It is only relatively recently that perennial ryegrass-dominated swards have become the popular choice for pasture-based livestock production in Ireland.
Prior to this, swards generally contained a more diverse mix of plants that offered greater botanical complexity and a wider choice to the grazing animal.
However, with the widespread availability of relatively cheap fertiliser nitrogen, perennial ryegrass increased in popularity due to its excellent ability to produce high yields (approaching 20t DM per ha in some instances) of high-quality forage for grazing and conservation.
However there is an argument to be made that reliance on a single species, which requires high levels of fertiliser nitrogen, is problematic from both economic and environmental perspectives.
In the absence of fertiliser nitrogen inputs, perennial ryegrass abundance will quickly diminish in swards.
So, what of these more diverse sward types which contain greater numbers of plants from different functional groups including grasses, legumes and herbs?
You will hear different names used to describe more complex sward types. These include: herbal leys, multi-species swards and species rich grasslands.
Herbal leys and multi-species swards are essentially different names for re-sown swards containing a combination of grasses, legumes and herbs.
While the numbers of species included can vary, they're usually relatively low, ie. less than 10. On the other hand, the term 'species-rich grasslands' generally refers to grasslands that receive relatively low-intensity agricultural management and consequently have a greater number of species present.
As these swards are not re-sown, the species in them generally reflect factors such as local seed sources, soil type, pH, fertility and moisture, topography and climate.
'Smartgrass' and animal performance
While much research has been done in Ireland on multi-species swards at a plot scale, and internationally at field scale, it was the animal performance results from the Department of Agriculture-funded 'Smartgrass' research project conducted at UCD Lyons Farm that really kicked off the national interest in multi-species swards as an option for grazing livestock.
This study, led by Dr Sheridan, Assoc Prof Lynch and Prof Boland of the UCD School of Agriculture and Food Science, examined the performance of sheep offered one of four different sward types.
The swards offered were:
■ PRG - a perennial ryegrass monoculture;
■ PRGWC - perennial ryegrass plus white clover;
■ 6S - a six-species mix containing perennial ryegrass, timothy, white clover, red clover, chicory and plantain;
■ 9S - a nine-species mix containing perennial ryegrass, timothy, cocksfoot, white clover, red clover, greater birdsfoot trefoil, chicory, plantain and yarrow.
The PRG sward had a fertiliser nitrogen application rate of 165kg per ha per year, while all other swards received 90kg N per ha per year.
Lime, phosphorous and potassium were applied in line with soil tests and no slurry or farm yard manure was applied during the course of the study.
All swards were stocked with 12.5 twin-rearing ewes per ha from turnout in March until housing in late November/early December over two consecutive years.
Animals grazing the six species sward had the best performance over the two-year study.
Lambs grazing this sward type were 2.5kg heavier at weaning than lambs grazing the perennial ryegrass-only sward.
Indeed when we compare the weaning weights of the lambs grazing the perennial ryegrass sward to the average of the other three swards, the perennial ryegrass lambs were 1.7kg lighter at weaning at 14 weeks of age (30.9kg vs 32.6kg).
This increased weaning weight for the lambs offered the more diverse swards reflected increased growth rate to six weeks of age when the lambs suckling ewes on the six species sward were 2.2kg heavier than the lambs suckling the ewes grazing the perennial ryegrass sward (20.4 vs 18.2kg).
This suggests increased milk yield and/or milk solids yield by the ewes grazing the multi-species sward and this is currently under investigation for dairy cows at UCD Lyons Farm.
These improvements in animal performance were carried through until slaughter, when lambs on the more diverse swards were finished two weeks earlier than the lambs fed the perennial ryegrass sward (167 days vs 181 days).
However, one of the most impressive results from this work is the fact that lambs grazing the herb containing swards (6S and 9S) had lower parasite burdens and a 50pc reduction in the quantity of anthelmintic used over the course of their lives.
In Ireland, sheep production is the smallest of our three main pasture-based industries, so work is ongoing at Lyons investigating the impacts of multi-species swards on the performance of dairy cows and beef cattle.
Additionally, the School of Agriculture in UCD has partnered with Devenish Nutrition and Wageningen University to investigate multi-species swards under mixed cattle and sheep grazing.
While this research is in its infancy the sheep performance recorded at Lyons is being replicated at Dowth, Devenish's research farm, and multi-species swards are supporting daily live weight gains in Hereford steers from the dairy herd of 1.1 to 1.2kg per day in their second summer at grass.
There are challenges with multi-species swards, just as there are with anything. Our experience suggests that the main challenges include ensuring persistency of the herbs and to a lesser extent, the legumes in the sward.
Blanket herbicide application is not possible post-emergence as any herbicide on the market in Ireland that will kill things like buttercup and dock, will also kill the herbs, and finally establishment can be challenging particularly in the autumn.
However, in light of the challenges laid down in the EU Farm-to-Fork strategy, we believe multi-species swards have a significant role to play in ensuring the ongoing sustainability of Irish agriculture.