With current research around feeding functional fibre in the dairy cow ration largely based on US studies, Hannah Park finds out more about recent UK-based research.
Getting fibre levels right is crucial to producing a balanced ration which promotes good rumen health for lactating dairy cows.
With most current recommendations based on North American studies feeding lucerne, haylage and/or maize silage, their suitability when applied to wetter, grass silage-based rations commonly fed in the UK may not be suitable.
To counter this a study has been carried out looking at the role of functional fibre in the dairy cow diet in a UK context.
Professor Sinclair, from Harper Adams, was involved in the study. He says while feeding more concentrates or high quality forages has increased milk yields in the UK, this has also led to lower dietary fibre levels and potentially exposes more cows to the risk of metabolic diseases, one being sub-acute ruminal acidosis (SARA).
He explains there are several components which need to be considered to promote healthy rumen function and performance in dairy cows, including neutral detergent fibre (NDF) concentration, non-forage carbohydrates and forage particle length.
With most existing studies looking at the relationship between physically effective fibre, intake and rumen pH undertaken using North American type diets, an AHDB-funded study, focusing on 50 commercial dairy herds throughout the UK, has looked at whether current recommendations are suitable for the UK dairy herd.
With the exception of maize silage which is not too dissimilar to that in the US in terms of average particle size, major differences have been established when it came to this for grass silage and TMRs.
With this in mind, the study looked at whether chop length of grass silage has an impact on rumen pH, cow performance and metabolism when it was fed alone in a ration or alongside maize silage, comparing a ‘long’ (UK average) with a ‘short’ (shortest 5 per cent in UK) chop length.
Determined by a rumen pH bolus, chop length was found to have no effect on rumen pH for the grass silage only TMR or grass and maize silage ration.
Within the study, a look at how effectively TMRs were mixed and whether any sorting was taking place was also looked at using the Penn State separator.
This highlighted that 58 per cent of farms had poorly mixed rations, with 68 per cent shown to have a degree of diet sorting taking place. Of equal concern, says Prof Sinclair, is that 34 per cent were shown to have no refusals, indicating that animals are being under-fed.
In terms of cow performance, decreasing chop length increased intakes by about 1kg DM/day for the ‘short’ chop length for both rations and while chop length had little impact on milk yield for the grass and maize ration, the ‘short’ chop grass ration alone lifted yields by about two litres per day.
Milk fat content was decreased for both TMRs containing ‘short chop’ lengths but milk fat yield was not decreased.
The relationship of chop lengths with carbohydrate sources was also looked at, with particular focus put on starch given the typically high levels fed in the US, and looked at the impact of upping starch in a ration from 10 to 32 per cent.
This was found to have no real effect on rumen pH, although Prof Sinclair says it was important to factor in the test conditions under which this result was reached.
He says: “Although there was found to be no effect at feeding 32 per cent starch in this particular study, this may have had a different effect on animals if we had investigated further and altered the form or how it was processed.”