Use of monensin to restrict feed intake in sheep destined for live export

Abstract

The accuracy with which monensin could control feed intake was studied in 200 3-4-year-old Merino wethers by measuring their intake of pelleted diets containing 5 levels of monensin: 0, 33, 66, 132 or 264 mg/kg of feed. The feed was offered ad libitum for 25 days except for the highest level of monensin where treatment was ended after 12 days.Mean daily intakes (g/sheep) of diets containing monensin at 0, 33, 66, 132 or 264 mg/kg feed were 1304, 959, 793, 403 and 137 respectively. Mean daily feed intake (Y, g) was negatively and linearly related to concentration of monensin (X, mg/kg feed) Y = 1244 - 6.57X (r2=0.98; P<0.05) Similarly there was a close negative relationship between the concentration of monensin (X, mg/kg feed) and daily liveweight change (Z, g/sheep) during the trial Z = 217 - 2.61X (r2=0.99; P< 0.01) From this relationship, maintenance of liveweight would have been achieved with a diet containing monensin at about 80 mg/kg feed. Signs of toxicity including deaths occurred in sheep receiving diets containing monensin at 66, 132 and 264 mg/kg feed. It was concluded that monensin could be used to restrict feed intake but further research is necessary to determine safe levels.