bulls and averaged 52. However, there was considerable improvement with increasing bull age; the proportion of acceptable ejaculates for the five 12-week postpuberal periods averaged 22, 47, 50, 57 and 66%.

Initial sperm motility of acceptable ejaculates did not improve with bull age, but post-thaw motility after 3-week storage at –196° C. showed a highly significant increase from 22% at 9 to 24 weeks to 28% at 45 to 60 weeks after puberty. Variation among bulls within breed and frequency groups was highly significant for both initial motility and post-thawing motility; breed and ejaculation frequency differences were nonsignificant.

Only 1108 ejaculates, or 39% of the 2822 collected during the first 60 weeks after puberty, froze satisfactorily. However, the percent of all ejaculates collected which froze successfully showed a highly significant increase from 34 at 9 to 24 weeks to 59 at 45 to 60 weeks postpuberty.

The theoretical number of inseminations per bull between puberty and 2 years of age was: 1x group, 3303 ±962; 3x group, 5818±630; and 6x group, 8226±1O16. Seven of the 17 bulls yielded 100 usable ampules by 52 weeks and 15 bulls by 60 weeks of age. As ejaculation frequency increased, there was a decrease in the average age at which 500 usable ampules were attained. By 60 weeks of age six of ten 3x and 6x and two of seven 1x group bulls yielded 500 usable ampules. These data suggest that many beef bulls can be sampled in a progeny testing program by 60 weeks of age.

¹ Authorized for publication as Paper No. 3167 in the Journal Series of The Pennsylvania Agricultural Experiment Station, University Park.

² Supported in part by the Pennsylvania Association of Artificial Breeding Cooperatives and the Linde Company, Division of Union Carbide Corp.

³ Dairy Breeding Research Center, Department of Dairy Science.