Stress and its influence on reproduction in pigs: a review

The manifestations of stress, defined as a biological response to an event that the individual perceives as a threat to its homeostasis, are commonly linked to enhanced activity of the hypothalamo-pituitary-adrenal (HPA) axis and the activation of the sympathetic adreno-medullary (SA) system. Activation of the HPA system results in the secretion of peptides from the hypothalamus, principally corticotropin releasing hormone (CRH), which stimulates the release of adrenocorticotropic hormone (ACTH) and beta-endorphin. ACTH induces the secretion of corticosteroids from the adrenal cortex, which can be seen in pigs exposed to acute physical and/or psychological stressors. The present paper is a review of studies on the influence of stressors on reproduction in pigs. The effects of stress on reproduction depend on the critical timing of stress, the genetic predisposition to stress, and the type of stress. The effect of stress on reproduction is also influenced by the duration of the responses induced by various stressors. Prolonged or chronic stress usually results in inhibition of reproduction, while the effects of transient or acute stress in certain cases is stimulatory (e.g. anoestrus), but in most cases is of impairment for reproduction. Most sensitive of the reproductive process are ovulation, expression of sexual behaviour and implantation of the embryo, since they are directly controlled by the neuroendocrine system

Effects of early vaccination with Improvac (R) on the development and function of reproductive organs of male pigs

Gonadotropin-releasing hormone (GnRH) vaccine (Improvac (R)) is effective at diminishing boar taint by interfering with testis function. Early pre-pubertal vaccination at 10 and 14 weeks-of-age could be desirable if sufficient and sustained effects could be achieved. Crossbred male pigs (n = 24) were randomly assigned to three groups each with eight individuals: an unvaccinated control group, one group vaccinated with Improvac (R) early at ages 10 and 14 weeks, and a third group vaccinated with Improvac at the standard ages of 16 and 20 weeks. The average age at slaughter was 25 weeks. At slaughter, reductions in testes weight and bulbourethral gland length of vaccinated pigs compared with controls were observed (P andlt; 0.001), accompanied by lowered testosterone concentrations in peripheral blood (P andlt; 0.001). The diameter of tubuli seminiferi was affected: being 18% smaller in standard and 38% smaller in early vaccinated males, compared with controls (P andlt; 0.01). Leydig cells in vaccinated pigs became pycnotic, and their number decreased in early vaccinated pigs. Spermatogenesis was disrupted, evidenced by spermatocyte loss among standard vaccinated pigs to severe spermatogenic arrest among early vaccinated pigs. This histological picture was reflected in the absence of epididymal spermatozoa in 5 of 8 early vaccinated pigs and a dramatic reduction in the remaining 3 early vaccinated pigs. Among standard vaccinated pigs, 5% of the spermatozoa were morphologically normal (andgt;70% in controls, P andlt; 0.01). Early vaccination caused a more severe disruption of testicular structure and function than standard vaccination, thus providing an alternative for immunocastration of male pigs.Funding Agencies|Swedish Board of Agriculture||Pfizer|