How herds can cut soya without hurting milk yields

Soya has long been a staple protein source in dairy cow diets, but its hefty environmental impact has led to questions over its continued use.

Many milk buyers are now incentivising its exclusion from rations to reduce greenhouse gas emissions.

This change has been met with some resistance from farmers, who fear a negative impact on yield.

However, new research has shown that it is possible not only to maintain yield but also increase it without soya in the diet by carefully balancing amino acid levels.

See also: How high-yielding dairy cut soya and lowered crude protein

The study

The study is a result of a three-way collaboration between the University of Nottingham, Wynnstay and Trouw Nutrition.

“The only reason we feed crude protein such as soya to ruminants is to satisfy a demand for amino acids,” explains David Howard, head of nutrition at Wynnstay.

David Howard © Wynnstay

“Crude protein is converted to 20 essential amino acids required to support maintenance, pregnancy, growth and milk production.”

Where amino acid supply is insufficient, these functions are inhibited because the cow cannot fully utilise other available nutrients.

Known as limiting amino acids, the most common deficiency in dairy cows is methionine, followed by lysine and histidine.

This means a dairy cow is only as efficient as the first limiting amino acid, David says.

“So, if we can closely match the animal’s amino acid requirement, we can reduce the amount of overall crude protein fed.”

The study was carried out at the University of Nottingham’s Sutton Bonington dairy unit, where cows are milked by robots, on average 3.2 times a day.

The 340-head indoor Holstein herd calves year-round and achieves a yield of about 11,500 litres a cow a year.

Ration evaluation

© Charlotte Cunningham

The first stage of the research was an evaluation of the current diet in March 2024.

While this showed it was reasonably well balanced, there was an excess of protein – 17.5% of dry matter (DM) – and phosphorous (0.51% of DM).

Protein was supplied predominantly from HiPro soya bean meal and an 18% soya dairy nut, explains David. “The challenge was to see if milk yield could be maintained – or even increased – without using soya products.”

Gradual changes were made to the ration to minimise impact to the herd, starting with a rebalancing of nutrients in April 2024.

This involved reducing phosphorus content, removing rolled barley, feeding more ground maize and swapping a molasses-based product for a slow-releasing protein alternative.

The following month, the soya-based 18% robot concentrate was replaced with a soya-free alternative balanced in amino acids.

Amino Balance 16 contains 16% protein and rumen-protected methionine and lysine.

Rumen-protected amino acids are formulated and designed to bypass degradation in the rumen, for absorption in the small intestine instead.

“We were confident we could take soya out of the ration [with no impact on production], provided we supplemented the amino acids,” says David.

The final step, in mid-July, was to change the 50:50 soya-rape blend to a blend of distillers’ grains, heat-treated rape meal and urea, with no soya.

As a result, protein in the ration was lowered by 0.8% to 16.7% of DM.

“The supplementation of the amino acids has allowed us to do that, because we’re now not wasting protein, as we’ve matched the diet to the amino acid requirement.”

Impact of new diet

A more balanced diet has led to daily yields increasing by 4.8 litres a cow, to 38.7 litres.

Some of the increase in yield is attributed to having more starch in the diet (in place of protein), with ground maize content up from 18.8% to 22.5% of DM.

“More starch tends to support better milk production, so if we can save on the protein and replace it with starch, you’re actually improving milk production,” says David.

Milk from forage has also improved, from 8 litres a cow a day in December 2023 to 26 litres a cow a day 12 months later, by replacing some concentrate feed with high-quality silage.

He says the figure he considered the most important during the analysis of the results was milk urea levels.

“This indicates the protein efficiency and utilisation by the cow, and with the new ration, [milk urea level] dropped to 176mg/litre from 249mg/litre.”

The new ration is cost-neutral in comparison with the previous one, and fertility is unaffected, with pregnancy rate remaining stable at 27%.

Milk quality has remained stable despite the changes, he adds.

Lower emissions

The impact on the dairy unit’s carbon footprint of removing soya from the diet was analysed by Trouw Nutrition.

The previous ration was analysed at 37kg of carbon dioxide equivalent (CO2e), says Trouw’s sustainability manager for ruminants, Dr Liz Homer.

Dr Liz Homer © Wynnstay

Since making changes to the ration and removing soya completely, this has fallen to 21kg CO2e.

“In terms of the impact on the overall farm carbon footprint, this has led to a reduction of more than 10% of overall emissions,” she explains.

Liz adds that it is essential that feed advisers review the whole diet and consider productivity, profitability and planet.

They should question why raw materials with high emissions are being used, and whether there is a better alternative.

“Feed is one of the biggest contributors to carbon footprint, and there are quick wins to reduce emissions by reviewing the diets, which have a positive impact straight away,” she says.

Next steps

The inclusion of rumen-protected amino acids has allowed for a more protein-efficient diet and a transition away from soya-based diet formulation on the dairy unit, with a positive impact on yield and greenhouse gas emissions.

The farm is aiming to continue to target efficiencies and bring down its overall carbon footprint.

This includes a goal of 5,000 litres of milk from forage, which David says they hope to achieve by selecting maize varieties for improved forage quality and intake, and feeding bespoke diets to cows, grouped according to yield.

In addition, first-lactation heifers will be fed a specific robot cake to better support yield and growth.

Nigel Armstrong, the farm’s dairy herd manager, is encouraged by the outcome of the research.

“We have only seen positive results, with higher milk yields, greater forage intake, and lower urea levels.

“As a high-production commercial herd operating within a university, we aim to lead in dairy innovation. I just wish we had done it sooner,” he says.