By Perle E. Boyer, University of Minnesota College of Veterinary Medicine, and Glen W. Almond, North Carolina State University College of Veterinary Medicine
Seasonal infertility is characterized by decreased breeding and farrowing performances in swine usually occurring in late-summer and/or early fall. The phenomenon is not recent and can be observed in a more obvious fashion in wild boars (Sus scrofa ferus), which do not mate after the month of September, avoiding winter farrowings.

Seasonal infertility is a multifactorial syndrome meaning that it is caused by several elements such as temperature, photoperiod, nutrition and genetics. Most of these parameters are influenced by the time of the year, giving first the name “summer infertility” then “seasonal infertility” to the syndrome.

How does it manifest itself?
The clinical manifestations of seasonal infertility are numerous and start with the pre-pubertal female. Indeed, warm summer temperatures have been shown to delay the first estrus in gilts. Reduced production of Luteinizing Hormone by the pituitary gland limits follicle growth beyond 5 millimeters and therefore, prevents the gilt from coming into heat. Reduced basal concentration of LH seems to be one of the major factors leading to female infertility during the summer. In addition to a delayed onset of puberty, the farm can experience an increased number of sows having a longer weaning to estrus interval or even not coming back into estrus at all. After the sows are bred, regular return into heat around 21 days after breeding can be experienced in the summer whereas irregular returns, after 21 days, are more common in the fall, suggesting a problem with the corpus luteum and the maintaining of the pregnancy. Early pregnancy loss can be due to lower LH concentration as well as problems with the maternal recognition of pregnancy, which happens around day 12 post-insemination.

All of these issues lead to a decreased farrowing rate, which can be recorded in production records as open sows during pregnancy check or as fail-to-farrow. Seasonal effect on litter size have been mainly associated with heat stress. Indeed, elevated temperatures can decrease the number of embryos and may lead to pregnancy loss if this number is too low to maintain the pregnancy.

Lastly, seasonal infertility can show as Autumn Abortion Syndrome. AAS is characterized by an increased number of abortions in a farm during the first fall days when temperatures are warm during the day but cold at night.

Effects of seasonal infertility are numerous but not all are necessarily seen in every farm. To assess the impact seasonal infertility has on your production, it is important to look at production records and at the evolution of the reproductive performances during the entire year.

In summary, seasonal infertility may manifest as delayed puberty, longer WEI, decreased conception and farrowing rates subsequent to summer matings, diminished litter sizes (increased stillbirths and decreased total born) and more abortions in the autumn months.

Is seasonal infertility only affecting the dam?
When talking about seasonal infertility, most people refer to the consequences on the breeding herd as detailed above. However, boars too experience a decrease in their fertility after a heat stress of short (two days) or long (couple of months) duration. This is particularly true when barn temperatures rise above 83 degrees F but consequences in sperm quality can be noticed with temperature just above boars’ thermoneutral comfort zone of 72 degrees F.

Heat can decrease a boar’s libido, but it also damages the germ cells in the testes. Germ cells are sperm cell precursors, created in the reproductive tract of the boar. Under heat stress, they can evolve into abnormal and inefficient sperm cells. For example, their morphology or the shape of their head can be modified, impairing their motility and their ability to fertilize the egg. Most recent studies suggest that beyond the morphologic modifications, the sperm cells’ DNA could also be damaged by the increased temperature, leading to embryonic death early after fecundation. Additionally, the collected volume of semen is also decreased during that time. Such consequences can still be observed for up to four weeks after the environmental temperature is back to normal.

How can I manage seasonal infertility in my farm?
Seasonal infertility can manifest itself in various ways and the severity of its consequences varies tremendously from one farm to the next. Therefore, before attempting any type of interventions, one should review and compile reproductive records for the past few years to analyze performances of the herd during summer/early fall compared to the rest of the year, looking for a repeatable pattern.

To minimize the effects of seasonal infertility, we need to understand the underlying causes and the mechanisms leading to its clinical manifestations. Increased environmental temperatures, above the thermoneutral zone of adult pigs (64-68 degrees F) as well as a reduction in feed intake during lactation have been shown to be the two major parameters influencing reproductive performances in pigs. Therefore, management practices should focus on these to limit the dip in reproductive performances.

• Maintaining the pigs in a cool environment in the summer
Because pigs cannot efficiently sweat and self-regulate their body temperature, it is important to maintain their environmental temperature as low as possible during the warm months of summer. Cool cells, misters or water drips are efficient ways to keep the sows comfortable. Enable access to fresh water at a volume of up to seven gallons per day for a lactating sow and four to five gallons a day for a gestating sow without counting spillage. Checking that water nipples deliver high volume per minute is necessary all year long but of utmost importance in the summertime.

• Feed intake during lactation and at weaning
Lactating sows tend to eat less in the summer due to the increased temperatures and end up with a negative energy balance at weaning. This is particularly true for first-parity sows which in addition to the energy required for lactation have extra needs to complete their own body development. A sow weaned in negative energy balance may take more time to come back into estrus or may produce fewer follicles and therefore fewer eggs, leading to a decrease in litter size at the end of gestation. Monitoring sows for feed intake during lactation is extremely important. Feed can oxidize quickly in hot temperatures and then, deter the sows from eating it. Mixing dry feed with water can help with ingestion but if left in the feeder for too long, the mix can ferment and again be turned down by the animals. Feeding sows small amounts more frequently and monitoring their intake is added work on farm employees but will pay off at weaning.

• Increasing LH basal levels
The lower basal concentration of LH has been shown to be a key element of seasonal infertility. One strategy to counteract its effects is to inject sows with a combination of human and equine chorionic gonadotropin (hCG and eCG); available commercial products usually contain a combination of those hormones at 600 International Units or IU concentration. Given at weaning, it leads to a more fertile estrus and better estrus detection whereas it helps maintaining pregnancy by improving maternal recognition when administered at day 12 post-insemination. Therefore, artificial hormonal treatment can be part of seasonal infertility management if the time of treatment is adapted depending on the farm situation.

• Delaying breeding
Skipping a heat and waiting for the following estrus to inseminate sows has been proven beneficial but can be a financial burden on an operation due to the increase in non-productive days. Another alternative is to delay estrus by using altrenogest.

Altrenogest prevents estrus by limiting the follicle size in the ovary. When fed altrenogest at weaning, the reproductive cycle of the sows is paused, allowing sows to recover from lactation and increasing ovulation rates at the end of the 12- to 18-day treatment. However, altrenogest should not be given to gilts before their first estrus as it has been shown to increase the development of ovarian cysts.

• Qualified labor
People are more likely to take vacation during summer and it can be difficult to find replacement help during that time. Making sure that new employees are properly trained, even if they are temporary help, is still beneficial to maintain reproductive performances during this challenging time of the year. Modify work schedules to allow labor to work during the early morning when the barns are cooler. This may have benefits with the animals as well.

References
De Rensis F., Ziecik AJ., Kirkwood RN., Seasonal infertility in gilts and sows: aetiology, clinical implications and treatments, Therio. 2017(96) 111-117

Peña Jr. ST., Gummov B., Parker AJ., Paris DBBP., Revisiting summer infertility in the pig: could heat stress-induced sperm DNA damage negatively affect early embryo development? Anim. Prod, Sci, 2016

Thacker BJ., Seasonal Infertility: management practices – causes and fixes, 2002, Proceedings of the Iowa Swine Disease Conference

Parrish J., Effect of heat stress on semen quality; recommendations for keeping AI boars, 2017, Proceedings of the 48th AASV meeting, 18-19