Comparison of Physiological Indicators of Chronic Stress in Confined and Nonconfined Gilts1

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Abstract
Two experiments were conducted to determine if confinement-induced delayed puberty in gilts was due to chronic physiological stress imposed by confinement housing. In both experiments, crossbred gilts, raised in total confinement, were moved to an outside dirt lot (nonconfined) or to a single pen in a confinement finishing unit (confined) at 100 to 110 d of age. Beginning at 150 d of age, estrus was checked daily with a boar to determine age at first estrus. Gilts were necropsied at 270 d of age. In Exp. I, 19 confined and 19 nonconfined gilts were cannulated by jugular puncture at 185 d of age. The day after cannulation, blood samples were collected for 4 h, 200 IU porcine adrenocorticotropic hormone (ACTH) was injected via the cannulae and blood samples were collected for an additional 8 h. Serum Cortisol, progesterone, luteinizing hormone (LH) and prolactin (PRL) concentrations were determined. In Exp. II, both jugular veins of six confined and six nonconfined gilts were cannulated at 204 d of age. The day after cannulation, blood samples were collected for 4 h and Cortisol was continuously infused for the last 2 h of the blood collection period. Cortisol metabolic clearance rate (MCR) and secretion rate (SR) were determined. By 270 d of age, 21 of 28 (75%) nonconfined gilts and 11 of 31 (35.5%) confined gilts (P<.01) in Exp. I and 18 of 25 (72%) nonconfined gilts and 12 of 25 (48%) confined gilts (P<.06) in Exp. II had exhibited estrus and ovulated. Body weight and adrenal weight at 270 d of age were similar for confined and nonconfined gilts in both experiments. Basal serum Cortisol, progesterone and PRL concentrations were similar for confined and nonconfined gilts. However, basal serum LH concentrations were greater (P<.02) in nonconfined than confined gilts. Serum progesterone levels after ACTH were similar for both groups, but serum Cortisol concentrations after ACTH increased more rapidly (P<.02) and to a greater concentration (P<.0001) in nonconfined compared with confined gilts. However, area under the serum Cortisol response curve to the ACTH challenge was similar for both groups. The Cortisol MCR and SR were similar for confined and nonconfined gilts. These data indicate that confinement-induced delayed puberty in the gilt may not be caused by chronic stress. Copyright © 1984. American Society of Animal Science . Copyright 1984 by American Society of Animal Science.