| Forty-eight Chinese Holstein bull calves (BW40±0.2kg) were used and supplemented with four concentrations (0,3,6and9g/d) of supplemental isobutyric acid to evaluate the effects of different isobutyric acid supplementation on body weight, size, rumen fermentation and ruminal cellulolytic bacteria of different growth period in Chinese Holstein bull calves. The results showed that:the weight of rumen, reticulum, omasum, abomasums and total stomach increased with the growth of bull calves and increasing supplemental level of isobutyric acid. At90day-old, the weight of rumen increased significantly in all groups. At120day-old, the weights of rumen in6g/d and9g/d group were higher than3g/d and control group(P<0.05). The percentage of rumen and omasum also were increased (P<0.05). At120day-old, the percentage of abomasum in6g/d and9g/d group were lower than3g/d and control group (P<0.05). The ratio of rumen, reticulum and omasum to body weight were increased significantly, whereas isobutyric acid level had no significant effect on the ratio of reticulum weight to body weight (P>0.05); The length of small intestine was increased significantly but there was no significant effect on the length of ileum (P>0.05). The body weight, body height, body length, the chest circumference and the rump length in bull calves were increased significantly(P<0.05). At120day-old, the body weight in6g/d and9g/d group were higher than3g/d and control group(P<0.05). At90day-old, the body length in6g/d and9g/d group were higher than3g/d and control group3g/d and control group (P<0.05). At120day-old, the body length in9g/d group were higher than3g/d and control group (P<0.05), but there were no significant effect than6g/d group(P>0.05). The supplementation of different level isobutyric acid had no effect on ruminal pH, the NH3-N concentration, propionate and isovalerate concentration (P>0.05). At90day-old, ruminal total volatile fatty acids, acetate, butyrate and valerate concentration in groups supplemented isobutyrate at9g/d and6g/d were higher than that of in group supplemented isobutyrate at3g/d and control group significantly (P<0.05). At120day-old, the concentration of isobutyrte in treatment groups were higher than control group significantly (P<0.05). At the beginning of experiment, the quantitative expression of ruminal cellulolytic bacteria of different growth period in Chinese Holstein bull calves in all groups have no significant different. At60day-old, quantitative expression of Ruminococcus albus also have no significant different. With the bull growth, quantitative expression of ruminal cellulolytic bacteria increased significantly. At90day old, the quantitative expression of Ruminococcus flavefaciens and Fibrobacter succinogenes in groups supplemented isobutyrate at6g/d and9g/d were higher than of3g/d and control groups. The quantitative expression of Butyrivibrio fibrisolvens are the highest bacteria of the four ruminal cellulolytic bacterias. These results indicated that the optimum dose of isobutyric acid supplementation was6g/d. |
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