Anticoccidial activity of combinations of narasin and nicarbazin

The efficacy of mixtures of narasin and nicarbazin were evaluated by comparing broiler performance, susceptibility to heat stress, and the mode of action against Eimeria. In a floor pen trial, narasin (70 ppm) alone or in combination with nicarbazin at levels between 10/10 and 50/50 ppm gave significantly better performance than unmedicated birds or birds given nicarbazin at 125 ppm alone. Amelioration of nicarbazin-associated mortality with heat as a stressor was observed in birds given the 50/50 ppm mixture of narasin and nicarbazin: mortality in these birds was similar to that of unmedicated birds and was reduced by 15 to 20% of that occurring in birds in the nicarbazin (125 ppm) treatment. The narasin/nicarbazin mixture (50/50) appears primarily to prevent further development of sporozoites. However, in birds treated with 25/25 ppm of narasin and nicarbazin, both the deleterious action of nicarbazin on merogeny and the antisporozoite activity of narasin were observed.