Acid Insoluble Ash as a Marker of Digestibility for Sheep Fed Corn Plants or Hay and for Lactating Dairy Cattle Fed Hay Ad Libitum

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Abstract
Research has shown acid insoluble ash (AIA) in feeds to be an acceptable natural marker for the determination of dry matter digestibility in sheep and steers fed diets of hay plus grain. However, in previous studies, animals were fed diets designed to ensure little or no orts. The purpose of this study was to determine the adequacy of AIA as an indicator of dry matter digestibility when sheep or dairy cows were fed ad libitum. Fecal, feed and ort samples from wethers and lactating Holstein cows from previous digestibility studies were used to determine the usefulness of AIA as an indicator of digestibility. Thirty-two wethers were fed whole corn plants or corn stover frozen and stored fresh or ensiled. Diets were fed ad libitum to ensure between 5 and 10% orts. In a second study, seven wethers and 10 lactating cows fed fed ad libitum alfalfa or orchard-grass hay diets with 23% grain to ensure at least 10% orts. Correlation coefficients for digestibility determined by total collection versus AIA for wethers fed corn plants, cows fed hay diets and wethers fed hay diets were .96, .95 and .40, respectively. The low correlation for wethers fed hay was apparently due to a high quantity of orts with a variable AIA content. The range of total recovery of AIA from all animals was 98 to 102% when ort AIA was taken into account, and 91 to 121% when ort AIA was not taken into account. The use of AIA as a natural marker for the estimation of digestibility when diets are fed ad libitum has potential, provided that a sufficient number of animals is used and diets are adequately mixed to limit feed selection and sorting, or intake is determined and feed and orts are sampled. Copyright © 1981. American Society of Animal Science . Copyright 1981 by American Society of Animal Science.