Nutrient selection by cattle from grass and grass/legume pastures

Abstract

Esophageal fistula and hand-clipped samples were collected from a 32-yr-old crested wheatgrass (Agropyron cristatum L.) pasture and an alfalfa (Medicago sativa L.)/meadow bromegrass (Bromus biebersteinii Roem & Schult.)/Russian wildrye (Psathyrostachys juncea [Fisch.] Nevski) pasture to compare estimates of nutritional quality. Samples were analyzed for crude protein (CP), in vitro digestible organic matter (IVDOM) and selected minerals. Fistula samples had greater (P < 0.05) CP and IVDOM contents than clipped samples at all times except that CP did not differ (P > 0.05) on two occasions and IVDOM did not differ (P > 0.05) on one occasion. Differences in mineral content between clipped and esophageal samples were less consistent, but when they occurred the mineral contents of esophageal samples usually exceeded (P < 0.05) those of clipped samples. We conclude that clipped pasture samples mostly provide biased estimates of the nutritional quality of herbage consumed by cattle grazing grass and grass/legume pastures and should be reported with caution.