The effect of three different growth rates from 15 to 40 kg live weight on some offal components of lambs was studied. The treatments were: high (H) ad-libitum feed intake, low (L) restricted feed intake and high-maintenance-high (HMH) ad-libitum feed intake from 15 to 25 kg followed by a 50-day period of weight stasis, which was followed by ad-libitum feeding. In each treatment, two animals were killed at 25, 30 and 35 kg and three animals at 40 kg. Analyses of covariance were used to compare linear regression equations representing results from each treatment using the logarithmic transformation of the allometric equation, y = axb.
Differences between treatments were found for the weight of certain non-alimentary tract offals including the liver (H, HMH > L), kidney (H, HMH > L), skin (H, HMH > L) and hind-hooves (H < HMH, L). The slope of the regression for the heart, liver, kidney, and the combined trachea and lungs was greater in the HMH, than in the H, treatment. These differences in slope were attributed to a decrease in weight of each component in the HMH animals during weight stasis except for the lungs and trachea, where the greater slope was due to an increased weight of this component in the HMH animals killed at 40 kg.
Fat-trimmed weights of the omasum, abomasum, small intestine and large intestine were greater in both the H and HMH animals than the L animals. The weights both of the rumen-reticulum and total alimentary tract (TAT) were less at 25 kg in HMH animals than in either H or L animals although, overall, the weight of TAT was greater in the H and HMH treatments than in the L treatment. A comparison of data for the H and HMH treatments showed that weight stasis decreased the weight of all separate parts of the alimentary tract, particularly the rumen-reticulum and the small intestine.
Chemical analyses (water, N × 6·25 and ether extract) were conducted on four alimentary tract components, namely the combined rumen-reticulum and omasum (RRO) abomasum, small intestine and large intestine. The results of these analyses showed that composition was similar in the three treatments despite treatment effects on the weight of some parts of the tract.
Chemical data were pooled across treatments to compare composition of the different alimentary tract components. This analysis showed that chemical composition was different both for all parts of the tract and for all chemical components with two exceptions. There was no difference between the RRO and small intestine for either water or ether extract.
Common regression equations are presented for each component of the alimentary tract relating the weights of three chemical components to tissue weight. Water and protein content were more closely related to tissue weight than was ether extract. It is suggested that both water and protein content may show a sufficiently close relationship to tissue weight whereby they may be predicted from a knowledge of the latter, particularly the RRO and small intestine.
There were no differences between treatments in the weights of fat trimmed from the alimentary tract despite treatment effects on either the weight of some parts of the tract or other offals.
Apart from a greater weight of digesta in the small intestine in the H animals than in L animals relatively minor differences between treatments were found in the amounts of digesta in different parts of the tract.