Performance and digestion by calves from limestone added to milk replacers containing soy protein concentrate.

Sixteen male Holstein calves were fed milk replacers containing milk protein or 50% of the protein from soy protein concentrate for study of limestone as a buffer in the small intestine. Experimental diets were: A) 19% of crude protein as milk protein; B) same as A but containing .8% limestone; C) 19% crude protein, 9.5% milk protein, and 9.5% soy protein; and D) same as C but containing .8% limestone. Milk replacers were reconstituted with water to 14% solids and fed at 8, 9, 10, 11, 12, and 12% body weight from 1 to 6 wk of age. Calves were fed twice daily, and clean fresh water was available at all times. Soy protein concentrate in the replacer resulted in 20% lower weight gains, lower dry matter and protein digestibilities. Apparent crude protein retention also was reduced, but intake of nutrients, feed efficiencies, fecal scores, and rectal temperatures were not different between protein sources. Limestone did not change any of these measurements. Xylose absorption tests at 3 and 6 wk of age showed differences from age but not treatment. Analysis of digesta from different sections of the gut of 6-wk-old calves sacrificed 6 h after feeding revealed that pH throughout the small intestine was above 6 for both proteins, which may explain the ineffectiveness of added limestone. Compared to milk protein, soy protein concentrate produced a lower pH in the large intestine and feces.