Effects of potentiated zinc oxide and crude protein levels in low acid-binding capacity diets on growth performance and mineral status in nursery pigs.

A total of 360 weanling barrows (DNA 200 × 400; initial BW 5.90 ± 0.03 kg) were used in a 38-d study to evaluate the effects of a potentiated zinc oxide (pZnO) and different crude protein (CP) levels on performance and mineral status. The diets were formulated with a low acid-binding capacity at pH 4 (ABC-4). Pens were randomly assigned to treatments while ensuring that mean initial body weight was balanced across dietary treatments: phase 1 (d 0 to 10), phase 2 (d 11 to 24), and phase 3 (d 25 to 38). All diets were formulated with low ABC-4 values. Treatments included a negative control (NC; 21.3% CP, 150 mg/kg Zn from pZnO), a positive control (PC; 3,000 mg/kg Zn in phase 1, 2,000 mg/kg in phase 2 from ZnO), and four experimental groups receiving pZnO at either 500 or 800 mg/kg in phase 1, and 300 or 500 mg/kg in phase 2, with or without CP reduction to 19.3% in phase 1 and 19.4% in phase 2 (pZ500, pZ500-LCP, pZ800, pZ800-LCP). In phase 3, all pigs received a common diet (21.2% CP, 150 mg/kg Zn from pZnO). During phase 1, pigs fed the pZ800 diet showed improved average daily gain (ADG), feed intake (ADFI), and gain-to-feed ratio (G:F; P ≤ 0.05) compared to NC. A linear dose-response effect of pZnO was observed for ADG, ADFI, and G:F (P < 0.05). From d 0 to 24 (experimental period), pigs fed low-CP diets (particularly pZ800-LCP) had poorer (P < 0.05) G:F than pigs fed higher-CP diets, despite similar or increased feed intake. Linear improvements in ADG and ADFI were observed with increasing pZnO (P ≤ 0.024). Across the trial, when pigs were fed 800 mg/kg pZnO, lower CP reduced (P < 0.05) G:F compared to pigs fed the pZ800 treatment. Pigs fed low CP diets had greater (P = 0.008) fecal dry matter content. Tissue and serum zinc concentrations increased (P < 0.05) with dietary ZnO. Pigs fed the PC treatment resulted in the highest serum and liver Zn levels at d 24 and 38, while liver manganese was significantly reduced in both PC and pZ800-LCP compared to NC (P < 0.05). Expression of zinc transporter ZIP4 was downregulated in PC and pZ800, whereas metallothionein and ZnT2 were upregulated in PC compared to NC (P < 0.05). In conclusion, potentiated ZnO at moderate concentrations maintained similar performance compared to pharmacological ZnO. Lowering crude protein levels, while improving fecal consistency, compromised feed efficiency, underscoring the importance of maintaining adequate amino acid supply in multifactorial feeding strategies.