Physiology and Endocrinology: Animal Physiology

Initiation of lactation and newborn piglet nursing ability are 2 factors that can influence preweaning mortality. We have developed the “immunocrit” that can assess both lactation initiation and neonatal piglet nursing ability based on the transfer of immunoglobulin G (IgG) from the sow to the piglet. To perform an immunocrit, 50 μL serum was mixed with 50 μL 40% ammonium sulfate, the mixture was loaded into a hematocrit capillary tube and centrifuged for 5 min. The result was the ratio of the mm precipitate to mm solution in the tube. To test the immunocrit, the smallest piglet in 205 litters was sacrificed, blood was collected and full and emptied stomachs were weighed to obtain the weight of stomach contents. Blood was analyzed for IgG by precipitation of serum samples with protein A-Sepharose followed by SDS-PAGE. Densitometry of the heavy chain of IgG was used to quantify IgG. To test use in cattle, blood samples from 96 calves were obtained 24 h after birth and IgG was measured (Bovine IgG radial immunodiffusion kit; VMRD, Inc.). Piglet and calf blood samples were also analyzed by immunocrit. For piglets, the correlation between densitometry and immunocrit values was 0.83. For calves, the correlation between kit IgG and immunocrit values was 0.90. Piglet immunocrit values were also correlated (r = 0.44; P < 0.01) with stomach contents at 24 h, indicating that immunocrits could be used to screen for piglet nursing ability. To assess the influence of immunocrit values on piglet preweaning survival, immunocrits were performed on every piglet in 48 1st and 68 2nd parity litters and survival to weaning was recorded. Preweaning survival was independently associated (P < 0.01) with birth weight of the piglet and immunocrit values. Second parity sows had greater litter average immunocrit values compared with 1st parity sows (0.133 ± 0.003 and 0.123 ± 0.004, respectively; P < 0.05). These results indicate that the immunocrit is a useful tool to monitor colostrum intake in piglets and calves.