The effect of grinding and pelleting hay on digestibility, fermentation rate, digesta passage and rumen and faecal particle size in cows

Abstract

High-quality grass hay was either chopped (CH) or ground and pelleted (PH) and given to two rumen-fistulated cows at about the maintenance level. Digestibility in vivo was measured as well as neutral detergent fibre (NDF) rate and extent of fermentation in sacco. Solids and liquid marker excretions in faeces were measured after a pulse dose in the rumen of Cr-mordanted NDF and LiCoEDTA. A 3-pool model with lag was fitted to the data and retention times were calculated for individual pools and for the total digestive tract. Core samples were taken from the rumen three times daily for particle size analysis by wet sieving. Faecal and feed mean particle size (MPS) was determined. Pelleting lowered dry matter and NDF digestibility from 0.73 to 0.67 and from 0.79 to 0.68, respectively. Fermentation rate decreased from an average of 0.094 to 0.051 h −1 and the unavailable NDF fraction was increased from 0.23 to 0.37 by pelleting. Digesta liquid retention was unaffected by pelleting, but total solids retention decreased from 73 to 54 h. The effect of pelleting on retention in different pools varied between the animals. Rumen MPS was largest, and faecal MPS smallest, when feeding on CH. Hay PH gave the lowest MPS after evening feeding and the highest before morning feeding. The opposite was observed for CH. The decrease in fermentation rate, increase in unavailable fibre and decrease in rumen digesta retention are believed to be the main factors responsible for decreased digestibility in vivo.