Decreasing the pH of milk replacer containing soy flour affects nutrient digestibility, digesta pH, and gastrointestinal development of preweaned calves.

We evaluated the effect of feeding soy flour-containing milk replacer (MR) with a lower than normal pH on growth, nutrient digestibility, digesta pH, and gastrointestinal development of preweaned calves. The study consisted of 48 neonatal calves, allocated to 8 treatments in a 2-factor 4×2 randomized design. The calves received 2 types of MR containing soy flour. The proportion of soy crude protein (CP) to total CP (SP/CP) in MR was 50% (MR50 treatment) or 80% (MR80 treatment), respectively. The pH of the reconstituted MR was decreased by 1 N HCl from to 6.2 to 5.5, 5.0, or 4.5. We measured body weight and dry matter intake and calculated feed conversion rate in the MR50 treatment. We monitored urinary and fecal pH consecutively for 5h when calves were 25d old. We also conducted a digestion trial to determine nutrient digestibility from 49 to 55d of age. At 63d old, calves were slaughtered, and gastrointestinal pH, mass index, and morphology were evaluated. Reducing the pH of MR containing soy flour improved average daily gain and feed conversion rate, increased Ca digestibility, and reduced urinary, fecal, and digesta pH in the rumen, reticulum, and omasum. Although treatments had no effect on gastrointestinal mass index, the pH 5.0 treatment led to favorable ruminal epithelium growth, and the pH 5.5 treatment led to better intestinal epithelium growth. Increasing SP/CP from 50 to 80% decreased P digestibility and fecal and digesta pH in rumen, reticulum, and omasum. Moreover, the MR80 treatment reduced the mass index of the abomasums and jejunum. In conclusion, decreasing the pH of MR containing soy flour to a pH of 5.0 to 5.5 improved the digestive tract of preweaned calves. A pH reduction to 4.5 had adverse effects on intestinal epithelium growth.