| Abstrakt: |
The mechanism regulating ovarian regression during incubation behavior in the domestic turkey has not been elucidated. This study was designed to determine whether ovarian steroidogenic potential is depressed during gonadal regression associated with the onset of incubation behavior. Hens were housed in floor pens equipped with trap nests that were checked 7 times per day. Hens were grouped, according to nesting frequency and egg production, into the following classifications: laying (laid an egg every day and trapped in the nest only once/day); transitional (laid an egg every day but trapped in the nest 4 or more times/day); and Day 1, Day 3, and Day 5 incubating (no egg for 2, 4, or 6 days, respectively, while trapped in the nest at least 4 times/day). Follicular atresia was evident in the largest preovulatory follicle (F1) in transitional hens, extensive in F1 through the third largest follicle (F3) in Day 1 incubating hens, and extensive in F1 through F7in Day 3 incubating hens. Levels of circulating LH, progesterone (P), androgen (A), and estradiol (E) decreased in transitional hens relative to concentrations in laying hens and remained low thereafter. In contrast, levels of prolactin were greater in Day 3 and Day 5 incubating hens than in laying, transitional, or Day 1 incubating hens. Basal production of P by F1 granulosa cells was lower from Day 1 incubating hens than from the other groups. Production of P in response to porcine-luteinizing hormone (pLH) was greater by cells from transitional and Day 1 incubating hens than from those of laying hens. The pLH response was absent in cells from Day 3 incubating hens. In contrast, both basal and pLH-stimulated A production by F5 theca interna cells was decreased in Day 1 incubating hens relative to laying and transitional hens. Similarly, both basal and P-stimulated 11 production by small white follicles (SWF) was lower from transitional hens than from laying hens and further diminished in follicles from Day 1, Day 3, and Day 5 incubating hens. We conclude that the onset of ovarian regression is not due to depressed responsiveness of ovarian granulosa and theca interna cells to gonadotropins. In contrast, reduced production of E by SWF may conthbute to lower circulating E levels in transitional hens and therefore may be involved in the initiation of ovarian regression. |
