Minimise contamination when harvesting silage this season

Farmers should take care to minimise the risk of soil or manure contamination when ensiling grass as this can have a negative impact on silage quality and subsequent animal health and performance advises CAFRE Dairy Technologist Stephen Gilkinson.

Friday, 9th July 2021, 8:35 am

Stephen outlines the risks posed by soil and manure contamination of grass at ensiling and suggests ways of minimising the risk of grass contamination when making silage.

Soil contamination is something that is not often talked about, but it can have negative impacts on forage intakes and production. It was seen as more of an issue when silage was mostly direct cut and the harvester shaved off uneven surfaces. However with a lot more field operations often employed with silage making, there is potential for additional contamination of the crop by both soil and micro-organisms.

What are the possible implications of soil contamination?

Reduced intakes may be relatively easy to see, but there are potential issues even when intakes are not impacted. Soil contamination can result in the increased presence of organisms such as clostridia, coliforms, salmonella and listeria in silage which can have potential health implications for livestock consuming this material.

Listeria is probably the most widely known bacterial contaminant, as the ingestion of this organism can result in abortion and death, particularly in sheep. Listeria is associated with pockets of grass/silage that have not been well compacted and with big bale silage. The organism can be present in milk, but should normally be killed by pasteurisation. Mortality can be a very high proportion of those animals that are ’sick’ with this infection.

Clostridium spp. occur naturally in soil and are associated with silages that are poorly preserved, high pH, low lactic acid and presence of butyric acid. The organism doesn’t like low pH, so additives that promote rapid lowering of pH should be effective at keeping this organism at bay. Clostridium spp breakdown proteins and produce ammonia, thus reducing the feed value for livestock. Poultry manure should not be applied to any land used for grazing/silage, although thankfully the presence of botulinum spores in silage is very rare.

Bacillus spp. can be found anywhere in nature and are associated with aerobic conditions in silages and feed-out temperatures. Use of an additive to promote a stable well preserved silage means these bacteria cannot compete for food reserves in the grass.

Mycotoxins can be an issue at feed-out, particularly in low density high dry matter silages, combined with high ambient temperatures. Big bale silages with air ingress can lead to mould development, which may impact intakes and in severe cases, lead to abortions. Whole crop silages along with maize are more prone to mycotoxin development, both in the field on the crop and during feed-out, as they may not be as well compacted as grass silage and the feed face is more open to air ingress and consequently, toxin development.

Iron from ensiled soil becomes more available in silages, due to lowering of the pH and this can negatively impact on the uptake of copper by livestock and potentially lead to a copper deficiency among these animals.

Manure is applied to silage fields mainly as slurry which could contaminate the harvested forage if it is applied too close to the cutting date (coliforms being the main concern with possible transmission to human via milk).

Trailing shoe applications minimise slurry contact with grass leaves, reduce ammonia emissions and afford a wider window for spreading. However, with high applications followed by dry weather, the fibre from the applied slurry can lift up into the crop. Little research has been carried out to assess the impact of this. However it would be prudent to take steps to minimise the risk of bringing this material in with the ensiled crop.

Minimising contamination in silage

In an attempt to minimise contamination, Stephen emphasises that: “Prevention is better than cure! Roll fields where needed to ensure a relatively level soil surface. Keep the mower up to at least 5-6cm to reduce dead matter in the grass and ensure that tedders and rakes are set so that tines are not scrapping the ground.”

Stephen continued: “Consider using an approved additive, fill silo in layers, roll constantly and seal well ASAP after job completed, so that unwanted micro-organisms do not get a chance to grow.”

A mineral analysis from a core sample is a useful addition, as it gives an indication of the level of soil contamination and also possible antagonisms between minerals in the forage. It also allows mineral deficiencies in forages to be counteracted with bespoke mineral pre-mixes if necessary. Discuss the implications of adopting these techniques on the farm with your local CAFRE Dairy Development Adviser.