Recent variation in litter size as a result of last year’s early autumn infertility could make sows more susceptible to lactational oestrus, according to Jennie Batt, Larkmead Vets.
“This year we are seeing greater variation in litter size across all parities with an increase in the number of pigs with litters of just four to five piglets.”
And less piglets could mean sows are not pushed to produce milk and could begin cycling early.
A sow coming into oestrus during her time in the farrowing paddock interrupts the service cycle and can lead to sow being out of sync with the rest of the group in batch systems, explains BPEX’s Helen Thoday.
And because sows coming into oestrus during lactation in a batch system are likely to be culled, it’s important to prevent it occurring.
To prevent sows from developing lactational oestrus, it is essential sows are pushed, says pig technologist Mark Hawe.
“When sows are suckling small numbers and not being pushed to produce milk, it is better to wean early and get her cycling, rather than run into problems later on.”
Poor performing cull sows can also be weaned early and her piglets used to boost the litter size of better quality animals, says Mrs Batt who recommends having litters of about 10 piglets.
And when grouped penned sows are displaying signs of lactional oestrus, it is important to split these animals off as soon as possible, she says.
“When penned together, a pig displaying signs of heat may set other animal off in the pen. Therefore, individual paddocks are better at confining the problem.”
Although it’s likely a sow will display unusual heat during the hotter months when the suckling pattern is disrupted, for example when a sow leaves her piglets to wallow, in reality, lactational oestrus is more commonly seen from December to April, says Miss Thoday.
Pig producers should aim to reduce the potential for lactational oestrus during the winter months by recognising the risks and managing accordingly, she says.
“Although not proven, it is presumed improving light levels and higher energy diets could be a cause of unusual oestrus at this time of year. The majority of cases are seen in outdoor pig units, as sows are more openly affected by environmental stimuli,” she says.
The higher level of piglet mortality during the cold weather could also be a key influence, reducing litter sizes further.
When litter sizes are reduced, diets should be modified to cater for fewer piglets, says Miss Thoday. “Diets should be tailored to suit individual sows – sows may need more in colder weather, but when milk requirements are less, diets should be modified accordingly. The key is to understand energy requirements are a scientific equation and keep re-visiting it to account for litter size and environment.”
Boar contact should also be limited to prevent the onset of abnormal oestrus, she says. “Keep boars away from farrowing paddock fence lines, as the stimulation can contribute to inducing oestrus.”
However, producers should ensure signs of oestrus during lactation are actually lactational oestrus and not “pseudo heats”, says Mr Hawe.
“Some mycotoxins can result in sows displaying signs associated with heat, including reddening of the vulva, so ensure poorly stored grain is not the root of the problem.”