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Title: Impact of bull development on reproductive success

item PERRY, GEORGE - South Dakota State University
item RUPP, GARY - University Of Nebraska
item Cushman, Robert - Bob

Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: 11/2/2010
Publication Date: 9/1/2011
Citation: Perry, G.A., Rupp, G.P., Cushman, R.A. 2011. Impact of bull development on reproductive success [abstract]. Journal of Animal Science. 89 (E-Supplement 2):65 (Abstract #52).

Interpretive Summary:

Technical Abstract: The herd bull influences overall herd fertility more than any other single animal. However, a bull must be developed properly and have reached puberty to be fertile. Puberty is defined by an ejaculate containing a minimum of 50 x 106 total sperm with at least 10% progressive motility; however, this is not sufficient to pass a Breeding Soundness Exam (BSE). Simply because a bull can produce semen does not mean he is fertile. Sperm quality and quantity continued to increase for months after the initiation of production, and morphology has been reported to positively influence pregnancy success. High levels of energy can increase wt, height, and scrotal circumference (SC) without affecting age at puberty or first mating. Birth wt, weaning wt, weaning hip height, weaning hip to wt ratio, birth to weaning ADG, yr wt, yr hip height, yr hip to wt ratio, weaning to yr ADG, % of BW gained from weaning to yr, sperm motility, sperm morphology, and pass/fail BSE have been collected on 1940, 13 to 20 mo old bulls in South Dakota. Analysis of the data indicated that age at time of BSE had the largest impact on motility (r2=0.06; P<0.001), morphology (r2=0.03; P<0.001), and ability to pass a BSE (r2=0.03; P<0.001). Inclusion of all variables only accounted for 10%, 9.5%, and 9.7% of the variation in motility, morphology, and ability to pass a BSE, respectively. Analysis of 259 BSE performed at USMARC also showed a significant increase in SC as age increased from 15 to 20 mo of age. While analysis of over 3800 BSE performed at USMARC on bulls from 12 to 98 mo of age showed a positive correlation between SC and both motility (r2=0.11; P<0.0001) and morphology (r2=0.07; P<0.0001). In summary, development of herd bulls can impact the reproductive performance of an entire herd, and while supplying proper nutrition is important to proper development, getting bulls over conditioned can have a negative impact on semen quality. However, the factors that have a large impact on semen quality are largely unknown.