Supplementary Lysine to Late-Pregnant Gilts Stimulates their Mammary Development

Increasing sow milk yield by stimulating mammary development - an initiative by Agriculture and Agri-Food Canada, Sherbrooke Research and Development Centre.

by Chantal Farmer

piglet feeding on mother's milk
Photo Credit: NARONG - stock.adobe.com

It is a known fact that sows currently do not produce enough milk to sustain the optimal growth of their litters. This is an area that is particularly important and challenging for pig researchers nowadays because the hyper-prolific genetic lines that were developed led to an even greater demand for sows’ milk.

The inadequate sow milk yield is a major problem for the hog industry, which makes it imperative to develop strategies that will increase the amount of milk available to suckling piglets.

One crucial factor determining a sow’s milking potential is the number of milk-synthesizing cells, hence mammary development, present at the onset of lactation (Figure 1).

sow eating and piglets feeding on sow's milk
Figure 1 Increasing sow milk yield via greater mammary development.

Rapid mammary development occurs at three distinctive periods during the life of a pig, and it is only during these periods that it is possible to stimulate it via nutritional or other strategies.

The first period of rapid mammary development is during pre-puberty - starting at approximately 90 days of age.

The second period takes place in late gestation - from 90 days of gestation until farrowing;

The third and last period occurs throughout lactation.

Of the three instances, nutrition in late gestation - the second period - appears to hold great promise to increase the number of milk-synthesizing cells before lactation starts.

More Lysine for Greater Mammary Development

Lysine is the first limiting amino acid in most swine diets, and it is most important during late gestation when the majority of fetal and mammary growth occurs.

However, the specific amino acid requirements to support the essential process of mammary development during that critical late gestation period are not known.

A recent project was undertaken at the Sherbrooke Research and Development Centre of Agriculture and Agri-Food Canada to determine the impact of a 40 percent increase in lysine intake of gilts from days 90 to 110 of gestation on mammary development.

To carry out this experiment gilts were fed 2.65 kilograms (~5.84 pounds) of either a conventional diet providing 18.6 grams/day (~0.656 ounces/day) of standardized ileal digestible (SID) lysine, representing the estimated lysine requirement for those animals or a diet that provided 26 grams/day (~0.917 oz/day) of SID lysine, being 40 percent greater than the estimated lysine requirement. Supplementary SID lysine was achieved via the inclusion of additional soybean meal in the diet.

Both diets provided the same amount of energy, and all other amino acids were at or above current recommendations.

On day 110 of gestation, gilts were euthanized to collect their mammary tissue for dissection and compositional analyses.

The results showed that feeding gilts a diet that included 26 grams per day of SID lysine increased the mass of milk-synthesizing tissue by 44 percent. On the other hand, the mass of the fat layer surrounding this tissue was not altered (Table 1).

chart comparing mammary gland composition on control diet vs high lysine diet
Table 1. Mammary gland composition of gilts fed a control diet versus a lysine-supplemented diet (HighLys) from days 90 to 110 of gestation.

The composition of milk-synthesizing tissue was generally not affected by dietary treatment, but greater total amounts of each of the components - such as protein, fat, DNA which is indicative of cell number, and RNA which is indicative of cell metabolic activity - were present due to the heavier tissue weight (Table 1).

These findings indicate that a greater uptake of lysine in supplemented gilts supported the enhanced growth of milk-synthesizing tissue. It is important to note that the beneficial effects of added soybean meal could have been due to an increased protein content or to greater concentrations of amino acids other than lysine and this is currently under investigation.

Data suggest that increasing lysine intake by 40 percent from day 90 of gestation until farrowing - as part of a two-phase feeding strategy - could benefit subsequent sow milk yield during lactation.

The Take-home Message

Results indicate that the current recommendations for dietary lysine during late pregnancy in gilts are underestimated.

The project demonstrated that by providing an additional 40 percent of dietary lysine to late-pregnant gilts with added soybean meal, swine producers will be able to stimulate the development of mammary tissue, thereby leading to better future milk production in sows. Such a novel nutrition practice will be of great benefit to the large litters of piglets that were developed in the swine industry.

Note that it is not known whether supplementary lysine in late gestation would also be beneficial for multiparous sows. To determine if that is the case a project is currently ongoing at the Sherbrooke Research and Development Centre and results should be available at the end of the year 2023.

Chantal Farmer

Chantal Farmer, Ph.D.; Research scientist / Swine lactation biology; Agriculture and Agri-Food Canada / Government of Canada