Summer Infertility

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Summer infertility is one of the most common seasonal challenges that pork producers face.  This phenomenon causes less than optimal reproductive performance in breeding herds throughout the world.  Among the challenges observed with seasonal infertility are; prolonged weaning to estrus interval, decreased farrowing rate, decreased litter size, delayed puberty, and increased “not in pig syndrome”.  Although seasonal infertility seems to occur regardless of geographic location, it does appear to be more severe in tropic and sub-tropic locations. This guide is an accumulation of information collected for our customers in an effort to lessen the severity of Summer Infertility in their operations.

        To accept the fact that we cannot totally eliminate summer infertility, it is best to understand that genealogy has a large influence on the way pigs react to changing seasons.  Although we have domesticated today’s swine herd, its ancestors were seasonal breeders.  Ancestors to today’s swine had certain biological rhythms that assisted them to avoid mating during the late summer and early fall, seasons that would have forced them into farrowing during the winter months.  Even today, these biological rhythms have an influence on the female. The primary objective today’s pork producer should strive for is to minimize the negative impact seasonal infertility has on the operation; this will allow him to achieve high productivity regardless of the season.

        The two most common components attributed to seasonal infertility are ambient temperature and photo-period.  Data from Scotland shows that the seasonal infertility phenomenon exists there, even in a relatively cool climate.  There is a small amount of evidence showing that limiting light exposure to 16 hr. per day will provide some benefit, but most results show this has very little effect in reducing the symptoms of summer infertility.  Therefore, producers probably need to focus most of their attention on thermal management in order to lessen its severity. Most research has shown that swine will begin to show signs of heat stress once the ambient temperature has reached 82^o F.  The primary way for pigs to cool themselves is through the blood vessels near the skin surface.  Humidity can have a detrimental effect on this cooling process.  Therefore, hogs can begin to show clinical signs of heat stress at temperatures as low as 75^o F if the relative humidity is reaching levels above 85%.  The following chart, collected by Ouiniou and Noblet in 1999, shows the affect that increased temperature can have on a swine herd.  

        The cooling ability of the sow can be increased with devices such as drip coolers or sprinklers.  These devices should be set on timers, so they will operate 1-2 minutes 4 times per hour.  When using drip coolers, it is best to set them so the water will drip behind the sow’s ear, as this is an area where the blood vessels are closest to the skin surface.

        The gilt pool offers one of the locations we look at in attempting to lessen the severity of summer infertility.  If the sow herd’s reproductive performance is going to drop, it becomes highly important to have an ample number of gilts available to pick up some of the “slack”.  During summer months, gilts will suffer a reduced ability to release the gonadotropic hormones required for the normal occurrence of puberty. Creating a gilt development strategy earlier in the year can help reduce this problem.  Gilts that are already cycling when the summer months arrive will have better reproductive abilities than gilts that are just reaching puberty.  Therefore, it will be a benefit to have a larger than normal number of gilts available for placement as the summer months approach.  

        Boar exposure is still the best method for stimulation of gilts. With exposure a minimum of once per day you can expect positive results. The adjoining chart shows a 60% increase in gilts reaching puberty by 225 days when offered boar exposure from day 160 on during summer months.

Although fence-line contact is the simplest method for this contact, research has shown that actual physical contact between the boar and prepubertal gilts will lead to a  higher number of females reaching puberty.  Likewise, constant exposure to the boar may make it difficult to properly diagnose which females are beginning to cycle.  Thus, it is best to attempt to design some sort of holding pen where a mature boar can easily be moved to and from the gilt pool with a minimum amount of labor.  Space allocation should also be a consideration; a minimum of 16 ft² per gilt is ideal to prevent overcrowding in the gilt pool. 

The negative effects of a reduction in gonadotropic hormone release can also appear in the mature sow herd.  Decreased lactation feed intake along with an increase in ambient temperature often cause delays in the period from weaning to estrus.  It is important to have strategies in place to minimize these delays.  All types of cooling systems in the farrowing barn should be designed to be at full operation before the temperature reaches 81^o F.  Cross fostering and early weaning may relieve some of the stress on the animal before weaning, and boar exposure similar to that in the gilt pool will assist after weaning. 

Maximizing feed and water intake in lactation will have the single-most positive effect on reducing the weaning to estrus interval.  Farrowing house personnel should consider three times per day feeding during the summer months.  Most herds that have tried this have observed a 10 to 15% increase in feed consumption.  When feeding 3 times per day (versus twice) it is important to reduce the amount of feed in per serving.  The reduction per serving will be made up for with the extra serving.  With less feed in a single feeding, the sow is more likely to clean the feeder, preventing a buildup of stale feed.

The primary benefit of an increased feeding frequency is related to the normal increase in body temperature that occurs after a sow consumes a meal.  There should no be as big an increase in a sow’s body temperature after she eats 4.5 pounds (as after she eats 6) because there will be less feed to be digested.   Consequently, this could be very important for sows whose body temperatures already may be in the upper end of the thermoneutral range due to high temperatures in their environment.

As ambient temperature increases, the sow’s demand for water will also increase.  Nursing sows need to consume 8 to 10.5 gallons of water every day, while gestating sows will need 3 to 5 gallons.  It is important that the supply of water flow at a minimum of .25 GPM and ideally at .5 GPM.  It should also be noted that a supply of fresh, cool (50^o F) water will result in nearly double the consumption of warm, stale (80^o F) water.

As little as 72 hours of exposure to temperatures in excess of 84^o F during the first 30 days of gestation will result in a decrease in conception and farrowing rates.  These decreases can usually be attributed to one of three causes: 

1)                  Normal sperm production in the male will see a decrease with an increase in ambient temperature.  Results will be an increase in fertility failure.  Normal signs are an increase in returns to estrus at the normal 21-day period.  Usually the effects of heat exposure to boars will show up in the period between 3 and 7 weeks after the exposure.           

2)                  Normal fertilization and embryo development may not occur due to an increase in ambient temperature.  When this occurs, sows and gilts will behave like they were never pregnant and returns will be observed at the normal 21-day interval. 

3)         Embryonic death may occur after the start of maternal recognition (day 11 to 14).  If the embryonic death occurs between days 11 and 19, one can expect returns to estrus between day 25 and 38.  If the embryonic death should not occur until after day 30, it is not uncommon to have sows maintain a “pseudo pregnancy”, where they will maintain endocrine, physiological and behavioral aspects of pregnancy with no viable fetuses present. 

        Although the detrimental effects of exposure to high ambient temperature can be observed in all  sows, it is more likely to be observed in sows under some type of stress.  Therefore, one should try to minimize mixing, moving, or crowding animals during their pregnancy.  If mixing of sows is necessary, it is highly recommended that you do it at weaning rather than after mating.

        An increase in “Not in Pig” events is another common outcome of summer infertility.  It can be described as sows that have a positive outcome from a pregnancy test and exhibit signs of pregnancy through day 75 to day 90.  After that period they may suddenly appear to “dry up”.  These situations often occur in early autumn as well as throughout the summer.  They may be sporadic within the herd and appear to be more prevalent in group housed sow facilities.

        There are many different Hormonal Strategies available for producers to battle summer infertility.  Most have a positive effect, although cost justification may be a major factor on the decision on whether they are practical.  One such method is the placement of Oxytocin in the semen at the time of insemination.  Oxytocin is a relatively inexpensive hormone that is commonly available on most operations.  The following table presents data that would appear to support the placement of 5 IU (1/4 ml) of oxytocin in the semen immediately prior to insemination, especially in the summer and fall months. 

^*Pena et al (1998) Theriogenology 49:829 

        It is important to remember that there is no single method that can be used to eliminate summer infertility.  Rather, it will take cooperation between farrowing house personnel, gestation barn personnel, and genetic suppliers and / or semen suppliers to minimize the negative effects that can be associated with summer infertility.  If there is anything we can do at International Boar Semen to assist you with this or any other questions you have, please call us at 800/247-7877.

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