Bacitracin methylene disalicylate in broiler breeder feeds.

A 32-week experiment was carried out in floor pens with Cobb X Cobb breeder pullets that were 28 weeks old at initiation. Ten replicate pens, each containing 13 pullets and 2 males, received one of four dietary treatments. These treatments were either an unmedicated feed or 27.5, 55, or 110 mg/kg of bacitracin methylene disalicylate (BMD). All feeds contained 13.2 mg/kg of hygromycin B. Feed was allocated at a rate of 159 g per day and water was provided continuously. Hen-day egg production was significantly improved by the feeding of 27.5 mg/kg or more of BMD. Egg weights were significantly lower for all groups receiving the drug. Eggs of birds receiving 110 mg/kg were significantly heavier than those produced with 27.5 mg/kg, but neither differed statistically from those of the 55 mg/kg group. Neither final body weight nor overall mortality was significantly related to treatment. Egg fertility was significantly improved by 27.5 mg/kg or more of BMD. Hatchability of fertile eggs was not affected by the drug, but total hatchability was significantly increased through BMD feeding, largely on the strength of improved fertility.