Feed quality restriction and compensatory growth in growing sheep: feed intake, digestion, nitrogen balance and modelling changes in feed efficiency

The effects of feed quality restriction on intake, digestion, nitrogen balance, feed conversion efficiency and performance were examined. A total of 56 crossbred Swifter (Flemish female x Texel male) male lambs born in March 1993 and weaned at approximate to 2-months old were fed grass straw (51 g crude protein (CP) per kg dry matter (DM)) ad libitum and 35 g kg(-0.75) d(-1) mixed concentrates (173 g CP kg(-1) DM). At an age of approximately 3 months, animals were randomly divided into a restricted (R) and a control (C) group. Group R was restricted in feed quality by withholding concentrates from 3-6 months of age. During restriction, the R animals lost weight and showed a slightly negative nitrogen (N) balance. Grass straw intake of the R animals gradually increased to a level significantly higher (P < 0.001) than of the C animals. The R animals showed a significantly (P < 0.001) higher rumen retention time (RRT). The shape of the growth curve changed by feed quality restriction. A model was developed to measure feed efficiency from the relation between cumulative feed intake and body weight. The feed efficiency was negative for R animals during restriction. After realimentation, R animals were more efficient in converting feed to body weight compared to C animals. The delay in growth after restriction was compensated during realimentation though with lower total feed consumption. (C) 1997 Elsevier Science B.V.