For beef units feeding silage or moist feed-based rations, extracting as much growth as possible from fibre in the diet is the key to minimising feed costs and maximising margins, says Dr Nicola Walker, AB Vista’s ruminant product development manager.
She says: “Fibre is an extremely important energy source in ruminant diets, as well as being vital for correct rumen function. Feeds high in fibre can be 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 account for 60-70 per cent of the ration, resulting in a total fibre content which is typically 40-50 per cent of the dry matter (DM) consumed.
Dr Walker says: “If the digestibility of this fibre is not maximised a good proportion of the best value energy in the diet can be lost, with knock-on effects for growth rates, feed costs and overall profitability.”
Improving fibre digestion in the rumen should 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 per cent under ideal conditions, but can quickly drop as low as 35 per cent if the rumen environment is not optimised.
Dr Walker says: “The amount of fibre 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.
“Anything that compromises fermentation efficiency in the rumen will limit fibre digestibility and the resulting energy supply, regardless of how much available energy the fibre might potentially contain.”
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. Excess oil in the diet will coat the fibre, delaying microbial attachment and colonisation.
Dr Walker says: “All are factors capable of restricting fibre digestibility. 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 increasing the speed at which rumen microbes colonise the fibre in the diet can improve feed conversion efficiency by 10 per cent. This increased average daily gain by 60-70g/day, equivalent to an extra 4kg in two months.
Dr Walker says: “This trial used a Trichoderma reesei-derived fungal extract applied as a fibre pre-treatment before feeding, which roughened and created pits in the surface of the fibre.
“The result was a substantial improvement in fibre digestibility highlighting how much additional potential there is if fibre digestion can be truly optimised.”
Dr Walker advises beef producers to examine all aspects of the ration, 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 if silages are also acidic and the risk of acidosis is high.
She says: “Make sure you include enough structural fibre to stimulate rumination and provide the rumen ‘mat’ that helps retain feed in the rumen until digested.”