Before the advent of highly prolific breeding stock, it was common practice to let first-litter sows suckle a maximum of 10 piglets in order to minimize their weight loss during lactation. With a lower feed intake compared to older sows, gilts are vulnerable to excessive weight loss, leading to an extended wean-to-estrus period and lower litter size in the second parity. However, as litter size has become larger due to genetic advances, not only has this strategy become impractical, but it has been shown to be counterproductive.
In Denmark, where average litter size is well over 14 pigs born alive, it is normal to let gilts suckle 14 piglets. The reasoning is that if teats are suckled in the first lactation, they will be more productive in the second and subsequent lactations. Recently published Canadian research not only supports the Danish practice, but has shown that piglets prefer to suckle a teat that was suckled in a previous lactation.
A research project carried out by Chantal Farmer and Nicolas Devillers at the Dairy and Swine Research and Development Centre in Sherbrooke, Que., involved two groups of gilts which suckled their piglets in different ways. In one group, piglets suckled the same teats in both first and second lactations and in the other group they suckled different teats. This was achieved by taping over some of the teats to make them non-functional. For the gilts’ first litter, all but six teats were taped over and piglets in both treatments suckled exactly the same exposed teats on their own mother. In the second lactation, one group had the same teats taped over, while the other group had the teats that were suckled in the first lactation taped over. In addition to regular weighing of the piglets, video recording was used to observe piglet suckling behaviour and establish the piglets’ degree of hunger. Piglets were weaned at 17 days and continued to be weighed until 56 days of age.
“The results of the trial showed that while birth weights were identical, piglets suckling the same teats in the first two lactations were 1.12 kg heavier at 56 days,” noted Farmer. “A difference in piglet weight gain was observed as early as days two to four of lactation, which suggests that colostrum yield, and not only milk yield, might also differ between the two groups.”
The researchers found that functional mammary glands suckled for two lactations contained more milk-secreting tissue than those which were not suckled in the first lactation. This tissue also had more cells with a greater metabolic activity.
“Sows with the same teats used in both lactations consumed more feed during lactation in parity two than sows with different teats being used, which is in agreement with their greater milk yield,” said Farmer. “Behavioural measures also indicated a greater degree of hunger on day three for piglets using teats that were not previously suckled, which corroborates the lower weight gain in these litters.”
More specifically, she said, piglets from litters with different teats used in the two lactations massaged the teat longer after milk let-down and had a greater incidence of fights so that they missed more nursings.
The trial results led to the question as to whether piglets can differentiate between a teat that was suckled in the previous lactation and a teat which was not used previously. In a second project, teats were sealed in first lactation as described earlier, but in the second lactation none of the teats were sealed and eight piglets were left with the sow, so that eight piglets were present with only six previously used teats.
“Amazingly, piglets could tell the difference between previously used and unused teats,” said Farmer.
“There was a greater incidence of fights which lasted longer at teats which were previously used. There was also a greater incidence of these teats being suckled by the piglets.”
The magnitude of the difference in 56-day weight between the two treatments indicates this research cannot be ignored by producers. With litter size continuing to increase each year, the gilt’s suckling capacity is valuable and should not be underutilized by limiting the number of piglets she suckles. Being able to maximize the number of piglets on the gilt and get the benefit of higher milk production in subsequent parities is a useful bonus.
However, it still leaves the challenge of getting enough feed into first-parity sows to avoid a detrimental loss in weight. Increasing the lysine level in the lactation diet to about 1.2 per cent total lysine is one strategy that has worked well on some farms. The Danish technique of using gilts as foster mothers is also worth considering as it helps to reduce the metabolic load during the lactation period. The gilt’s own litter is weaned early — in Denmark about 20 days — and a litter of seven-day old piglets placed on her. The demand for milk drops sharply, while the gilt continues to eat the same amount of feed, which allows her to recover any weight loss by the time she is weaned after a total lactation length of about 35 days.