Effects of monensin feeding and withdrawal time on growth and carcass composition in broiler chickens

Four experiments were conducted to evaluate the effect of monensin feeding and withdrawal on broiler performance and carcass characteristics. It was shown that monensin (100 ppm) feeding depressed growth. Withdrawal of monensin from the feed for 5 or 7 days produced higher feed consumption and weight gain values compared with those of unmedicated broilers. Increasing the withdrawal period to 10 days did not produce greater growth improvement. Whole body composition of protein, water, lipid, and ash were not significantly affected by monensin feeding or withdrawal. Abdominal fat pads of unmedicated female broilers were significantly larger than those of broilers medicated with monensin even when expressed as a percentage of body weight (3.53 vs. 2.99%). Amount of lipid per fat pad was also higher in unmedicated broilers than in medicated broilers (43.5 vs. 30.6 g). Values for fat pad weight (as a percentage of body weight) and grams of lipid per fat pad of unmedicated birds were not different from those measures in medicated birds after 5 or 7 days of withdrawal. Fat pad weights and lipids per fat pad of birds after 10 days of monensin withdrawal were intermediate between those of unmedicated and monensin-medicated broilers. Monensin feeding or its withdrawal for 5 or 10 days did not influence the female broiler abdominal fat pad lipid fatty acid composition when compared with that of unmedicated fat pad lipid.