The objective of this study was to determine the effects of partial replacement of soybean meal with extrudedin starter on performance characteristics of dairy Holstein calves. Forty five calves were assigned in a complete randomized design to 1 of 3 treatments; 1) control (starter feed with hay), 2) control plus 25 percent extruded soybean and 3) control plus 50 percent extruded soybean. Calves received milk in trial fixed and equal to 10% of BW/D (half in the morning and half in the evening). At birth, all calves were fed enough amounts of colostrums daily for the first 3 d. All calves had free access to water and starter feed. All calves were weaned at d 56. The starters were formulated to Isonitrogen, Isocalory and isoenergitic. All calves were weaned 56 d. The study finished when calves reached 70 d old. Calves were individually housed. Diets and water were fed ad libitum throughout the trial. Feed intake and body weight Measured weekly. Ruminal pH, ammonia and nutrient digestibility were measured at 6, 8 and 10 weeks. Fecal scoring calves daily and these structured growth indices, recorded at weaning age and at the end of the experimental period. Experimental data were analyzed by repeated Measurement with the MIXED procedure of SAS (SAS version 9.1, SAS Institute Inc., Cary, NC. Results showed that, starter intake had a significant effect among treatments. Control treatment had a greater starter intake than other treatments during pre-weaning and entire experimental period (P 0.05) while calves consuming 50 percent extruded soybean in their starter feeds has lower intakes than others Average daily gain and feed efficiency had not affected by treatments. Calves fed control had lower OM and nutrient digestibility compared calves fed 25% and 50% extruded soybean (P 0.02).Fecal scour, fecal pH and rectal tempture were not affected by treatment. Calves fed 50% extruded soybean had more blot than other treatment (P 0.05), but disease, diarrhea and pneumonia were not significant difference between treatments. In conclusion, replacement of extruded soybean as a protein source had no beneficial effect on performance except of some cases structured indices of dairy Holstein calves. Keywords: Holstein calves- extruded soybean - starter- performance.
