Immunocastration in male cattle

Summary

The objective in this project was to examine the potential to apply late immunocastration in male cattle as a strategy to enhance body composition, carcase yield and meat quality. Bulls remained entire during the pre-pubertal period in order to utilise the superior growth efficiency of entire bulls compared with steers. At an appropriate time relative to puberty and the anticipated age at market, bulls were immunocastrated and subsequently slaughtered at different times to ascertain effects on carcase yield and meat quality.

From the time of immunocastration, the carcase progressively changed from that of an entire bull to that of a steer. Late immunocastration had the potential, therefore, to provide an additional management option to influence meat quality in male cattle. The approach had application in both feedlot-finished and pasture-finished male cattle.

BACKGROUND

Active immunization against the brain reproductive hormone gonadotrophin-releasing hormone (GnRH) induces an immunocastration response in entire bulls. Accordingly, immunocastrated bulls have carcase characteristics typical of steers. In one study using Zebu crossbred bulls, animals immunocastrated at 22 months of age yielded carcases that were graded as steers. The latter study indicated that, subsequent to immunocastration of sexually mature bulls, body composition and carcase type change from that of an entire bull to that of a steer. The progressive shift to features characteristic of steers subsequent to immunocastration provides the opportunity to control car case type and meat quality by altering the interval between immunocastration and slaughter.

The aim of this project was to identify the effects of late immunocastration on carcase yield, carcase type and meat quality in male cattle. Strategies to enhance growth and meat quality in cattle and feed conversion efficiency were undertaken both in feedlot-finished and pasture-finished male cattle. Groups of contemporary steers (n = 30-50), late immunocastrated bulls (n = 30-50) and entire bulls (n = 30-50), will be feedlot-finished or pasture-finished and compared for carcase yield, carcase type and meat quality. The age at immunocastration, and interval between immunocastration and slaughter, were dependent on genotype, management system and target market. The project was designed within a commercial framework.