Association between scrotal circumference, live weight and sperm output in cattle

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Abstract
The relationships between scrotal circumference, live weight and sperm output were examined in 3 samples of bulls selected for use in AI [artificial insemination]. In Study 1, the linear correlation between live weight and scrotal circumference in 418 British Friesian bulls at .apprx. 400 days of age was + 0.28 and the circumference of the scrotum was related to the live weight of the bull by + 0.179 .+-. 0.060 mm/kg live wt. At 400 days of age the mean (.+-. SE) live weight and scrotal circumference of 22 British Friesian bulls in Study 2 was 412 .+-. 7 kg and 332 .+-. 4 mm, respectively. Rates of growth were 1.11 .+-. 0.023 kg/day and 0.426 .+-. 0.023 mm/day. The correlation (+0.42) between the size of the scrotum and the number of spermatozoa per ejaculate was not significant. British Friesian (average age 9 yr) and Hereford (average age 6.5 yr) bulls were examined in Study 3. For the 25 Herefords, correlation between the number of usable straws over 6 mo. and the scrotal circumference was +0.43 compared with +0.21 among the 28 British Friesians. Scrotal circumference is unlikely to be an accurate predictor of sperm output in AI bulls.