Liquid feeds delivering more protein efficiency

With rising input costs on farm, it’s no longer enough to feed well – cows need to be fed with both efficiency and environmental footprint in mind. British Dairying reports.

Using dietary protein more efficiently has become an increasing priority and is an area where improvements can be made, yielding production and financial benefits.

“Traditionally, many dairy rations in the UK have relied on high crude protein levels compared to rations in other major milk producing countries; typically 17-18% to drive milk production,” says Dr Phil Holder at ED&F Man. “But crude protein tells us little about what the cow can actually use. It’s a blunt tool in a system that now demands precision:”

Cows don’t actually need protein – they require amino acids, which are the molecules that make up protein. These amino acids are used by the body to produce different types of proteins, including milk proteins.

“It is not just how much protein we feed that matters, but how well we feed it.”

All proteins are made up of a combination of 20 amino acids. Ten of these amino acids are classified as ‘essential, which means that they must be supplied in the cow’s diet. When protein is fed to the cow, a significant proportion of the protein is broken down into nitrogen and amino acids. These are reconstituted in the rumen into microbial protein, a good source of amino acids. This microbial protein then passes into the small intestine to supply amino acids for the cow to use.

To be effective, a diet must provide the amino acids the cow requires to supplement microbial protein, which is not directly linked to the amount of protein fed. As soon as an amino acid becomes limiting – in other words, there is not enough to meet the cows’ requirements – her performance is affected. In most UK dairy diets, methionine is the first limiting amino acid, with an estimated 90% of diets being deficient.

“The usual approach when formulating diets has been to overfeed metabolisable protein (MP) to try and ensure that the cow is supplied with the correct level of amino acids,” explains Phil. “This is an imprecise approach, pushing up protein use and costs. If we can be more precise, supplementing diets with specific amino acids, we could reduce the total amount of protein fed, reducing costs and improving nitrogen use efficiency (NUE), the efficiency with which protein is used.”

Compelling results

Research from the University of Reading, completed in 2025, clearly demonstrates that feeding specifically formulated molasses-based products can help address this challenge and improve protein utilisation. By using liquid feeds as a carrier for rumen-protected methionine, it is possible to lower overall protein levels in the ration while improving the cow’s ability to use what she is fed. The results are compelling, both nutritionally and economically.

In the trial, three groups of Holstein cows were fed different diets over a nine-week period. The first was a conventional control diet with around 17.5% crude protein, while the other diets were formulated to reduced protein levels of 15.5%. One was a lower-protein diet using Regumix, a 27% protein, highly palatable, molasses-based liquid, while the third diet included Regusmart, a molasses liquid based on Regumix but with added rumen-protected methionine (MetaSmart from Adisseo).

Designed diets

The diets were designed to test how cows perform when crude protein is reduced but amino acid balance; especially methionine, is optimised. In the lower protein diets, 1.1kg of a protein blend was replaced with 1.4kg of either Regumix or Regusmart.

The trial showed that milk yields did not decline when crude protein levels were reduced (see table). Cows on the trial diets produced as much milk as those on the control diet, challenging the long-standing assumption that high protein is always necessary to support high yields.

“However, the real difference came in how efficiently that protein was used. Total protein efficiency (TPE), which measures how much milk protein is produced per unit of dietary protein, improved significantly in both liquid feed groups,” notes Phil. “The control group had a TPE of 0.29, while the Regumix-only group reached 0.32. The Regusmart group, which received protected methionine, achieved a TPE of 0.34, a 17% improvement in protein efficiency compared to the control, without feeding more, and without compromising performance.

Nitrogen metabolism

“This is not just a technical improvement but has significant implications on farm. Higher TPE means more of the protein you buy is converted into saleable milk protein and less is excreted as waste he adds. “This not only reduces nitrogen loading in slurry, helping to meet environmental goals, but also reduces the metabolic burden on the cow.”

Lower milk urea levels were seen in both of the liquid feed groups, especially in the Regusmart-fed cows, indicating improved nitrogen metabolism and lower rumen ammonia. “From a fertility standpoint, that matters.”

To further explore the formulation potential of the Reading trial diets, a ration modelling exercise was conducted using AMTS, one of the industry’s most advanced nutritional evaluation platforms. The objective was to assess where protein savings could be made using Regusmart, without compromising metabolisable energy (ME), MP, or amino acid supply – particularly methionine.

The results showed that 300g/cow of Hipro soya could be removed per day while still meeting all nutritional requirements, not compromising on ME, MR or methionine requirements. Across the UK dairy herd this equates to a saving of 510t/day of vegetable protein, or over 186,000t annually. In addition to the protein saving, the AMTS exercise showed that, compared to the control diet, the Regusmart formulation achieved a 10% reduction in nitrogen intake.

Methionine’s influence doesn’t stop at protein efficiency It is also a key player in liver function and antioxidant status – all critical elements in supporting health, immunity, and fertility.

“In the final weeks of the trial, cows on the Regusmart diet showed higher body condition scores, suggesting better energy balance and potentially greater resilience, particularly important in later lactation:’ says Phil. “While there were no significant differences in liveweight or somatic cell count, this improvement in body condition adds further weight to the argument that methionine supports whole-animal health, not just protein output.”

Return on investment

From an economic perspective, the numbers are striking. When the immediate production benefits of feeding reduced protein levels and a balanced amino acid approach are considered, a typical herd producing 9,000 litres will see a return on investment of around 2.1 to one based on feeding costs. This is before factoring in wider environmental benefits.”What makes this approach especially attractive is its practicality. Using molasses-based liquid feeds to supply protected amino acids is low-labour, highly palatable, and can be easily integrated into existing feeding systems,” he explains. “There’s no need for additional premix carriers or complex blending on-farm. Liquid feeds also help reduce sorting in mixed rations, improving diet consistency across the herd.”The findings from the Reading study and the subsequent diet formulation exercise are part of a growing body of evidence supporting a more precise, amino acid-focused approach to protein feeding.

For UK dairy farms, the message is clear: It is not just how much protein we feed that matters, but how well we feed it. “Feeding protected methionine through liquid feeds is an efficient, hassle-free delivery strategy that improves cow performance while reducing nitrogen wastage. In the years ahead, farms that focus on in protein efficiency, not just protein quantity, will be the ones that stay ahead.”