WS Effects of dietary phytoestrogens on testicular growth and semen quality characteristics in developing Angus bulls

Abstract Text: This study investigated the impact of scrotal growth and semen quality parameters of bulls consuming dietary phytoestrogens versus bulls that are not exposed to phytoestrogen-containing diet ingredients. Angus bulls born in consecutive years were used in 2 independent trials.  Bulls born in the spring of 2014 (n = 39) and 2015 (n = 24) were stratified by weaning weight, age of dam (AOD), and sire into a soybean meal diet group (SBMTRT) or a cottonseed meal diet group (CSMCON). At weaning (d -42), bulls were assigned to treatment and adapted to concentrate diets. At d 0, 21, 54, and 86 scrotal circumference measures were collected with semen collection and assessment also being conducted at d 86.  Differences in scrotal circumference were detected due to the diet × day (year) interaction. On d 54 and 86, SBMTRT in 2014 exhibited larger scrotal measures than SBMTRT in 2015 (P ≤ 0.05).  At d 54, SBMTRT scrotal measures were also greater than the CSMCON scrotal measures in 2015 (P = 0.05). Scrotal growth from d 0 to 21 was greater for SBMTRT across both years (P < 0.0001). This pattern of larger teste growth was also observed from d 54 to d 86 (P = 0.05), and from d 0 through d 86 (P < 0.0001). Variation in semen concentration was due to the diet × AOD (year) interaction. The SBMTRT, produced from 2-year old females, expelled higher concentrated semen samples in 2014 (P = 0.026) and 2015 (P = 0.0006), and this was inconsistent with the 2015 CSMCON out of 5+ year old cows who were higher for semen concentration (P < 0.0001).  The diet × AOD(year) interaction was also a source of variation for motility. The 2014 bulls from 2 and 5+ year old cows ranked higher than the CSMCON cohorts of like aged cows (P < .0001). This trend was not evident in 2015 however, as the CSMCON mean was greater than the SBMTRT from 3 year old cows only (P = 0.0129). Variation from the effect of diet for motility was also observed as well, as SBMTRT scored higher than CSMCON (P= 0.0308). These data suggest that dietary phytoestrogens at 10% soybean meal diet inclusion improves scrotal growth and semen quality and this is particularly evident in bulls produced by 2-year old, first calf females.

Keywords: bull development, phytoestrogen, semen quality