Grazing ruminants in New Zealand are vulnerable to serious health and welfare issues due to facial eczema. Facial eczema is caused by ingesting the toxic spores of the fungus, Pseudopithomyces chartarum. The fungus lives on the dead litter of pastures and produces spores in summer and autumn. These spores contain a toxin that when ingested in large quantities can lead to liver damage and photosensitivity of the skin in ruminants. As well as facial eczema (FE) and its primary impacts, there can be further consequences for animal health and welfare, growth, reproduction and milk production (Olykan and Moot, 2024). The impacts of facial eczema are therefore a critical issue for individual farming businesses and the wider New Zealand economy.
Sonya Olykan and Derrick Moot of the Dryland Pastures Research Group at Lincoln University found that much of the recent research into facial eczema (FE) has focused on the animal health and wellbeing of cattle and sheep. While research on animal health is a critical component of managing FE, there has been a lack of focus on pasture as an important component. Olykan and Moot undertook a literature review of research about the effect of pasture plant species, farm management practices and associated environmental factors on FE in New Zealand. Their findings have been presented in a recent journal article ‘A review of pasture mixes and management strategies to reduce the impact of facial eczema in New Zealand’, published in the New Zealand Journal of Agricultural Research.
This blog will give an overview of the key findings of their research and dive deeper into how pasture selection and management is a critical tool in managing FE risk in New Zealand.
Why are pasture mixes and management strategies a critical part of managing FE risk?
As mentioned above, the fungus and spores that cause facial eczema (FE) live on dead plant litter in pasture. Figure 1 shows the relationship between seasonal ryegrass growth rates and the spore numbers of P. chartarum (the fungus that causes FE). As ryegrass growth declines in summer, there is a build up of dead plant litter due to grass dying. The increase in dead plant litter over summer results in a large increase in spore numbers of P. chartarum over February/March, and therefore increases the risk of FE. Ryegrass has another increase in growth over Autumn which consequently leads to another decline in growth rates through grass dying. This second source of dead plant litter from ryegrass means there is a second increase in spore numbers and FE risk in mid-Autumn.
Many factors can impact the amount of dead plant litter present including dry summers, urine-scorched herbage, topping with tractors, plant diseases and pests. An exacerbation of these factors therefore increases FE risk. Grazing management can also impact the amount of dead litter material and FE risk.
As dead plant litter is the critical component that houses the P. chartarum fungus that causes FE, choosing pasture mixes and adopting effective grazing management strategies to reduce dead plant litter is a very important part of the wider picture to reduce the risk of FE on farm.
'Safe' and 'unsafe' pasture and pasture mixes
Olykan and Moot’s review of the literature indicated that general-purpose grazed pastures in New Zealand livestock systems are largely ryegrass-white clover based due to their suitability for high fertility, summer moist, and intensive systems. Over time many pastures sown in these species have seen a change to being strongly grass dominant and often with grasses that are not always desirable. Moot points out that New Zealand farmers have a large range of improved grass, legume and forage crop species, and cultivars to select from when developing grazing pastures. This is an important point as it stresses that there is choice and ability to create the best conditions for your environment and system to reduce the risk of FE while also maintaining production and other goals.
The 'unsafe' FE pasture
An ‘unsafe’ FE pasture is defined as one dominated by ryegrass. Ryegrass produces litter during summer and autumn. This increases FE risk due to increased spore numbers on the litter.
Cocksfoot, browntop and danthonia have also been found to be high-risk species.
'Safe' FE pastures
Olykan and Moot (2024) state that ‘safe’ pasture monocultures or forage crops are low risk for the growth of P. chartarum and therefore will not be a risk during the FE season. Using alternative pastures to high risk ryegrass etc. can significantly reduce spore load in pasture.
Table 1 provides a summary of the major pasture plant species that can be used in ‘safe’ FE pastures and their suitability for pasture monocultures or pasture mixes. It is important to note that ‘safe’ pastures do not have the absence of spores, but spore loads that are at much lower levels and hence provide the lowest risk for FE.
The key ‘safe’ pasture monocultures to mitigate FE risk are chicory, white clover and red clover due to them all providing conditions for reduced spore counts. Tall fescue is also a safe grass that has been found to have more stable spore populations over the seasonal fluctuations, however it is better suited in a pasture mix with clover due to the need to manage N deficiency of the crop. Lucerne also has been stated as a safe pasture, however there hasn’t been sufficient data regarding FE and spore counts. Despite this, it has been recommended as a way to provide safe grazing during times of high FE risk.
'Safe' FE pasture mixes
The review of key literature found that the legume, grass and herb species that will provide safe pastures to reduce the risk of FE are already widely grown in New Zealand as monocultures or mixtures. These species have been incorporated into farming systems for reasons other than reducing the effects of FE such as failure of ryegrass persistence, providing winter feed, high-quality feed for lactating stock or finishing lambs, or wanting to grow more diverse and resilient pastures (Olykan and Moot, 2024).
The species that provide lower FE risk are also ‘summer-species’ which are able to provide higher quality feed when high-risk species are of lower quality. The suitability of different species and mixes is however, dependent on farm environment. There is great potential to look to incorporate alternative pasture mixes into current farm systems in order to lower FE risk while also looking to achieve other key goals of your farming operation.
Table 1: Summary of the major pasture plant species in New Zealand that can be used in safe pastures to mitigate the effect of facial eczema.
(Olykan and Moot, 2024)
Pasture Management
In the past, managing pasture was the only way farmers could limit the impact of facial eczema. Today, it remains an important tool that hasn’t had enough focus of late.
When managing pasture to manage FE risk there are two key aspects, as identified by Olykan and Moot:
- using appropriate grazing and other practices for safe FE pastures to maximise their persistence and control re-invasion of perennial ryegrass, and
- careful grazing of existing ryegrass-based pastures to reduce FE risk
On-farm management practices that reportedly reduce the impact and risk of FE include:
Incorporating safe-FE pastures into your farm system
- These have the potential to provide low-risk FE pastures that are also sources of high-quality feed during the summer months. This can be done by:
- having a pasture renewal programme that includes an appropriate proportion that targets FE-safe pastures
- in areas of hill and high country – develop satellite-safe pastures where it is possible to cultivate, with north-facing slopes targeted. Satellite pastures are small areas of cultivatable land that can be developed within larger hill blocks to support the lower producing steeper country surrounding it.
Reducing litter in the pasture pre-summer
Large amounts of plant litter due to lax spring/summer grazing (removal of 50% of the leaf) presents a higher FE risk. Controlling late-spring pasture before the FE season is important and can be done through close grazing with appropriate stocking rates or chemical topping. This boosts clover content and reduces the build up of dead matter.
Grazing management
Several interacting factors are involved in pasture grazing management: pre-grazing pasture sward length, duration of grazing, stock type and grazing intensity.
Existing grass-based pastures
- Key advice for grazing grass-based pastures is to ‘lightly’ graze in order to prevent the base of the pasture from being grazed hard. Having a higher post-grazing pasture mass will result in reduced spore intake as spores are most abundant in the parts of pasture that is closest to the ground.
- Grazing strategies for safe FE pastures will need to be based on species and mixtures, however, the objective needs to be on ensuring pasture persistence. Understanding the specific management requirements of your pasture or mix is critical in order to ensure that you can maximise growth rates.
- Multi-species mixtures require farmers to be more dynamic and intentional in how they graze. Understanding how to ensure resilience in your system when using new pastures is really important.
Legume focus
- The focus of grazing management for pasture mixes that contain legumes needs to be on minimising competition from grass species while also ensuring that hard grazing doesn’t occur.
- Set stocking is not recommended if clover dominance is the goal. Rotational grazing is preferred as it avoids clovers being preferentially grazed.
- Olykan and Moot stress that defining the grazing management rules for different pasture species is a key requirement for the adoption of pastures with a legume focus. The methods used for perennial ryegrass won’t be suitable for such pastures.
- Perennial clovers are the only option due to the need for grazing in summer and autumn.
- Legumes/clovers can be introduced into existing pasture via direct drilling or oversowing with clover seed. The nutritional requirement of the legumes needs to be of focus in fertiliser applications to ensure high growth rates.
Early culling/sale of stock
Reducing grazing pressures on pastures can also be achieved by destocking. This is of course dependent on your farm system and what works for you.
Suggestions from some research studies have been:
- selling non-capital sheep stock before the FE season (West et al. 2018)
- selling off stock or drying off milking cows as ways of reducing grazing pressure on the pasture (Smith et al. 1998)
- focusing on high-quality feed such as legumes for lactating stock in spring or for finishing lambs will allow a farmer to grow lambs quicker and quit them earlier. This reduces grazing pressure during FE season by remaining stock (Chapman et al. 2021).
There are various factors that impact facial eczema risk and spore counts will vary on any given farm, as well as paddock to paddock. Seasonal climate and aspect, pasture management through pasture type and grazing methods, as well as pasture profile, will all influence what level of risk FE poses for your farm.
Table 2: Facial eczema risk factors in hill country management (Olykan and Moot, 2021)
In summary...
Olykan and Moot have highlighted the importance of considering the influence of pasture in managing the risk and impact of facial eczema in New Zealand. Ryegrass-dominant pastures have a high risk for FE due to the dead plant litter that is produced over summer and autumn from grass death. The fungus and spores that cause FE reside and accumulate on this dead plant litter and therefore is a critical component of the problem that needs to be managed. Pasture species and mixes, as well as grazing management, are therefore critical components of the wider picture of managing FE risk on-farm. Pure legumes and resilient grass-legume-herb mixes are recommended options for looking to adopt safe FE pastures and lower the risk of FE outbreaks on your farm.
Managing pasture means managing the source of the problem and will allow for a more robust response to the very real issue of FE in New Zealand.
Alot of what is mentioned above is not applicable to a lot of upper north island properties (where FE is most prevalent in NZ).
How do we lightly graze or prevent the bade of the pasture being grazed through a autumn drought?
A dairy farm isn’t able to effectively reduce stocking rate through removal of non capital stock – all stock are capital stick and most farms may only have a replacement rate of 15%.
It isn’t possible to do forage cropping on more than 10-12% of dairy platforms, as you end up with a massive hole in the feed wedge in late autumn.
Incorporating more legumes is a great idea, but WC, when summer drought comes on, fizzles out pretty quick. Red Clover isn’t suited to a fast rotational grazing system.
There was no mention of supplementary feeding, the use of feed pads etc.
In terms of grazing management, pastured on UNI dairy properties through late spring early summer are grazed effectively and relatively hard to reduce the impacts of leaf litter (recommended down to 1500kgDM/ha). This in itself is a toss up between managing for pasture persistence over the summer dry and cleaning up the pasture. These dairy properties are still extremely susceptible to facial eczema, with spore counts through autumn of over 100,000. The same occurs on sheep n beef properties post weaning. The ewes are Mob stocked and effectively are on clean up duty until mating.
Long term exposure to low spore counts can be as damaging as short term exposure to high spore counts is what we are told. So on this basis the only real effective strategy is to completely remove livestock from pastures with moderate – high spore count levels. More use of forage cropping(safe pastures) and supplementary feeding- silage, feedpads etc.