Effect of hormone implantation on growth rate and carcass composition of cattle grazing paspalum-dominant pasture

Abstract

Twelve 4-year-old steers and 12 3-year-old steers were divided into four comparable groups. One group was slaughtered at the commencement of the experiment; the other three groups were placed on good quality paspalum pasture. Of these three groups on pasture one was implanted with 200 mg progesterone and 20 mg oestradiol benzoate, another received an implant which contained in addition to the above 25 mg cholesterol and 4.9 mg hydrocortisone acetate and the third was an untreated control.
Body-weight gains over the 103 days of the experiment were 2.8 lb per head per day for the group receiving progesterone plus oestradiol, and 2. 7 lb per head per day for the group receiving in addition cholesterol and hydrocortisone. There was no significant difference between these two rates of gain but both were significantly greater (P < 0.01) than the 2.2 lb recorded for the non-treated group on pasture. The mean carcass weights of the progesterone plus oestradiol group, the progesterone plus oestradiol plus cholesterol plus hydrocortisone group and the control group on pasture were 114, 121 and 85 lb greater respectively than that of the group slaughtered initially. As determined from chemical analysis of the 9th, 10th and 11th rib cut, the weight of protein in the carcass of both implanted groups was significantly greater than that of the control group slaughtered at the same time.