VALIDATING LABORATORY TECHNIQUES THAT INFLUENCE ESTIMATES OF INTAKE AND PERFORMANCE IN BEEF CATTLE

Two experiments were conducted to evaluate effects of inoculum source on in vitro and in situ digestion procedures performed on grass hay and corn residue samples. Steers were fed 70% brome or 70% corn residue. Inoculum from each steer was used to perform in vitro procedures to determine IVDMD, organic matter digestibility (OMD), and neutral detergent fiber (NDF) digestibility and for in situ procedures to determine NDF digestibility. There were no interactions for inoculum source and IVDMD, OMD, or NDF digestibility. Three cattle digestion studies were used to evaluate the relationship between TDN and digested OM (DIGOM). Total tract collection and OM analysis of feed and feces were used to determine digested OM. Gross energy of feed and feces was determined using bomb calorimetry and used to calculate TDN. The difference between TDN and DIGOM was least (3.58 percentage units) for traditional corn diets. However, the difference between TDN and DIGOM was greater (9.96 percentage units) for diets containing wet distillers grains. n-Alkanes and long-chain alcohols were used as markers to delineate the parts of the corn plant and, separately, 8 western rangeland grasses and legumes. The corn plant parts were easily delineated with over 98% of the variation between variables described within a 2-dimensional plane with visible separation. The PCA for the 8 species of the western rangeland had less distinctive separation with only 90.5 or 93.2% of the differences described 2-dimensionally, depending on the growth stage. Plant waxes were utilized to predict dietary intake of 26 heifers that were individually fed a ration of 70% corn silage and 30% alfalfa with a daily dose of an internal marker. Predicted values of intake overestimated actual intakes, but improved if the diet was assumed to be a total mixed ration. A sensitivity test was conducted to examine the effects of incomplete dose consumption. Predictions were improved when accounting for losses in the amount of internal marker eaten, which likely occurred in practice. Advisor: James C. MacDonal