Techniques for determining intake by grazing animals

Vita.Available forage and esophageal samples of Coastal bermudagrass were obtained at three different periods (December, January and May) and evaluated for factors affecting their nutritive value. Esopageal and ruminally fistulated Angus x Hereford heifers were grazed separately to facilitate fecal collections. Esophageal and fecal samples were analyzed on a daily basis for each animal in every trial to evaluate daily variation. Although relatively large variation occurred in the quantity of available forage both within and between pasture means, variation in in vitro digestibility of organic matter (IVDOM) and crude protein (CP) was comparatively smaller. Animals selected material approximately 7, 8 and 10 percentage units higher in IVDOM than was found in available forage in the December, January and May trials, respectively. This higher IVDOM of esophageal samples was due to a higher proportion of more digestible leaf (Trial 1, IVDOM 40%; Trial 4, IVDOM 62%) to less digestible stem (Trial 1, IVDOM 36%; Trial 4, IVDOM 48%) in esophageal as compared to available forage during each collection period. A comparison of the various techniques to estimate organic matter digestibility of grazed forage revealed that IVDOM of esophageal extrusa was the least variable method (overall standard deviation 3.4%). Digestibility values estimated from indigestible neutral detergent fiber were numerically similar, but more variable (overall standard deviation 5.5%) than IVDOM. Digestibility estimates based on chromogen (overall standard deviation 5.5%) yielded similar values to IVDOM in periods when high concentration of chromogen occurred in esophageal samples, but erratic digestibility values occurred when low concentration of chromogen existed.