The objective was to study the effects of partial replacement of soybean meal (SBM) with xylose-treated SBM (XSBM) as a source of rumen undegradable protein (RUP) in the starter concentrate of calves on performance, health status and selected blood metabolites. Twenty-one female Holstein dairy calves (body weight=39.6±2.3 kg) were randomly assigned to 3 groups (n=7 each): i) starter concentrate with 25% SBM [control (CTR)]; ii) starter concentrate with 17.5% SBM +7.5% XSBM (7.5XSBM); and iii) starter concentrate with 12.5% SBM+12.5% XSBM (12.5XSBM). Calves received 2 L of milk twice daily, with ad libitum access to starter concentrates from d 4 until weaning (d 56). Performance and health status were recorded throughout the experiment. Blood samples collected on d 4, 35 and 56 were assayed for concentrations of glucose, total protein (TP), and plasma urea nitrogen (PUN). Starter intake (560, 400, and 420 g/dfor CTR, 7.5XSBM, and 12.5XSBM, respectively), average daily gain (0.67, 0.6 and 0.57 kg/d), and feed to gain ratio (0.83, 0.67, and 0.74) were affected by treatments (P<0.05). Hearth girth, height at withers, body length, rectal temperature, faecal score, and respiratory score did not differ among treatments. Mean plasma glucose and TP were not affected by treatments, whereas PUN in the 12.5XSBM group was lower than in the other groups (P<0.05). In conclusion, the present results showed that partial replacement of SBM by XSBM may improve efficiency of dietary protein utilisation in pre-weaned calves, which warrants further studies.
