Effects of Dietary Protein on Nitrogen Balance, Reproductive Performance, Colostrum and Milk Compositions, and Blood Immune Characteristics of Sows

Abstract An experiment was conducted to test the null hypothesis that there are no differences in nitrogen balance, reproductive performance, and blood immune characteristics between sows fed low- or high-protein diets. Two diets for gestating sows and two diets for lactating sows were formulated. Diets were based on corn and soybean meal (SBM). Within each phase of production, one diet was a high-protein diet and corn and SBM were the sources of protein, whereas the other diet was a low-protein diet that contained less SBM, more corn, and crystalline amino acids. A total of 193 gilts and sows were randomly allotted to the two gestation diets on the day of breeding in a randomized complete block design with eight blocks. Ninety of the 193 sows were housed in metabolism crates from days 45 to 57 of gestation. Feces and urine were quantitatively collected for five days. Sows were moved to the lactation unit on d 105 and fed lactation diets. Blood, colostrum, and milk samples were collected, and pigs were weaned on d 20 after farrowing. The statistical model included diet as fixed effect, and block and replicate within block as random effects. Results indicated that daily nitrogen intake, 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 (Table 1). However, nitrogen retention (% intake) was not different between treatments. Rectal temperature 24 h after farrowing of sows fed the low-protein diet was greater (P 0.05) compared with the high-protein diets. Number of live born and total born pigs was not different between treatments, but sows fed the high-protein diet tended to produce less (P 0.10) mummified pigs than sows fed the low-protein diet. Litter weights at birth and weaning were not different between treatments. 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. Serum interferon-gamma (tendency, P 0.10) and interleukin (IL)-4 (P 0.05) were greater, but IL-2 tended to be reduced (P 0.10) in sows fed 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 the low-protein diet, but no differences between treatments for colostrum fat and milk somatic cell count. In conclusion, feeding a low-protein diet to gestating sows decreased daily nitrogen retention. Reproductive performance was not affected, but feeding a high-protein diet resulted in better milk composition and immune characteristics compared with feeding a low-protein diet.