Abstract Reducing dietary crude protein (CP) in nursery pig diets is a strategy to decrease post-weaning diarrhea (PWD), optimize feed costs, and reduce nitrogen excretion. One way by which high CP (HCP) diets increase PWD involve potentially cytotoxic proteolytic fermentation metabolites produced in the hindgut from unabsorbed proteins. Increasing dietary fiber fermentability with carbohydrase inclusion may mitigate this modality by shifting microbial fermentation towards carbohydrate substrate. To evaluate these interactions, a 3 × 2 factorial design assessed pig performance, nitrogen retention, hindgut fermentation, and health outcomes using high- and low- CP diets with or without a non-starch polysaccharidase (NSPase; xylanase). A total of 792 newly weaned 17 to 22- d-old mixed sex pigs (6.2 ± 0.12 kg body weight BW) were randomly allotted to three CP diets with or without NSPase (n = 12 pens/treatment), fed in three phases (10, 11, and 21 d). The CP and Lys per diet and phase were: 1) 16% CP containing 1.20, 1.15, and 1.10% standardized ileal digestible (SID) Lys per phase (LCP1.2); 2) 17% CP containing 1.40, 1.35, and 1.30% SID Lys (LCP1.4); 3) 24% CP containing 1.40, 1.35, and 1.30% SID Lys (HCP1.4). On d 10, one barrow per pen (n = 12 pigs/treatment) was moved to metabolism crates and fed at ∼5% of their average BW for 7 d on phase 2 diets, after which total fecal, and urine output were collected over a 4-d period for nitrogen retention analysis. On d 21, pigs utilized for metabolism evaluation were euthanized to collect intestinal tissue and luminal contents. The highest overall average daily gain and feed efficiency were observed in pigs fed HCP1.4 (both P 0.0001). During phase 1, a tendency for a diet × NSPase interaction on PWD incidence was observed (P = 0.063), as NSPase numerically decreased incidence in HCP1.4 pigs but increased it in LCP1.4 and LCP1.2 pigs; overall, HCP1.4 pigs had greater PWD incidence than LCP1.4 and LCP1.2 pigs (P 0.045). Pigs fed HCP1.4 diets observed increased nitrogen excretion and retention (g/d) when compared pigs fed either LCP diet (both P 0.001, respectively). Pigs fed HCP1.4 had the highest production of total volatile fatty acids (VFA, P = 0.027). Polyamines cadaverine and putrescine were unaffected by CP (P 0.05), but NSPase tended to reduce cadaverine production in all pigs (P = 0.079). Herein, pigs fed HCP diets observed improved performance concurrently with increased nitrogen excretion and PWD incidence.
Nisley et al. (Wed,) studied this question.