Effects of age at slaughter and feeding regime on slaughter weight and carcass composition in mice

Mice from three outbred stocks (PGH, J, and SWO) were fed either pelleted feed from overhead hoppers or ground feed from jars, from weaning at 21 days old to slaughter at 42, 49 or 56 days old. Live weights, weights of carcasses before and after extraction of carcass moisture and fat, and feed consumption were recorded. The PGH stock gained more in dry lean tissue and deposited less fat, and had a greater feed efficiency, compared to either of the other stocks. Males gained more than females, in both dry lean tissue and fat; females had a higher proportion of lean tissue and a greater feed efficiency. Increases in live weight between 49 and 56 days of age were mainly increases in fat content, especially in the offal portion of the body. Jar feeding restricted feed intake and reduced live weight gains. The reduction, however, was principally in fat deposition; feed efficiency was also greater for jar fed mice. It was found that the amount of lean tissue could be accurately predicted from carcass weight and carcass moisture measurements. It may be possible to estimate lean tissue accurately without employing the expensive and time consuming process of either extraction.