Date of this Version
Published in Proceedings, Western Section, American Society of Animal Science (2009) 60:
Reductions in forage intake can influence the extent of ruminal degradability of protein and supplemental fats can reduce forage intake. Therefore, the effects of supplemental flax oil on in situ disappearance of soybean meal was evaluated utilizing six ruminally cannulated beef cows (Initial BW = 639 ± 30.2 kg) grazing bromegrass pasture. Cows were given 287 g (DM basis) of soybean meal and randomly assigned to one of three treatments that were 0, 3, or 6% dietary flax oil. Supplements were dosed intraruminally at 0730 daily for 28 d. In order to confirm that the level of flax oil fed reduced forage intake, masticate was collected from each cow and TiO2 was dosed twice daily starting on d 13. Then on d 22, in situ bags (50-μm pore size) containing 5 g of soybean meal were inserted into the rumen and collected at 0, 3, 6, 9, 12, 15, 18, 24, and 48 h after insertion. Effective ruminal degradation was estimated using a combination of this experiment’s non-linear regression data and previously determined fluid passage rates. Despite a numerical decline in forage intake ranging from 10,144 to 8,219 g/d as dietary inclusion of flax oil increased, no differences (P ≥ 0.29) were observed across treatments. Total tract digestion (g/d) and digestibility (% of intake) of DM, N, and NDF did not differ (P ≥ 0.14) with the exception of total tract NDF digestibility, which tended (P = 0.06) to decrease linearly with flax oil inclusion. In situ N disappearance was not different (P ≥ 0.18) at 0, 3, 6, 9, 12, 15, 18, and 48 h incubation times. However, N disappearance tended (P = 0.13) to increase linearly at 24 h. Nitrogen fractions A and B did not differ (P ≥ 0.54) with level of flax oil. Likewise, no differences (P ≥ 0.26) in ERD ruminal degradability of N were observed. Overall, supplemental fat fed at levels reported herein were not sufficient to alter the ruminal disappearance of soybean meal when cows grazed brome grass pasture.