Factors and mechanisms influencing seasonal disorders in pig reproduction

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The problem of unsatisfactory reproductive results in pigs is visible in a significant percentage of herds, especially during summer months and early autumn (seasonal summer infertility). This is reflected mainly in the reduced percentage of sows entering estrus after weaning and the effectiveness of mating/insemination. The consequence is a significantly lower number of births in November, December and sometimes even in January, compared to other seasons. There are many causes of seasonal summer infertility. The first things mentioned are usually the length of the light day and the high temperature in the pigs environment. An important reason that is not often discussed is the daily temperature fluctuations which usually occur at the end of summer and the beginning of autumn. Persistent unfavorable conditions are responsible for long-term stress. Hormonal disorders related to stress, leading to reproductive disorders, result from connections taking place in the hypothalamus between the hypothalamus-pituitary-gonadal axis (HPG), which regulates, among others, the reproductive functions of the ovaries, and the hypothalamus – pituitary – adrenal axis – HPA which governs organism reaction to stress. Under stressful conditions, glucocorticoids (cortisol, corticosterone) secreted in large amounts by the adrenal glands, as well as adrenaline, norepinephrine and, in small amounts, dopamine, may inhibit reproductive functions at the level of the hypothalamus, reducing the secretion of GnRH. At the same time, by reaching the pituitary gland, these hormones limit the sensitivity of the cells of this endocrine gland to GnRH. As a consequence, the maturation of follicles slows down, the number of ovulating and rupturing follicles decreases, and the secretion of estrogen is reduced. The consequence is the absence of heat or, more often, the so-called “silent heat”. Another problem is the uneven maturation of the follicles, which leads to a delayed appearance of estrus and its longer duration: 3-4 days. The final effect of these is a decrease in the rate of females presenting heat after weaning of piglets, a deterioration in the mating/insemination success rate, an increase in the rate of early abortions and percentage of litters with a small number of piglets in a litter. The summary stated that despite the identification of various seasonal causes of reproductive disorders in pigs, depending on both sows and boars, and the availability of various “tools” to reduce phenomenon of seasonal infertility, the presented problem has not been solved in a large percentage of swine farms. Its intensity varies and depends primarily on awareness, knowledge of ways to eliminate unfavorable conditions and determination in this regard. The first step, as always, is to objectively assess the situation. The assessment can be made through a detailed analysis of production data.