Maximising Fibre Digestibility is Crucial to Improving Performance With Jonathan Huxtable, Zinpro; Dr Dana Tomlinson, Zinpro and Professor Michael Van Amburgh, Cornell University
The more dairy farmers and nutritionists can improve fibre digestion
“What nutritionists need to ensure is that the diet provides
and rumen microbial growth, the better cows will perform. This will
sufficient NDF and that this is digestible. If we can increase the rate
be particularly important this year, with diets likely to be based on
of digestion, several things happen.
variable, often higher fibre first cuts, according to Jonathan Huxtable
“Firstly the rate of passage through the rumen increases which
from Zinpro, opening a recent nutrition event organised by the
leads to higher dry matter intakes. Secondly, we see nutrient supply to
company.
the cow increase, both energy and metabolisable protein (MP). Faster
“Farmers will need to challenge their nutritionists to focus on fibre digestion to increase intakes and production,” he comments.
digestion means there are more bacteria, and it is these bacteria that are the source of the higher MP and VFA production.
Professor Michael Van
“As a guide, a 750kg cow needs 8.2kg NDF in the diet, about
Amburgh from Cornell University
1.08% of bodyweight, to ensure effective rumen fill. Remember that
suggests that nutritionists are
a significant proportion of NDF may come from high fibre ingredients
only as good as the forage they
other than forages. It is not forage that is important but NDF.”
are feeding. “They have to be
All digestion in the rumen is carried out by the rumen microflora
able to work with both good
– particularly bacteria, fungi and protozoa. In general terms, the
and poor-quality forage and
higher the population, the more effective and faster the digestion
keep the rumen full of something
Professor Michael Van
digestible,” he explains, adding
Amburgh, Cornell University
All micro-organisms perform key roles thus all are needed.
that low digestibility silage fills clamps but does not produce milk.
By increasing the understanding of rumen function it is possible to
Professor Van Amburgh explains that NDF describes the material in the cell walls principally cellulose, hemicellulose and lignin with each
will be.
influence performance, specifically by meeting the requirements of rumen microbes more accurately.
digesting at different rates in the rumen. The higher the proportion of
“If we can directly fuel the rumen microbes, we can improve fibre
rapidly digestible material, the faster it will pass through the rumen
digestion and also protein utilisation,” explains Dr Dana Tomlinson
thus promoting better intakes.
from Zinpro. “One way we can do this efficiently is by increasing
“NDF figures for forages can be artificially increased if there is soil contamination in the crop which increases ash content when
a product of digestion called Branch Chain Volatile Fatty Acids (BCVFAs) or Isoacids.
analysed. In grass silages, this increase may be as much as 2-3%
“BCVFAs are essential
which is enough to impact digestibility and the overall dietary NDF.
nutrients required by the fibre-
If cows don’t seem to be milking, it is best to get NDF assessed and
digesting bacteria. They are
to exclude the ash element and this might be worth considering,
needed to produce the essential
especially after a wet growing season.”
microbial protein that is utilised
Professor Van Amburgh explains that digestibility drives rumen
by the cow to produce milk and
function and the formation of the rumen mat. He explains that while
muscle. As much as 25% of
particle size is important, what matters is how fast those particles
microbial protein comes from
are digested.
BCVFAs. If we can increase this supply it will increase rumen
When particles enter the rumen, they are colonised by bacteria which digest them, producing volatile fatty acids (VFAs) and gas.
Dr Dana Tomlinson, Zinpro
efficiency, reducing the need for higher dry matter intakes to support higher production.”
Particles of feed rise to the top of the rumen on this gas. As particle
Normally, fibre-digesting bacteria are supplied BCVFA through
size declines due to rumination and digestion, gas production reduces,
the digestion of rumen degradable proteins such as soya and
particles sink and move out of the rumen.
rapeseed which are digested by the starch and sugar-digesting
Feed Compounder November/December 2024 Page 1