Site and extent of cell-wall neutral monosaccharide digestion in dairy cows receiving diets with ear and husk meal maize silages from three different stages of maturity

Abstract

In this study, the effect of stage of maturity of maize ( Zea mays L., cultivar ‘Felix’) on site and extent of cell-wall neutral monosaccharide (CWM) digestion in dairy cows receiving diets with ear and husk meal (EHM)-silages was investigated. Ears and husks were harvested at the early, soft and hard dough stages of maturity, respectively, chopped and ensiled. Three diets were formulated to contain (percentage of diet dry matter) EHM-silage (42%), grass hay (39%), soybean meal (17%) and mineral-vitamin mix (2%). Diets containing EHM-silages from the early, soft and hard dough stages of maturity were designated ED, SD and HD, respectively. Three lactating German Friesian cows equipped with ruminai, duodenal and ileal cannulae were used in a 3 × 3 Latin square design to evaluate apparent organic matter (OM) and CWM digestibilities in the whole-tract, and in the rumen, and in the small and the large intestines, respectively. Titanium (IV)-oxide and chromium ethylene diamine-tetra-acetic acid were used as flow markers. In all diets, glucose was more digestible in the whole-tract and in the rumen than xylose, the main hemicellulose constituent. Apparent wholetract digestibilities of OM (ED, 74.6%; SD, 71.8%; HD, 72.1%) and total CWM (ED, 78.1%; SD, 71.7%; HD, 73.7%) were higher with ED compared to SD and HD, but none of these differences were significant. Ruminal characteristics (pH values and NH 3-N) were not different among diets ( P > 0.10) and indicated similar conditions for rumen microbial CWM fermentation. However, apparent ruminal CWM digestibilities were higher with ED compared with SD and HD, and differences were significant ( P < 0.10) for glucose (ED, 72.2%; SD, 59.6%; HD, 61.3%), arabinose (ED, 85.2%; SD, 78.3%; HD, 74.8%) and mannose (ED, 84.1%; SD, 80.4%; HD, 81.3%). Apparent digestibilities in the small intestine (up to 7.6% for glucose with SD) indicated appreciable microbial fermentation in the ileum. Extremely negative apparent digestibilities (ED, −71.3% for arabinose) were also observed. Apparent OM, total CWM, glucose and xylose digestibilities in the large intestine were similar across all diets and constituents, ranging from 18.7 to 24%.