241 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 CP concentration with concomitant incremental inclusion of crystalline AA (CAA) does not decrease whole body N retention of sows during the last week of pregnancy compared with 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 in 2 replications. Gilts and sows were allocated to 4 dietary treatments in a completely randomized design. Diets were corn–soybean meal based and contained 2,650 kcal/kg NE. The percent 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 was 0.13, 0.25, and 0.38% for the Med, MedLow, and Low diets, respectively. Sows were fed 2.21 kg once per day in the morning, starting at d 95. Analysis of N balance was conducted from d 105 to 110 of gestation by complete urine collection and the dietary marker (titanium oxide) dilution principle to determine fecal N output. Data were analyzed using a mixed model of SAS (SAS Inst. Inc., Cary, NC) and contrast statements were used to compare the Med, MedLow, and Low diets with the control diet. Number of piglets born alive, numbers stillborn and mummified piglets, and total litter weight at birth did not differ between low-protein diets and the control. In gilts, compared with the control diet (43.0 ± 2.48), N retention (g/d) did not differ (P= 0.18) in the Med diet (38.2 ± 2.48), tended to be lower (P= 0.09) in the MedLow diet (37.0 ± 2.48), and was lower (P= 0.04) in the Low diet (35.1 ± 2.70). In sows, compared with the control diet (37.9 ± 2.09), N retention did not differ (P= 0.14) in the Med diet (33.5 ± 1.93) and was lower for the MedLow (27.55 ± 1.76; P< 0.01) and Low diets (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.