The objective of this study was to investigate the effects of conditioning time during pelleting process on performance, apparent digestibility, rumen fermentation, and blood metabolites of pre-weaned calves fed with pelleted starter diet. Thirty-six 3-d-old Holstein dairy calves (41 ± 0.5 kg of BW) were randomly assigned to one of 3 experimental diets: T1) starter without super- conditioning (Control); T2) starter with superconditioning at 85°C for 2 min; and T3) starter with super-conditioning at 85°C for 4 min. All calves were weaned on age 56 d and remained in the study until d 70 of experiment. Data were analyzed by GLM procedure of SAS (P < 0.05) using a completely randomized design with 12 replications for every treatment. Starter intake, feed efficiency and fecal score were not affected (P > 0.05) by super-conditioning time during the pre- or post-weaning periods, but average daily gain (ADG) significantly increased (P < 0.05) in calves fed with T3 during the postweaning period (0.92, 0.98 and 1.16 kg/d in T1, T2 and T3, respectively). The pH, ammonia nitrogen, total VFA and the molar proportions of acetate, propionate and butyrate were not different (P > 0.05) among treatments, but ammonia nitrogen (6.76, 5.81 and 5.44 mg/dL in T1, T2 and T3, respectively) and molar proportions of propionate (33.81, 36.12 and 39.72 mol/100 mol total VFA in T1, T2 and T3, respectively) were shown high tendency (P = 0.085) in calves fed with T3 during the post-weaning period. Body measurements were not affected (P > 0.05) by the treatments. The concentration of blood glucose and insulin was higher (P < 0.05) in calves fed with T3. Apparent digestibility of dry matter, starch, crude protein, NDF and ADF were not different (P > 0.05) among treatments during the pre-weaning period, but starch and dry matter digestibility during the post-weaning period were significantly increased (P < 0.05) in starter T3 (76.44, 78.83 and 79.59% for dry mater and 94.71, 96.63 and 97.4% for starch digestibility in T1, T2 and T3, respectively). Results of the present study indicated that enhancing of super-conditioning time from 2 to 4 min during pelleting process improved ADG and apparent nutrient digestibility in post-weaning period of dairy calves.

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