effects of starter protein levels and amounts of milk fed on animal health and rumen microbiota changes in holstein male calves

The aim of this study was to investigate the effect of two different levels of starter protein and amounts of milk fed on animal health, fecal score, immune responses and microbial population in the rumen of holstein male calves. two levels of starter crude protein (17 and 20% of starter dry matter (dm) and two levels of milk fed (7 and 10% of body weight) were combined in a 2 × 2 factorial experimental design. forty newborn male holstein calves (initial body weight 40±2 kg) were used for 75 days. feeding the colostrum was performed immediately after birth for 3 days. every calf consumed the probiotic mixture of protexin and saccharomyces cerevisiae via milk (2 g/day). water and calf starter were offered free choice. individual fecal score was measured daily. ‌results showed that starter intake and weight gain were affected by days of age (p<0.05). but, there were no interactions between starter protein levels and amounts of milk fed on starter intake and weight gain (p>0.05). starter protein levels, amounts of milk fed and their interactions had no effect on protozoa population, fecal consistency, general health score (ghs) and number of days with diarrhea (p>0.05). there were significant interactions between amounts of milk fed and starter protein levels on bacteria population (p<0.05). also, amounts of milk fed and starter protein levels did not affect fecal fluidity, but interaction between them was significant (p=0.046). by increasing starter protein levels, the numbers of bacteria and protozoa decreased and increased, respectively. the effects of starter protein levels, amounts of milk fed and their interactions on immune response of calves were not statistically significant.