Getting grass greener?
Can more diverse pastures offer a viable way to reduce methane and total farm gate emissions? Research at Teagasc Athenry is examining the benefits of diverse swards in lamb finishing systems.
Lambs grazing diverse swards show potential for enhancing the sustainability of pasture-based sheep systems. Photo credit: Andrew Downes.
Increasing lamb growth rates directly from pasture while reducing enteric methane emissions is an important strategy for improving production efficiency and promoting more sustainable lamb finishing systems.
In Ireland, pasture-based production systems are mainly based on perennial ryegrass, a high-yielding and nutritious grass species. Although perennial ryegrass can maintain productivity year-round, its nutritional quality, digestibility, and growth vary seasonally. During summer and autumn, this decline in quality can limit lamb intake and hinder growth rates.
Pastures with a greater diversity of plants, including legumes like white and red clover and herbs such as chicory and plantain, have shown strong potential to improve pasture quality post-weaning, supporting superior intakes, leading to improvements in performance. Furthermore, biological nitrogen fixation by legumes can support increased sward production from a reduced rate of artificial fertiliser.
Additionally, there is a constant pressure, nationally and internationally, to reduce methane emissions and the environmental impact of ruminant livestock, explains Sarah Woodmartin, Research Officer in grassland science at Teagasc Athenry.
“Methane reduction strategies relying on daily supplementation of the basal diet are not currently feasible in most drystock pasture-based systems. However, implementing strategies to increase the daily live-weight gain of growing animals at pasture such as improved grassland management and sward diversification can reduce age at slaughter, thereby decreasing the animal’s lifetime emissions.”
Companion comparison
Research conducted at Teagasc Athenry across five production years evaluated the inclusion of companion forages to the sward alongside perennial ryegrass. The sward types investigated were perennial ryegrass (PRG), perennial ryegrass and white clover (PRG+WC), perennial ryegrass and red clover (PRG+RC), perennial ryegrass and chicory (PRG+Chic) and perennial ryegrass and plantain (PRG+Plan).
Sward and animal performance, as well as the environmental impact of companion forage inclusion, were assessed within an intensive sheep production system. The swards were stocked at 11.5 ewes/ha, managed in a rotational grazing system, and received 120kg N/ha/yr.
“Our research question was twofold,” Sarah explains. “Can more diverse pastures offer a viable way to reduce methane and total farm gate emissions? And can this be done while improving lamb growth rates and overall production efficiency in pasture-based sheep production systems?”
All swards produced similar annual herbage yields of 10.5-11.5t DM/ha. Sward quality was enhanced in the post-weaning period with companion forage inclusion. The inclusion of any companion forage reduced sward fibre content. Sward digestibility and crude protein content were increased with white or red clover inclusion, while the addition of chicory and plantain resulted in an increased ash proportion, signifying a higher sward mineral content.
Improving performance
Lamb performance was positively influenced by the addition of any companion forage, primarily post-weaning. Post-weaning lamb average daily gain was increased by 33, 41, 40 and 25g/day for lambs grazing PRG+WC, PRG+RC, PRG+Chic and PRG+Plan, respectively.
Driven by the increased performance post-weaning, overall lifetime lamb performance was significantly improved, Sarah notes.
“This resulted in lambs reaching the target slaughter weight 16-32 days earlier when grazing a more diverse sward compared to the PRG sward. Reducing age at slaughter decreased the need for anthelminthic treatments – treatments against parasitic worms – in lambs grazing diverse swards, compared to those grazing PRG only.”
Improved performance on diverse swards also reduced the requirement for concentrate feeding to finish lambs, thereby maximising the contribution of forage in their diet. Concentrate use was reduced by 5-10kg/head for lambs grazing diverse swards relative to the PRG sward. Top performing lambs were those grazing the PRG+WC, PRG+RC and PRG+Chic, followed by those grazing PRG+Plan, which all outperformed lambs grazing PRG only.
A promising strategy
Methane output from lambs was recorded throughout the post-weaning period using Portable Accumulation Chambers. Methane production was reduced by 5, 8 and 13% in lambs grazing PRG+WC, PRG+Plan and PRG+RC, respectively, when compared to those grazing the PRG sward.
The inclusion of any companion forage lowered total farm gate emissions, whether expressed per kilogramme of carcass weight (see Figure 1) or per hectare. These reductions in total farm gate emissions were primarily driven by the reduced age at slaughter and the decreased reliance on concentrate feed in more diverse swards.
“Our research suggests that increasing the botanical diversity of the grazed sward is a promising strategy,” Sarah concludes.
“It shows potential to enhance the sustainability of pasture-based sheep production systems, supporting increased sward quality and enhanced lamb performance from pasture, while also lowering total farm gate emissions. However, to fully reap the benefits of including diverse swards within lamb finishing systems, changes to grazing and sward management will be required.”
Funding
The funding provided by the Teagasc Walsh Scholars Programme as well as The Department of Agriculture, Food and the Marine are gratefully acknowledged.
Contributors
Sarah Woodmartin, Research Officer, Grassland Science Research Department, Teagasc Athenry.
sarah.woodmartin[at]teagasc.ie
Philip Creighton, Sheep Enterprise Leader, Grassland Science Research Department, Teagasc Athenry.
Fiona McGovern, Research Officer, Animal and Bioscience Research Department, Teagasc Athenry.
Jonathan Herron, Research Officer, Livestock Systems Department, Teagasc Moorepark.