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Use silage analysis to guide feeding strategy

October 22, 2020

Nigel Gould, CAFRE Beef and Sheep Adviser, Enniskillen

Grass silage is the primary source of feed during the winter housed period on most beef and sheep farms in Northern Ireland, with concentrates used to supplement it where required. Knowing the quantity and quality of silage available to you will allow an informed decision to be made on your feeding strategy this winter. Different classes of stock will have different requirements. The target you set for animal performance will also affect it. For example, for average quality silage, supplementation of dry suckler cows with concentrates is generally not necessary and for top quality silage, a restricted intake is advisable to manage body condition so that it doesn’t affect cow calving ability later. For the case of finishing cattle, supplementation will be required, the level of which will be dependent on animal type, an example being that native bred cattle will generally require less supplementation compared to continental bred cattle for the same level of finish. Target live weight gain of weanlings over the winter is generally 0.6-0.7 kg/day which will facilitate compensatory growth the following grazing season. This level of gain can require 0-3 kg of concentrates, depending on silage quality. Where different silages are available on farm, those of higher quality should be targeted toward the higher priority stock.

As is the case every year, initial silage analysis to date on the 2020 crop from farms in CAFRE’s Business Development Groups in the Western region (table 1) indicate wide variation in silage quality between farms and even between different silages on the same farm. The main reasons for this variability are generally attributed to grass growth stage at harvest, level of fertiliser application the crop received and weather conditions at harvest impacting on the level of wilt achieved.

Target dry matter (DM) 30%. Lower dry matter silage will have lower total feed value compared to higher dry matter silage.  For example, on a weight basis only, 1 tonne of fresh silage with a dry matter of 30% is equivalent to 1.2 tonnes of fresh silage with a dry matter of 25%. In reality, very low dry matter silage also tends to have poorer fermentation leading to poorer overall silage quality, compared to silage with the target of 30% dry matter content. On the other hand, very high dry matter silages can be prone to mould growth at the feed face.

D-value is a measure of silage digestibility and will ideally be higher than 70. This will be primarily affected by cutting date in relation to heading date of the crop. It is for this reason that silage cut in May will generally have a higher D-value than silage cut in June when the level of seed emergence in the crop will be greater.

Metabolisable Energy (ME) and Crude Protein (CP) are also important considerations with younger growing cattle needing particularly high concentrations in the diet. Target silage ME and CP of greater than 11 MJ/kg and 12% respectively.

As feed costs account for the largest proportion of variable costs in livestock systems, the aim should be to reduce these as much as possible. This can be achieved by maximising silage quality and balancing the diet with concentrates only when necessary.