Why using willow leaves as sheep feed is worth investigating

Studies have indicated that willow leaves offer a viable option as a sheep feed.

Willow leaves can match grazed grass, in terms of the supply of energy and protein, and they also contain valuable micronutrients, said Dr Nigel Kendall of the University of Nottingham, who explains the potential advantages.

“Willow leaves have high concentrations of cobalt and zinc and these nutrients can help to promote lamb growth rates, especially during a dry summer,” said Dr Kendall. “The uptake of cobalt in grassland is reduced during periods of low rainfall and lambs will only require a small quantity of leaves, to supplement cobalt deficient grazing.”

The dry periods frequently correspond with July, August and September, when the majority of lambs are expected to achieve high growth rates. Producers will often supplement their livestock with micronutrients at this time of year, but they may not be necessary if they are given access to willow leaves, he explained.

“A cobalt deficiency will have a negative effect on lamb growth rates, as it is needed for vitamin B12 production in the rumen and is linked to the utilisation of dietary energy in the rumen and the liver. Zinc also plays a valuable role in the diet, but it is less likely to be deficient in lambs during summer grazing.”

A 2019 study by the Animal and Plant Health Agency found that almost ten per cent of tested lamb carcases showed cobalt deficiencies. Meanwhile, work at the University of Belfast has indicated that feeding willow leaves to sheep may reduce the animals’ methane emissions, he said. Willow is also highly palatable and its properties are thought to have an anthelmintic effect, which could help to reduce the use of worming product treatments.

He cited a number of possible alternatives for the practical feeding of willow.

“Willow branches could be cut and placed in the field. The lambs will browse the leaves and the branches can subsequently be chipped for mulch or burned in biomass boiler systems.

“Producers could give their lambs access to willow if they have trees already growing on the farm, or they could set up new plantations, with larger areas strip grazed. However, it can be difficult to fence between trees using electric fencing, as it will short the wires unless the rows are separated.

“Another option is to create ‘living fences’ using willow and these have the added benefit of providing shelter and shade. The willow leaves will re-grow on the tree branches, after being grazed.”

The dry matter of willow leaves is about 33 per cent. As part of a trial, Dr Kendall has fed willow leaves as 50 per cent of the diet over a period of a fortnight without any ill effects, but he recommended an inclusion rate of two to three per cent of the dietary dry matter. Together with grazed grass, the leaves will supply lambs with their full cobalt requirement.

Willow is easy to grow, he commented. It favours wet conditions and it could be planted in boggy, unproductive areas of the field to supplement the flock’s diet. Planted alongside watercourses, it can help to stabilise the banks and reduce soil erosion. For short-rotation willow coppice for biomass production, the leaves are currently considered a by-product, but they could be utilised by sheep as part of these systems in the future. Willow trees are extremely fast-growing, so coppicing or pollarding is a good way to harvest the branches.

There are many varieties of willow, but the UK research into its potential as a livestock feed has focused on goat willow, which is well known worldwide as a source of browsing feed for goats. Research has shown that all the willow tree varieties that have been tested to date contain similar concentrations of cobalt, he stated.

“Given the multiple potential benefits of willow as a sheep feed, I feel that it is worth further investigation. At present, willow trees are not utilised as a livestock nutrient, but hopefully that may change, as we learn more about its possible benefits to sheep health.

“A trial is being planned for this summer, with the aim of feeding willow leaves to select lamb groups, with their growth rates measured and blood samples taken. The results will be compared against groups which have been managed on grazed grass alone,” said Dr Kendall.

The Soil Association and the Innovative Farmers organisation have teamed up to launch an agroforestry network, which will include a project to investigate the potential benefits of feeding willow to growing lambs.

More information can be found at www.innovativefarmers.org/field-labs/feeding-willow-to-lambs-agroforestry-network.