Comparison of Microscopic and Pinitol Techniques in Determining Legume Composition of Steer Diets

Knowledge of botanical and chemical composition of herbage consumed by grazing livestock is essential in understanding animal performance and improving pasture and animal management. Esophageal fistula samples are considered to best represent cattle (ᴮᵒˢ spp.) diets, but current microscopic methods used to determine botanical composition are time consuming, expensive, and may be subject to large operator error. Pinitol (1-D-3-O-methyl-chiro-inositol) has been found unique to the leguminosae family and accurate in determining alfalfa (Medicago saliva L.) percentage in greenhousegrown alfalfa-tall fescue (Festuca arundinacea Schreb.) mixtures (R² = 0.99). Its utility in estimating the legume composition of esophageally collected grass-legume samples was compared to that of two widely used microscopic techniques. No significant differences were found between microscopic methods in pasture or hay aftermath of any treatments or dates. Sensitivity analysis showed no differences in the two methods related to their ability to detect dietary legume concentration changes in esophageal samples. Pinitol estimates of legume content were less (P<0.05) than those from microscopic estimates taken from orchardgrass (Dactylis glomerata L.) + legume [red clover (Trifolium pratense L..), birdsfoot trefoil (Lotus sp.), or alfalfa] pasture and hay aftermath, but not from nearly pure orchardgrass. The three methods provided similar estimates late in the grazing season when all values were low. With few exceptions the pinitol method underestimated legume composition of esophageal samples. In a separate experiment, the pinitol content of alfalfa, red clover, and birdsfoot trefoil extrusa after mastication and salivation was lower than that of unfed samples, suggesting that leaching may have been partially responsible for low estimates of legume composition by the pinitol metho