Improving the sustainability of UK dairy farming can be achieved by focussing on areas such as nitrogen, carbon and phosphorus reduction, new research shows.
There is considerable public and government interest in lowering the environmental cost and improving the sustainability of milk production.
The recent Defra Clean Air Strategy identified that 88% of ammonia emissions in the UK were from agriculture, with 28% of these due to dairy cattle.
One area of interest is the reduction in nitrogen output by feeding low protein diets.
Purchased feeds such as soyabean meal have a high and volatile cost, coupled with a significant environmental cost.
Harper Adams University researchers have been focussing on home-grown forage legumes such as red clover, lucerne and forage pea silages.
These forages are of interest because they are higher in protein than traditional feeds such as grass silage, and therefore require less supplementary protein to be fed.
They also have the added benefit of not requiring artificial fertiliser nitrogen as they naturally fix it from the atmosphere.
“Only about 25% of the protein that a dairy cow consumes ends up in the milk, but by lowering the protein in the diet to 15% we were able to increase this to 35%”, said Professor Liam Sinclair, leader of the research programme.
"This is a tremendous improvement and means that less N is excreted that could end up in watercourses," he added.
“Additionally, most of the reduction was due to less nitrogen in the urine which is then lost to the environment as ammonia.”
This reduction will greatly help dairy farmers meet the UK government’s requirement to reduce ammonia emissions by 16% by 2030, he said.
In the study, the improvement in N use was also achieved without affecting milk performance or quality, and it also reduced the cost of purchased soyabean meal by around 1p per litre.
“This reduction in purchased feed costs will improve dairy farmers profitability, but it is very important that the diet is properly formulated to meet the cows' requirement for absorbed protein", added Prof Sinclair.