Description and effect of functional fibre in forages on rumen function, performance and health of UK dairy cows


Adequate dietary fibre content, in particular physically effective fibre (peNDF) and forage particle size (PS), is necessary to maintain a ruminal pH above pH 5.8 (through chewing saliva production) and to produce a rumen fibre mat to retain smaller forage and feed particles and increase their digestion.

On the other hand, a short chop length grass silage is often desired by farmers and contractors to improve compaction in the clamp and reduce aerobic spoilage at feed out. Also, too long a forage particle size promotes sorting in the feed passage, resulting in some cows receiving excess concentrates and others insufficient.

Accurate assessment of forage PS in dairy cow diets is difficult, and current feeding tables and nutritional programs do not include this important parameter. The currently available methods to assess PS and peNDF in the diet have been developed for drier North American diets based on lucerne and maize silage. These methods and recommendations may not be suitable for the wetter grass and maize silages commonly fed in the UK.

 Aims of the project

  • to characterize the PS and functional fibre content of grass and maize silages in a sample of 50 farms, and to determine the consistency of diet mixing and the extent of cow selection
  • to evaluate the effect of PS and functional fibre on rumen pH, fermentation, intake, performance and milk composition in dairy cows, and examine the interaction with level and rate of degradation of supplementary starch sources

 Key findings

  • The currently available methods and tools to characterize the particle distribution of UK diets are not suitable and require some modifications
  • Poor or moderate diet (TMR) mixing, sorting and absence of feed refusals are common findings on UK dairy farms
  • If the diet is correctly formulated and mixed, shortly chopped grass silages (within the shortest 5% fed commercially) can be fed with positive effects on performance and no adverse effects on rumen pH.
  • A short grass silage can be supplemented with high starch concentrates without adversely affecting rumen pH as long as
    • Cows are not fed high amounts of rapidly fermented starch such as wheat
    • the grains are not finely ground
    • the diet is well mixed and
    • there is no sorting activity

Completion Date
September 2018

Lead Investigator
Harper Adams University - Research Partnership study 

AHDB Dairy

View the summary report (link)

For further information please contact: or call 024 7647 8632

*This project is part of the Research Partnership between AHDB Dairy and SAC (Lead Contractor). Other subcontracted investigators and delivery partners within the Research Partnership are: Harper Adams University, SRUC, University of Reading.

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