A striking difference between pig farms in the U.S. and EU is the preferred body condition for gestating sows. Everyone who has walked through a gestating sow barn in the U.S. will attest that sows tend to be on the lean side. In contrast, a similar farm in Europe — using similar genetic lines, if not the same — will have gestating sows leaning towards the overweight side. Obviously, there is a misunderstanding that needs a clarification.
Talking with many pig farmers, nutritionists and veterinarians in Europe, I realized they strongly believe a well-fed sow will produce a heavy litter and she will then continue milking well. Let’s examine this position in detail.
First, an overweight lactating sow milking off her backfat wastes feed. Indeed, it is very inefficient to convert feed energy to body lipids and then to milk energy (about 50 percent total efficiency, or half the energy eaten is lost). Instead, it is more economical (energetically) for the lactating sow to use energy from the feed to make milk (about 80 percent efficiency).
Second, an overweight gestating sow almost invariably has difficulty giving birth. This often results in prolonged intervals between births and several pigs that would normally be born alive end up being stillborn due to lack of oxygen during the birth process. Thus, litters tend to smaller.
Third, heavier litters can be produced, by overfeeding during gestation, only when sows are emaciated. In other words, normal sows will not benefit from extra feed (or any other form of increasing energy intake, such as high-fat diets).
Fourth, an overweight sow entering lactation always has reduced appetite and, as a consequence, will produce milk at the expense of her body fat reserves. This often leads to emaciated sows that lose condition very rapidly. As a result, not only milk yield is diminished, but such sows take longer to come to heat and their subsequent litters are usually small.
I have always suggested keeping sows on a lean condition. On a scale of 1 (emaciated) to 5 (very fat), gestating sows should be kept at a body condition around 3 or 3.5. This is not an easy task, but there are methods that can ensure the target is met and sow productivity is at maximum with the least possible cost.