Parity-associated changes in slaughter weight and carcass characteristics of 3⁄4 Charolais crossbred cows kept on a lowland grass/grass silage feeding and management system

Abstract

AbstractA total of 77 heifers (3⁄4 Charolais crossbred) completed a study which examined the effects of parity number on growth, changes in size of the carcass, carcass composition and meat quality. The experiment had a factorial design based on the factors: parity and level of finish. The parities were: 0 (maiden), 1, 3 and 5. At each parity animals were slaughtered at medium (EU fat class 3) and high (EU fat class 4H) levels of finish. All data were analysed by analysis of variance using individual animal observations, and linear, quadratic and asymptotic trends were explored. Where appropriate, regression equations were derived using individual animal values to describe the relationships between key parameters and the parity status of the finished animal. Animals calved at turn-out to grass in spring (April/May) and the cows were housed at weaning in mid October (mean lactation length of 163 days) and all pregnant animals were given a diet of grass silage without concentrate supplementation during the winter period. The medium level of finish animals were slaughtered 24 days after commencement of the breeding programme for parity 0 or at the end of lactation for the remaining parities, except for parity 1 animals which had a short finishing period. For the high level of finish treatment, parity 0 heifers had a longer finishing period, while all bred animals had a post-weaning finishing period. The high finish animals were finished on a diet of grass silage and concentrates. Birth weights of calves increased until the fourth parity, while weaning weights increased linearly until the fifth parity. Mean daily milk yield increased until the third lactation. Live weight, carcass weight and weights of saleable beef, separable lean and separable fat all followed asymptotic patterns of rapid initial increase and then tended to plateau with increase in parity. The asymptote values for live weight and carcass weight were 723·0 and 383·2 kg respectively. Statistically significant asymptotic relationships with parity number were obtained for live weight and various tissue weights. Nominal mature weight was assumed to be 0·99 of the asymptote and nominal mature weights for live weight, carcass weight, saleable beef, separable lean and separable fat were attained at parity (age, years) 4/5 (6·1), 3/4 (5·3), 4/5 (6·2), 3/4 (4·7) and 1/2 (2·7) respectively. The proportion of high-priced joints declined with increase in parity (linear trend P 0·01) thus indicating a reduction in relative growth of the main muscle groups of the hind limb. Shear value measurements on cooked muscle from the maiden and first parity animals indicated very tender meat, but tenderness declined with increase in parity (asymptotic trend P 0·001). Taking animals to the higher level of finish effected increases in carcass weight and separable fat in the carcass of 55·1 kg (P 0·001) and 72 g/kg (P 0·001) respectively, while separable lean declined by 53 g/kg (P 0·001). Cooked muscle from the high finish animals was less tender than from the medium finish animals (P 0·05). It was concluded that slaughtering cows at the third parity would enable a self replacing closed herd to be operated, while obtaining 0·97 of the potential maximum output of saleable beef from the cow, but there may be some compromise in the tenderness of the meat for some consumers by the third parity.