The effects of pharmacological levels of zinc, diet acidification and dietary crude protein on growth performance on nursery pigs
Abstract This experiment was conducted to evaluate potential replacements for pharmacological levels of Zn (provided by Zn oxide), such as diet acidification (sodium diformate), and low dietary crude protein (CP: 21 vs 18%) on nursery pig performance and fecal dry matter (DM). A total of 360 weaned pigs (Line 200 × 400, DNA, Columbus, NE; initially 5.90 ± 0.014 kg) were used in a 42-d growth study. Pigs were weaned at approximately 21-d of age and randomly assigned to pens (5 pigs per pen). Pens were then allotted to 1 of 8 dietary treatments with 9 pens per treatment. Experimental diets were fed in two phases: Phase 1 from weaning to d 7 and phase 2 from d 7 to 21; with all pigs fed the same common diet from d 21 to 42. The eight treatment diets were arranged as a 2 × 2 × 2 factorial with main effects of Zn (110 mg/kg from d 0 to 21 or 3,000 mg/kg from d 0 to 7, and 2,000 mg/kg from d 7 to 21), diet acidification, (without or with 1.2% sodium diformate), and dietary CP (21 or 18%, 1.40 and 1.35% in Phase 1 and 2 vs 1.20% standardized ileal digestible Lys, respectively). Fecal samples were collected weekly from the same 3 pigs per pen to determine DM content. No 2- or 3-way interactions (P > 0.05) were observed throughout the 42-d study for growth performance; however, there was a Zn × acidifier × CP interaction (P < 0.05) for fecal DM on d 7 and for the overall average of the 6 collection periods. Reducing CP without acidification or pharmacological levels of Zn increased fecal DM, but CP had little effect when ZnO was present in the diet. From d 0 to 21, significant (P < 0.05) main effects were observed where average daily gain (ADG) and gain:feed (G:F) increased for pigs fed pharmacological levels of Zn, sodium diformate, or 21% CP (P < 0.065). In the subsequent period (d 21 to 42) after the experimental diets were fed, there was no evidence of difference in growth performance among treatments. Overall (d 0 to 42), main effect tendencies were observed (P < 0.066) for pigs fed added Zn or sodium diformate from d 0 to 21 whereas pigs fed 21% CP had greater G:F than those fed 18% CP. Pig weight on d 42 was increased by adding Zn (P < 0.05) or acidifier (P < 0.06) but not CP. In summary, none of the feed additives had a major influence on fecal DM, but dietary addition of pharmacological levels of Zn or sodium diformate independently improved nursery pig performance.