Feeding excess protein in dairy cow rations would cause cows to mobilise energy to cleanse them of excess nitrogen, rather than using energy for milk production, said Ken March, ruminant adviser for Countrywide.

But substantial cost savings could be made by reducing crude protein levels and instead balancing rations for metabolisable protein relative to yield, to optimise rumen function and improve protein efficiency.

Studies from Pennsylvania University showed milk protein content and yield could be increased by improving the profile of amino acids in metabolisable protein and reducing surplus protein in the diet.

The two main limiting essential amino acids are lysine and methionine, which are readily available in microbial protein, he told farmers at the company’s seminar at Coomb Farm, Llangynog, Carmarthenshire.

“When you improve the supply of starch and rumen degradable protein (RDP) to the cow you will improve the supply of microbial protein, which in turn improves the level of metabolisable protein,” said Mr March.

“The more microbial protein we supply, the better we will be able to match a cow’s nutrient requirements for lysine and methionine. In doing so we will have a positive effect both on milk yield and milk protein percentage.”

However, he said many dairy farmers believed feeding 16-17% crude protein was not enough and were therefore “nervous” about reducing crude protein levels.

“In this country we feed 18-19% of crude protein in the hope it will supply some of the cow’s nutrient requirements,” he added.

“But we ruin cows by overfeeding protein because we are nervous about lowering it to levels that are better suited to the cow’s requirements. A cow is like a Ferrari, she needs a four-star diet.”

He said feeding protein at lower levels could not only stimulate milk production, but save 0.45kg of protein a head when feeding cows a dry matter of 22.7kg a day.

“Any excess protein the cow has in the diet requires energy to reduce the excess urea.” This equated to about 0.8MJ of energy for every 100g excess rumen nitrogen, he explained.

“If the diet is better balanced, then rather than using energy to cleanse herself of excess nitrogen, the cow can put more energy into milk production and other functions.

“In milk terms, 5.3MJ of energy is required to produce one litre of milk, so 400g of excess urea will cost you just over half a litre of milk.”

He added: “With soya at £400/t, if you can save half a kilo, feed a bit more forage and make more money, it has to make sense, hasn’t it?”

Mr March said reducing crude protein levels worked well with maize silage, because it provided cows with a steady release of starch, enabling them to improve protein use and reduce waste.

“Because it is a slow-release starch you can feed higher levels of maize silage without causing acidosis, and when balanced with a synergistic supply of RDP you will increase rumen efficiency, leading to better animal performance.”

One farmer who has seen the benefits of feeding lower crude protein in his dairy rations is Sion Davies, Coomb Farm, Llangynog.

His 650 Holstein cows are fed 16.6% crude protein in their overall diet, with combined starch and sugars totalling 26%.

On top of strong average daily yields of 37.6 litres a cow a day, Mr Davies also has 10 cows giving in excess of 65 litres daily.

His feeding regime epitomises feeding regimes in Canada and the USA, where Mr Davies has spent much of his working life.

“It works on this farm and it will work on most farms if you actually take the plunge,” added Mr March.