| Popis: |
The effects on rumen fermentation and blood metabolites when barley or cane molasses were offered as isoenergetic and isonitrogenous supplements at 610 g kg−1 of total dietary dry matter (DM) intake were studied in steers fed grass silage. Six rumen fistulated steers were used in a 2 (supplements) × 2 (periods, 28 days duration) cross-over experiment. The animals were offered 35.2 g supplement DM and 22 g silage DM kg−1 bodyweight0.75 daily at 08:30 and 16:30. Rumen fluid samples were collected from all animals on Days 27 and 28 of each period before the morning feed and 1, 2, 3, 6, 8, 9, 10, 14 and 24 h thereafter. Blood samples were collected from each steer on Day 26, before the morning feed and 1 and 3 h thereafter. Mean rumen pH (6.9 vs. 6.9), concentration of total volatile fatty acids (71.2 vs. 71.7 mmol−1) and molar proportion of propionate (15.8 vs. 16.6) were similar for both supplements. The molasses-based supplement resulted in a lower (P < 0.01) rumen concentration (mg dl−1) of ammonia-N (5.6 vs. 9.3) and l-lactate (26.2 vs. 49.3), and as proportions of total volatile fatty acids, lower (P < 0.01) acetate (58.4 vs. 66.5) and higher (P < 0.01) butyrate (23.0 vs. 14.0) than the barley-based supplement. Type of supplement did not affect the concentration of haemoglobin in blood. Plasma glucose concentration was higher (P < 0.01) before the morning feed and mean plasma urea-N was lower (P < 0.06) in animals offered the molasses-based supplement. Sampling time significantly affected all blood metabolites and rumen fermentation variables measured. It is concluded that under the conditions of this study, plasma glucose and urea-N concentrations and the pattern of rumen fermentation differed between barley and molasses-based supplements to grass silage. |
