Effects of ruminal SCFA concentration and pH on intestinal digestibility and digesta pH of dairy calves

     

Although the importance of pH and short-chain fatty acids on rumen development are well known, their impact on the small and large intestine are unclear. This study investigated the effects of ruminal short-chain fatty acid concentrations ([SCFA]) and pH on the rumen and intestine of calves. Holstein bull calves (n = 32) were individually housed and fed milk replacer (900 g/d) twice daily and calf starter and water ad libitum. At 10 ± 3 d of life, the rumens were fistulated and cannulated. At 21 d of life, calves were grouped by body weight and assigned in a 2 × 2 factorial arrangement of treatments: high or low [SCFA] (285 vs. 10 mM) and high or low pH (6.2 vs. 5.2), forming 4 treatment groups: high [SCFA], high pH (HH); high [SCFA], low pH (HL); low [SCFA], high pH (LH); and low [SCFA], low pH (LL). On wk 3, 5, and 7, feces were sampled for digestibility analysis, after which the rumen was evacuated and washed for 4 h with 1 of 4 treatment buffers. After completion of rumen wash on wk 7, calves were harvested, and the tissue weight and length, and digesta pH of the rumen, cecum, colon, and rectum were recorded, along with the digesta pH of duodenum, jejunum, and ileum. Data were analyzed with main factors as fixed effects and repeated measures for weekly measurements. Body weight and calf starter intake were unaffected by treatments but increased over time (P < 0.01). Digestibility was unaffected by treatments and weeks. High [SCFA] increased milk replacer intake by 255 g (P < 0.05). Fecal pH on wk 3 was lower than wk 7 (P < 0.05) and tended to be lower than wk 5 (P = 0.09). Rumen digesta pH on wk 3 was higher than on wk 5 and 7 (P < 0.05). Duodenum and jejunum digesta pH was higher for HH than LH (P < 0.05). Ileum digesta pH was higher for HH and LL than LH (P < 0.01). High [SCFA] increased colon and rectum digesta pH (P < 0.01) and tended to increase cecum digesta pH (P = 0.06). In summary, although ruminal [SCFA] and pH impact intestinal digesta pH within hours, the rumen digesta pH reduction did not decrease fecal pH, digestibility, and BW gain.

Key Words: Digestibility, rumen pH, rumen SCFA, digesta pH.