The first ever AHDB Dairy research seminar included a strong focus on dietary protein and how to reduce its waste. Ann Hardy reports from Derbyshire.
Lowering protein in milking cow rations has the scope to save feed costs and reduce nitrogen pollution, but it must be done with care and the help of an experienced nutritionist to avoid a hit in milk production or consequences for lifetime performance.
This message was delivered by several speakers at the AHDB Dairy Discover, Innovate and Grow seminar, held in Derbyshire, some of whom had focused their research on reduced protein rations, while others attempted to improve the available (metabolisable) protein from home-grown forages.
Although all tended to agree the urgency for a lower protein solution had diminished as soya prices had eased, there was a general acceptance that longterm trends in protein pricing would be upwards, while pressures on the environment would drive the need to reduce nitrogen waste.
Kevin Sinclair, professor of animal science at the University of Nottingham, illustrated the scope for improvement. “The nitrogen we feed is used very inefficiently – only 25-35% goes into milk,” he said.
Focusing on research at Nottingham and Harper Adams Universities on diets of 15-18% crude protein, he observed a small (3%), nonsignificant reduction in milk yield on the lowest protein diet but found some or all of this loss was mitigated by increasing starch in the ration.
However, he was wary of the potentially detrimental rumen effects of increasing starch, especially if sourced from wheat, and said diets would need to be carefully formulated by a nutritionist who understood the principles of rumen health.
“If your diet is high in grass silage or silage with legumes, you may well see a benefit of feeding extra starch because it might improve nitrogen capture in the rumen,” he said.
A behavioural pattern of cows on the trial also suggested adding starch may be beneficial, as cows on the low protein diet visited robots in search of feed more often, while those on low protein with added starch visited fewer times.
Financial savings on the low protein diet were significant (£70-£131) but were eroded if there was a significant drop in milk yield (worth around £85/lactation). However, the low protein diets reduced nitrogen excretion, improved nitrogen efficiency and had no detrimental effects on lameness or fertility.
“If you want to reduce protein to 15% or 16%, you are pushing the system to the limit so you must monitor everything closely or you may take a hit on yield,” said Prof Sinclair. “This means your diet formulation has to be spot on and you must sample your silage clamp regularly to fine tune your diets.”
On balance, he suggested 15% protein in late lactation may be manageable, but 16% was safer, although it still needed careful balancing especially at peak production.
Ongoing trials undertaken by Chris Reynolds, professor of animal and dairy science at the University of Reading, took up the same theme, but would span more than six years to reveal long-term effects of low protein.
Studying 14%, 16% and 18% protein diets, providing metabolisable protein below, at, and above predicted requirements, Prof Reynolds found a significant yield reduction with the lowest protein diet in first calvers, although ‘not as much as expected’, while the 16% and 18% protein diets each achieved similar production.
However, lower dry matter intakes by heifers on lower protein diets helped explain their better feed and nitrogen efficiency, while overall margin over concentrate cost was lowest for the low protein and highest for the medium protein group.
He said 16% dietary protein appeared to be achievable without substantial increases in starch concentration, although anecdotally he noted the lowest protein group mirrored the Nottingham/Harper trial by stealing food from their neighbours.
“Energy drives efficiency but we need to be careful about feeding too much starch – it’s about finding a balance,” he said, remarking a higher starch supply increased the efficiency of nitrogen utilisation through effects both on rumen fermentation and the metabolism of the cow.
With many aspects of the Reading trial still incomplete and several years to run to determine low protein’s long-term effects, he said full results to date were only in first calvers and differences were expected in subsequent lactations. He said more work was underway on low protein diets supplemented with rumen-protected proteins and essential amino acids. Effects on heifer growth rates were also being monitored and the impact on farm economics and the environment were being modelled as part of the project.
At Harper Adams University, Liam Sinclair, professor of animal science, had turned his attention to increasing the rumen by-pass or undegradable protein obtainable from forage, which is required in proportionately higher quantities by higher production cows.
Focusing particularly on tannins, which are naturally present in some legumes, his expectation had been that high tannin levels would bind to protein and prevent rumen microbes from breaking it down.
While peas high in condensed tannins had shown no production benefit when fed to dairy cows, he was hopeful forages high in hydrolysable tannins – which had given rise to significant yield increases in dairy ewes – would replicate these effects in the dairy cow.