New opportunities for feeding beans

Kelvin Cave Ltd is a participant in farming’s major Innovate UK-funded project which aims to replace imported soya with home-grown protein. One part of the trial is already showing great promise with this ambition.

New opportunities to use beans as a ruminant feed could be developed if the early indications from UK trials lead on to improved livestock performance.

The trials suggest it may be possible to increase the percentage of bypass protein in beans by as much as 90%, so improving the crop’s credentials as a soya replacement for ruminants. 

This work is part of the major national NCS (Nitrogen Efficient Plants for Climate Smart Arable Cropping Systems) Project which was launched in summer 2023. Its ultimate objective is to see UK-grown protein crops displace soya imports as a livestock feed.

The high protein in beans makes them a promising option in this endeavour, but work is ongoing which will indicate with more precision how they respond to different types of processing and how to optimise their nutritional value. 

The trials are part of the project’s Work Package 4, and are being undertaken at McArthur Agriculture’s Scunthorpe site, where grain drying, processing and storage systems for combinable crops are designed and manufactured.

Here, beans are being processed and toasted at a range of different temperatures and by two different techniques. Then, they are rolled through a Murska 220SM mill with a pre-crimper – supplied by Kelvin Cave Ltd who are participants in the NCS Project – to achieve a physically suitable sample for ruminant feed. 

John McArthur, MD of McArthur Agriculture, explains: “We are dehulling the beans and then toasting them with heat which is either provided by an oil burner or by electrical resistance.

“We are using a temperature range from 125°C to 225°C and with different residence times,” he says.

“The Murska mill, used after the toasting, has two sets of rollers which achieve a really good finish,” he says. “The top set rolls the beans and the lower rollers can be set to process a different sized pulse or grain if a mixed crop is rolled. 

“This technique will be increasingly useful as farmers carry out more intercropping or bi-cropping in future,” he says.  

Aiming to establish which heating technique achieves the greatest nutritional improvement, this is also being weighed up against both the financial and carbon cost of toasting and processing the beans. 

Lower temperatures are associated with the electric toaster, while the oil burner toasts at greater speed and higher heats.

“We anticipate the electric toasting will be more cost- and carbon-efficient, but we want to make sure it can achieve the nutritional improvement,” says John.

“If it can, the electric roaster will support the case for processing beans as a substitute for soya,” he believes.

It is envisaged that the smaller capacity electric roasters could have a place on UK farms, where they could run on renewable energy and be ‘as green as the grid’ supplying the power.

“The oil roasters are much bigger units, using more energy, but toasting up to 10 tonnes an hour,” he adds. “This makes them more likely to be mobile units, used by contractors visiting farms.”

Cattle trials

The dehulled and toasted beans are being fed to cattle in experimental conditions so digestibility and other parameters, can be measured.

The animal trials are taking place using fistulated cattle in a Belgian research facility and on UK farms.

Similar dehulling and toasting processes to those in the trial have been used by farmers in Scandinavia for many years and are anecdotally reported to improve the beans’ nutritional value and livestock performance. However, the optimal method of processing and rates of inclusion within cattle rations have yet to be determined.

“We will continue to build on the really positive data we have so far,” says John. “This shows that these processes are likely to have a role in substituting soyabean meal for home-grown protein. 

“We know that switching to home-grown legumes is one of the single most efficient interventions that can be made in farming in terms of carbon reduction,” he says.

“Highly productive livestock benefit from increased bypass protein that makes their growth and milk production more efficient,” he says.

“Soya is a good source of bypass protein when processed so if we are trying to replace soya with beans, we need to shift the protein degradability from the rumen to the hindgut,” he says.

Toasting is said to alter the protein structure, changing its rumen degradability, but the degree of this change at different temperatures has yet to be defined.

“We want digestible undegradable protein [DUP] but we don’t know how much each specific toasting condition creates,” he says.

“If we find that protein is also protected from digestion in the hind gut, then it will be lost in faeces, undigested. Thus, we are testing heating to different temperatures for different time periods to assess which provide the optimal processing conditions,” he says.

The dehulling process also has the potential to change the protein degradability, due in part to the hulls’ higher content of secondary plant compounds (or anti-nutritional factors) than in the bean itself.

But the effects of the anti-nutritional factors aren’t always negative. 

“For example, some secondary plant compounds at a certain level are known to reduce rumen protein degradability and thus enhance total gut protein digestibility. Some can also inhibit methanogens, improving the energy status of the ruminant,” he says.

“So, we should interrogate the processing options to improve the efficiency of the feed,” he says. “It is all a question of balance, and we still need to find out how much processing is needed to optimise protein digestion.”