Response of lambs fed low quality roughage to supplements based on urea, cereal grain, or protein meals

Abstract

The intake and growth responses of lambs fed barley straw to a range of supplements provided on a 3- or 4-day cycle were examined. Supplements were urea and sulfur (N/S) added to the straw, or 3 increments of each of 3 approximately isonitrogenous supplements consisting of barley grain mixed with urea and sulfur (Bar/N), cottonseed meal (CSM), and a 0.4 : 0.6 mixture of fishmeal and lucerne hay (FM/L). Lambs fed straw alone consumed 38.3 g dry matter (DM)/kg W0.75 day of straw and an estimated 2.54 MJ metabolisable energy (ME)/day, and lost 20 g liveweight (LW)/day. Supplementation with N/S increased estimated ME intake by 32%. Substitution rates of Bar/N, FM/L, and CSM supplements for straw were 0.50, 0.36, and 0.25 g/g, respectively, but these rates did not differ (P > 0.05) between supplements. Digestibilities of organic matter (OM) and neutral detergent fibre (NDF) were affected differently depending on both the type and amount of supplement. Estimated ME intake was increased 7.1, 7.9, and 8.6 kJ/g supplement DM by Bar/N, FM/L, and CSM, respectively. LW gain and wool growth were increased (P < 0.01) by consecutive increments of each of the supplements, and were increased more (P < 0.01) by the FM/L and CSM than by the Bar/N supplement. The slopes of the linear relationships between LWgain and estimated ME intake were greater (P < 0.05) for CSM and FM/L than for Bar/N supplement, ingested ME being used with about twice the efficiency for LW gain when the protein meal supplements rather than the cereal grain–urea supplement was fed. However, across all supplement treatments, LW gain was correlated (r = 0 .9 1 ; P < 0.001) with the absorbed amino acid supply as estimated from feeding standards. In conclusion, although supplements based on either cereal grain or protein meals increased LW gain in these young lambs, there were much greater responses to the protein meals due principally to more efficient utilisation of ingested ME for LW gain.