Twenty-four new born crossbred (Bos indicus$\times$Bos taurus) calves were distributed in two equal groups and assigned to two different pre-starter diets with (Group 1) and without (Group 2) fish meal to study the effect of replacement of animal protein by vegetable protein in the diet and the age of animals on ruminal metabolic development. All calves were fed colostrum for 24 h and whole milk until weaning at 8 weeks of age. Rumen fluid samples were collected on 4 d, 1 wk, and then weekly interval up to 8 wk of age. Rumen fluid samples were analysed for pH, TVFA, lactic acid and N fractions (total N, total soluble N, trichloro acetic acid (TCA) soluble N, TCA precipitable N and ammonia N). Weekly feed intake and live weight gain pattern showed an increasing trend with the advancement of age, but were similar in both groups. The pH fell steadily during 0-4 wk of age and then stabilized in later period. A close relationship (r=0.80) between starter intake and TVFA concentration was observed in both the groups. Lactic acid (meq/l) and ammonia N (mg/dl) concentration showed initial rise (0.55 and 14.97 on day 4 to 3.38 (7 wk) and 32.85 (4 wk), respectively) to fall (2.74 and 17.60) again during 8 wk of age in response to increase in dry feed consumption (10% initially to 83% of diet dry matter at 8 wk of age). The TCA precipitable fraction of N did not show any change during 0-8 wk of age. Data indicate that the metabolic changes responded rapidly to dry feed intake which did not differ in fish meal and non-fish meal groups, and a poor voluntary consumption of oat hay retards the progressive changes in live weight and rumen microbial development.
Rumen;Calves;Metabolic Development;Animal Protein