Effect of drying method on the nutritive composition of esophageal fistula forage samples: influence of maturity

Abstract

Researchers continue to oven- and air-dry extrusa samples from esophageally fistulated animals, despite evidence that this practice leads to erroneous nutritional evaluations. Two studies were conducted to determine how method of drying affects the nutritional composition of esophageal extrusa collected from sheep and goats browsing forage at different stages of maturity. In trial 1, extrusa collected from free-ranging sheep and goats in Northeast Brazil from July to April was freeze- or oven-dried (40 degrees C) and analyzed for neutral detergent fiber (NDF) and lignin (L). NDF and L were artificially elevated (31-93%) in oven-dried extrusa collected from January to April when forage was immature. No differences were observed in the fiber content of oven- and freeze-dried extrusa collected during the dry season (July-December). In trial 2, Dactylis glomerata, Medicago sativa, Acer grandidentatum and Purshia tridentata were hand-harvested and fed to esophageally fistulated sheep. Extrusa was either freeze-, air- or oven dried (40 degrees C) and analyzed for hemicellulose, cellulose, L and in vitro organic matter digestibility (IVOMD). Hemicellulose and L concentrations were significantly increased in air- and oven-dried forage for all plant species. Cellulose was least affected by method of drying. IVOMD was depressed most by oven- and air-drying in species containing phenolic compounds. When there were significant treatment by period interactions, method of drying was most critical early in the growing season. Results reemphasize that freeze-drying extrusa is an important preliminary step to obtain accurate nutritional information.