Glucose metabolism in reproductive sows

Glucose is an important energy source for sows throughout the production cycle. It directly affects oocyte maturation, glycogen deposition in the fetal piglet during gestation and it is a precursor of lactose and therefore important for milk production. In this paper the effects of glucose metabolism on performance of gestating and lactating sows are discussed. The developing fetus and the uterus rely on glucose as their main source of energy. Studies have shown that increasing the level of starch in diets of gestating sows can increase birth weight of piglets and possibly also affect vitality in new born piglets. At the end of gestation, the fetuses grow fast and the sow develops a reversible insulin resistance, in order to increase the glucose transport to the fetuses. Glucose transport can be increased because during this period of insulin resistance, lowering insulin sensitivity results in higher blood glucose levels for a longer period of time. Studies have shown that insulin resistance in sows can be affected by e.g. the dietary fatty acid profile. Possible effects of other dietary nutrients such as protein need further investigation. It has been shown that piglet survival, especially of the lighter piglets within a litter, can be improved by feeding medium chain triglycerides to gestating sows. Increasing insulin resistance, however, seems to have a negative effect on piglet survival. In contrast to other species that maintain insulin resistance during lactation in order to stimulate glucose transport to the udder, insulin resistance in sows only seems present during the end of the gestation period. However, glucose requirements of the lactating sow are high as it is the main precursor for lactose. About 140 grams of glucose is required to produce 1 liter of milk. Higher levels of starch in the lactation diet result in a higher milk production with a higher lactose content but lower fat and energy contents. Piglet gain, however is improved. These positive effects of starch are the result of a higher level of available glucose. The level of dietary glucose has been also found to affect sow reproduction. Increasing the level of glucose in the sow diet during the weaning to oestrus interval positively affects litter size and within-litter variation. At present is not clear how glucose affects reproduction, but the general thought is that it acts via insulin. In conclusion, dietary glucose is of importance throughout the entire reproductive cycle of the sow. Therefore, requirements for glucose in the modern sow during each of the different stages of the reproductive cycle should be further studied.