‘Whatever You Do, Don’t Underfeed’

Friday, September 25, 2026

When milk flows, piglets grow

By Geoff Geddes

They may turn up their snouts at juice and soda pop, but piglets love milk. That’s a good thing, as the sow’s milk is vital for growth. No surprise, then, that ensuring a proper supply is a key focus of producers and scientists. One authority in this area is Dr. Chantal Farmer, who presented some key findings at the 2026 Manitoba Swine Seminar.

“At peak lactation, sows produce more milk than cows on a per kilogram body weight basis,” said Dr. Farmer, research scientist in Swine Lactation Biology with Agriculture and Agri-Food Canada (AAFC) at the Sherbrooke Research and Development Centre.

“Yet, they are still not producing enough to meet the nutritional requirements of all their piglets, and this is even more prevalent with the hyper prolific sow genotypes. It is therefore imperative to develop novel strategies to assist sows in maximizing their milk output.”

As Farmer noted in previous research, the number of mammary epithelial cells present at the onset of lactation has a major impact on sow milking capacity and may be affected by nutrition. However, nutrition can affect mammary development during only three periods: from 90 days of age to puberty, in the last third of gestation, and during lactation.

“Consequently, increasing mammary development in the late gestation period using nutrition is one avenue of interest to improve sow milk yield in the subsequent lactation,” said Farmer.

In research, part of deciding what does work is finding out what doesn’t.

“Changing the energy intake or the source of energy fed is not a potential tool to stimulate mammary development of late-pregnant gilts and could even have a negative effect,” said Farmer. “As well, supplementing the diet of gilts with polyunsaturated fatty acids did not alter mammary development.”

The joy of soy

On a positive note, “recent findings show that feeding 40 per cent more lysine than current estimated requirements — by adding soybean meal to the diet of gilts from Days 90 to 110 of gestation — increased the mass of mammary parenchyma (tissue where milk is synthesized) by 44 per cent.”

The same effect was not present in multiparous sows, where feeding a soybean meal-supplemented diet providing 40 per cent more lysine than required did not impact mammary development on Day 110 of gestation.

While the latter might sound negative, the two lysine results demonstrate the critical concept that the nutrient requirements to fully support mammary development differ between parities, being greater in the first gestation. According to Farmer, this could be linked to the fact that pregnant gilts are still growing.

“It is therefore apparent that a phase-feeding regimen to provide more lysine (protein) in late gestation via additional soybean meal could be advantageous in the first gestation only.”

For studies like this to net meaningful findings for producers, the devil is in the details. Scientists thus took a comprehensive approach to some recent research, testing a range of diet/ lysine combinations.

Keen on lysine

“When gilts received supplementary lysine in that late gestation period starting on Day 90 and were subsequently allowed to farrow, we observed beneficial effects,” said Farmer. “Gilts were fed one of seven diets with lysine contents ranging from 70 per cent to 160 per cent of estimated requirements, using soybean meal to supply the additional lysine.”

Increasing lysine intake 15 per cent above the current recommendations maximized whole body nitrogen retention in late gestation, as well as piglet birth weight.

Whole body nitrogen retention is crucial for sows as it helps in preparing them for the demands of lactation.

Additionally, feeding lysine at 19 per cent above current recommendations maximized milk yield in the subsequent lactation.

For producers, this means that providing supplementary lysine in the diet of late-pregnant gilts may improve lactation performance.

“Interestingly, decreasing lysine intake below estimated recommendations in that same late-gestation period did not affect mammary development of gilts,” said Farmer.

When gilts received diets containing 18.2 g/day of SID lysine (estimated requirements), 12.4 g/day of SID lysine (22 per cent below requirements), or 14.6 g/day of SID lysine (34 per cent below requirements) from Days 90 to 110 of gestation, neither mammary tissue mass nor composition were altered.

“Therefore, at least in the short term, gilts appear to have the capacity to compensate for dietary deficiencies in order to sustain their mammary development,” said Farmer. “Hence, providing lysine up to 34 per cent below estimated requirements via soybean meal in late gestation had no immediate detrimental effect on mammary tissue.”

Weight watchers

For both pigs and people, the amount they eat directly affects their body condition, and this is especially important in gilts.

“The volume of feed offered to gilts in gestation can impact their mammary development through an effect on body condition,” said Farmer. “An early study showed that when altering body composition of gilts via changes in protein and energy intakes during gestation, obese (36 mm backfat) and leaner gilts (24 mm backfat) had similar weights of mammary tissue at the end of gestation, but the mammary tissue from obese gilts contained three times less cells that can synthesize milk.”

Of note, however, these body conditions are not representative of what occurs in a commercial setting. In keeping with the growing focus on real- world application of research results for the pork sector, two projects were carried out to establish if differences in body fat that are commonly seen in the industry can lead to changes in mammary development at the end of gestation.

“When gilts were fed different amounts of the same feed throughout gestation to achieve backfat thicknesses of 12–15 mm (lean), 17–19 mm (medium), or 21–26 mm (fat), lean gilts had a much-reduced mammary tissue mass,” said Farmer.

“These findings suggest that being too thin at the end of gestation is detrimental for mammary development. Personally, I’m thrilled to tell people that, for once, it’s not good to be lean.”

On the other hand, when backfat thicknesses that already differed at mating were maintained throughout gestation via varying feeding levels, mammary tissue mass was unaffected.

“These findings imply that feed intake during gestation is more important than body condition at mating to achieve the optimal backfat thickness to support mammary development in late gestation,” said Farmer.

“Whatever you do, don’t underfeed.” BP