Using a lamb's early-life liveweight as a predictor of carcass quality

Abstract

The commercial value of lamb carcasses is primarily determined by their weight and quality, with the latter commonly quantified according to muscle coverage and fat depth. The ability to predict these quality scores early in the season could be of substantial value to sheep producers, as this would enable tailored flock management strategies for different groups of animals. Existing methods of carcass quality prediction, however, require either expensive equipment or information immediately before slaughter, leaving them unsuitable as a decision support tool for small to medium-scale enterprises. Using seven-year high-resolution data from the North Wyke Farm Platform, a system-scale grazing trial in Devon, UK, this paper investigates the feasibility of using a lamb's early-life liveweight to predict the carcass quality realised when the animal reaches the target weight. The results of multinomial regression models showed that lambs which were heavier at weaning, at 13 weeks of age, were significantly more likely to have leaner and more muscular carcasses. An economic analysis confirmed that these animals produced significantly more valuable carcasses at slaughter, even after accounting for seasonal variation in lamb price that often favours early finishers. As the majority of heavier-weaned lambs leave the flock before lighter-weaned lambs, an increase in the average weaning weight could also lead to greater pasture availability for ewes in the latter stage of the current season, and thus an enhanced ewe condition and fertility for the next season. All information combined, therefore, a stronger focus on ewes' nutrition before and during lactation was identified as a key to increase system-wide profitability.

Keywords: Conformation; Ewe condition; Farm management; Fat class; Sheep systems.

Fig. 1

Conditional boxplots for lamb weaning weight. A significant difference in weaning weight (kg) was observed between different carcass conformation score groups (p < .001) (left) and between different fat class groups (p < .001) (right) at slaughter. Groups with the same letter are not significantly different with each other (p > .05) based on Tukey's honestly significant difference (HSD) test.

Fig. 2

Physiological development of lambs inferred from the present study. Different tissues develop at alternate stages, with organ, bone and muscle developing rapidly in early life (1), followed by muscle (2), muscle and fat (3) and finally fat only (4) as mature weight is approached. Faster growing lambs reach finishing weight while still in an earlier stage of tissue development (a), resulting in a larger proportion of the carcass composed of muscle than in slower growing lambs (b). Straight lines are used for clarity; actual growth curves are likely to be nonlinear.

Fig. 3

Predicted changes in lamb carcass score under enhanced weaning weight. When weaning weight becomes heavier by 13.25 kg, the likelihood of the animal attaining the fat class of 2 was found to increase dramatically (from n = 364 to n = 1708). The effect on likelihood of the animal attaining the conformation score of U, on the other hand, was only moderate (from n = 216 to n = 356). IQR: interquartile range of lamb weaning weights. U2, U3L, R2 & R3L: combined carcass quality (conformation and fat scores) under the EUROP grading system.