Should we be feeding trees to ruminants?

Collecting willow leaves at Loddington

Turn sheep or cattle into a field of fresh grass and some of them invariably prefer to eat the hedge!  And why are livestock so determined to eat the young trees we have planted to give them shade in hot weather and shelter in strong winds? If tree leaves are so palatable to ruminants, perhaps we should know why?

That was the rationale for a short project in which we and our Nottingham University partners joined forces with the Organic Research Centre and Bangor University, with funding from the Woodland Trust.  We wanted to understand better the potential nutritional value of tree leaves to ruminants.

We sampled oak, alder and willow leaves in early and late summer across three sites, the Henfaes research farm in North Wales, the Organic Research Centre in Oxfordshire, and our own farm at Loddington.  The leaves were analysed for minerals known to be important to ruminant nutrition.

Cobalt and zinc concentrations were higher in willow than in 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.  This is particularly important for cobalt, the availability of which declines through the summer in grass swards. For selenium, another important mineral, the sampling site had a greater influence than the tree species or sampling date.  More detailed results are now available as a pdf here.

There are clearly practical challenges to feeding willow leaves to sheep or cattle on a large scale, but these results provide a useful insight into the potential role of trees, and willow in particular, in meeting the nutritional requirements of livestock. We are investigating this further at Loddington, in partnership with the Vet School at Nottingham University.