The effect of genotype and zeranol implantation on performance of steers grazing Mitchell grass pastures in north-west Queensland

Abstract

[Summary]: Steers of seven different genotypes were purchased from six locations in north-west Queensland and their liveweight performance was compared while grazing Mitchell grass pastures. Only small differences were recorded in liveweight gain between steers containing the approximate breed components of Africander 3 Shorthorn 5, Sahiwal 3 Shorthorn 5, Santa Gertrudis, Brahman 4 British 4, and Brahman 6 British 2. The Bos indicus infused steers had annual liveweight gains of 135 compared with 110kg / head / year in the comparable age Hereford group. Zeranol implantation gave 6% advantage in liveweight gain durin the first 84 d post implantation. This response was consisten across genotype groups. Final liveweight of treated steers was 3% heavier than of untreated steers, although zeranol treatment was given 444 d before slaughter.