Targeting fibre: a nutritional strategy to maximise the potential of your beef rationPublished Monday, 30th September 2019
For beef units feeding silage or moist feed-based rations, extracting as much growth as possible from the fibre portion is the key to both minimising feed costs and maximising margins, our Technical Support Manager Dr Jamie-Leigh Douglas explains.
“Fibre is an extremely important energy source in ruminant diets, as well as being vital for correct rumen function,” she highlights. “Feeds high in fibre like silage and moist feeds are also some of the most cost-effective sources of energy available, so it makes sense to utilise them as efficiently as possible.”
In silage-based beef systems, preserved forages can routinely account for 60-70% of the ration. The result is a total fibre content that’s typically 40-50% of the dry matter (DM) consumed, and potentially even greater this winter due to the higher fibre grass silages reported by Trouw Nutrition.
Potential lost energy
“If the digestibility of this fibre isn’t maximised, then a good proportion of the best value energy in the diet can easily be lost, with knock-on effects for growth rates, feed costs and overall profitability,” Dr Douglas adds.
Improving fibre digestion in the rumen should therefore be a top priority for all beef producers. The rumen digestibility of plant cell walls – the main source of fibre in the diet – can be as high as 65% under ideal conditions, but it can quickly drop to as low as 35% if the rumen environment isn’t optimised.
“The amount of fibre that’s actually broken down and converted into energy by rumen microbes is determined by two key factors: the potential maximum digestibility of the fibre and how well the rumen is functioning,” Dr Douglas explains.
“So anything that compromises fermentation efficiency in the rumen is going to limit fibre digestibility and the resulting energy supply, regardless of how much available energy the fibre potentially contains.”
Rumen fibre digestibility
Low rumen pH (acidosis) caused by acidic silages or too much unbalanced starch in the ration will reduce the populations of fibre digesting microbes and slow the rate of fibre breakdown. Increased rumen outflow rates following addition of sodium bicarbonate can limit the time available for digestion, whilst excess oil in the diet will coat the fibre, delaying microbial attachment and colonisation.
“All are factors capable of restricting fibre digestibility, undermining overall feed efficiency and reducing profitability,” continues Dr Douglas. “It means that minimising or avoiding these factors needs to be a priority if you want to extract as much growth as possible from forage and fibre.”
Recent research has shown that by making the fibre portion of the ration more accessible in the rumen, it’s possible to increase microbial attachment and increase nutrient utilisation, leading to a 10% gain in overall feed conversion efficiency. This result was a 60-70 g/day increase in average daily gain, which is equivalent to an extra 4kg in just two months.
Improved fermentation efficiency
“This particular trial used a Trichoderma reesei-derived fungal extract (VistaPre-T) applied as a fibre pre-treatment before feeding, which roughened and created pits in the surface of the fibre, increasing the surface area for microbial attachment,” Dr Douglas continues. “The result was a substantial improvement in fibre digestibility, and highlights just how much additional potential there is available if fibre digestion is optimised.”
As a result, Dr Douglas is urging beef producers to examine all aspects of the ration as part of an ongoing process, continually fine-tuning nutrient supply and the rumen environment to optimise fibre digestion. Ensure a balance between the rapid energy release from starch and more slowly fermented digestible fibre, and consider the use of a slow-release rumen conditioner like Acid Buf if silages are acidic to reduce the acidosis risk.
“In addition, make sure you include enough structural fibre to stimulate rumination and provide the rumen ‘mat’ that helps retain feed in the rumen until digested,” Dr Douglas concludes.
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