Reducing dietary acid-binding capacity of low-zinc diets increased growth performance of weaned pigs in a commercial environment

To address post-weaning problems in piglets fed diets without pharmaceutical doses of zinc oxide (ZnO), the effect of reducing dietary acid-binding capacity (ABC) on weaned pig growth performance and diarrhea prevalence was evaluated. Immediately after weaning, 1,445 pigs [body weight (BW), 5.04 kg] were fed five test diets during phase 1 (d 0–7) and 2 (d 7–21), respectively. All pigs were fed a common diet during phase 3 (d 21–42). All diets were wheat and barley based. The dietary treatments included a high-Zn diet with pharmaceutical levels of ZnO (3000 mg/kg of Zn for phase 1, 2000 mg/kg of Zn for phase 2) and four low-Zn (150 mg/kg of Zn) treatments with gradually reduced ABC4 from 326 to 150 meq H+/kg for phase 1 and 364 to 202 meq H+/kg for phase 2. The gradual reduction of dietary ABC was achieved by replacing enzymatically-treated soybean meal with a low-ABC soy protein concentrate, replacing limestone with calcium formate, and adding formic and benzoic acid. All diets maintained a constant net energy (NE; 2.5 Mcal/kg for phase 1, 2.46 Mcal/kg for phase 2), standardized ileal digestible (SID) lysine (1.43% for phase 1, 1.37% for phase 2), and calcium (0.55% for phase 1, 0.6% for phase 2). Removing pharmaceutical doses of ZnO from weaned pig diets for phase 1 + 2 reduced (P < 0.01) average daily feed intake (ADFI) by 73 g, average daily gain (ADG) by 80 g, BW by 1.64 kg, and gain-to-feed (G:F) ratio from 0.786 to 0.712, and increased (P < 0.01) diarrhea prevalence by 1.9-fold during the first 21 days. Reducing ABC4 in low-Zn diets for phase 1 + 2 linearly increased (P < 0.05) ADFI by 17 g, ADG by 22 g, and BW by 0.44 kg from the high to very low ABC diet, and linearly and quadratically increased (P < 0.05) G:F that plateaued at 0.769 for the low-ABC diet. The diarrhea prevalence in phase 2 was linearly and(or) quadratically decreased (P < 0.05) due to the reduction of ABC4 for low-Zn diets. Overall (d 0–42), the ADFI, ADG, and final BW were reduced (P < 0.05) due to the removal of pharmaceutical ZnO supplementation. However, pigs fed low-Zn diets with reducing ABC linearly increased (P < 0.05) ADFI, ADG, and quadratically increased (P < 0.05) G:F. In conclusion, removing pharmaceutical ZnO supplementation reduced growth performance and increased diarrhea prevalence during the first 3 weeks after weaning. Reducing dietary ABC of weaned pig diets partly recovered the loss in growth performance and alleviated diarrhea prevalence.