The possible role of prolactin in laying performance and steroid hormone secretion in domestic hen (Gallus domesticus).

The aim of this study was to investigate the basic physiological mechanism involved in taking pauses between the sequences of egg laying in domestic hen to improve egg production by extending the sequence length and decreasing the intersequence pause days by modulating the prolactin concentration in birds. Fifty healthy female white leghorn birds were administered anti-prolactin agent (2-bromo-alpha-ergocriptine, Sigma, USA) subcutaneously at 100 microg/kg body weight at weekly intervals from 17th to 36th week of age. Another group of fifty birds was given placebo in place of the modulating agent. The level of prolactin remained lower in the treated birds than in the control birds throughout the production cycle up to 72 weeks of age. The level of prolactin in the control group was found to decrease during the peak production period. The average percentage of egg production from 19 to 72 week period was 87.67 in the treatment group as compared to 83.56 in the control group. Oestradiol-17beta and progesterone concentrations in the treated birds were significantly (P<0.01) higher than those in control birds, during and after withdrawal of the treatment. Prolactin level was negatively correlated with egg production (r=-0.02; r=-0.12) and with oestradiol-17beta (r=-0.75; r=-0.38) and progesterone (r=-0.20; r=-0.83), respectively, in control and treatment groups. The total number of pause days during the production period decreased significantly (P<0.01) in the treatment group, resulting in a 4.11% increase in egg production. It is concluded that there is a consistent relationship between plasma prolactin in the physiological range and laying performance in domestic hen.