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Ovarian responses of the laying hen to heat stress
Abstract
Little is known about the effects of hyperthermia on the hens ovulatory cycle after heat onset. Heat stress reduced plasma progesterone during the first 24h after heat onset, indicating a rapid, direct effect of heat on the ovary. Heat stress also caused delayed ovulation and a higher percentage of delayed eggs, possibly because of the low level of progesterone and/or its delayed feedback to the hypothalamus. However, the mechanism for the early expulsion of the eggs in heat-stressed hens is not known. To elucidate the luteinizing hormone (LH)-progesterone interaction under heat stress, the profiles of these two hormones were examined closely during the stage in the ovulatory cycle where their peaks are expected to occur. Both hormones decreased during the six hours preceding the first predicted ovulation after heat onset. The reproductive decline during heat stress may be caused by decreased progesterone secretion, failure of the positive feedback to the hypothalamus, and a consequent lower LH secretion. Evidence for a direct effect of heat stress on the ovary was shown in an in-vitro experiment involving isolated granulosa cells. Acute hyperthermia suppressed the ability of the cells to synthesize progesterone, even with LH stimulation. The progesterone profiles of shortened, normal and extended ovipositions of hens exposed to two days of heat stress were characterized to determine the involvement of progesterone in oviposition. Heat stress reduced progesterone levels rapidly in hens with early eggs. It is suggested that the absence of progesterone surge, possibly essential for timing oviposition under normal condition, allows the ovipository hormones to expel the egg prematurely. Although progesterone profiles vary relative to oviposition, a temporal relationship between ovulation and oviposition was not established. Altogether, the data suggest a direct and rapid effect of heat stress on the ovary. This indicates that the reproductive decline in hyperthermic hens is mediated at least in part by the inability of the ovary to secrete progesterone and by the failure of positive feedback to the hypothalamus.
Subject Area
Livestock
Recommended Citation
Novero, Ruben Pegenia, "Ovarian responses of the laying hen to heat stress" (1991). ETD collection for University of Nebraska-Lincoln. AAI9129567.
https://digitalcommons.unl.edu/dissertations/AAI9129567