Effects of zinc source and copper level on growth performance, fecal dry matter, plasma mineral concentrations, and apparent total tract digestibility of minerals in nursery pigs fed low acid-binding capacity-4 diets

The aim of this study was to evaluate the effects of Zn source and Cu level in low acid-binding capacity (ABC)-4 diets on growth performance, fecal dry matter (DM), plasma mineral concentrations, and apparent total tract digestibility (ATTD) of Zn, Cu, Ca, P, and nitrogen (N) in nursery pigs. A total of 360 weaned pigs (18 ± 1 d old; initially 5.7 ± 0.02 kg) were randomly allotted to one of six treatments, with 5 pigs housed in each pen and 12 pens per treatment, considering three initial body weight (BW) blocks. The experiment included three phases (d 0 to 10, 10 to 24, and 24 to 46). Treatments consisted of a 2 × 3 factorial with two Cu levels (18 or 150 mg/kg from Cu₂O) and three Zn treatments: low (150 mg/kg) or high (800 mg/kg) potentiated ZnO (pZnO) during phase 1 and 2, or pharmacological Zn from conventional ZnO (3,000 and 2,000 mg/kg in phases 1 and 2, respectively). In phase 3, dietary Zn was standardized to 150 mg/kg from pZnO, while Cu levels were maintained at 18 or 150 mg/kg from Cu₂O. The basal diets in phases 1 and 2 were formulated to ABC-4 levels of 199 and 248 meq/kg, respectively, whereas phase 3 diets were formulated without considering ABC-4 level (437 meq/kg). There were no Zn × Cu interactions or Zn effects observed for growth performance. However, pigs fed 150 mg/kg of Cu from Cu2O had greater average daily gain (ADG) in phase 3 (P = 0.021) and greater overall ADG (P = 0.049) and final BW (P = 0.048). Plasma Zn concentrations decreased below initial (d 0) levels on d 10 and 24 in pigs fed 150 mg/kg of pZnO. However, all plasma Zn concentrations, regardless of treatment, did not differ on d 46 after the common feeding period. Compared with 150 mg/kg of Zn from pZnO, pharmacological levels of Zn from ZnO resulted in greater fecal Zn excretion (P < 0.001) and lower ATTD of Zn (P = 0.03) on d 10, and greater fecal Zn excretion (P < 0.001) and a tendency for lower ATTD of Zn (P = 0.10) on d 24. In conclusion, in the absence of sanitary or diarrheal challenges, low levels of Zn from pZnO in low ABC-4 basal formulations maintained growth performance comparable to pharmacological Zn from ZnO. However, because Zn source, Zn level, and analyzed dietary ABC-4 differed among treatments, their individual contributions to the observed responses could not be separated.