2015-01-19   facebook twitter rss

Beware of Acidic Silages

When it comes to silage analysis, averages can hide a lot of problems on farms. The analysis results we have seen a-plenty over recent weeks have particularly emphasised the lower energy values of this year’s pits.

However, it is clear there are a multitude of issues that need to be taken into account warns Dr Richard Kirkland of Volac International.

Of particular note is the significant number of silages coming through with low pH values this winter, according to Duncan Rose, who was formerly based in NI, but is now with Carrs Billington the compounder supplying farmers across SW Scotland and northern England.

Dairy cattle

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“While this suggests the forages will be more stable in the clamp and at feed-out, it also means the silage component of the ration is more acidic, which will increase the risk of acidosis if not properly balanced. Coupled with the low pH is often a low dry matter (DM), making these forages even more of a challenge to balance.” An example analysis is presented in Table 1.

Dairy cattle

“Wet silage reduces DM intake and the high acid loading in the rumen shifts the microbial population to one that is less efficient at fermenting fibre. This impacts on the supply of key energy yielding nutrients, microbial and rumen-bypass protein.”

Dr Kirkland continues: “If not addressed, acute or sub-acute rumen acidosis (SARA) will lead to a significant drop in DM intake, milk yield depression, lethargy, low milk fats, reduced fertility and other health issues.

“While the normal culprit of acidosis is over feeding / slug feeding of concentrates, this year the risk is compounded by these high-lactate, acidic silages together with the temptation to overfeed lower-priced, rapidly-fermentable starch sources such as wheat and barley.”

So what are solutions? Duncan Rose and Richard Kirkland discuss the following seven options.

  • Digestible fibre. First of all consider displacing some of the wet acidic silage with any other drier sources of forage fibre on the farm such as big bale or Chopped straw, but not too much so as to reduce the energy density of the diet too far. From a concentrate point of view consider replacing some cereals with feeds such as sugar beet pulp and soya hulls. These fibre sources are well-digested and hence provide a higher energy supply compared to straw, but do not provide the same ‘scratch’ or effective NDF. Early lactation rations should be targeted to a minimum 33% NDF and 19% effective NDF per kg DM.

  • By-pass starch. High yielding cows need starch in their diet but excessively high levels of rapidly-fermented starch add to the acid loading, so think about switching some to a slower-releasing starch source such as maize rather than wheat or barley. Caustic- or Alkagrain-treated wheat are also safer options than rolled or ground wheat.

  • Fat. Proven fat supplements such as Megalac contain over 2.5-times the energy of cereals, but crucially are not fermented in the rumen so supply energy without increasing the acid load. It’s important to ensure that fats used are rumen-protected – in other words they pass through the rumen for digestion in the lower digestive tract, avoiding any negative effects on fibre digestion and risk of low milk fat %.

  • Dry the diet out. Consider reducing the inclusion of wet moist feeds such as brewer’s grains and carrots. High yielding cows maximise their DM intake when the overall diet has a DM of between 45 to 55%.

  • Rumen buffers. There are a number of buffers on the market and the key factor is to feed enough. This varies depending on which type is used – e.g. 250 g/day sodium bicarbonate or 80 g/day of products like Acid Buf.

  • Live Yeast. Live yeasts help by scavenging oxygen and lactic acid and improving the rumen environment for the growth of fibre digesting bacteria.

  • Protein. Rumen bacteria can supply up to 60% of the total protein requirements of dairy cows if the rumen environment is favourable for their growth. High-producing cows also require a source of high-quality, rumen-bypass protein to meet their total protein requirements and supply essential amino acids to maximise production. However, where there is a risk of acidosis, extra supplementary digestible undegradable protein (DUP) should be considered. High-DUP feeds such as AminoMax are well-proven to provide this essential bypass protein requirement.

Dr Kirkland adds: “The key message for farmers this winter is to ensure they are aware of the quality of the forages they have on farm this year. Whilst average silages have lower digestibility than last year, there is a significant proportion of wet acidic silages that need to be balanced in a very different way to normal.”


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