Rc. Mulley et al., GROWTH AND BODY-COMPOSITION OF ENTIRE AND CASTRATED FALLOW BUCKS (DAMA-DAMA) TREATED WITH ZERANOL, Animal Science, 63, 1996, pp. 159-165
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.