Could willow be the answer to better lamb growth?

The study, which was led by the Woodland Trust, sampled leaves from three native deciduous species – willow, alder and oak – from three sites across the UK and analysed their mineral, energy and protein content.

Willow leaves from all three locations were found to provide sheep with zinc and cobalt at concentrations exceeding the requirement in mg/g of dry matter, in some cases up to 17 times more.

Correct deficiencies

This elevated concentration found in willow leaves could actively correct deficiencies of these minerals in grass, meaning farmers could get better growth from their flock by integrating trees on their land.

Dr Nigel Kendall, lecturer in nutrition at the School of Veterinary Medicine and Science, University of Nottingham, who was involved in the research explains: “There are 22 essential minerals relevant to ruminant nutrition and some of these are prone to imbalances, either providing too much, too little or interacting with other elements.

“The minerals likely to cause issues in grazing ruminants are imbalances in trace elements such as cobalt, selenium, iodine, copper and zinc. Our analysis found that tree leaves can be considered good sources of a number of those key minerals within the requirement range for sheep, potentially offering similar or better concentrations than sward.”

He adds that the elevated cobalt and zinc concentrations in willow leaves could actively correct deficiencies of these minerals in grass that usually require supplementation. He says: “This could be especially useful in growing grazing lambs where cobalt deficiency is typically prevailing across the dry summer periods.

Growth rates

“Lambs tend to perform well in the spring because they are still getting the ewe’s milk, but as they take less and you go into the dry summer period there is an issue because the cobalt levels in grass begin to deteriorate.”

He said the research suggests willow leaves could help ‘remedy’ this growth rate decline.

The University of Nottingham is carrying out a further trial into the palatability of willow and its use as a supplement. This will look at how many trees and what type of planting would be required to support a ruminant diet, how the palatability of leaves from different tree species affect intake and what impact the varying content of anti-herbivorous compounds such as tannins can have on potential medicinal value.