SCROTAL CIRCUMFERENCE, SEMEN CHARACTERISTICS, GROWTH PARAMETERS AND THEIR RELATIONSHIPS IN YOUNG BEEF BULLS

The records of sixty-six yearling and 2-yr-old beef bulls selected for breeding in 1980 and 1981 were used to study the relationships between body weight (BW) and gain measurements, scrotal circumference (SC) and semen characteristics in young beef bulls. The bulls belonged to four breed groups; Hereford, Beef Synthetic, Dairy Synthetic and Pee Wee. A week before the start of breeding season, the bulls were weighed and measured for scrotal circumference. A single prebreeding semen sample was collected by electro-ejaculator from each bull in 1980, while three samples (pre-, mid- and postbreeding) were collected by artificial vagina in 1981. The mean SC ranged from 31.3 cm in the Pee Wee to 38.6 cm in the Beef Synthetic, while SC per 100 kg BW was maximum in the Pee Wee (8.36%) and minimum in the Dairy Synthetic group (6.28%, P < 0.05). The relationship between BW and SC was linear within yearling and 2-yr-old bulls. Age did not have any effect on SC over and above BW within each age group. Preweaning daily gain accounted for a higher fraction of variation in SC compared to BW in all the breed groups except Dairy Synthetic. The relationships between BW, SC and feedlot daily gain with semen quality and quantity were positive but generally small (r < 0.30, P > 0.11). Semen volume and sperm motility had lower values and percent secondary abnormalities were higher in prebreeding compared with mid- or postbreeding samples. Repeatability estimates of the semen characteristics were generally low, ranging from 0 to 0.49. Key words: Beef bulls, scrotal circumference, semen characteristics, growth rate