Samples Show High Variability in Silage Quality

UK - Frank Wright Trouw has analysed over 5,700 grass silage samples (first, second and third cut) from the 2012 season in order to reveal some key areas to think about when feeding this winter. Adam Clay, Ruminant Manager at Frank Wright explains how the samples compare to 2011 figures and what the results mean.
calendar icon 8 October 2012
clock icon 3 minute read

Overall we're seeing a higher fibre content and lower energy in the 2012 samples, due to the wet weather, but overall averages are not that different from the 2011 samples. But this really clouds some issues of concern.

What we are seeing are lots of farms with wet first cut silage and dry second cut, so they are kind of balancing each other out. But both these types of forage need careful management.

Wet silage

Unsurprisingly there are many wet silages, particularly amongst first cuts, with the lowest analysis so far being 13.6% DM. There are some particular problems associated with feeding wet silages;

  • Intakes are potential lower with wet silage and the inclusion of drier forages or chopped straw may be the only way to boost DM intakes.
  • Wet silages have a higher acid loading and there will be an increased risk of acidosis with the higher levels of PAL (potential acid loading). PAL is combination of the total acid intake from forage plus the prediction of the acid that will be produced by the rumen. Linked with higher levels of lactic acid, buffers may have to be used to neutralize the acid and allow rumen pH to rise.
  • A wet forage with high acids will need that dryer fibre element to help create a rumen mat, but will also require a buffer or ingredient to help neutralise the acid.
  • Wet silages frequently supply excess rumen nitrogen relative to rumen energy and we're seeing some high MPNs (Metabolisable Protein from Nitrogen), with the average being 147g/kg DM, compared to 49.5 g/kg DM in the dryer forages. If MPNs are high more energy will be used to break down protein, taking away energy from milk production and fertility.
  • These silages require additional rumen energy supply to utilise the excess MPN, typically from cereals, molasses or other sugary feeds. But caution is needed not to further increase the risk of acidosis.

Dry Silage

The analysis has shown that second cut silages are, on average, higher DM and lower in energy than first cut silages. With higher intake potential than wetter silages, drive up forage intakes to minimise concentrate use, but again there are some issues associated with feeding drier silage.

  • Dry forages, when used alone in mixed ration, are more prone to sorting in the feed passage, leading to an increased risk of acidosis. Using a chop length of 20-25mm can help with sorting, as well as the application of a moist feed such as molasses. Push up the feed to the barrier repeatedly, as much as eight times a day.

  • The dry forage samples have an average pH of 4.4 meaning there is potential to see heating in the clamps and secondary fermentation taking place. The heat is coming from the development of yeasts and the microbes that develop mould. As they heat up they use energy, in the form of sugars robbing the diet of energy. The loss can amount to about 0 .64 ME over a 24 hour period and this equates to a milk yield loss of about 1 litre/8kg DM intake. In higher yielding herds this can as much as three litres a day.

With evidence that there are such large differences in forage quality around this year, often within the same farm, regular silage sampling this winter is essential in order to avoid sudden drops in cow performance.

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