SOME TREES MAY OFFER NUTRITIONAL BENEFITS
TURN sheep or cattle into a field and some find the hedgerows simply irresistible. Likewise, fresh grass is shunned in favour of saplings planted to give them shade and shelter.
Tree browsing was encouraged historically and it’s long been known that tree leaves can provide pain relief or help animals manage internal parasites.
However little is known about the underlying science and whether it offers a feed opportunity for profit-conscious livestock farmers.
With trees set to dominate some farmscapes in the coming decades, a new study set out to dissect the potential nutritional value of trees to ruminants.
Commissioned by the Woodland Trust, the project was led by the GWCT’s Allerton Project and involved tree sampling at three sites, including Bangor University’s Henfaes Farm, Abergwyngregyn.
Leaves from oak, alder and willow were analysed for minerals that are important to ruminants.
This revealed that willow had higher levels of cobalt and zinc than the other two species.
“More importantly, concentrations of these minerals were higher in the willow leaves than in grass swards, and well above the nutritional requirements of growing lambs,” said lead author
Prof Chris Stoate, head of research at the Allerton Project.
“This is particularly important for cobalt, the availability of which declines through the summer in grass swards.”
The finding raises the prospect that supplements derived from willow leaves could be used to correct cobalt and zinc deficiencies in grass.
More work is needed to find out how much of these willow supplements would be needed.
Other trace minerals were also found to occur in tree leaves at similar levels to grass, and within the requirement range for sheep. Exceptions included molybdenum and iron.
All three tree species contained calcium at levels almost twice that of grass.
In theory, therefore, their leaves could benefit lactating ruminants – though calcium intakes in late dry cows are often restricted to prevent milk fever.
In terms of energy and protein, levels differed between tree species and from season to season.
As expected, crude protein content was higher in leaves sampled in June than in September.
Containing the most of both was alder, with willow the least. Nevertheless the results suggest tree leaves contain energy and protein in amounts that, if used as a supplementary feedstuff, they would “not be detrimental to the growth rate of livestock”.
Prof Chris Stoate said agroforestry offers multiple benefits, from soil health to flood mitigation.
He added: “It can be designed in such a way that avoids potential trade-offs between food production and the delivery of public goods.”
Even so, questions remain and a further trial into the palatability of willow is being undertaken by Nottingham University and the Allerton Project.