Effects of primiparity and subsequent management on carcass composition and quality of continental beef heifers

Abstract

A total of 81 continental maiden heifers (1/2 Blonde d’Aquitaine, 3/8 Charolais breeding) were committed to eight experimental treatments. The experiment had a core factorial design (2×3) based on the factors, bred status (unbred and bred) and stage (fresh calved, fresh weaned, and finished namely weaned plus finishing period). Within each stage, once-bred and unbred animals were slaughtered at similar carcass weights and ages. Bred and unbred animals were individually fed restricted allowances of grass silage/concentrate mixtures with the same proportion at any specific time, and the level of feeding was manipulated to provide the same rate of carcass gain for the bred and unbred animals. The target carcass gains were 45 kg for each of the three stages. In two additional treatments maiden heifers were also slaughtered at the mid service point to provide a baseline measurement, and a further treatment group was taken to the third parity and slaughtered at weaning. The data were analysed as a (3×2)+2 experimental design. Primiparity had a consistent negative effect on killing-out yield and the difference between bred and unbred became smaller with advance in stage (interaction P<0.001). No significant interactions between bred status and stage were obtained for other carcass data. Primiparity had no significant effect on carcass fat class, but produced significant increases in weights of fat depots in the abdominal cavity. In the bred animals the proportion of separable fat in the forerib joint and the estimated separable fat in the carcass were significantly higher, while separable lean was significantly lower. Breeding also significantly reduced the cross-sectional area of the m. longissimus dorsi and the proportion of high priced joints in the carcass. There was no difference in any of the measured meat quality parameters due to gestation. Increases in stage, i.e. carcass weight, also produced reductions in the proportion of high-priced joints, together with increases in all measurements of fatness, separable fat in both the forerib joint and carcass, and reduced separable lean in the carcass. Increases in stage resulted in a decrease in cooking loss and increase in yellowness of fat, but no change in any of the other meat quality parameters. It is therefore concluded that gestation in young heifers increased fatness in both the carcass and body cavity, and reduced carcass leanness, but had no effect on ultimate pH or tenderness of muscle. Animals slaughtered at the post-calving stage were underfinished, while those slaughtered at the weaned and finished stages had acceptable levels of carcass fatness.