Evaluation of feed additives for increasing wool production from Merino sheep. 2. Flavomycin and tetronasin included in lucerne-based pellets or wheaten chaff fed ad libitum

Abstract

The feed additives flavomycin, a glycolipid antibiotic, and tetronasin, an ionophore, were evaluated for their ability to improve wool growth and liveweight gains in Merino sheep. Each was included in 2 diets: one was a pelleted mixture of (g/kg) lucerne (590), lupins (250) and barley (1 50); the other diet was wheaten chaff. Flavomycin was included in each diet at 10 and 20 mg/kg feed; tetronasin at 5 and 10 mg/kg feed. During an 8-week experimental period, the diets were fed ad libitum to weaner Merino wethers, with 15 sheep receiving each treatment diet at each level of additive inclusion, and 30 sheep receiving each diet without additives. Liveweight changes, feed intake and wool growth were measured over 2 consecutive 4-week periods, and rumen fluid samples were taken from all sheep after 6 weeks. Feed intake, liveweight gain and wool growth rate were all higher for animals eating the pelleted diets compared with those eating chaff. Rumen volatile fatty acids (VFA) and ammonia (NH3) concentrations were also higher with the pelleted diet. On the pelleted diet, flavomycin and tetronasin inclusion significantly increased liveweight gains during the second 4-week period (296, 277, 231 g/sheep.day for flavomycin, tetronasin and controls respectively, P<0.001), but neither additive had any significant effect on feed intake. The amount of clean wool grown during both measurement periods was greater for animals receiving flavomycin or tetronasin with the pelleted diet compared with control animals. Neither additive had any significant effect on liveweight gains or wool growth of sheep eating chaff. Fibre diameter (FD) was measured on wool clipped in the second period, and was not significantly altered by either additive: mean FDs for animal receiving pellets were 25.1 ¦m, compared with 18.5 ¦m for animals receiving chaff. Total rumen VFA concentrations were lower with flavomycin or tetronasin treatments on both diets, and ammonia concentrations were lower with both additives on the pelleted diet and with tetronasin on the chaff diet. It is concluded that both flavomycin and tetronasin were able to increase liveweight gains and wool growth in rapidly growing sheep eating a high-protein diet, but had little or no consistent effects with animals eating a lower quality, low-protein diet.