Impact of Feeding Reduced Dietary Crude Protein Diets with Crystalline Amino Acid Supplementation in Late Gestation on Nitrogen Balance of Sows

The objective of this study was to test the hypothesis that feeding pregnant sows once per day diets reduced in crude protein (CP) concentration with concomitant incremental inclusion of crystalline amino acids (CAA) does not decrease whole body nitrogen (N) retention of sows during the last week of pregnancy compared to sows fed a diet solely containing AA from feed ingredients. Two experiments were conducted, one with 28 pregnant gilts and another one with 25 pregnant multiparous sows (parity ≥ 3), each into 2 replications. Gilts and sows were allocated to 4 dietary treatments in a completely randomized design. Diets were corn-soybean meal based, and contained 2650 kcal/kg net energy. The % CP (analyzed) in diets were as followed for gilts and sows, respectively: 19.3 and 16.1 (control), 18.1 and 14.6 (Med), 16.1 and 12.6 (MedLow), and 14.2 and 11.6 (Low). Except for control diet, all diets contained CAA to meet the SID requirement for Lys, Thr, Trp, Met and Ile during d 100 to 114 of gestation. The additional crystalline lysine in both gilt and sow diets were 0.13, 0.25 and 0.38% for Med, MedLow and Low diets, respectively. Sows were fed 2.21 kg once per day in the morning, starting at d 95. Nitrogen balance was conducted from d 105 and to d 110 of gestation by complete urine collection and dietary marker (titanium oxide) dilution principle to determine fecal N output. Data were analyzed using mixed model of SAS and contrast statements were used to compare Med, MedLow and Low diet to control diet. Number of piglets born alive, stillborn and mummified piglets, and total litter weight at birth did not differ between low protein diets and control. In gilts, compared to Control diet (43.0 ± 2.48), N retention (g/d) did not differ (P = 0.18) in Med (38.2 ± 2.48), tended to be lower (P = 0.09) in MedLow (37.0 ± 2.48), and was lower (P = 0.04) in Low diet (35.1 ± 2.70). In sows, compared to Control diet (37.9 ± 2.09), N retention did not differ (P = 0.14) in Med (33.5 ± 1.93) and was lower for MedLow (27.55 ± 1.76, P < 0.01) and Low (27.52 ± 1.90, P < 0.01). Feeding once per day diets reduced in CP beyond 2 percentage units to pregnant gilts and sows decreases N retention.