Take heat off sows to cut seasonal infertility rates

1 June 2001




Take heat off sows to cut seasonal infertility rates

By Hannah Velten

OUTDOOR pig units must take precautions to reduce the effect of seasonal infertility on farrowing rates and embryo loss.

Although infertility during the summer and early autumn is common, it is variable between farms in terms of magnitude and pattern, says Richard Potter of Oxon-based Larkmead Vet Group.

"Rapid rises in temperature, causing heat stress and shortening day length, play their part in causing reduced fertility in sows and boars," he says.

When farrowing rates drop between November and January, it may be an indicator of seasonal infertility. Also, returns to heat, particularly in July, will immediately show a problem with heat stress, says Mr Potter.

Sows in early pregnancy are particularly vulnerable to embryo loss due to heat. "A high percentage of embryos will reabsorb and sows will come back on heat 12-20 days after service," he adds.

Signet pig consultant, Derek Wells suggests recording temperatures in the service area during the summer.

"This will highlight any possible connection between high temperature days and returns, so precautions can be put in place."

Preventing heat stress on indoor and outdoor units follows the same principles.

Providing shade and increasing ventilation in housing is one precaution, says Fergus Howie, owner/manager of a 300-sow indoor herd at Wicks Manor Farm, Malden, Essex.

"Netting hangs over dry sows dunging areas and over the service area to provide shade and protect pigs against sunburn: Sows will not stand for boars when their skin is burnt," he says.

But there must be enough shelter to allow pigs to spread out, particularly on outdoor units, as heat will be produced when they have to huddle out of the sun, warns Mr Potter.

"In summer, all windows are taken out of the farrowing house in the morning to improve air flow. Apart from cooling, this also helps avoid disease build-up," says Mr Howie.

Richard Wright, manager of a 2200-sow outdoor herd at Brettenham Manor, Thetford, Norfolk, opens the back of all huts to allow a through draft and shade. Wallows are also crucial for pigs to cool themselves.

Wallows serve several purposes, says Mr Potter. "Mud acts as a sun barrier to the skin and body heat is lost through evaporation. But they must be big enough for pigs to sit in, must be prepared before hot weather and regularly replenished." Feeding, moving pigs and serving in cooler parts of the day will also help alleviate heat stress, but boars also become lazy in the heat.

Being overweight aggravates heat stress, so Mr Potter advises cutting feed for rotund pigs in the early spring.

Mr Wright reduces dry sow ration by 0.25-0.5kg in summer. Feed is not restricted in farrowing paddocks, but pigs will generally eat less in the heat, he says.

To add to infertility problems, pigs are naturally seasonal breeders. This is so they do not farrow in winter when feed is restricted under natural conditions. So late summer, when daylight hours decline, will generally see sows failing to cycle and boar libido and sperm quality reduced, says Mr Potter.

To counter boar infertility and laziness, many producers use AI to back up natural service. Mr Howie, who has used boars, but now uses AI, sees the benefits of using this method in summer.

Putting more gilts to the boar in order to maintain productivity levels when sows may stop cycling is a common practice, says Mr Potter. "But because of foot-and-mouth, producers may not have enough gilts to do this. Putting potential cull sows to the boar instead may not help, as they could have poor fertility anyway. So attention must be paid to reducing heat stress and improving mating efficiency." &#42

Mud, mud, glorious mud… It acts as both a sunscreen and a coolant – perfect for preventing heat stress.

SEASONAL INFERTILITY

&#8226 Rises in temperature.

&#8226 Pigs seasonal breeders.

&#8226 Ventilation and shade crucial.


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