Cross-fostering;  how to pick the right nurse sow and piglets

Sarah Mikesell, editor of The Pig Site working in collaboration with LifeStart Swine, recently spoke to Thomas Bruun, a senior swine specialist with SEGES Innovation. Bruun has worked at SEGES Innovation for 13 years and is based in Denmark. His research is focused on the impact of sow nutrition on milk production and sow metabolism as well as the nutrition of pre-breeding gilts on growth and subsequent reproduction.

Today's highly prolific sows can cause some significant issues in the nursery. One solution is cross fostering. Bruun recently conducted research on this topic that resulted in several practical on-farm applications.

Which sows are best suited for cross fostering?

“We need to take sow parity into consideration. We've done some studies in Denmark showing that if we use first parity sows as nurse sows, the preweaning mortality in the litter will be lower than using multiparous sows,” said Bruun. “However, if we use first parity sows, they will typically have a lower average daily litter gain that will result in a lower weaning weight of the litter.”

Bruun says he recommends using a young sow with easily accessible teats that’s able to take care of the new litter. It’s also important to consider the number of lactation days of the sow when selecting the nurse sow. Look for sows between four to eight days into lactation then move her piglets to another sow which will nurse and wean her piglets.

“She becomes nurse one sow – a sow, having at least 21 days of lactation due to legislation in Europe – then she will receive those 4-to-8-day-old piglets, and nurse them for an additional 14 to 17 days or slightly longer, then they're old enough to be weaned,” he said. “The newborn piglets, after ingestion of colostrum, should be moved to the nurse two sow that had already 4 to 8 days of lactation with her own litter.”

Considering the more practical side, Bruun says to never choose a sow with a very low body condition as a nurse sow because then the risk of shoulder ulcers will increase.

Which piglets should be moved to a nurse sow?

The most important aspect when choosing piglets for a nurse sow is to construct a very uniform litter, so the piglets should be close to the same size. A review of literature shows that every time you have a less uniform litter, the big piglets will survive, and smaller or lighter-weight piglets have a higher tendency to die.

“To construct a uniform litter, look at the excess piglets on that day and determine if you have a surplus of small or big piglets, then work with what you have that day and aim for uniformity,” he said. “Construct either a uniform litter of small piglets or big piglets after ingestion of colostrum. It’s really important to state that piglets must have enough hours with the birth sow to receive colostrum and their immunity after birth – for big piglets wait about eight hours before moving and for small piglets about 12 hours. Then, select the sow based on the piglet size. If piglets are small, choose a sow with smaller teats so the smaller piglets will be successful in suckling.”

As described in his published study, producers could alternatively use the three-step nurse sow program that's used on some Danish farms. Instead of having the step with the sow weaning their own piglets, nurse one sow at 21 days or more, and step two at four to eight days. Then add step three, that includes a sow that has just finished farrowing.

Figure taken from “Bruun et al. (2023): Selecting the optimal strategies when using nurse sows for supernumerous piglets. Molecular Reproduction and Development.

“Her own piglets have received enough colostrum to be moved to other sows, but she will still have some time remaining in the colostrum period, so you can move piglets in the very last litters to this sow to make sure the piglets get colostrum at a sow,” he explained. “Some publications show that the mother’s colostrum is the best, but to survive, colostrum from a neighboring sow is also close to being as good as from their own mother. So, that's the way of selecting piglets, construct a good, uniform litter that can be ready to be moved to another sow.”

Consequences of using a nurse sow on subsequent reproduction?

The consequence of using a nurse sow in subsequent reproduction is causing a big discussion, according to Bruun. It's been debated that the prolonged lactation period could be a problem due to welfare issues.

“Looking at the productivity level, I'm not concerned about the nurse sows. They might have a small delay in heat, but it doesn’t occur regularly. The delayed heat is mostly happening because they start cycling during lactation. This tells us they are in a good energy balance because otherwise they would not be cycling at weaning,” he said.

Bruun conducted a study in 2014 looking at around 80,000 farrowings with more than 15,000 nurse sows.

“The study shows that nurse sows gave birth to about 0.6 extra piglets in the subsequent cycle and the risk of being culled was also lower. But the culling part may not actually be the truth,” he explained. “When farmers are selecting nurse sows, they are typically selecting the best group of sows as nurse sows, so the risk of culling is naturally lower. It’s important to understand that if you’re a farmer who is good at selecting nurse sows and providing the proper feed management – maybe a feed reduction when receiving the new piglets and then quite rapidly back to the former feeding level – then you can actually use nurse sows with only benefits on the subsequent reproduction.”

The 2014 study also showed that the litter size by parity was the same in both groups. The nurse sows were not selected because they were bigger in litter size. They were chosen simply because they looked better.

“The farmers believed the sows chosen had the right body condition, good appetites and were already nursing nice piglets,” he said. “When you decide if a sow should be a nurse sow, body condition is important. She should already be nursing nice, good-looking piglets with a high litter size when you select her. Always aim for the good sows because they are ready to accept a new litter and to provide milk for some additional days.”

Farmers cannot always avoid using first parity sows as nurse sows. If that’s the case, do not select first parity sows with a low body condition score. Thinner sows will have a higher risk of delayed heat, and there’s a higher risk of problems developing with shoulder ulcers, either in the current parity or in the next parity.

“When we see farms that have very high success with these nurse sow strategies, they are weaning a lot of additional piglets,” he said. “There’s the number of piglets weaned at each sow, then you can add the proportion of piglets weaned as a nurse sow. We see Danish herds weaning more than 17.5 piglets per litter, so that's quite high and is due to the contribution from nurse sows alongside with the traditional lactation.


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