Effect of soy protein on intestinal absorptive ability of calves by the xylose absorption test

Five calves per group were fed whole milk (control) or one of three milk replacers with one-thrid of the total protein provided by a soy product. Soy products were Promocaf (a commercial soy protein concentrate), an experimental soy flour. After a 24-h fast, calves were fed xylose solution. Urine was collected for 5 h. Jugular blood was sampled at 0, .5, 1, 1.5, 2, 2.5, 3, 4, and 5 h after xylose administration. Xylose tests were weekly on each calf through 5 wk of age. Urinary xylose excretion, as a percentage of xylose fed, was higher in the control group during the last 4 wk than in groups fed milk replacers. Mean urinary xylose excretions during 5 wk from calves sampled 5 h after xylose administration were 12.4, 4.2, 4.2, and 4.3% of xylose administered for calves fed milk, soy flour, soy protein concentrate, and Promocaf, respectively. Mean increases in peak of xylose concentration in plasma were 55.7, 44.4, 42.8, and 45.3 mg/100 ml. Peak values for control calves were higher than those for calves fed soy products at wk 4 and 5. Times required to reach peak value did not differ significantly. Neither xylose concentration of plasma nor urinary xylose excretion differed among the groups fed soy products.