Impact of dietary carbohydrate balance on rumen fermentation, eating behaviour, growth and development of 8–10-month-old heifers

Abstract

The present study was undertaken to determine an optimal balance between the amount of physically effective fibre and rumen readily fermentable carbohydrates in the diets of heifers. The dietary carbohydrate balance index (CBI) was expressed as the ratio of physically effective neutral detergent fibre (g/kg of DM) to rumen degradable starch (g/kg of DM). Twenty-four Chinese Holstein heifers aged ~8 months were randomly divided into four groups of six. The length and content of Chinese wild-rye hay and the content of rumen degradable starch in diets were used to adjust dietary CBI, and treatment diets consisted of the following four CBI levels: 1.21 (Treatment A), 1.53 (Treatment B), 1.86 (Treatment C) and 2.29 (Treatment D). The feeding trial lasted 75 days, with 15 days for adaptation. DM intake of heifers was not influenced by different treatments (P > 0.10). Average daily gain of heifers varied (0.86 ± 0.10, 1.03 ± 0.06, 1.12 ± 0.08 and 0.98 ± 0.04 (mean ± s.d.) kg/day among groups respectively), with significant (P < 0.05) differences among treatments, but the initial and final bodyweight of heifers were not different (P > 0.10). In addition, the abdominal girth of heifers in Treatments C and D was significantly (P < 0.05) greater than that in Treatment A. With the increment of CBI, eating and chewing time increased significantly (P < 0.05), while eating frequency decreased significantly (P < 0.05). Rumen fluid pH increased significantly (P < 0.05) with the increasing of CBI level, while there was little difference in total volatile fatty acid concentration, and propionate, butyrate and valerate concentrations. Acetate concentration was significantly (P < 0.05) higher in Treatments C and D than in Treatment A. Moreover, ammonia-nitrogen concentration of Treatments B and C was significantly (P < 0.05) higher than that of Treatment D. These results indicated that 1.86 is the optimal CBI in diets for 8–10-month-old heifers in the present study.