Introduction
Growing animals use ascorbic acid for tissue development, as an antioxidant, and to reduce stress. The pig is one of the animal species that can synthesize the vitamin, but the timing of when this process begins and if supplemental vitamin C needs to be added to the pigs diet has been an area of controversy. Fetal tissue ascorbic acid concentration increases during gestation, but is this because of the synthesis by the sow and the subsequent transfer of ascorbic acid to the fetus or is it due to the synthesis by the developing fetus? Regardless of the mechanism, fetal pigs accumulate increasing amounts of ascorbic acid during gestation so that at birth their ascorbic acid status is at a high level. Consequently, pigs that are born earlier because of induced farrowings may have lower tissue ascorbic acid concentrations. Lutalyse is frequently injected in pregnant sows 1 to 3 days prior to farrowing in order to induce the birthing process in order to have uniform farrowing schedules. This process may reduce the neonates ascorbic acid content and compromise its survival. Because of farrowing stress, the neonate's ascorbic acid concentration has been shown to decline (Brown et al., 1972). Pigs that are born early in the birthing sequence may therefore have a different ascorbic acid status than these born later which could also affect their livability.
Upon weaning, the pig no longer receives ascorbic acid from the sow and thus becomes de pendent upon its own synthesis mechanism or it must have the vitamin added to the diet. Sow colostrum and milk have a high ascorbic acid content and therefore can provide the nursing pig with an ample supply of the vitamin.
The early research of Braude et al. (1950) concluded that from the increased serum ascorbic acid they observed in a set of early-weaned pigs that ascorbic acid synthesis was establilshed by about one week of age. L-gulonolactone oxidase is the enzyme found in the liver that has been used to evaluate ascorbic acid synthesis in the pig and other species but is missing in humans and guinea pigs. Measuring GLO activity in the liver would be a more accurate method in determining the age at which ascorbic acid synthesis begins rather than by evaluating tissue or serum ascorbate concentrations.
Our studies evaluated the synthesis of ascorbic acid during early fetal development through 42 day of age. We also evaluated the effect of Lutalyse injection, birth order, and weaning age on the rate of ascorbic acid synthesis in pigs.