The Impact of herbal leys on the health and performance of grazing lambs

Herbal leys, also known as multi-species pastures, are characterised by a combination of grasses, legumes and herbs. In grazing systems, increasing the biodiversity of the sward is one possible strategy that could reduce the reliance on chemical anthelmintics, with legumes and herbs being rich in compounds with potential anthelmintic properties. It is believed that herbal leys could help to: 

  1. reduce worm burdens in grazing lambs
  2. maintain/improve liveweight gain
  3. reduce the need for fertiliser input

This project, involving three farmers from Ceredigion and Carmarthenshire, aimed to assess the effect of using a herbal ley in comparison to a more conventional ryegrass and clover ley, in its effect on both daily liveweight gain and worm burdens of growing lambs. 

Project Plan

  • On each of the three farms, one field was split into two plots of equal size (ranging from 1ha to 3ha per plot), with one plot sown with two ‘off the shelf’ seed mixes.
  • The herbal ley used was a mix of 50% perennial ryegrass varieties and other species such as chicory, plantain, yarrow, timothy and white clover.
  • The conventional grass mix used was a more common perennial ryegrass, timothy and white clover mix.
  • A worm burden was also evenly introduced onto the new pasture. The two plots on each farm were then subdivided into quarters to be rotationally grazed, with lambs grazing the plots from weaning to the end of October, grazing from 2500 kgDM/ha down to no lower than 1500 kgDM/ha.
  • A sample of 10 lambs from each trial plot were weighed and faecal sampled across the three farms every two weeks throughout the period.

Project Results:

  • On average, there was a 35% reduction in worm burden within the lambs on the herbal pasture in comparison to the conventional plots.
  • The pasture grown by the herbal leys was comparative to the conventional pasture in terms of overall dry matter yield, with herbal leys responding better in dry conditions.
  • Daily liveweight gains of the lambs on both the herbal and conventional plots were similar. The lambs on the herbal pasture had higher growth rates in 2022, probably due to the herbal leys dealing with the drought conditions better than the conventional leys.
  • On average, the herbal pasture had a higher sugar content than the conventional pasture.
  • The herbal pasture did not deplete the soils of calcium as much as the conventional pasture.
  • It would be beneficial when using herbal pasture to have a 30+ day grazing rotation, as the 27/28 day rotation which the project was working on seemed to affect plant population by year 3, as far as having a reduced herbal population.