GROWTH AND BODY-COMPOSITION OF ENTIRE AND CASTRATED FALLOW BUCKS (DAMA-DAMA) TREATED WITH ZERANOL

A 2 X 2 factorial experimental design was used to compare growth in en tire and castrated fallow bucks, implanted with zeranol at 6 and 9 mon ths of age, or left as controls (no. = 10 per group). Growth pattern a t pasture was assessed using 10-monthly growth periods from weaning (6 months) to 17 months. There were no overall castration or zeranol eff ects on growth rates from weaning to 17 months (P > 0.05), although th ere were significant interactions of zeranol and castration with time (P < 0.05). Zeranol-treated animals grew faster than the controls from 6 to 14 months, compared with the last 3 months (P < 0.05), indicatin g that the zeranol implants given at 6 and 9 months of age were no lon ger effective over the last 3 months of the experiment. The interactio n between castration and time was significant (P < 0.05), whereby enti re males grew relatively faster than the castrated males in both sprin g and the average of the winter and spring periods, whilst there was l ittle difference in growth rates between entire and castrated males du ring the autumn period. At 17 months of age all animals were slaughter ed following a 16-h fast. Entire bucks were 46 g/kg live weight and 56 g/kg carcass weight heavier than the castrated bucks at slaughter (P < 0.05), although there was no effect of zeranol treatment on either l ive or carcass weights (P > 0.05). The mean dressing proportion for de er in all groups was 0.61. A subset of each treatment (no. = 5) were s laughtered and half carcasses dissected into muscle, bone and fat. Whe n compared at the same carcass weight, both castration and treatment w ith zeranol significantly reduced the muscle weight and increased carc ass fat weight (P < 0.05). There was no effect of either castration or zeranol treatment on the distribution of primal cuts. There were sign ificant castration X zeranol interactions (P < 0.05) for muscle: bone and muscle: fat ratios, the entire control group having the highest mu scle: bone and muscle: fat ratios. It was concluded that there is litt le commercial basis for the use of the growth promotant zeranol in fal low bucks being grown for version. Although castration resulted in low er carcass weights and muscle proportion, these disadvantages should b e considered against the management advantages of easier handling and lower bruising of castrates.