The adverse effects of nicarbazin on reproductive activity in the hen

The effects of the anticoccidial agent nicarbazin on reproductive activity in the female fowl have been studied. 2. The drug had no effect on the plasma concentration of luteinising hormone, but treated hens showed a reduced hypothalamic sensitivity to exogenous progesterone, whilst the capacity of the pituitary to respond to luteinising hormone releasing hormone was unimpaired. 3. It is suggested that nicarbazin not only prevents yolk deposition within the ovary but also adversely affects the stimulatory function of the hypothalamus, possibly through an unsuitable hormonal environment.