The Effects of Hexoestrol Implantation on Carcass Analysis, Energy Balance and Nitrogen Retention of Cattle

Abstract

Seven pairs of indentical twin steers were used, one animal of each pair acting as the control to its treated counterpart; the selection of these steers was based initially on their phenotypic similarity and was subsequently confirmed by blood tests. Each treated steer was implanted, in the ear, with four 15 mg. pellets of hexoestrol. All the animals were from two to three and a half years old and weighed between 320 and 450 kg at the start of• the experiments. A brief description of these animals is given in Table I. The rations were designed to provide a range of energy intakes from near maintenance (M) to approximately 2M and were based on AR C. standards; they were composed of varying proportions of hay, barley meal, meat meal and dairy cubes. Protein intake was also varied. The animals were weighed daily throughout the experiments which lasted from 90 to 120 days. Water was available at all times and the quantity consumed was measured. Mineral licks were provided for each animal and the amount eaten was recorded. All the animals were kept under uniform conditions in individual pens for the duration of• the experiments, except for their periodic visits to the respiration chamber, where they were confined for 24 hours. During this time• the oxygen consumption, carbon dioxide output and methane production of each animal was determined. All the calorimetric measurements were conducted at 22 C+ 10 and at 60 per cent+ 5 per cent relative humidity. The energy nitrogen and carbon balances of each of the 14 animals were measured on several days during the course of each experiment and the data reported in Table II-are averages of these separate determinations. The type of chamber used and a brief description of the experimental routine were given in an earlier paper (Rogerson, 1960). It should be noted that the animals had been handled frequently from weaning age and had been accustomed to the respiration chamber prior to the commencement of these experiments.