Abstract
A total of 360 barrows (initially 6.0 kg and 21 d of age) were used to evaluate the effects of added Zn in low acid-binding capacity at a pH of 4 (ABC-4) diets on nursery pig growth performance, fecal dry matter (DM), plasma Zn, and apparent total tract digestively (ATTD) of Zn. At weaning, pigs were divided into two body weight categories and then randomly assigned to dietary treatments in a generalized random block design. There were 5 pigs per pen and 12 pens per treatment. All diets contained 110 mg/kg of Zn from zinc sulfate in the trace mineral premix. The control treatment was a low ABC-4 diet (200 and 250 meq/kg from d 0 to 10 and 10 to 24 after weaning, respectively). In the next four diets, Zn (from zinc oxide; ZnO) was added at 500, 1,000, 2,000, and 3,000 mg/kg in phase 1, and 333, 666, 1,332, and 2,000 mg/kg in phase 2. The sixth treatment diet was formulated without considering ABC-4 (441 and 430 meq/kg from d 0 to 10 and 10 to 24, respectively) with 3,000 and 2,000 mg/kg of Zn from d 0 to 10 and 10 to 24 after weaning, respectively. In all periods, no differences were observed between pigs fed the low and high ABC-4 diets with 3,000 mg/kg Zn in phase 1 and 2,000 mg/kg Zn in phase 2, except for d-10 fecal DM, where pigs fed the low ABC-4 diet had increased (P = 0.002) fecal DM. From d 0 to 24, average daily gain (ADG) and average daily feed intake (ADFI) increased (linear, P < 0.05) with increasing dietary Zn, with no differences in gain: feed ratio. However, for the overall 46 d period, no response to dietary Zn was observed for any performance criteria. Zinc intake, absorption, and excretion increased linear and quadratically (P < 0.001) and ATTD of Zn tended to linear increase (P = 0.074) with increasing dietary Zn. Pigs fed the low ABC-4 diet had greater (P < 0.05) Zn intake, absorption, and ATTD of Zn than pigs fed the high ABC-4 diet at the same Zn concentration. No difference was observed for fecal Zn excretion between ABC-4 formulation strategies. Day 24 serum Zn concentration increased linear and quadratically (P < 0.001) as dietary Zn increased, and a marginal increase (P = 0.095) in the low ABC-4 diet was observed between formulation strategies. In conclusion, low ABC-4 diets containing 3,000 and 2,000 mg/kg of Zn from ZnO in phases 1 and 2, respectively, increased d 10 fecal DM, Zn absorption, and ATTD of Zn. Increasing Zn in low ABC-4 diets improved ADG and ADFI during the first 24 d post-weaning, but not for the overall study.