Abstract:
Proc. Aust. Soc. Anim. Prod. Vol. 18 EFFECTS OF MONENSIN SODIUM AND AVOPARCIN ON THE LIVEWEIGHT GAIN OF STEERS DURING THE NORTH QUEENSLAND WET SEASON J.A. LINDSAY*, I.E. KENDALL*, B.A. GELLING* and R.J. MAYER** It has been amply demonstrated in temperate countries that the rumen modifiers monensin and avoparcin will stimulate growth of beef cattle when fed at pasture. The present Australian study examined the effect of supplementing growing cattle with either monensin or avoparcin during the tropical wet season in north Queensland. Responses to implanting with oestradiol 17B were also measured. Fifty-four Bos indicus crossbred steers were randomly allocated to one Lof nine The treatments were: paddocks to give three replicates of three treatments. no additive (NP); 320 mg/d monensin sodium via a controlled release bolus (MON) and 200 mg/d avoparcin as a solution in the drinking water (AVP). Half of the animals in each treatment also received 24 mg of oestradiol 17B as a long acting ear implant. The steers graze d unfertilized native pastures (predominantly Heteropogvn contortus) at the rate of 0.3 animals/ha for 195 days. Table 1 Mean liveweight gain (LWG) of steers given one of two rumen modifiers plus oestradiol 17B and grazed for 195 days The experiment was conducted during the northern wet season from December 1988 and the control (NP) animals gained at 0.47 kg/d. There was a significant increase (P~0.05) of 15% in liveweight gain (LWG) when the oestradiol 17B implant was administered to the NP and MON animals. However, there was no response to oestradiol 17B with the AVP group. Similarly, giving monensin and avoparcin did not significantly increase LWG. The response in LWG when oestradiol 17B is given to growing animals is well documented. The lack of response to MON and AVP may be due to the high dose rate and some break down in the water respectively. Other work suggests that monensin will improve LWG at about 100 to 180 mg/d (Watson and Laby 1978) and that avoparcin will stimulate growth when fed using cottonseed meal as a carrier (Lindsay, unpublished). However, it is clear that the simplest and most economical way to boost wet season LWG is to implant with oestradiol 17B or a similar substance. WATSON, M.J. and LABY, R.H. (1978). Proc. Nutr. Soc. Aust. 3:86. * ** Queensland Dept Primary Industries, Swan's Lagoon, Xillaroo, Qld. 4807. Queensland Dept Primary Industries, P-0. Box 1085, Townsville, Qld. 4810. 513
