Effects of cottonseed meal, methionine analogues and avoparcin on the wool production of young, grazing wethers

摘要

A series of experiments were conducted which aimed to develop a feed supplement that was more cost-effective at increasing wool growth in sheep than those currently available commercially. In experiment 1, young wethers grazing cereal stubble for 1 month were offered ad lib. blocks containing sorghum, urea and sodium bentonite (buffered Goldenpro, average intake 66 g/day), ad lib. blocks containing molasses, lupins and urea (Ultrapro 30, average intake 52 g/day), or pellets containing cottonseed meal (CSM, 50 g/day) plus hydroxymethyl- methionine (MEP, 3 g/day). Changes in liveweight were similar in all sheep fed supplements but liveweight losses in unsupplemented wethers were significantly (P<0.05) higher than in supplemented wethers. In experiment 2, supplementation of Merino weaners grazing ryegrass-subterranean clover pastures with 37.5 g/day of a pellet containing CSM plus MEP (plus vitamins and minerals) for 3 months resulted in increases in wool growth (+ 7%) and liveweight gain (+38%) compared with wethers fed control (vitamins plus minerals) pellets. In experiment 3, Merino hoggets grazing a ryegrass-subterranean clover pasture were rotationally supplemented for four 6-week periods with 37.5 g/day of CSM plus methionine hydroxy analogue (MHA), CSM plus avoparcin (AV), CSM plus MHA plus AV and 12.5 g/day of control pellets. The sheep grew 11, 18 and 12% more clean wool respectively when fed CSM plus MHA, CSM plus AV and CSM plus MHA plus AV compared with control pellets. The additional wool grown in response to the CSM plus AV pellet was valued at approximately twice the cost of the pellets. Although economic responses to supplementation were obtained, the response levels were well below those obtained in post-ruminal, amino acid infusion studies and conflict with data from pen-feeding experiments.