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Physical contact with the boar is required for maximum stimulation of puberty in the gilt because it allows transfer of boar pheromones and not because it induces cortisol release



Physical contact with the boar is required for maximum stimulation of puberty in the gilt because it allows transfer of boar pheromones and not because it induces cortisol release



Animal Reproduction Science 27(2-3): 209-224



Two studies were conducted in which we examined the endocrine and pubertal response of gilts to boar exposure and adrenocorticotropic hormone (ACTH) injections in order to establish whether physical contact with the boar is essential for maximal stimulation of puberty because it initiates endocrine changes via a release of cortisol, or because it permits the physical transfer of primer pheromones present in boar saliva. Three experiments were performed in Study 1. Experimental 1 established that the dose of exogenous ACTH required to mimic the endogenous release of cortisol seen in gilts in response to full boar contact in previous studies was 10 IU given intramuscularly. In Experiment 2, the treatments were imposed for 31 days from a mean gilt age of 168.0 .+-. 1.35 days and consisted of: (1) control (isolated from boars); (2) isolated and injected with 10 IU ACTH each day; (3) daily fenceline contact with a mature boar; (4) daily fenceline boar contact plus ACTH; (5) full physical contact with a mature boar each day. Injection of ACTH caused a rapid acute elevation in plasma cortisol in all treatments and on all days when samples were collected (days 1, 3, and 5). Among gilts not given ACTH, plasma cortisol secretion was elevated only in the fenceline boar contact treatment. Overall, a significantly higher proportion of gilts reached puberty in response to full boar contact than in response to either the control, fenceline, fenceline plus ACTH or ACTH alone treatments (overall, 12/15 vs. 14/46, P < 0.01). In Experiment 3, treatments 1, 3 and 5 in Experiment 2 were repeated, along with the two additional treatments of daily contact with a mature boar restricted in a cage, and daily contact with the caged boar plus injection of 10 IU ACTH. Treatments commenced at a mean gilt age of 170.1 .+-. 0.61 days and continued for 28 days. The pubertal response to the two caged boar treatments (8/16 gilts) was intermediate between the control (1/7) and full contact treatments (6/7). Injection of ACTH had no effect on the efficacy of the control, fenceline or caged boar treatments. In Study 2 the treatments were imposed for 130 days from a mean gilt age of 159.8 .+-. 1.8 days and consisted of: (1) control (isolated from boars); (2) daily full physical contact with a mature boar with the gilts wearing a snout mask; (3) daily unrestricted full physical contact with a mature boar. The mean interval from start of treatment until puberty was significantly longer for the control gilts (30.3 .+-. 1.28 days) than for the masked gilts (17.4 .+-. 1.13 days, P < 0.05) r the full contact gilts (9.1 .+-. 1.11 days, P < 0.001). The mean interval for the full contact gilts was shorter (P < 0.001) than for the masked gilts. The results of these experiments do not provide any evidence that an elevation in plasma cortisol is causally involved in mediating the stimulation of precocious puberty by boar contact. In contrast, the present results indicate that physical contact with the boar is essential for a maximal pubertal response because the priming pheromones from the boar need to be directly transferred to the snout of the recipient gilts.

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Accession: 002184965

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DOI: 10.1016/0378-4320(92)90059-M


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