The effect of ovariectomy on concentrations of plasma prolactin and LH and parental behavior in the domestic fowl.

The role of ovarian hormones in the expression of parental behavior and in the regulation of LH secretion was investigated in incubating commercial meat-type hens. After ovariectomy, incubating hens continued to incubate eggs normally and brooded day-old chicks given to replace eggs, in a manner similar to sham-ovariectomized control hens. The concentration of plasma LH increased significantly in incubating hens after ovariectomy while the concentration of plasma prolactin remained high. Plasma LH remained depressed in sham-ovariectomized incubating control hens. The increase in plasma LH in incubating hens after ovariectomy (3.92 +/- 0.7 ng/ml) was less than that following the ovariectomy of nonincubating, nonlaying hens (5.3 +/- 1.2 ng/ml). The two groups of hens differed in that plasma prolactin concentrations were high (527 +/- 7.4 ng/ml) in the incubating hens and low (70 +/- 9 ng/ml) in the nonincubating hens. Nest deprivation resulted in an increase in plasma LH in both ovariectomized and sham-ovariectomized incubating hens with a significantly larger increase occurring in the ovariectomized hens (8.5 +/- 1.41 ng/ml compared to 2.48 +/- 0.65 ng/ml). Nest deprivation resulted in a similar rapid decrease in plasma prolactin in both ovariectomized and sham-ovariectomized hens. Replacement of eggs with day-old chicks in ovariectomized or sham-ovariectomized incubating hens resulted in a rapid decrease in plasma prolactin and after 6 days, in an increase in plasma LH in the ovariectomized but not sham-operated hens. It is concluded that once incubation behavior is established, ovarian hormones are not required for its maintenance or the readiness to brood day-old chicks. Ovarian hormones do, however, suppress LH release during incubation while the high concentration of plasma prolactin supplements this suppression.