MONENSIN TOXICITY IN 2 BREEDS OF LAYING HENS

A case of monensin toxicity in laying hens is reported. The drug was i ncorporated, by error, at a concentration of 800 mg/kg in the rations which were fed for 4 days to light (Leghorn X Rhode Island Red, LR) an d heavy (White Rock, WR) breeds of laying hens. Egg production (initia l levels of about 80% and 57%, in the LR and WR hens, respectively) de creased markedly 24 h after feeding the monensin-supplemented rations, and 8 days later it was less than 10% in the LR hens and had stopped completely in the WR birds. Egg production in both strains regained no rmal levels 30 days from the beginning of the episode. Mortality start ed 48 h after monensin administration, reaching a peak on the 9th and 6th days in the LR and WR hens, respectively. Mortality was much highe r in the WR hens (38.3%) than in the LR hens (3.7% in shed A and 8.3% in shed B). It seems, therefore, that the WR hens were more susceptibl e to monensin toxicity than LR hens.