Rumen Balance Key To Making Most of Silage

Looking beyond the headline figures on your silage analysis will ensure diets are better balanced and more cost-effective

New parameters included in silage analyses give a much better indication of how the forage will perform in the rumen, allowing more efficient supplementation and purchased feed costs savings according to Dr Liz Homer from Trouw Nutrition GB.

“Most farmers and nutritionists don’t go much further than metabolisable energy (ME) and crude protein when assessing the quality of silages,” she comments.  “However, and significantly these parameters do not indicate how a feed will perform in the rumen and the type of supplementary feeds which will be required to best balance the diet.

“The consequence will be diets which do not perform as expected leading to poorer production.”

Dr Homer explains that cows do not produce milk from silage, but from the products of digestion when feeds are fermented in the rumen or pass through to the intestines.  New parameters included on most silage analyses now better predict what these products of fermentation will be and Dr Homer advises farmers to ensure their nutritionist makes full use of them.

“These parameters describe how feeds will perform when eaten, what the rumen bugs require and also how much bypass energy and protein is needed to balance the overall diet.

“Unless the rumen is balanced in nutrient terms, but also in terms of rate of fermentation cows will not perform as expected,” she continues.

She advises farmers and their advisors to ration cows based on NDIP which is the metabolisable protein available to the cow and Dynamic Energy (DyNE) which is the net energy available to the cow.  She explains that DyNE is the sum of all energy sources fermented in the rumen including sugars, NDF, residual organic matter and even lactic acid and protein which explains why silages with the same ME content can have different levels of DyNE.

Alongside these she says attention needs to be paid to the amount of Total Fermentable Carbohydrates and Protein and the Rapidly Fermentable proportions.

“These describe how much of the energy and protein will be fermented in the rumen and an indication of how rapidly this fermentation will happen.  Overall the diet will need to be balanced for fermentable energy and protein and also the speed of fermentation.”

Finally, she says the acid load and fibre index help predict the impact of a silage on rumen function.

“Based on these parameters, it is possible for two silages with the same ME level to perform very differently in the rumen and consequently require different supplementary strategies.

“The table compares two silages which are both first cuts with a similar dry matter and both are 11.3MJ/kgDM so on first assessment would be expected to perform similarly.  Although the ME is the same, the DyNE varies, primarily due to the amount of NDF and lignin.”

Silage one is higher in crude protein and in fermentable protein but has lower total fermentable carbohydrates than silage two as a result of being lower in NDF.  Silage two has more rumen fermentable energy but less fermentable protein.

“When we look at the balance of rumen fermentable energy and protein, silage 1 has an excess of protein while silage two has a shortage of fermentable protein, in part due to having lower crude protein.  This means, that despite having the same ME, they will need to be balanced differently.

“Assuming they are correctly balanced and if cows are consuming 10kgDM, then the DyNE in silage one will support M+7.3 litres while silage two would give M+8.3 on this basis.  But if incorrectly balanced, both will under-perform.”

Dr Homer says diets based on silage one would need to be supplemented with Slowly Fermented Carbohydrate sources to balance the excess protein.  This could include feeds like soya hulls and beet pulp.  She advises not feeding too many rapidly fermented carbohydrates like cereals as the acid load of the silage is high, increasing the risk of acidosis.

With silage two, the need is for supplementary feeds to supply fermentable protein to boost the supply of microbial protein.  Consequently, diets based on this silage would benefit from distillers, soya or rape.

“Accurate description of how feeds perform in the rumen is paramount if maximum value is to be made of forage to help support margins this winter. These new parameters allow nutritionists to go further than traditional parameters used to assess silage quality such as ME and crude protein. 

“By balancing the diet more effectively, thinking outside the box and not always buying the same compounds and supplements we calculate the savings could be around £180/cow per year for a 9000 litre herd.”