Cottonseed meal and molasses as sources of protein and energy for cattle offered low quality hay from pastures of the North Coast of New South Wales

Abstract

Cottonseed meal and molasses, regarded as sources of protein and energy for cattle, were included with a basal ration of low quality pasture hay and fed to beef cattle in an experiment that contained two periods of 50 d each. The hay was made from a pasture consisting predominantly of Rhodes grass (Chloris gayana). The pasture site was on the North Coast of New South Wales with a subtropical climate and an area where cattle lose liveweight during the winter or cool-dry season. The experiment aimed at determining whether the intake of hay, and liveweight of cattle, could be increased by supplements of either cottonseed meal or molasses or both. The experimental design was based on a response-surface with 12 treatment combinations. Twenty-four Hereford steers, aged about 26 months and having a mean liveweight of 315 ¦ 28 kg were used. They were offered the low quality hay (435 g digestible organic matter (DOM)/kg dry matter (DM); 7.3 g nitrogen (N)/kg DM) in amounts expected to be 15% greater than that eaten. Fixed amounts of the energy supplement (undiluted molasses) were offered in separate containers at 0,0.5, 1.3 and 2.1 kg/d. Cotttonseed meal (930 g organic matter (0M)lkg DM) was added to the hay to raise the N content of the ration from the 7.3 g N/kg DM of the basal ration (A) to 14.1 (B), 19.4 (C) and 25.7 (D) g N/kg DM. Steers on ration C ate 19.3% more hay (P c 0.05) than steers on ration A; steers on rations B and D ate 11.0 and 14.5%, respectively, more hay than steers on ration A ( P < 0.10). Molasses had no significant effect on hay intake, but as did cottonseed meal, it increased steer liveweight. Final liveweight (LW: kg) was a function of the initial liveweight (IW: kg) and of the amount of supplements eaten (kg/d) for both cottonseed meal (CSM) and molasses (Mol). LW = 16.7(+ 11.0) + 5.9(+ 2.0)Mol + 38.3(¦ 5.6)CSM - 9.2(¦ 2.0)CSM2 + 0.88(¦ 0.03)IW; Residual standard deviation ¦ 8.7. N balance, and excretion of N in faeces and urine, were increased (P < 0.05) by cottonseed meal but not by molasses supplements. Liveweight change (LWC: g/d) was a function of N balance (NB: g/d). LWC = - 1 08.3(¦ 48.0) + 19.7(¦ 2.1 4)NB; Residual standard deviation ¦ 243. Liveweight change was also a function of the digestible organic matter intake (D0MI:gld) from the total ration. LWC = - 996(¦ 104) + 0.364(¦ 0.032)DOMI; Residual standard deviation ¦ 182. The results highlight the limitation to cattle growth imposed by the low N intake from the pasture hay, and a consequent low intake of DOM. They suggest that cottonseed meal is a suitable source of protein for cattle on the North Coast although in districts growing sugar cane economics may favour the use of molasses as an energy source provided that some protein is added to it