Seasonal infertility in gilts and sows: Aetiology, clinical implications and treatments
Introduction
In swine, summer and early autumn are the periods when reproductive variables consistently show their lowest values. This period is often referred to as summer infertility or, more appropriately, as seasonal infertility since effects can be apparent outside of the summer months [1], [2], [3], [4]. Manifestations of seasonal infertility include delayed puberty [3], [5], [6], prolonged or irregular weaning to oestrus intervals [4], [7], [8], [9], reduced farrowing rates [2], [4], [10], [11], [12], [13], anoestrus and reduced litter sizes [1], [14].
Seasonal infertility can be attributed to various factors but is primarily associated with seasonally high environmental temperatures negatively impacting lactation nutrient intakes [1], [2], [15], [16]. However, an influence of photoperiod on seasonal infertility is suggested by a 5 year study in France showing consistent seasonal infertility apparently independent of annual environmental temperatures [17]. These latter authors documented that in each year 25% of French herds had pregnancy rate reductions of at least 7.1% during the seasonal infertility period even when environmental temperatures were not particularly high. Similarly, Peltoniemi et al. [3] describe seasonal infertility in Finland where barn temperatures did not exceed 25 °C, suggesting photoperiod was more important than environmental temperatures. Reduced feed intakes may also interact with photoperiod as feed restriction resulted in higher circulating melatonin in pigs under a long photoperiod (ie. summer) but not under a short photoperiod [2]. Generally, seasonal infertility is expressed more often in gilts and primiparous sows than in older sows [18], [19], likely because these younger animals have innately smaller appetites and are still growing to their mature size.
Various management protocols can be implemented to counteract seasonal infertility including the control of temperature, humidity and, if possible, photoperiod. However, where these approaches are not feasible or not sufficiently effective, the utilization of exogenous hormones can be considered to stimulate follicular development, oestrus, ovulation, and to help to maintain pregnancy. The aim of this review is to discuss factors mediating seasonal infertility and to present some hormonal protocols to combat the infertility in female swine.
Section snippets
Endocrinology of seasonal infertility
The underlying cause of seasonal infertility of sows is unclear but is likely multifactorial and involves effects on ovarian follicular and/or corpora luteal function, presumably driven by alterations in gonadotrophic stimulation, resulting in some sows being more sensitive to changes in their environment. The trigger(s) for seasonal infertility in these sensitive sows is variously suggested to be low lactation nutrient intake consequent to elevated temperatures and the longer photoperiods of
Puberty onset
Temperature and photoperiod during warm seasons are two environmental factors that can potentially delay puberty onset [2], [16], [36], [37]. However, while there is clear evidence that elevated temperatures influence age at puberty, the effect of photoperiod is contentious. There are reports showing a benefit from an increased photoperiod on age at puberty [37], [38], [39] but these effects have not been observed in other studies [6], [40] and in a tropical country such as Thailand, delayed
Hormonal treatment to counteract seasonal infertility
As described above, several factors are involved in the mechanism causing seasonal infertility in swine; heat stress and/or photoperiod are involved but the effects of photoperiod are often masked by the presence of heat stress. Heat stress can influence the secretion of hormones including cortisol [67], [68] and prolactin [69], [70], and can reduce feed intakes with problems for the energy balance of the animal. One consequence could be that during the summer season the activity of the
Conclusion
Fig. 1 summarizes the main effects of heat stress and photoperiod on hormonal and metabolic mechanism that may impact sow fertility during the hot summer season with some hormonal treatments that can be utilized to counteract these effects. During summer, heat stress and photoperiod can alter the development of follicles and the quality of corpora lutea, oocytes and embryos, with deleterious effects on pregnancy rate and total piglets born. Seasonal infertility in swine includes delayed
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2021, Animal Reproduction ScienceCitation Excerpt :In the present study, fewer gilts developed large follicles and expressed behavioral estrus within 6 days after imposing the PG600 treatment regimen and these problems were attributed to effects of the replicate performed during summer. The temperature and humidity were greater in the summer and results from previous studies have indicated that greater temperatures during summer can result in an older pubertal age of gilts due to lesser concentrations of gonadotropins in circulation, lesser numbers of gonadotropin receptors in the ovaries, and compromised follicle development (Flowers and Day, 1990; De Rensis et al., 2017). Although in the present study, there were no effects of heat stress on the number of CL, there were however, fewer viable embryos and a lesser embryo survival in the summer than winter period.
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2020, TheriogenologyCitation Excerpt :Heat stress is characterized by an increase in core body temperature (hyperthermia) that exceeds the physiological range for the species [9]. The deleterious effects of heat stress on fertility has been shown in cattle [10–12], sheep [13], buffaloes [14], pigs [15], horses [16], rabbits [17], and mice [18]. This scenario has been worsened by climate changes.
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2019, Animal Reproduction ScienceCitation Excerpt :Results of the present study indicate there was a positive effect of SuinFort on sow fertility and prolificacy whereas, in contrast to results from previous studies (Bertoldo et al., 2012; De Rensis et al., 2017), there was not an effect of season. Seasonal infertility is an economic problem in many pig breeding systems, with a complex etiology likely related to lesser ovarian activity and lesser oocyte developmental competence when there is heat stress (Bertoldo et al., 2012; De Rensis et al., 2017). There have been previous studies of the seasonal effect the when there was supplementation of oxytocin to the seminal dose and utilization of the semen when there were greater ambient temperatures and there was less fertility when these samples were used as compared with use of non-oxytocin supplemented semen samples (Peña et al., 1998).