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Preventing Summer Infertility in Your Pigs

07 August 2015

Summer infertility in pigs can largely be attributed to heat stress but other factors tailor in, with awareness and management key to maximising production. Melanie Jenkins reports.

Outdoor pig systems are highly susceptible to seasonal infertility, mainly due to the long days and high temperatures. Although neither cause can be modulated, they can be managed.

Indoor pigs are less susceptible but can still suffer from heat loss, with good insulation and adequate ventilation playing a key role in minimising the risk.

Dr Charlotte West, technical innovation manager at AHDB Pork, says that heat stress can be caused when a pig’s body temperature rises a couple of degrees above normal, which can have a negative impact on reproductive performance.

“In these circumstances the pig will first increase its respiration rate in an attempt to keep cool, then search for environmental opportunities for cooling such as wallowing and lying in urine.”

Heat stress can cause unnecessary suffering and reduce productivity, says Dr West.

“Pigs subjected to high temperatures may have dramatically reduced growth rates and in the breeding herd farrowing rates could decline by as much as 25 per cent, with litter size showing a small drop as well.” 

Factors to consider:

High temperatures - The 'normal' thermoneutral zone for pigs can range from 7-21°C. If pigs are exposed to prolonged periods of higher temperatures it can lead to heat stress and reduced productivity, and in some cases mortality. Outdoor pigs tend to have a lower resilience for high temperatures than housed pigs, as they are more adapted to cold weather.

Heat stress can also affect piglet birth weight if blood flow to developing foetuses is redirected to the skin to help reduce body temperature.

Sunburn - Prolonged exposure to sunlight can result in sunburn, with gilts being particularly susceptible when they first move outdoors or into sow accommodation with an outdoor run.

Feed intake – Angela Cliff, knowledge transfer manager of AHDB pork, says it is difficult to maintain a sow’s appetite in hot weather, but it’s essential to maintain sow condition and therefore nutrient intake, especially in lactation. Sows with minimal loss of condition should return to oestrus 4-5 days after weaning.

Water intake and quality - Hot temperatures can put pigs off their food and they can then drink less as they try to conserve energy, which can hinder growth. Water quality can also suffer in warm weather, with increased microbial growth.

Fluctuating wean to oestrus interval and reproductive failure - “High temperatures can disrupt the hormones involved in pregnancy and interfere with the oestrus cycle, leading to variable standing heat lengths, reduced ovulation rates and increased embryo mortality,” says Ms Cliff. Sows can be particularly susceptible during the first 15 days post-mating.

Boar libido - Hot weather can make boars lethargic and reduce their interest in working.

Semen quality - Raised temperatures can reduce sperm quality for up to eight weeks.

Semen storage - Semen should be stored in a thermostatically controlled storage box out of the sun to avoid any deterioration.

Prevention is better than cure

Wallowing and rooting in the cool earth are the two primary methods used by pigs to cool down when outdoors, says Dr West. “Heat is lost through the evaporation of water from the skin and a layer of mud can reduce sunburn.” 

It is advisable to prepare wallows before the summer, ensuring they are regularly topped up with water in dry periods, although they should not be allowed to become stagnant, as this can lead to infections.

“Wallows should provide enough space for twice the number of pigs they are intended for as this will enable the more submissive animals to use the wallow,” she adds.

Shade is another important factor. Pigs are likely to be more susceptible in late spring and early summer when they are exposed to the first strong sunlight after winter. Severe sunburn, when the skin blisters, can cause pregnancy failure, and the pain and discomfort will lead to increased stress levels.

Mud can reduce sunburn in pigs but it is still important to provide shade with clean straw bedding underneath that will encourage the pigs to make use of the area.

Outdoor accommodation should also be managed to maintain the lowest temperatures possible in the summer heat. One of the most effective ways of doing this is to paint the exterior white.

According to Dr West, this can reduce the internal temperatures by as much as 7°C. Other methods include keeping arcs well insulated, taking advantage of the prevailing wind and opening the back vents to improve ventilation.

For breeding herds, it can help to serve sows at the beginning and end of the day when it is cooler.

“It is also important to maintain good hygiene, particularly as sows are likely to have been wallowing,” says Dr West.

Heat stress can also reduce the boars’ libido and reduce the viability of semen for up to eight weeks so it is important to check semen quality after the last period of heat stress or ill health. “Boars will not work in hot conditions so all DIY should be done at either end of the day.”

How to minimise heat stress indoors 

Reducing the risk of heat stress indoors can be managed in a number of ways, from ensuring insulation in buildings is effective, to having alarm systems that monitor the temperature.

Ventilation is also important, as is avoiding daily temperature fluctuations. “Consider using supplementary fans for large pens, making sure the system is clean and in good working order as dirt can restrict its efficiency,” says Ms Cliff. Sprinkler systems work well alongside fans to help keep pigs cool, she adds.

Water access is also key. It is recommended that nipple drinkers are provided at a rate of one per 10-15 pigs and troughs at a minimum of 1cm space a head up to 35kg live weight. For lactating sows the water supply should have a flow rate of 2–2.5 litres a minute, while grower and finisher herds should have 1-1.5 litres a minute from 30-70kg live weight.

Genetics may also have a role to play. A study carried out by AHDB Pork of 32,935 sows in 29 herds between 2004-09 found that seasonal infertility could be partially down to genetics as over 25% of sows were totally unaffected.

August 2015

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