Today’s sows are larger, leaner, produce more milk but have smaller appetites than sows a decade ago. Consequently, sows often loose too much weight during lactation. First-litter females seem to suffer the most, especially in terms of reduced milk production and subsequent reproductive performance.

The thing is, weight loss isn’t restricted to fat tissue, lean (or protein) tissue also disappears.

Canadian researchers Emma Clowes, Vickie Baracos and Frank Aherne, looked at various levels of protein loss in sows during lactation and the impact on production. They established a threshold level of protein loss and worked from there.

To test whether sow performance declines once a sow loses more than the threshold level of protein, the researchers fed first-litter sows an isocaloric diet during lactation in order to lose either:

1. Less than the threshold level of protein (Diet=868 grams crude protein and 49.6 grams lysine per day).

2. The threshold level of protein (Diet=650 grams crude protein and 34.8 grams lysine per day).

3. More than the threshold level of protein (Diet=519 grams crude protein and 25.6 grams lysine per day).

Sows fed to lose more than the threshold level of protein during the 24-day lactation lost more weight (-28.2 kilograms) than sows fed to lose either less than the threshold level of protein (-12.7 kg), or the threshold level of protein (-17.0 kg). The fact that there was no difference in backfat loss among treatments (-1.3 mm) strongly suggests that the difference in weight loss seen among treatments was mainly protein tissue.

Subsequent fertility declined in sows that lost more than the ‘threshold’ level of protein during lactation. They had 70 percent fewer medium-sized (4mm to 6 mm) follicles on the ovary at weaning.

While piglet and litter growth rate did not differ among treatments, milk protein concentration declined during late-lactation in sows fed to lose more than the threshold protein level. Also, litter growth rate declined in sows that lost more than 25 kg of live weight in lactation, or 12 percent to 15 percent of their lean body mass.

The researchers determined that limiting maternal protein loss during lactation ensures that first-litter sows will maintain milk production throughout lactation, and rebreed promptly and successfully after weaning.