The present study was conducted to evaluate the effect of different levels of tomato pomace powder (TPP) on growth performance, ruminal fermentation and health of Holstein calves. Experiment was carried out based on a completely-randomized design with 3 treatment groups including 10 individual pens per each dietary treatment (5 male and 5 female Holstein calves) until 70 days of age. Dietary treatments consisted of 1) pelleted starter (control group), 2) pelleted starter + 7.5% TPP, 3) pelleted starter +15% TPP. Inclusion of different TPP levels in starter diet hadn’t any significant effect on daily dry matter intake, feed conversion ratio and average daily gain throughout the trial period. Also, using 7.5 and 15% TPP in starter diet had no marked impact on body conformation indices including hip depth and height, breast and abdomen perimeter, wither height and body length at the end of trial period. Dietary inclusion of TPP in starter ration had no effect on fecal score at pre- and post-weaning periods. The highest number of leukocytes allotted to the calves fed on 15% TPP diet, which was significantly (P 0.05) different from control calves, but not from 7.5% TPP group. Moreover, the highest proportion of lymphocytes was observed in calves fed on 15% TPP-supplemented diet that was different (P 0.01) with other treatment groups. The highest (P 0.05) lymphocyte to neutrophil ratio was seen in calves supplemented with 15% T however, there was no significant difference between control and 7.5% TPP calves for lymphocytes proportion and lymphocyte to neutrophil ratio. The contrast comparisons (control versus TPP-fed calves) indicated that dietary inclusion of TPP had no marked effect on feeding behavior including chewing, eating and licking. No significant difference was seen among dietary treatments for rumen ammonia nitrogen at the end of trial period, however, the highest (P 0.05) pH value was assigned to 15% TPP-supplemented calves at both 35 and 70 days of age, which wasn’t different from calves on diet containing 7.5% TPP. Dietary inclusion of TPP had no significant effect on concentrations of acetate, propionate, butyrate and total volatile fatty acids at the end of trial period. At days 35 and 70 of age, dietary treatments hadnt the significant (P 0.05) effects on serum concentrations of triglycerides and low-density lipoproteins, respectively. Similarly, serum high-density lipoproteins and cholesterol were not affected by experimental diets at both 35 and 70 days of age. The present findings indicated that although TPP had no marked effect on growth performance of dairy calves, however, could improve immune system and blood lipid profile Keyword : Dairy calf, Tomato pomace, Growth performance, Ruminal fermentation, Immunity, Health
