Gilts born during the spring that attain puberty during the summer commence estrous activity at a later age that gilts born during the fall that reach puberty in the winter or early spring. Slaughterhouse evaluations of gilts indicated that immature reproductive tracts are more prevalent during the summer that other months. Various investigators demonstrated that heat stress disrupts implantation and decreases embryo survival in sows. Thus, the number of animals returning to estrus after mating increases during or shortly after the onset of summer. Farrowing rates in a farm affected with seasnonal infertility.
Decreased rates are evident in winter months, subsequent to summer matings.
Although deficiencies in diagnostic techniques may contribute to this low success rate, particularly with new or unknown pathogens, it is likely that many abortions occur without an infectious agent. Sows may abort form 30 to 110 days after breed and affected sows do no show signs of fever or toxemia. In addition, the aborted fetuses are normal in size, devoid of pathologic lesions and infectious agents are absent. Serologic testing of affected sows fails to demonstrate a pathologic agent. Frequency of undiagnosed abortions in a commercial swine farm.