Date of this Version
In beef cattle productions systems, feed costs accounts for the majority of production costs. In year-round grazing systems, knowledge of diet quality is important for supplement formulation and predicting animal response in order to meet production goals without increasing feeding costs. The objectives of these two trials were: to develop a set of feed standards to use in in vitro laboratory procedures to estimate in vivo digestibility of forages, determine the effect of moisture, day, and grazing level on diet quality, and develop prediction equations to estimate diet quality using the variables moisture, day and grazing level. Trial 1 used 8 crossbred yearling steers to determine in vivo digestibility of 5 chopped hays (Malf, Ialf, Mbrome, Ibrome, and prairie). Feces, feed, and feed refusals were analyzed for DM, OM, CP, NDF, IVDMD and protein fractions. Feed samples were included in 21 separate IVDMD runs and regressed against the in vivo digestibilities. As hay digestibility increased DMI increased (P < 0.01). Slopes of the 21 regression equations did not differ; however, there were differences between the individual IVDMD runs. In vivo and in vitro digestibilities were correlated and the average for all 21 runs was r = 0.831. In trial 2, diet samples were collected using esophageally-fistulated cows from pastures varying in grazing pressure from May 2003 through November of 2005 in the Nebraska Sandhills. Diet samples were analyzed for CP, IVOMD, NDF, and protein fraction. In Vitro OMD was adjusted to in vivo digestibility using the regression equations generated from the hay standards within each run. Diet digestibility and CP were used in a series of multiple regression equations to predicted diet quality using the variables moisture, day and grazing pressure. Diets were higher in CP and OMD during the growing season and remained constant during the dormant season. Predicted digestibility and protein were correlated to observed values.