Modulation of prolactin hormone and intersequence pause days in domestic chickens

CIRCULATING prolactin in domestic chickens is widely assumed to play a key role in egg production on commercial poultry farms (Sharp and others 1988, 1989, 1993). Broodiness is a common productive problem due to higher levels of prolactin, with a concomitant decrease in egg production during the active period of laying (Burke and Dennison 1980, El Halawani and others 1980, Burke and others 1981, Proudman and Opel 1981, Zadworny and others 1985, Robinson and others 1990). Control of its biological activity by decreasing the rate of secretion and/or preventing its effectiveness should enhance egg production by reducing the number of pause days under normal husbandry practices. New approaches using immunological/neutralising strategies to change the secretion of prolactin or its biological activity have been reported to be satisfactory at the experimental level (Crisostomo and others 1998). The use of immunological/pharmacological approaches, such as neutralising or decreasing the levels of prolactin for increased egg production, are of economic interest. However, until recently none was appropriate for commercial use. This study was undertaken to examine the influence of neutralisation on prolactin, using bromoergocriptine to extend the clutch length or reduce the number of pause days, and to extend the laying performance and egg production (table eggs) in domestic chickens. This approach is of practical interest, although its use needs to be carefully evaluated under commercial conditions. One hundred white leghorn birds, housed in individual cages (one bird per cage) under a two-tier battery system were divided into two groups of 50 birds at the age of 12 weeks. Feed was provided as recommended by Ranjhan (1981). The same amount of feed was offered to both the control and treatment groups, and feed intakes were not affected by the treatment. Clean water was available throughout the experimental period. Bromoergocriptine (Bromoergocriptine; Sigma) was used as an antiprolactin agent. Since there was no information available on the quantitative prolactin blockage response of bromoergocriptine in birds, a preliminary study was performed to standardise an appropriate dose of this compound in a separate group ofbirds before the start of the experiment. Bromoergocriptine doses of 100, 150, 200 and 250 rig/kg bodyweight (dissolved in absolute alcohol) were tested until the effects observed, in terms of prolactin blockage, were found to be similar for all four dosage levels. Each dose was tested on six chickens and blood was collected once a day on day -3, day-1, day 0, (day of bromoergocriptine administration) and subsequently on days 1, 3, 5 and 7 after bromoergocriptine administration. From the results of the dose standardisation study, it was concluded that bromoergocriptine could be used as an antiprolactin compound in layers, and a dosage of 100 rig/per kg bodyweight in a single injection was sufficient to suppress prolactin for seven days. At 17 weeks old, the birds in the treatment group were given 100 rg/kg bromoergocriptine subcutaneously, at weekly Control group(n=50) Treated group (n=50)