Genetic parameter estimation for beef bull semen attributes

Improvements in bull reproductive performance are necessary to optimize the efficiency of cattle production. Female fertility has been enhanced through assisted reproductive technologies as well as genetic selection; however, improving beef bull fertility has been largely ignored. Phenotypes routinely collected at bull semen collection facilities are believed to affect fertility and provide the phenotypes necessary for a genetic evaluation. The first objective of this study was to determine the significant fixed effects for modeling beef bull fertility using data from bull semen collection facilities. The second objective was to estimate variance components, heritabilities, repeatabilities, and correlations between beef bull semen attributes. Beef bull fertility phenotypes including volume (VOL), concentration (CONC), number of spermatozoa (NSP), initial motility (IMot), post-thaw motility (PTMot), 3-h post-thaw motility (3HRPTMot), percentage of normal spermatozoa (%NORM), primary abnormalities (PRIM), and secondary abnormalities (SEC) were obtained from two bull semen collection facilities. A total of 1,819 Angus bulls with 50,624 collection records were analyzed. Of the fixed class and covariate effects tested, the significant class effects were collection location and collection day within year and the significant covariate effects included age at collection, days since previous collection, and cumulative comprehensive climate index (CCI). For this study, the CCI was calculated for a 75-d period including the 61-d spermatogenesis cycle and 14-d epididymal transit time. The 75 d prior to collection accounted for the environmental stress a bull may have experienced over the course of development of the spermatozoa, which was more significant than the CCI calculated for collection day or spermatogenesis start date. Pre-thaw beef bull semen traits had low heritability estimates of 0.11 ± 0.02 (VOL), 0.09 ± 0.02 (CONC), 0.08 ± 0.02 (NSP), and 0.12 ± 0.03 (IMot). Heritabilities of post-thaw beef bull semen attributes were more variable at 0.10 ± 0.02 (PTMot), 0.05 ± 0.04 (3HRPTMot), 0.10 ± 0.04 (%NORM), 0.03 ± 0.03 (PRIM), and 0.18 ± 0.04 (SEC). Correlations of breeding values for these traits with scrotal circumference (SC) expected progeny difference (EPD) are low. The low to moderate heritability estimates indicate that genetic improvement can be made in beef bull semen quality traits if new tools are developed to augment the scrotal circumference EPD that are currently available within the industry.

96 Estimation of the genetic parameters of beef bull semen attributes

Fertility is a critical factor in cattle production because it directly relates to producing offspring to offset production costs. A number of semen attributes are believed to affect fertility and are frequently measured as part of routine breeding soundness exams or semen collection procedures. The objective of this study was to estimate the variance components for different semen quantity and quality traits that may influence fertility using phenotypes collected on 369 Simmental bulls. A total of 7,436 bull collection records including volume and concentration were obtained from two bull studs and evaluated utilizing a linear univariate animal model with repeated records. The five-generation pedigree used in the analysis consisted of 3,336 sires and 7,225 dams. Volume is the total amount of ejaculate and measured as milliliters of total ejaculate. Volume measurements ranged from 0.100 to 41.30 milliliters, with an average of 7.599 milliliters. Concentration is a measurement of millions of spermatozoa per milliliter. Concentration measurements ranged from 10 to 3,651 with an average of 1,053 million spermatozoa per milliliter. Fixed effects were included in the model if the effect was significant (P ≤ 0.05) for either backward or forward selection. Fixed effects included bull owner, collection center, location within center, collection day within year as a Julian day, collection year fit as class variables. Fixed effects fit as covariates included age of bull at collection (linear and quadratic), days since previous collection (linear and quadratic), and scrotal circumference (quadratic). Heritability estimates of volume and concentration were 0.43 ± 0.14 and 0.40 ± 0.15. These moderate heritability estimates indicate genetic improvement can be made in beef bull semen quality traits through selection.

Selection for bull fertility: a review

Fertility is a critically important factor in cattle production because it directly relates to the ability to produce the offspring necessary to offset costs in production systems. Female fertility has received much attention and has been enhanced through assisted reproductive technologies, as well as genetic selection; however, improving bull fertility has been largely ignored. Improvements in bull reproductive performance are necessary to optimize the efficiency of cattle production. Selection and management to improve bull fertility not only have the potential to increase conception rates but also have the capacity to improve other economically relevant production traits. Bull fertility has reportedly been genetically correlated with traits such as average daily gain, heifer pregnancy, and calving interval. Published studies show that bull fertility traits are low to moderately heritable, indicating that improvements in bull fertility can be realized through selection. Although female fertility has continued to progress according to increasing conception rates, the reported correlation between male and female fertility is low, indicating that male fertility cannot be improved by selection for female fertility. Correlations between several bull fertility traits, such as concentration, number of spermatozoa, motility, and number of spermatozoa abnormalities, vary among studies. Using male fertility traits in selection indices would provide producers with more advanced selection tools. The objective of this review was to discuss current beef bull fertility measurements and to discuss the future of genetic evaluation of beef bull fertility and potential genetic improvement strategies.

Medical Management of Hemorrhagic Bowel Syndrome in a Beef Bull

A two and a half-year old Simmental bull was presented to Iowa State University’s Food Animal and Camelid Hospital for anorexia and lethargy of several days. Clostridium perfringens type A was identified via fecal culture and toxin genotyping. Hemorrhagic bowel syndrome (HBS) was diagnosed based on microbiological results along with abdominal ultrasonography, complete blood count, and serum biochemistry. Aggressive multi-modal therapy was employed including intravenously administered fluid therapy, potassium penicillin, lidocaine, flunixin, and pantoprazole among other supportive care. The bull was discharged after 15 days of hospitalization and recovered uneventfully to full function by the next breeding season. Currently all case reports with regard to HBS in beef cattle describe mortality. While the dairy cattle literature demonstrates that HBS has a high mortality rate, and suggests that surgical intervention has a higher prognosis when compared to medical therapy in dairy cattle. Our case would provide support to aggressive medical treatment for HBS in beef cattle.