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US Department of Agriculture Clay Center, NE 68933
Abstract
Semen characteristics were evaluated every 2 wk from 7 through 13 mo of age in 31 beef bulls representing six breed groups (Hereford, Angus, Hereford x Angus crossbreds, Angus x Hereford crossbreds, Red Poll and Brown Swiss). Breeds differed in age at puberty, defined as the age at which an ejaculate was first obtained that contained a minimum of 50 x 106 total spermatozoa with at least 10% progressive motility (Hereford, 326 ± 9 d; Angus, 295 ± 4 d; Hereford x Angus, 300 ± 8 d; Angus x Hereford, 296 ± 9 d; Red Poll, 283 ± 9 d and Brown Swiss, 264 ± 9 d). Significant breed differences also were observed in concentration of spermatozoa, progressive motility, seminal protein concentration, abnormal spermatozoa and acrosomal morphology. Considerable variation was observed for the majority of pubertal traits among the 31 bulls, indicating that differences in stage of pubertal development existed among and within breeds of beef bulls between 7 and 13 mo of age. However, adjustment of data to age at puberty negated breed differences (P>.10), indicating that the pubertal patterns of change occurring in each semen characteristic were similar for the breeds evaluated. Concentration of spermatozoa, progressive motility, seminal protein concentration, percentage spermatozoa with normal head and tail morphology and percentage spermatozoa with normal acrosomal morphology increased (P<.01) from puberty through 16 wk after puberty in all bulls and all breeds. During the first 6 wk after puberty, rapid increases (P<.01) were observed in percentage spermatozoa exhibiting normal head morphology (excluding acrosomes) and progressive motility, and a rapid decrease (P<.01) was observed in percentage spermatozoa with proximal cytoplasmic droplets, with values at +6 wk approaching those reported for mature bulls. Percentage spermatozoa with normal acrosomal morphology and concentration of spermatozoa improved more slowly and had not reached mature levels by 16 wk after puberty. Because age at puberty varied by 62 d among breeds and 88 d among bulls and important characteristics of semen quality improved slowly after puberty, careful evaluation of the stage of pubertal development in individual bulls is recommended before selecting young bulls for natural breeding or artificial insemination. Additional investigations are needed to define the patterns of pubertal development through sexual maturity in beef bulls and to establish relationships to fertility.
1 The authors gratefully acknowledge the technical assistance of Ms. Shari Ellis, Mr. Ray Sampson, Mr. Steve Furman and Mr. Dave Mitchell with the collection of data.
2 Roman L. Hruska US Meat Animal Research Center, ARS.
3 Mention of trade name, proprietary product or specific equipment does not constitute a guarantee or warranty by the USDA and does not imply its approval to the exclusion of other products that may also be suitable.
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