Effect of duration of feed quality restriction on body dimensions in lambs

We measured the effect of duration of feed quality restriction and the consequent compensatory growth on body dimensions in 18 crossbred Swifter (Texel sire x Flemish dam) male lambs born in March 1994 and weaned at approximately 2 mo of age. The lambs were fed grass straw (46 g CP/kg DM) for ad libitum consumption and 35 g CP.kg(-.75).d(-1) mixed concentrates (173 g/kg DM). At approximately 3.5 mo of age and average live weight of approximately 34 kg, the lambs were allotted to six blocks, each block with three lambs of approximately the same live weight. Within each block, the three lambs were then randomly assigned to two restricted treatments (R1 and R2) and a control (C) treatment. In treatments R1 and R2, feed quality was restricted by withholding concentrates for 3 and 4.5 mo, respectively. A growth model was developed to study the effects of restriction and subsequent compensation after realimentation (6.5 and 8 mo for R1 and R2 groups, respectively). During restriction, live weight and growth in body dimensions were suppressed. Bone length measures such as body length and ulna length were less affected than live weight. The response in testes girth to restriction was almost immediate. At the end of the experiment (age of about 14 mo), R1 animals fully compensated. However, the R1 animals had higher testes girth (P <.001), chest girth (P < .01), and chest depth (P <.05). Extending the duration of feed restriction did not have a significant effect on the rate of losses in live weight and body dimensions during restriction. At the end of the experiment, except for withers height and trunk length, the R2 animals did not compensate fully in live weight and other dimensions. However, the parameter estimates suggested that the R2 animals may need a relatively longer period of realimentation to reach to the same size as R1 and C animals.