Feed International - October/November 2017 - 32
32 ❙ FeedInternational
ACCURATE RUMINANT RATIONS
clamp. Within the same year, silage protein levels can vary
substantially and differences of 50 to 100 grams CP/kg DM
have been found in some grass silages. Having an accurate
idea of exactly how much protein is in the forage part of the
ration is essential to be able to correctly balance the diet with
other protein sources. Knowledge of the split between rumen
degradable and undegradable protein (RDP and RUP, respectively) is also critical to balancing the ration fed to the cow.
Forage vitamins and minerals
Energy and protein are the underpinning parameters
used to create diets for cows, but minerals and vitamins
also need to be considered when thinking about forage
analysis. Mineral content and availability in forages is related to soil conditions, most notably mineral content and pH.
5 tips to keep cattle
healthy during winter:
While mineral levels can be a little more stable over
time compared with DM and protein levels, it's still crucial to be aware of the mineral content of forages to tailor
mineral supplementation. Mineral content and ratios between key minerals are important when rationing animals,
particularly through the dry and transition period in dairy
cattle, for example, the ratios of potassium to sodium and
calcium to phosphorous. Watching out for excess potassium in close-up dry cows is also key, especially when
dealing with grass silage and fresh grazing. Trace minerals can also be deficient in some forages, selenium being
a good example. Many geographical areas have soils that
are selenium deficient, including Scandinavia and the U.K.
and Ireland. Diets including forages from these soils will
need to be aware of selenium levels in order to avoid deficiency or sub-optimal performance.
Equally, high levels of minerals, such as molybdenum,
iron and aluminium, must be taken into account due to
their antagonistic action toward other, required minerals thus reducing the availability of those minerals. For
example, molybdenum forms insoluble complexes with
copper and sulphur, called thiomolybdates, in the rumen
reducing the availability of dietary copper to the animal.
In severe cases, copper deficiency symptoms will be seen.
Therefore, it is beneficial to know levels of antagonists
present in forages to inform the specification of mineral
Forage quality, safety
One aspect that is often overlooked is the analysis of
the hygienic quality of the forage. Yeast, molds and mycotoxins all reduce the quality of the forage and can have
negative impacts on animal health and performance.
One of the biggest impacts is reduction in DMI with
subsequent reduction in performance. Mycotoxin contamination, in particular, is known to elicit a drop in DMI.
Analysis of the hygienic quality of forages can help with
management decisions regarding feeding of that forage.
Utilize NIRS for accuracy
NIRS forage analysis is a common practice. Assuming
the calibrations behind the NIRS come from a sufficient
number of representative samples, then results can be very
accurate. Preparing diets for ruminants is based on matching nutrient demand with supply, and forages make up a
large proportion of the nutrients in a ration. One of the
greatest sources of variation is forage DM, which can vary
substantially. Knowledge of variations in forage nutrient
content makes matching supply to demand much more accurate and less of a guessing game. ■
Dr. Helen Warren, owner of HW Consulting, achieved her Ph.D. from Bristol University. After working in academia,
she worked for a global animal health company. She is currently chair of the British Society of Animal Science Industry
Association, a registered animal scientist and certified Cow Signals trainer.
www.WATTAgNet.com ❙ October/November 2017