Effects of supplementing a wheat straw diet with urea or a urea-molasses block and/or cottonseed meal on intake and liveweight change of lambs

Abstract

A feeding experiment was conducted in which lambs were given a basal diet of wheat straw plus 0.5% mineral mixture, supplemented with either 2.5% urea, 150 g day −1 cottonseed meal (CSM), 2.5% urea + 150 g day −1 CSM, urea-molasses block (ad libitum) alone or with 150 g CSM. Supplementation of the basal diet with the urea-molasses block increased straw dry-matter intake by lambs significantly ( P < 0.001) from 333 to 420 g day −1, and a liveweight loss of 53 g day −1 on the basal diet was improved to a liveweight gain of 10 g day −1. Supplementation with CSM alone or CSM plus urea increased straw dry-matter intake from 333 to 439 g day −1 and consequently converted a mean liveweight loss of 53 g day −1 on the basal diet to mean liveweight gains of 38 and 40 g day −1. The combined supplement of CSM and urea-molasses block further increased straw dry-matter intake to 475 g day −1 and lamb liveweight gain to 90 g day −1. The supplementation of 2.5% urea alone did not affect either straw intake or liveweight gains. The use of the urea-molasses block as a urea supplement was superior to urea alone. The digestibility of straw as indicated by the loss of dry matter from straw in nylon bags in the rumen was increased by supplements of protein meals, but was highest when the urea-molasses block was also consumed. Wool growth was increased by 60% above that on the basal diet by supplementation with the protein or protein plus fermentable-N sources.