Pig producers looking to maintain optimum herd fertility should consider the effects of prolonged hot weather on semen quality, be it in natural service boars or artificial insemination packs.
According to BPEX’s Helen Thoday, heat stress can significantly reduce semen viability in boars used for natural service.
“When daytime temperatures are maintained at 24C for a sustained period of time, semen production can become affected and can remain poor for eight weeks after temperatures return to normal.”
To prevent this, natural service systems should consider using artificial insemination, she says. “In these conditions, it is worth buying in semen rather than taking the risk.”
Many systems will have a central holding area which could be adapted for service, but when this is not available, a square baled, walled tent with a barred gate can be set up relatively easily.
“Temperature-controlled boxes used for vaccines can also be re-set to 17C to transport semen for AI,” she says.
“It is well worth the hassle – boar serve is 50% of the total outcome. When semen quality is poor, you will experience low litter sizes up to three months after the summer.”
And this in itself will affect subsequent sow performance and have significant financial implications. “When a sow produces a poor litter, she won’t come into heat as well and will have poorer subsequent litters.”
Hotter weather brings so many challenges on farm that boars are often overlooked, says Annie Davis, The George Vet Group.
“However, boars can be as much of a contributor to summer infertility as sows. Hot weather not only causes poor libido, but also results in poor semen production a few weeks later. “
However, boars should still be allowed to work up to a certain extent, says Miss Thoday.
“Load requirement should be reduced so boars are used as chaser animals and not on weaned sows.” Keeping them mating will maintain their ability to work and will also clear out heat-affected semen.
Individual boars will react in individual ways to heat, but it is always good practice to rotate boar packs regularly, says Ms Davis.
There is still use for natural service bulls, even in the hot weather, Miss Thoday continues. “It is good management to let boars run with served sows for 6-8 weeks after service as hormone interaction between sow and boar can help maintain pregnancy.”
To improve comfort, boars should be provided with wallows, shades and straw day beds. “In AI systems, work teaser boars early in the morning and change them more regularly during hot weather to reduce the chances of heat stress.”
Those farmers AI-ing should also consider the hotter weather when handling semen, says Ms Davis.
“We talk a lot about keeping semen warm during the cold months, but allowing semen to get too hot in the summer is just as damaging.
“Semen should be transported from fridge to sow in insulated boxes. Do not leave them in the tractor – temperature rises when semen packs are exposed to hot weather can be dramatic.”