Possible aspects of normal and unphysiological commercial conditions on the estrus and early pregnancy in pigs

Gilts and sows kept under unphysiological commercial conditions may show delayed puberty, delayed estrus postweaning and delayed returns after insemination. It is postulated that in all three manifestations gonadotropic insufficiency is the causative factor, produced by inadequate exteroceptive stimulation, mainly of olfactory origin, or by a configuration of stimuli which is experienced as in-appropriate by the individual organism. Pituitary L.H. is necessary to induce tertiary follicles to secrete estrogens, which play a prominent part in estrus expression and in turn evoke the pre-ovulatory L.H. peak flow. Pituitary L.H. also appears to be necessary for persistence of the corpora lutea during early pregnancy and this L.H. release may also be inhibited under inadequate physiological conditions. Therefore anaphrodisia in big commercial piggeries can be a normal physiologic reaction of the animal and more or less an adaptation to these unfavourable circumstances. For the greater part delayed puberty and delayed estrus postweaning seem to be coupled with anestrus and can easily be overcome by gonadotropin treatment in this case. Resulting fertility can be normal, even under severe stressful conditions. The delayed returns after insemination are partly caused by embryonal mortality. This mortality is at least for a part caused by gonadotropin insufficiency which in future may be prevented by application of a proper treatment as well.