Sharpening the sward
At Teagasc Athenry, researchers have been investigating the use of mixed swards in pasture-based sheep production systems. The results suggest increased diversity may be beneficial for animal performance.
Grass measuring in a perennial ryegrass and chicory sward
In recent years, there has been growing interest in the inclusion of clovers and herbs into grassland seed mixes to form more diverse sward mixtures. These mixed swards have the potential to improve sward quality and increase animal intakes leading to significant improvements in animal performance.
Clovers are associated with increased crude protein content in the sward and a reduced requirement for artificial nitrogen application through biological nitrogen fixation. Deep rooting herbs such as plantain and chicory are drought-tolerant and can uptake minerals from deeper in the soil, giving a high mineral content in the sward.
An experiment was established in Teagasc Athenry in 2018 and ran for four production years (2018-2021) investigating a range of mixed swards and their impacts on both sward and animal performance under a pasture-based sheep production system.
The sward types included in the study were:
- perennial ryegrass (PRG)
- perennial ryegrass and white clover (PRG+WC)
- perennial ryegrass and red clover (PRG+RC)
- perennial ryegrass and plantain (PRG+Plan)
- perennial ryegrass and chicory (PRG+Chic)
The swards were stocked at 11.5 ewes/ha, managed in a rotational grazing system and received 130kg N/ha/yr.
“Results from this study found that all swards produced similar annual herbage yields of 10.5-11.5t DM/ha. However, lamb performance was significantly affected by sward type,” explains Research Officer Philip Creighton.
“Lifetime lamb performance was significantly improved when grazing any of the mixed sward types compared to the PRG sward type, resulting in lambs reaching the appropriate slaughter weight between 16 and 28 days earlier. Results show that most of this improvement in lamb performance was coming from the post-weaning period, during which lambs grazing the mixed sward types were gaining 22-43g/day more than the PRG lambs.”
As a result of this improved performance there was also significantly less concentrate feeding required to finish lambs that were grazed on the mixed sward types. The highest performing lambs were those grazing PRG+RC and PRG+Chic, followed by those grazing PRG+WC and PRG+Plan, all of which were performing significantly better than those grazing PRG.
Philip adds that ewe performance was largely similar across sward types, with some improvements in ewe body weight and body condition score occurring from six weeks post-lambing until the following mating period.
Weighing red clover to determine clover content in the sward
Sow far, sow good
Achieving good establishment of a mixed sward is essential for its future productivity and persistence. Following the findings of the farmlet study, a series of detailed plot trials were established to investigate the effects of establishment method, seeding rate and perennial ryegrass ploidy, post-grazing sward height (PGSH) on the mixed sward types (PRG+WC, PRG+RC, PRG+Plan and PRG+Chic).
Preliminary results show that the establishment method had no effect on the establishment of white clover, red clover or chicory; however, the direct drill method aided the establishment of plantain in a PRG+Plan sward, relative to the conventional method (plough, till, sow).
Walsh Scholar Lisa McGrane explains: “Within a set total seeding rate of 25kg/ha clover and herbs were included at a low, medium or high level. Clover seed was included at a rate of 2.5, 5.0 or 7.5 kg/ha and herb seed was included at a rate of 2.0, 3.5 or 5.0 kg/ha for the low, medium and high seeding rate treatments respectively.”
Results show that seeding rate had a significant effect on forage content in all of the mixed swards. “The low inclusion rate of 2.5kg clover/ha was sufficient to establish white clover, whilst the medium inclusion rate of 3.5kg herb/ha was sufficient to establish chicory. For the PRG+RC and PRG+Plan sward types high inclusion rates of 7.5kg clover/ha and 5kg herb/ha respectively were beneficial and led to higher red clover and plantain contents in the sward,” says Lisa.
“When the mixed sward types were sown using a diploid or a tetraploid perennial ryegrass, these were higher contents of white clover and plantain when sown with a tetraploid perennial ryegrass. However, there were similar levels of red clover and chicory when sown with a diploid or tetraploid perennial ryegrass.”
Following the successful establishment of a diverse sward, grazing management can also have significant impacts, particularly on sward persistency, Lisa further explains. In a plot trial, three target PGSHs of 4.0, 4.75 and 5.5cm were implemented over a three-year period.
“It was found that red clover persistence was particularly poor under severe grazing to 4.0cm PGSH, the lax grazing to 5.5cm PGSH had a negative impact on plantain and chicory persistence, whilst white clover persistence was similar under all three PGSHs applied. Across all sward types the intermediate 4.75cm PGSH was most suitable.”
In conclusion, the mixed swards in this study provide significant improvement in animal performance whilst producing similar levels of herbage production relative to that of a perennial ryegrass monoculture, explains Philip. “Issues around forage persistency exist. However more detailed agronomy work will help to identify appropriate management advice for the use of mixed swards under sheep grazing.”
The researchers are confident that implementing appropriate management advice can maximise sward persistence without negatively affecting animal performance and sward quality, thus supporting the successful incorporation of mixed swards on commercial sheep farms.
“Lambs grazing mixed swards reached slaughter weight 16-28 days earlier.”
Lisa McGrane uses a quadrat and shears to cut a pasture sample, which will be used to measure clover content in a perennial ryegrass and white clover sward
Funding
This project is funded by the Teagasc Walsh Scholarships programme.
Contributors
Lisa McGrane, Teagasc PhD Walsh Scholar, Teagasc Animal and Grassland Research and Innovation Centre, Athenry.
Philip Creighton, Research Officer and Sheep Enterprise Leader, Teagasc Animal and Grassland Research and Innovation Centre, Athenry. Email:philip.creighton@teagasc.ie
Further Information
Find out more about the 2023 Teagasc National Sheep Conference here.
Read this published research paper:
[pic credit] Andrew Downes