Short communication: Diet digestibility measured from fecal samples and associations with phenotypic and genetic merit for milk yield and composition

摘要

Selection for improved feed utilization is of highinterest globally but is limited by the high cost of obtainingfeed intake for individual cows and relies onindirect measures of feed efficiency. Supplementingselection with mechanistic measures of feed use couldmake selection for feed utilization more direct and effective.The objectives of this study were to evaluatefecal sampling as a method of determining digestiveefficiency of individual cows and to evaluate associationsof digestive efficiency with genetic and phenotypicmerit for milk yield and composition. Fecal sampleswere obtained manually from the rectum of 90 Holsteincows in the morning, afternoon, and evening on a singledate and composited across the day. The fecal sampleswere dried, ground, and stored. Diet and fecal neutraldetergent fiber (NDF) were determined using the filterbag method, and indigestible NDF was determined insitu with a 12-d rumen incubation. Fecal NDF (60.1%)and indigestible NDF (41.9%) were higher than thatfrom feed samples (14.2 and 35.9%, respectively). Total-tract digestibility was calculated using the markerratio method. Total-tract dry matter (DM) digestibilityaveraged 66.0 ± 2.4% and total-tract NDF digestibilityaveraged 42.8 ± 3.0%. Higher milk fat percentand genetic merit for milk fat percent were associatedwith greater NDF and DM digestibility. Milk yield wasnegatively associated with NDF and DM digestibility.Fecal sampling is a feasible method to directly measuredigestive efficiency, and substantial variation wasobserved among cows. Given significant between-cowvariation and associations with milk fat percent andgenetic merit for milk fat percent, potential selectionfor total-tract NDF digestibility estimated via fecalsampling warrants further exploration.