Strain Differences in the Blood Concentrations of Luteinizing Hormone, Prolactin, and Growth Hormone in Female Chickens

Blood concentrations of luteinizing hormone (LH), prolactin, and growth hormone were measured during growth and sexual maturation in a commercial egg laying-type breed (White Leghorn, WL) and a broiler type (White Plymouth Rock, WPR) breed. Two lines of each breed were used in the study; these were a control line and a line selected for an increased production of double-yolked eggs. The concentrations of LH and prolactin were significantly higher in the WPR than in the WL at all stages of development. Selection for increased production of double-yolked eggs tended to increase the blood concentration of LH but did not consistently affect the concentrations of prolactin or growth hormone. The blood concentration of growth hormone was significantly higher in WL than in WPR at ages between 3 and 12 weeks but between 15 and 23 weeks of age, the concentration of growth hormone was significantly higher in the WPR than in the WL.