PS1-14. Effects of Dietary Crude Protein and Added Zinc on Nursery Pig Growth Performance and Fecal Dry Matter

Abstract A total of 360 weanling pigs (DNA 241 × 600; initially 5.44±0.03 kg) were used in a 42-d trial to evaluate the effects of dietary crude protein (CP) and pharmacological levels of Zn from ZnO on nursery pig performance and fecal dry matter (DM). Pigs were balanced for sex, stratified by weight, and allotted to pens (5 pigs/pen, 12 pens/treatment) in a generalized randomized block design. Treatments were arranged as a 3 × 2 factorial with main effects of CP (low, medium, high) and Zn (110 or 3,000 mg/kg). Crude protein levels were 20.5, 22.0, and 23.5% in phase 1 (d 0–10) and 20.0, 21.5, and 23.0% in phase 2 (d 10–25), respectively. A common diet was fed during phase 3 (d 25–42) containing 20% CP and 110 mg/kg Zn. A CP×Zn interaction was observed (P = 0.035) during phase 1, where no evidence of a difference in G:F was observed with 110 mg/kg added Zn, whereas a quadratic response (P = 0.035) was observed for pigs fed 3,000 mg/kg added Zn with the medium-CP treatment having the lowest G:F. Increasing CP linearly decreased (P ≤ 0.047) ADG and ADFI, with no effect on G:F. In phase 2, increasing CP tended to decrease ADFI (linear, P = 0.063) and increase G:F (quadratic, P = 0.005) for pigs fed the medium-CP diet. Pigs fed pharmacological Zn had increased ADG (P = 0.034) and ADFI (P = 0.026) with no evidence of a difference for G:F. From d 0–25 (experimental period), increasing CP decreased ADFI (linear, P = 0.011) and tended to decrease ADG (linear, P = 0.100), whereas G:F tended to be optimal at medium CP (quadratic, P = 0.052). Pharmacological Zn improved ADG, ADFI, and G:F (P ≤ 0.002). During the common phase, pigs previously fed medium CP had the lowest ADG (quadratic, P = 0.018), and pigs previously fed increasing CP had decreased G:F (linear, P = 0.045). Pigs previously fed pharmacological Zn tended (P = 0.052) to have reduced ADG, with no effect on ADFI or G:F. Overall (d 0–42), pigs fed medium CP tended (quadratic, P ≤ 0.098) to have lower ADG and ADFI, while G:F was unaffected. Pigs previously fed pharmacological Zn tended (P = 0.066) toward greater overall ADG, with no differences in ADFI or G:F. A Zn×day interaction was observed for fecal DM (P = 0.015), where pharmacological Zn increased fecal DM on d 10 (P 0.001) and d 25 (P = 0.024), with a greater magnitude on d 10. Pharmacological Zn raised plasma Zn on day 10 and 25 (P 0.0001). While CP×Zn interactions were minimal; low-CP diets increased intake and gain, while pharmacological Zn improved growth in the experimental period with only a tendency for improved ADG for the overall trial period.