Oxidative stress in high-producing transition sows' bodies affect sow milk yield and piglet performance

For decades, pig production has had a breeding goal of more piglets per sow. And they have been successful. 

This results in a sow whose body has to perform harder than ever – especially in the weeks around farrowing, when both foetal growth and colostrum and milk production place high demands on her metabolism.

A new study from the Department of Animal and Veterinary Sciences shows just how great that strain is.

What is oxidative stress?

The body's cells constantly produce so-called free radicals as a natural part of metabolism. Under normal conditions, they are neutralised by the body's own antioxidant defence system.

But when the production of free radicals becomes too high – or the defence is too weak – oxidative stress occurs, and the free radicals can instead damage cells, tissue and organs.

Assistant Professor Takele Feyera from the Department of Animal and Veterinary Sciences at Aarhus University uses an everyday image to explain it:

“You can imagine a free radical as a spark of fire, and an antioxidant as a firefighter. When there are only a few sparks, there is no problem, because the firefighter can control it. But if there are too many sparks and too few firefighters, that leads to damage. That's what we call oxidative stress,” he says.

This is the balance Takele Feyera and his colleagues have studied in 24 sows during the transition and lactation periods – from three days before farrowing to 17 days into lactation.

A paradox in feeding

The researchers took blood samples from the sows at five points and measured three indicators: malondialdehyde (MDA), which shows the degree of oxidative stress; creatine kinase, which indicates muscle damage; and haptoglobin, a sign of inflammation.

Their results showed that all three markers peaked at the same time – on day 3 of lactation.

This suggests that the sow's body is under the greatest strain right after farrowing, when milk production really gets going. According to Feyera, this reflects a basic mismatch in how sows are fed in the final weeks of gestation today:

“When sows come to the last 14 days of gestation – what we call the transition period – there's a very dynamic shift in the growth of the foetuses. But the paradox is that we're feeding the sows the same level from mid to late gestation, even though the nutrient demand is shifting a lot,” says Takele Feyera.

Large litters increase the burden

The study also showed two clear relationships. The larger the litter, the higher the sow's level of oxidative stress. And the higher the oxidative stress, the lower amount of milk she produces.

Sows with lower MDA levels produced more milk – those with higher levels produced less. Feyera points to a concrete example to illustrate why large litters put such a strain on the sow:

“In Danish sows, you can have a sow that gives birth to 9 piglets and one that gives birth to 37. If you give both of them the same three kilos of feed, you can see the imbalance – the sow with the large litter simply doesn't get what she needs from the diet, and she has to compensate the deficient from her own body. That predisposes her to oxidative stress,” explains Takele Feyera.

No fixed threshold – yet

There is currently no established threshold level at which oxidative stress in sows becomes a problem, which makes it difficult to know when intervention is needed to minimise the real cause for concern.

“There is no stated threshold – no clear-cut level that says: above this level is high oxidative risk, below this level is low oxidative risk. That's a knowledge gap in this field,” says Takele Feyera.

The researchers also stress that the current study was carried out on a relatively small number of sows, and that more research is needed before the findings can be translated into concrete threshold values.

Supplement produced heavier piglets – but not less stress

Feyera and his colleagues investigated whether a supplement plant extract made from Scutellaria baicalensis, known for its antioxidant properties, could dampen oxidative stress in sows. The project was made in collaboration with the company that provides the supplement.

The supplement showed promising positive effects: piglets were born heavier, and sows tended to produce more milk and have better litter survival.

But the supplement did not significantly reduce the sows' levels of oxidative stress or inflammation compared with the non-supplemented sows – a result that did not surprise the researcher:

“It didn't surprise me because research result does not always turn out as expected. We only gave the supplement from the last week of gestation, and there was no existing recommendation for the right dose – so it was really trial and error. For the farmer, I don't think a statistically significant difference is what matters most. If they wean one extra piglet, or a piglet that weighs one kilo more, that's a benefit for them,” says Takele Feyera.

Timing is critical

According to Feyera, the clearest practical message from the study is timing.

Oxidative stress rises gradually in late gestation, peaks early in lactation, and only falls once lactation is well established.

This means preventive measures should be started no later than the final week of gestation. Yet that is far from common practice today:

“Based on a previous collaboration, SEGES Innovation published a recommendation suggesting that farmers should adjust up the feeding level in the last few weeks of gestation, to help the sows farrow faster and have more piglets survive at birth. Similar recommendation could potentially be developed for feed additives with antioxidant properties if sufficient evidence supports their benefits. But generally, most farmers are not changing much,” says Takele Feyera.

Hopes for better dosing and technology

The researchers now hope to continue investigating how oxidative stress in sows can be prevented and managed.

According to Feyera, an obvious next step is to test several doses and sources of the plant supplement, to establish whether the positive effect on milk yield and piglet weight is real – and to understand the mechanism behind it:

“I would like to do a dose-response study, to see if this is really a true effect – or something that happened by coincidence. We're not just focused on production numbers; we want to understand the mechanism behind the effect,” says Takele Feyera.

Another challenge is that researchers simply do not know how many piglets a sow is carrying until after she has given birth, which makes it difficult to target feeding precisely during gestation:

“That is one of the most challenging parts of working with gestating sows – we scan and can see there are foetuses inside the uterus, but we never know exactly how many. If AI technology and computer vision could develop techniques to count the number of growing foetuses, that would a major breakthrough for both researcher and farm management,” says Takele Feyera.