RALGRO® IMPLANTS FOR INTACT MALE CALVES

Forty-eight spring-born bulls (representing early-, medium- and late-maturing breed groups) and 30 fall-born bulls (representing medium- and late-maturing breed groups) were randomly assigned to either a control or treatment group within each breed group. Treated bull calves were initially implanted with Ralgro ® at approximately 55 d of age and reimplanted every 84 d for a total of four implants. All bulls were weaned after 140 d on trial at an average age of 195 d, placed into a feedlot in pens of three or four within breed and treatment groups and gradually adjusted to a high grain ration. Bulls were slaughtered when they reached approximately 7 mm of backfat over the 12/13th ribs, determined ultrasonically. Weaning weights and daily gain to weaning were increased slightly, but not significantly, by implanting in both calving groups. Effects tended to be more pronounced with the earlier (medium) maturing breed groups. No effect of implanting on feedlot performance was observed in either the spring- or fall-born bulls. A reduction in the morbidity rate of the spring-born implanted bulls tended to occur during a period of disease outbreak shortly after weaning. Testicular weights were reduced (P < 0.05) with the use of implants in both calving groups. Scrotal circumference was decreased (P < 0.05) by implanting in the spring-born bulls only. For both of these traits, effects were also more pronounced in the early- and medium-maturing breed groups. Effects of implanting on carcass characteristics were slight. Key words: Ralgro ® , bulls, live performance, carcass characteristics, testicular development