A comparison of the growth rate and carcase characteristics of steers and heifers when entire, spayed, pregnant or fitted with an intravaginal device

Abstract

Four separate experiments were conducted at three localities in Victoria to compare the growth and carcase characteristics of steers and heifers either as entire (not pregnant), spayed, fitted with a HEIGRO intravaginal device, or pregnant. All treatments were compared in the major experiment of the series with two or more of the treatments compared in the other experiments. A total of 212 yearling cattle was used in the experiments, which were conducted mainly at pasture for periods of 4-11 months. The differences between the growth rate of steers and entire heifers (3.5%) and entire and spayed heifers (5.0%) were not significant. Pregnant heifers gained weight faster during mid-pregnancy (P < 0.05) but their dressing percentage and carcase weight were lower (P < 0.05) than all other groups. There were few significant differences in fat depth and only small differences in any of the carcase characteristics measured. We conclude that entire heifers grew and fattened as well as steers and that neither spraying nor the use of the HEIGRO device improved carcase weight gain but that pregnancy reduce it.