Effects of dietary protein and rapidly fermentable carbohydrate contents on bacterial metabolites and intestinal microbiota composition in weanling pigs

Abstract Text: One hundred and eight barrows weaned at 21 d (5.82 ± 0.96 kg initial BW) were used to evaluate the effects of dietary crude protein (CP) and dried citrus pulp (DCP; rapidly fermentable carbohydrate source) contents on lactate concentration and bacterial counts in the hindgut digesta. Pigs were blocked by initial BW and randomly assigned to 4 treatments with 9 replicate pens per treatment and 3 pigs per pen in a randomized complete block design. Treatments were arranged as a 2x2 factorial, with 2 CP contents (HCP and LCP; high- and low-CP diets, respectively) and 2 DCP contents (0 and 7.5%, as-fed basis). The HCP treatments consisted of feeding 20 and 21% CP diets (as-fed basis) throughout the pre-starter I (1 to 14 d) and pre-starter II (15 to 28 d) phases, respectively. For the LCP treatments, CP contents were 16 and 17% for the pre-starter I and II diets, respectively. Dietary AA contents were balanced by supplementation with crystalline AA to maintain constant ratios in relation to standardized ileal digestible Lys. Cecum and colon digesta samples were collected from 1 pig per pen on d 7 and 28 postweaning for lactate determination by colorimetry and Lactobacillus and total coliform enumeration (TCE) using de Man, Rogosa, and Sharpe medium and Petrifilm coliform count plates, respectively. Statistical analyses were conducted using the MIXED procedure of SAS. No treatment x day interactions were observed (P>0.05) for all variables. Lactate production in the cecum was not influenced (P>0.05) by treatment. There was a CP x DCP interaction for colon lactate concentration (P=0.02), in which adding 7.5% dietary DCP increased (P=0.01) colon lactate concentration only for pigs fed the LCP diet. Lactobacillus count in both cecum and colon was not affected (P>0.05) by treatment. There was also a CP x DCP interaction for TCE in the colon (P=0.02) and cecum (P=0.05). Added DCP decreased (P=0.04) TCE in the colon of pigs fed the LCP diet (3.24 and 1.47 log₁₀ cfu/g for 0 and 7.5% DCP, respectively), and tended to increase (P=0.08) TCE in the cecum only for pigs fed the HCP diet (2.76 and 4.37 log₁₀cfu/g for 0 and 7.5% DCP, respectively). In conclusion, adding 7.5% DCP in low-protein AA-supplemented diets inhibits the proliferation of harmful bacteria in the hindgut, thus enhancing intestinal health of piglets. However, those positive effects are not observed when feeding diets higher in protein.

Keywords: intestinal health, lactate, piglets