Particle size turns finishing-diet fibre into a meat-quality management variable

A finishing ration cannot be adequately described by its total fibre percentage alone. An update published by Michigan State University Extension on October 26 focuses on physically effective neutral detergent fibre (peNDF): the share of fibre whose structure and particle size promote rumination and help stabilise ruminal pH. For feedlot cattle, that makes particle size an operational variable rather than merely a nutritional one.

The reason is physiological. During rumination, cattle reduce particle size and produce saliva, which helps buffer ruminal pH. Two diets with a similar neutral detergent fibre concentration can therefore differ in intake, average daily gain, rumination time and acidosis risk. The source recommends use of the Penn State Particle Separator: the fraction retained above 4 mm is multiplied by the diet’s NDF content to estimate peNDF.

Reference values should not be treated as a single recipe. The synthesis cited identifies different targets depending on whether the criterion is performance, feed intake or reduced liver abscesses. More recent studies assembled by the university link higher peNDF with less daily time below pH 5.5; in those studies, about 9.5% peNDF corresponded with the threshold of 180 minutes per day below that pH. The sieve definition used is crucial when comparing recommendations.