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Evaluating the effect of feeding willow leaves on growth rates in weaned lambs

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In this field lab Tom Fairfax, a farmer in the Northeast of England, will be feeding willow to weaned lambs. Willow leaves have been shown to have high concentrations of cobalt, an essential trace element which supports growth.  The aim of the trial is to find out whether eating willow improves the lambs’ health and growth rates by providing them with extra cobalt, and if so can it reduce the need for supplementary cobalt such as boluses and drenches.

Alongside the field lab, IF and the Soil Association are hosting an Agroforestry Learning Network on the topic of feeding willow to lambs.  This aims to enhance the learnings from the trial, and share farmer experiences, including the practicalities of planting willow for different livestock systems, methods of feeding to lambs and the anecdotal impact of willow on animal health and welfare.  The group will also be holding their own mini trials to support the main IF trial.

This field lab is funded by The Oglesby Charitable Trust


Cobalt deficiency (also known as ill thrift/pine) can be common in weaned lambs.  Cobalt is used to make vitamin B12 which supports lamb growth, and deficiency can cause significant production losses even at a sub clinical level due to poor growth rates.

Grass pasture rarely meets the daily requirement for lambs throughout the season and can be lowest in the dry summer months when weaned lambs should be at maximum growth rates. Cobalt and/or vitamin B12 are therefore often supplemented. 

However, administering boluses and drenches adds cost both in terms of product and time to administer, and free access supplements cannot guarantee consistent intakes in all animals.

Willow leaves have been shown to have high concentrations of cobalt, and lambs seem to find willow leaves highly palatable.  It is therefore hoped that costly supplements can be replaced by willow browsing, thereby improving lamb health more naturally.    

Trial design

Tom will keep his lambs together for the majority of the time, but once a week the group will be weighed, and a treatment group split from the main flock. The same lambs will be in the treatment group throughout the trial. This treatment group will be kept separate for a day and given access to willow leaves for feed. They will then be returned to the main flock for the rest of the week. Growth rates will be recorded throughout the trial, and at the end, when the lambs are finished, blood tests will be taken to establish cobalt levels in the two groups.

Latest updates

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Please check back later.

Trial set up and start trials at end of weaning

End of July 2024

Mid-point Bloods

August 2024

End of trial - end-point Bloods

autumn 2024

Analysis of results & final report

November 2024

Group Coordinator

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Tabitha Allen

Soil Association


Tabitha joined the Soil Association from previous roles within the NFU as county advisor for Northumberland and AHDB as a Knowledge Exchange Manager within the Farm Economics and Beef and Lamb teams covering the North of England. This experience sits alongside farming at home with her partner on a hill farm in Northumberland producing pedigree sheep and cattle.

Tabitha’s academic background lies within the human health sector with a BSc Hons in Biomedicine and Nutrition and a MRes in Immunobiology from Newcastle University. Tabitha’s main focus is on the practical application of research within the farming sector and supporting businesses to be in the best position moving forward.


A portrait of Dr. Nigel Kendall.
Dr. Nigel Kendall

University of Nottingham


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