How to reduce seasonal effects on sows’ fertility

As summer’s hot temperatures approach, farmers should enact preventive measures to maintain sow performance.

by Kate Ayers

Many people happily welcome the summer sun and heat because they think of time spent outdoors swimming, playing and lounging. While farmers also embrace the sun and heat to support field crop and forage development, the summer also brings some livestock management challenges. For hog farmers, seasonal infertility can be a costly consequence of higher temperatures outside and inside barns.

“Temperature is not only important in breeding and gestation areas, but also in the farrowing house,” says Dr. Glen Almond. He’s a professor of swine health and production management at North Carolina State University (NCSU).

“In other words, temperature is important throughout the entire production cycle,” he says.

Farmers cannot control the weather or ambient air temperatures. Producers can, however, manage barn settings and feed composition to ensure, for example, that their animals remain as productive as possible during the hotter months of the year.

Hogs with less exposure to stressful environments will perform better than uncomfortable animals, says Dr. Robert Friendship. He’s a professor in the population medicine department at the University of Guelph’s Ontario Veterinary College.

Better Pork speaks with professors, reproduction and management specialists, and veterinarians to learn about the onset of seasonal infertility in sows and its effect on herd efficiency and business profitability. These experts highlight how producers can reduce the incidence of sow infertility on their farms during the summer.


Producers most often experience seasonal infertility in their herds throughout the summer and in the early fall. During this time, farmers might observe such reproductive problems as anestrus, extended weaning-to-estrus intervals, poor conception rates, increased embryo mortality rates and low farrowing rates, says an NCSU fact sheet, “Management Practices to Reduce the Impact of Seasonal Infertility on Sow Herd Productivity.”

    Martin Schwalbe photo

The underlying causes of seasonal infertility fall into two camps. Some reproductive specialists attribute the issue to higher temperatures and humidity. Other experts think seasonal infertility occurs because pigs are inherently seasonal breeders and day length plays a role.

In wild pigs, photoperiod is a key determinant of seasonality in breeding, studies show. Many species of animals use the change in daylight length to determine the time of year when offspring survival is most favourable, says “Effects of Season and Regulated Photoperiod on the Reproductive Performance of Sows.” Researchers published this South African paper in 2009.

While both phenomena can cause infertility, most Canadian farmers house their pigs indoors where producers can manipulate lighting and photoperiod.

Heat stress in hogs can occur when the animals’ internal temperatures rise above their thermoneutral zone, which falls between 4.4 C (40 F) and 21.1 C (70 F), the NCSU fact sheet says. Generally, heat begins to affect sows’ reproduction at temperatures above 26.7 C (80 F), studies show.

Farmers can use rectal thermometers on sows to identify heat-stressed animals, “but this job is labour-intensive and time-consuming for producers and sows may not co-operate,” Almond says.

Alternatively, farmers can “use the respiration rate of sows to determine if they are susceptible to infertility. Generally, the respiration rate of sows is around 20 to 25 breaths per minute. But during the summer, it is not unusual to see rates around 100,” he says.

“The respiration rate of sows indicates if they have increased body temperatures. It’s easier to count respiration rates than to take body temperatures,” he says.

Farmers should watch for pigs that may have elevated temperatures during “late June, July, August and maybe early September,” Almond adds.

Genetics, parity level and body condition all contribute to a sow’s ability to cope with heat stress. These factors influence the duration of the animal’s recovery.

As a result, farmers might need to provide individual care for animals, but the care depends on the sows’ reproductive resiliency. The effectiveness of management strategies to reduce seasonal infertility varies from farm to farm, depending on operation size and production approaches, the NCSU fact sheet says.

Susceptible sows

Some females are inherently at a higher risk for infertility, which is augmented during the summer months.

First-parity sows are generally more susceptible than mature sows to reduced fertility rates, says Dr. Aileen Keating, an associate professor in the department of animal science at Iowa State University.

“If environmental conditions change rapidly – for example, it gets hot and humid suddenly – those animals experience heat stress, which has negative effects on fertility.” First-parity sows often experience “reduced conception rates and loss of the litter early in pregnancy,” she says.

Friendship agrees.

“First-parity sows are still growing and are sensitive to nutritional imbalances,” he says. As a result, these animals are in a poor nutritional state after weaning, and they take longer to get back into heat.

“So, they don’t fit back into their farrowing group. Even then, they are more likely to have smaller litters or poor farrowing rates,” which can cause production and management challenges, Friendship says.

In addition, gilts may experience delayed puberty in the summer.

These animals “usually come into first estrus from 180 to 185 days of age, but this time frame gets delayed. And the number of gilts that never show estrus will increase too,” Almond says.

“Older sows that are kept beyond parity six or seven” could be less resilient to increases in temperature, says Friendship.

Sows that are too heavy or too thin could be more susceptible to reproductive complications because of heat stress than animals that have healthy weights.

“If the farrowing house is too hot, the sows are not going to consume sufficient feed and they’ll come out in bad body condition. And then you will have post-weaning issues,” Almond says.

Underconditioned sows “may come into heat and get re-bred, or they may not show heat at all for 10, 14 or 21 days instead of after the first week post-weaning,” he adds.

However, “it is difficult to know in advance if a sow will have fertility issues as there are no tests to predict that,” Keating says.

So, “maintaining a good body condition score and good health, in general, is important for good fertility,” she says.

Economic effects

Sows that are more susceptible to seasonal infertility or poor performance during the warmer months will affect operations’ bottom lines.

“The premise of profitability is driven by the number of females successfully bred per week,” says Dr. Frank Marshall. He’s a veterinarian and owner of Marshall Swine and Poultry Health Services in Camrose, Alta. Marshall is also a sessional instructor at the University of Calgary’s faculty of veterinary medicine.

Farmers need to hit their breeding targets since these numbers drive net income, he adds.

“Sows are bred, farrowed and then piglets are weaned … Then the animals are sent to market,” he says. “Running into surprises and experiencing more non-productive sow days can be costly.”

“Infertility in sows impacts overall herd efficiency” in many ways, Keating says.

Some of farmers’ direct and indirect expenses include “feed, vaccinations, labour, barn space, power, heat, etc. If a sow does not get pregnant or even has delays in conception rates, costs add up.” Producers incur these costs even if a sow does not produce marketable piglets, and infertile pigs can result in a negative return on investment.

For sows that do conceive in the summer, warmer barn temperatures could result in lower weaning weights. In turn, these weights “will affect growth rate and performance in the nursery and finishing barns,” Almond says.

Farmers won’t see the effects of seasonal infertility until November or December, he adds. By then, it is too late to mitigate losses. So, producers must be diligent in the spring to manage the issue.

Arno Joosten, a reproduction specialist at Topigs Norsvin in the Netherlands, emphasizes the link between a sow’s body condition and her offspring’s productivity.

Animals can experience “weight loss during lactation because feed intake during this time is lower,” he says.

piglets suckling
    Christina W. Kroeker Creative photo

“When the sows lose too much body weight, the follicles on the ovaries are not of great quality.” Lower-quality follicles have “direct effects on production, litter size in the next parity and the quality of the piglets born,” Joosten adds.

“Piglets have lower body weights, which could lead to higher mortality,” he says. “There is a correlation between piglet body weight and the efficiency of the finisher pig.”

In addition, “your stillborn rate may rise from 7 per cent to 9 or 10 per cent. It’s hot and harder on the sows to give birth,” Almond says. A rise in this rate causes a reduction in the number of pigs weaned per sow per year. The relationship influences farm economics.

Preventive measures

Fortunately, producers can use management strategies to keep animals comfortable and decrease the number of unproductive sow days.

“Farmers can bring losses under control with good management and supervised farrowing. It just takes more work,” Almond says.

“Cleanliness, attention to the body condition of sows and animal illness, and being cognizant of when environmental conditions change are all important,” says Keating.

Water systems play an important role in keeping sows cool and healthy.

Farmers can install drippers in farrowing houses, Almond says.

Sow barn fan
    National Pork Board and the Pork Checkoff, Des Moines, Iowa photo

Water lines run “above the sows. When the barn reaches a critical temperature, typically 29 C (84 F), water will drip onto lactating sows, and fans will blow over top of them to facilitate evaporative cooling,” he says.

“But these systems can cause a damp environment, which can cause problems with the piglets.”

Some producers may decide to use cooling cells or portable air-conditioning units.

Farmers should check to ensure ventilation systems function optimally to keep air moving and could turn off heat lamps to keep barn temperatures down.

sow drinking water
    National Pork Board and the Pork Checkoff, Des Moines, Iowa photo

Year round and especially in the summer, “water consumption is important. I encourage producers to check drinkers before sows go into the farrowing house,” Almond says. Farmers should also observe flow rates.

“I prefer a rate of one litre (0.22 gallons) per minute. If drinkers are restricted, then sows’ feed intakes will drop, which affects milk production.”

And “you have to make sure that the water is cool,” Almond says.

Since sows might not eat as much in the heat, they must consume high-quality food. Feed specialists can help farmers fine-tune rations to meet the animals’ needs.

“Nutritionists will want to look at the diets’ ileal digestibility values and have amino acid sources balanced,” Marshall says. Amino acids should come from a variety of sources including peas, soybeans and canola.

Before a young hog enters the farrowing stage, farmers should “increase gilt gut capacity so that she can consume what she needs,” Marshall adds.

Ideally, “we have a big, robust gilt in the farrowing crate and are adding 27 grams (0.95 ounces) of lysine to sow rations … for every kilogram (2.2 pounds) of gain on the litter,” Marshall says.

“She will be able to convert this diet to milk for the piglets (and produce) four kilograms (8.8 pounds) of milk for every kilogram of litter,” he says. “We need to take every opportunity to maximize feed intake without backing her off feed.”

During the sow’s lactation, “we might go to three feedings per day, especially for gilts. Or do a larger feeding at night.”

Almond agrees.

At this stage, “producers can do ad lib feeding. Feed early in the day and late at night when the temperature is cool,” he says. This strategy will help set up the sow to recover and return to heat for the next breeding cycle.

Precision feeding can also be an effective mitigation strategy.

“Farmers need to know how much a sow eats every day,” Joosten says.

This information can help producers “feed animals according to their body conditions and make sure sows are getting what they need during lactation.

“RFID (radio-frequency identification) tags can allow farmers to provide exactly what the sows need,” he says. “Feeding stations provide the best results, but the feeders require proper training of the gilts.”

Farmers should also carefully consider when to breed gilts. To help mitigate a gilt’s typically lower farrowing rates, producers should not breed the animal “too young; that is, not during her first heat cycle,” Friendship says.

Marshall agrees.

Operation productivity “goes right back to gilt development,” he says.

“The recommendation is to breed gilts that are at least 136 kilograms (299 pounds) and (are in) their second or third estrus. This (approach) builds the foundation for (animal) longevity and ability to tolerate lactation,” he says.

And if producers want to achieve a 90 per cent farrowing rate, they should divide the number of farrowing crates that they want to fill by 0.9 to determine the number of sows that should be bred at a time, Marshall adds. Breeding a few extra sows can help prevent a deficit created by seasonal infertility at the farrowing stage.

Overall, keeping sows comfortable and making pre-emptive management decisions can help you to protect your operation’s bottom line. Consider the effects of seasonal infertility in yearly planning to help keep your animals cool during the summer heat. BP

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