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Improving Swine Reproductive Efficiency — Seasonal Infertility and Heat Stress

According to Ken Stadler, an animal science professor with Iowa State University, the U.S. pork industry experiences an annual sow replacement rate of greater than 50%, meaning sows are being culled from the herd at an average parity of 3.5 to 3.8, producing fewer than 40 pigs during a sow’s lifetime.  Many herds in the US are below this average parity.  

Eighty-six percent of sows are culled due to reproductive failure and there are underlying factors (lameness, age, post weaning issues, etc.) that need to be discussed and addressed by pork producers.

This blog post is part of a series that will delve into sow reproductive efficiency and identify the underlying reasons why sows may not be breeding back. To start off, we will talk about seasonal infertility and heat stress and its underlying role in reproductive failure.

Seasonal Infertility

Year after year, we see a decline in the number of pigs produced from late-summer and early-fall matings. Seasonal infertility in swine during the warmest months of the year is a natural biological occurrence. As day length begins to shorten in late summer (photoperiod — perceived change in the amount of exposure to daylight), the pineal gland located in the brain releases the hormone melatonin, which can negatively impact the fertility rate of your breeding herd.

While you can’t control the photoperiod very easily, there are a number of management practices that will minimize the adverse effects of nature and the problems associated with summer infertility.

The two production issues that can impact seasonal infertility the most are heat stress and decreased nutritional intake. By protecting against heat stress and keeping the nutritional plane as high as possible, we can minimize the effects of seasonal infertility. Minimizing the impact of summer influences will help optimize the consistency of pigs produced per week throughout the year.

Steps to Help Avoid Heat Stress


The first line of defense against heat stress is to control the animals’ environment with adequate ventilation and cooling … keep air moving. For good circulation without drafts, the air should enter the room at a speed of 600 to 1,000 feet per minute (183 to 305 meters per minute) with an average inlet speed goal of 900 feet per minute (274 meters per minute).

Recommended summer ventilation rates:

  • Breeding sow – 8.5 cubic meters (27.9 cubic feet) per minute
  • Gestating sow – 4.2 cubic meters (13.8 cubic feet) per minute
  • Sow and litter – 14.1 cubic meters (46.3 cubic feet) per minute

Supplemental cooling systems should be activated when the heat index is over 84° F (29° C). These systems include evaporative drip or spray cooling and circulating fans. The preferred method in swine is to sprinkle water in large droplets directly onto the skin and then allow it to evaporate. When water evaporates from the skin, it removes heat from the animal and causes cooling.

Manage animal stress

Unnecessary animal movement, change in animal location or mixing sows during the breeding period and for 30 days following can impair embryo implantation and result in embryo detachment and loss. If movement is necessary, schedule it for the early morning or during the evening when temperatures are cooler.

Water consumption

A constant and ample supply of fresh water is essential to good animal nutrition. On average, gestating sows need 3.6 to 6.0 gallons (13.6 to 22.7 liters) per day, and nursing sows require 9.6 to 12.6 gallons (36.4 to 47.7 liters) per day. When the temperature increases from a range of 54.5° F to 60° F (12.5° C to 15.5° C) to 86° F to 96.8° F (30° C to 36° C), water consumption increases by 50 percent or more.

Animal management

A well-designed breeding program with sufficient animals will also decrease the impact of seasonal infertility. You should establish farrowing goals based upon past records and compensate for the 10 to 15 percent of animals in seasonal anestrus, and project the number of sows and gilts that need to be inseminated to meet your farrowing goals during the hot weather months. This will likely mean an increase in the size of the gilt pool, although it should not increase beyond the housing capacity.

Begin selection of gilts at a younger age and begin exposure and physical contact with the boars beginning in research trials by 140 days and in most farm situations by at least 170 days of age.  Research in Canada by Foxworth and Aherne showed a much-improved reproductive performance of gilts with early-age boar exposure. This practice also permits identification and rejection of sub-fertile females, and litter sizes should improve because gilts will be in their second and third heats when mated.

Avoid late inseminations, as these may interfere with uterine preparation for implantation and cause embryo loss. Conduct accurate heat detection, and breed only on the basis of strong, standing heat response. One possible way to decrease mistimed inseminations is to determine the average estrus length in the weaned sows, gilts and repeat breeders.

Sow Nutrition and Trace Minerals

High temperatures and humidity not only cause heat stress, but they also decrease sows’ appetites, which can negatively impact metabolism and reproductive performance.

To maintain the sow’s appetite, feed smaller quantities of fresh feed more often. While the total quantity of feed provided remains constant, the feed offered will always be fresh and appetizing. Uneaten feed can spoil quickly when left in a trough during hot weather, and pigs will reject even slightly spoiled feed. Feeding smaller quantities of feed more frequently can reduce feed wastage and improve feed intake, but overall feed consumption needs to remain high. Offering feed to sows early in the morning and later at night can also help maintain feed consumption.

Feeding diets with higher synthetic amino acids helps reduce heat increment (heat production due to digestion), and the addition of fat in summer lactation diets can lower the amount of heat created from the diet.

Feeding trace minerals, such as Availa®Sow, from Zinpro Performance Minerals®, also helps mitigate seasonal infertility by improving feed intake in sows when compared to feeding inorganic trace minerals. Research has shown that feeding zinc, manganese and copper amino acid complexes found in Availa-Sow improves feed intake during lactation, which in turn helps improve milk production and minimize body weight loss of sows.  One of the consistent responses we see to feeding Availa-Sow is improvement of wean to estrus interval.  The cost of a non-productive day in most sow herds is $2-$3/sow/day.   Shortening wean to estrus interval particularly on parity one sows has a large financial benefit to the sow herd. 

Contact Zinpro today to learn how to better manage seasonal infertility in your herd, and learn how Availa®Sow can help enhance your herd reproductive health.

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