Effects of Diet Fed During Backgrounding in Drylot on Ruminal Function of Cattle During Adaptation to Pasture1

This experiment was conducted to determine the effects of type of diet fed in drylot on the changes in the ruminal environment and in situ forage DM disappearance during adaptation from drylot diet to vegetative pasture. Sixteen ruminally cannulated steers were used in a randomized complete block experiment (BW = 535 ± 3.6 kg in Block 1 and 333 + 3.2 kg in Block 2). Eight steers were assigned to four treatments in each block: ad libitum bermudagrass hay with either a dry supplement (DS) or a molasses-based supplement (MBS) or limit-fed a high-concentrate diet with either a dry-protein supplement (LFDS) or molasses-based protein supplement (LFMBS). Kentucky-31 tall fescue forage was incubated in situ 24 h on grazing d-1, 0, 3, 6, 9, 14, 20, and 27. Ruminal contents were collected at 0800, 1200, 1600, and 2000 h on grazing d -1, 3, 9, 16, and 23 for pH, ammonia, and VFA analyses. Ruminal acetate:propionate (A:P), pH, and DMD were less (P<0.05) for limit-fed steers than steers fed hay on d-1. Across treatments, the A:P and ruminal pH were less (P<0.01), and ruminal ammonia concentrations were greater (P<0.01) on d 16 than on d 9. This variation in ruminal parameters indicated that unstable ruminal environment caused the impaired forage DMD observed on d 14, 20, and 27. Limit feeding high-concentrate diets in drylot appears to allow cattle to adapt to grazing high-quality forage diets as readily as feeding hay-based diets.