PSI-39 Retrospective analysis of semen quality attributes of bulls in the Cal Poly Bull Test

Abstract

Abstract The Cal Poly Bull Test has been offering valuable information for genetic improvement via a performance test of yearling beef bulls across the western United States since 1951. Growth and reproductive performance phenotypes were measured and collected over time. Therefore, the objective of this study was to determine the relationship between growth traits and semen quality traits. Performance records and semen samples of Hereford and Angus bulls were collected over a 12-year span from 2001–2013. A total of 1,982 records from Angus (n = 1692) and Hereford (n = 290) bulls were analyzed. All bulls were fall-born and weaned prior to the start of test in May. Bulls were fed for 99.83 ± 0.37 days in accordance with the guidelines of the Beef Improvement Federation where growth performance was assessed monthly during that period. After the conclusion of the test, usually in August, semen was collected from bulls and assessed for sperm motility, morphology and total sperm count. Bulls were retrospectively classified as low (0–1.4 kg), moderate (1.4–1.8 kg), or high (1.8–2.7 kg) average daily gain (ADG) bulls. The correlation among traits was evaluated using Pearson correlation, whereas a linear mixed model was used to evaluate the effect of growth on semen quality attributes. Bull age was moderately, negatively correlated (P < 0.01, r2 = -0.3) with scrotal circumference. Sperm motility and morphology were moderately correlated (P < 0.01, r2 = 0.35). Bull ADG was not strongly correlated (P < 0.01, r2 = 0.15) with semen motility or morphology. The results indicated a significant breed effect (P < 0.01) on semen motility and morphology. Angus bulls had a higher percent of progressively motile spermatozoa (P < 0.01; 72.23% ± 0.73) when compared with Hereford bulls (65.88% ± 1.37). Additionally, Angus bulls had a higher percentage of morphologically normal sperm (P < 0.01; 73.65% ± 0.59) when compared with Hereford bulls (66.29% ± 1.1). However, ADG as a class variable had no impact (P ≥ 0.50) on semen motility or morphology. Thus, these results indicate that higher levels of ADG during the testing period did not negatively impact semen quality attributes. More data must be collected to assess the biology behind the breed effects and validate the effect of body weight gain on semen quality attributes.