The effect of oestradiol-17β (Compudose ®) on liveweight gain, herbage intake and circulating hormone concentrations in steers at pasture : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Animal Science at Massey University, New Zealand

Abstract

World food production needs to increase as world population is increasing. One method of achieving this is to improve the efficiency of food production. Efficient meat production in steers is affected by growth rate, mature weight and composition of the growth. It is possible manipulate growth rate by the administration of sex steroids. Compudose® (oestradiol-17β) improves liveweight gain (14-17%) and feed conversion efficiency (10-12%) in beef cattle under feedlot and grazing conditions. There is little information available on feed intake and hence efficiency of liveweight gain under New Zealand pastoral systems. Therefore, this study was designed to evaluate over a 203 day period the effect of Compudose® on liveweight gain, herbage intake, grazing behaviour and circulating hormone and metabolite concentrations in steers grazing ryegrass-white clover pastures. Twenty 14-month-old Friesian steers and sixteen 14-month-old Angus cross were randomly assigned within breed to either Compudose® or no-Compudose®. Herbage intake and grazing behaviour were measured on two occasions (days 34-50 and days 168-184). Blood samples from the steers were taken at 50-day intervals throughout the trial. Compudose® steers gained a mean of 856 g/d compared with 710 g/d by control steers (P<0.001). The total fasted and unfasted LWG of treated steers was improved by 29.6 kg (20.5%) or 36.3 kg (25%), respectively, over the untreated steers. There were no significant (P>0.05) differences in the amount of herbage eaten between treated and untreated groups (7.4 vs 7.1 kg DM/hd/day). Feed conversion efficiency in the implanted group was improved by 15.7% over the untreated steers. Grazingbehaviour, hormone and metabolite concentrations between treated and untreated steers were not significantly different (P>0.05). The use of Compudose® resulted in a net income of $55 per implanted steer. In conclusion Compudose® implants proved to be a useful management tool to increase performance and productivity in finishing steers under New Zealand pasture-based systems.