Rm. Dixon et Ar. Egan, Response of lambs fed low quality roughage to supplements based on urea, cereal grain, or protein meals, AUST J AGR, 51(7), 2000, pp. 811-821
The intake and growth responses of lambs fed barley straw to a range of sup
plements provided on a 3- or 4-day cycle were examined. Supplements were ur
ea and sulfur (N/S) added to the straw, or 3 increments of each of 3 approx
imately isonitrogenous supplements consisting of barley grain mixed with ur
ea and sulfur (Bar/N), cottonseed meal (CSM), and a 0.4:0.6 mixture of fish
meal and lucerne hay (FM/L). Lambs fed straw alone consumed 38.3 g dry matt
er (DM)/kg W-0.75 day of straw and an estimated 2.54 MJ metabolisable energ
y (ME)/day, and lost 20 g liveweight (LW)/day. Supplementation with N/S inc
reased estimated ME intake by 32%. Substitution rates of Bar/N, FM/L, and C
SM supplements for straw were 0.50, 0.36, and 0.25 g/g, respectively, but t
hese rates did not differ (P > 0.05) between supplements. Digestibilities o
f organic matter (OM) and neutral detergent fibre (NDF) were affected diffe
rently depending on both the type and amount of supplement. Estimated ME in
take 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 co
nsecutive 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 th
e linear relationships between LW gain and estimated ME intake were greater
(P < 0.05) for CSM and FM/L than for Bar/N supplement, ingested ME being u
sed with about twice the efficiency for LW gain when the protein meal suppl
ements rather than the cereal grain-urea supplement was fed. However, acros
s all supplement treatments, LW gain was correlated (r = 0.91; P < 0.001) w
ith the absorbed amino acid supply as estimated from feeding standards. In
conclusion, although supplements based on either cereal grain or protein me
als increased LW gain in these young lambs, there were much greater respons
es to the protein meals due principally to more efficient utilisation of in
gested ME for LW gain.