Influence of Genetic Increases in Egg Production on Traits Associated with Broodiness in Turkeys

Abstract

Egg production, nesting frequency, and serum levels of prolactin, estradiol, and total phosphorus were monitored in relatively nonbroody (egg) and relatively broody (RBC1) strains of turkey hens during a reproductive period. In the egg strain, prolactin levels were increased in a group with a relatively high frequency of nesting in comparison to a group with a relatively low frequency of nesting. No differences between these two groups were detected for serum estradiol, total phosphorus, or egg production. In the RBC1 strain, prolactin levels did not differ between a group of hens that did not exhibit broodiness and a group that exhibited one or more bouts of broodiness. A broodiness treatment was used for the latter group. The broody group exhibited extremely variable levels of prolactin. In individual broody hens, the levels of prolactin were relatively high. After broodiness in 12 of 13 hens, the level of prolactin fell to relatively low levels. In the one hen not responding to broodiness treatment, the level of prolactin became low levels. In the one hen not responding to broodiness treatment, the level of prolactin became extremely high. Nesting frequency, total serum phosphorus, and egg production were generally not different between the two groups. The level of prolactin showed seasonal changes in both strains of hens, starting low, increasing to maximal levels between 40 and 80 days of production, and then declining to low levels late in the reproductive period. Laying hens always had higher levels of prolactin than nonlaying, nonbroody hens.

Relationships between broodiness expression laying persistency and concentrations of hormones during the first productive period in turkey hens (Meleagris gallopavo)

“…The present observation does not exclude however an increase in prolactin concurrently with broodiness expression. Similarly, Bacon et al (1983) . We cannot exclude therefore that under our experimental procedure these hens had low circulating prolactin levels but high central levels of prolactin.…”

“…Indeed, the present data suggest the existence of a proportional relationship between laying persistency and the presence of high plasma concentrations in prolactin between the 5th and 11 th week of production. On the other hand, prolactin has been reported to inhibit LH secretion and to exert antigonadal effects in turkey hens (Opel and Proudman, 1980 (Lea and Sharp, 1982;Bacon et al, 1983;Zadworny et al, 1986) showing that large increases in plasma prolactin concentrations do not anticipate the development of gonadal regression and/or photorefractoriness in turkey hens unlike some wild galliform species (Stokkan et al, 1988) or other wild species of birds (Dawson and Goldsmith, 1983 (Zadworny et al, 1989) which are the major source of this steroid (Robinson and Etches, 1986). Therefore, the observed high concentrations of prolactin in long persistency hens may be the cause of their lower concentrations of plasma cestradiol.…”

“…The physiological significance of this increase in prolactin is not known. It does not seem to be related to the expression of broodiness since it is observed in both broody and non-broody hens (Etches and Cheng, 1982) and no differences in basal plasma prolactin concentrations were observed between broody and non-broody hens (Bacon et al, 1983). The photoinduced increase in LH induces a rise in oestrogens (Bajpayee and Brown, 1972;Wineland and Wentworth, 1975) and in progesterone (Mashaly and Wentworth, 1974;Godden and Scanes, 1977).…”

Endocronological and behavioural effects of p-chlorophenylalanine (PCPA) oral administration to broody turkey hens (Meleagris gallopavo)

“…Subsequently, by the end of the trial, the differences between the plasma prolactin concentrations of these birds and those of the photorefractory hens were no longer significant (P > 0.05) (Burke et al, 1981;Proudman and Opel, 1981;Lea et al, 1981;Bacon et al, 1983;Zadworny, 1985 . The data presented in Tables I and II do not support this hypothesis since the change in feed and water intake that followed the disruption of broodiness occured when plasma prolactin was at lower levels.…”

Effect of anti-prolactin drug and peppermint on broodiness, laying performance and egg quality in indigenous hens

“…Physiologically, it has been well established that prolactin (PRL) plays an important role in the onset of incubation of hens (Sharp et al, 1988;March et al, 1994;Ohkubo et al, 1998). Increased plasma PRL concentration is associated with the occurrence of broodiness (Burke and Dennison, 1980;Bacon, 1983). During incubation, PRL mRNA reaches its highest level (Talbot et al, 1991;Karatzas et al, 1997) which infers that PRL is important in the maintenance of broodiness.…”