Microbial is the ‘new’ protein

Published 14 November 13

With soya prices recently peaking at over £400/t, a new review suggests reducing the protein content of dairy cow diets from 18% to 16% and increasing the effectiveness of microbial protein production could reduce costs and environmental impact – without hitting yields.

Forecasts indicate the days of soya at £180 are well and truly over with prices likely to remain over double that.  As the predominant source of feed protein in the UK, it has huge strategic importance.

It is estimated that British dairy cattle diets contain around 10% soyabean meal, which is about 0.16% of world production.  We are increasingly reliant on imports from Argentina, which have risen from 50% of imported soyabean meal in 2007/8 to 63% in 2010/11.

But when you consider that 70% of dietary protein is excreted by the cow in faeces and urine, there’s scope to think a bit differently about how we meet the protein needs of milk production, says DairyCo’s Dr Jenny Gibbons. 

“We carried out a literature review of studies looking at how protein content of dairy cow diets could be cut back without impacting production,” she explained.  “When dry matter intake was reduced in rations with less than 16% crude protein (CP), this was at least partially offset by either improving the digestibility (and amino acid profile) of the undegradable protein (UDP) component of the diet, or by increasing fermentable ME.”

It’s all about training the rumen microbes to function more efficiently, says Dr Gibbons. “We tend to focus on dietary protein, but microbial protein actually supplies between 50% and 80% of the animal’s metabolisable protein requirement.

“When high starch feeds ferment in the rumen, the supply of fermentable energy alongside a release of ammonia means the microbes are better able to capture that nitrogen and turn it into protein.”

There are other benefits aside from reducing costs of buying and feeding protein that is ultimately wasted – while protein levels of 17-20% in diets can be linked with poor fertility, lower protein diets around 14-15% have shown no apparent detrimental effect on either cow fertility or health, however, this effect requires confirmation in the modern high-yielding dairy cow.  And with the cow’s limited ability to store nitrogen or protein, less protein in the feed means there is less impact on the environment.

Dr Gibbons says trials have shown microbial nitrogen capture varies between 14 and 33g microbial N/kg, so it’s should be possible to more than double the effectiveness of nitrogen capture.

“Microbial protein is utilised more efficiently in the gut because it’s a better biological ‘fit’ to the cow’s requirements and matches the rumen environment better than a vegetable sources such as soya.

“And while level and balance of intestinally absorbable amino acids, in particular methionine and lysine, may become limiting at lower CP concentrations, in general, the amino acid composition of microbial protein is superior to that of UDP. 

“This means that dietary strategies aiming to promote microbial protein synthesis in the rumen may also go some way to correcting amino acid imbalances in low CP diets.”

Read the full report 

Prof Kevin Sinclair of University of Nottingham, presenting an overview of the project to investigate the possibility of reducing crude protein in dairy rations which is part of the DairyCo Research Partnership led by University of Nottingham.

It is important that professional advice should be sought before making any changes to your dairy cow diets.