Reducing dietary crude protein for gestating and lactating sows reduces daily nitrogen retention, but reproductive performance is not impacted by diet protein concentration

Abstract Background Soybean meal (SBM) is a primary protein source in swine diets, but partial replacement with crystalline amino acids (AA) is commonly used to reduce dietary protein. Adequate dietary protein and energy are essential to support fetal development, milk production, and litter growth. However, crystalline AA are absorbed more rapidly than AA from intact protein, which may limit protein synthesis due to a lack of AA availability. Therefore, an experiment was conducted to test the hypothesis that feeding sows diets based primarily on corn, SBM, and no crystalline AA will result in improved reproductive performance and immunity of sows compared with sows fed diets with less SBM and more corn and crystalline AA. Results Nitrogen excretion in feces and urine, absorbed nitrogen, and retained nitrogen (g/d) were greater ( P < 0.05) in gestating sows fed the high-protein diet compared with sows fed the low-protein diet. Rectal temperature 24 h after farrowing of sows fed the low-protein diet was greater ( P < 0.05) compared with sows fed the high-protein diet. Number of live-born and total born pigs was not different between treatments, but sows fed the high-protein diet tended to produce fewer ( P < 0.10) mummified pigs than sows fed the low-protein diet. Malondialdehyde was greater ( P < 0.05) in sows fed the low-protein diet, but serum glutathione peroxidase and white blood cell count were greater ( P < 0.05) in sows fed the high-protein diet. Colostrum immunoglobulin G and concentrations of fat, protein, urea nitrogen, lactose, and immunoglobulin G were greater ( P < 0.001) in milk from sows fed the high-protein diet than in milk from sows fed the low-protein diet. Conclusions Feeding a low-protein diet to gestating sows decreased daily nitrogen retention. Reproductive performance was not affected, but feeding a high-protein diet without crystalline AA resulted in greater concentrations of fat, protein, and lactose in milk and improved immune-related characteristics compared with feeding a low-protein diet.