Relationship between plasma concentration of luteinising hormone and intensity of lay in the domestic hen.

The concentration of plasma luteinising hormone (LH) in samples taken at frequent intervals from 6 weeks of age until the onset of lay, and also at 9 months after the onset of lay, was significantly greater in hens with a high rate of egg production than in comparatively poor layers. 2. The difference was most marked during the period 7 to 9 weeks of age when there was a transient increase in plasma LH concentration remained stable in comparatively poor layers. 3. The concentration of LH in plasma, particularly at 7 to 9 weeks of age, before gonadal growth, or during the prepubertal peak of LH secretion, at about 2 to 4 weeks before the onset of lay, may be a useful criterion in the selection of laying strains.