Facial eczema (FE) season is imminent and we have already had a couple of clinical cases reported. Prevention is definitely better than cure with FE, so monitoring the situation on your farm is vital.
Pithomyces chartarum is the Latin name for the toxic mould which causes FE; the toxin is called Sporidesmin. It grows on dead plant material in most parts of the world but only occurs in great enough numbers to cause regular outbreaks of disease in the North Island of New Zealand.
The toxin is produced by the mould at the same time as it spores. The mould needs warm moist conditions to spore rapidly. Summer crops such as maize or rape are safe as they do not provide a ‘moisture retaining carpet’ on the soil surface which favours the mould growth. As spore counts are dependent on warmth and moisture they vary from place to place depending on the slope of the land and shelter as well as temperature and rainfall. For example on a flat farm in the same paddock, there was a count of 255,000 spores/g in a sheltered corner and 70,000 spores/g in the centre of the paddock.
In ideal conditions, when night temperatures remain high and pasture is wet during most of the day, a spore can germinate and produce another generation of spores within 48 hours, so spore numbers can rise very quickly. They drop down again more slowly; being removed from the pasture by wind and rain, being eaten by soil animals as well as cows and sheep and being destroyed by germination and drying.
Collection of pasture samples
The number of paddocks to be sampled and their selection will depend on the type of farm and the country it lies on. A dairy farmer with animals all in one mob can simply sample the paddock they are to graze later that day. On hill country, spore counts on north and west facing slopes are almost always higher than those on east and south faces. At night cool air flows down hill, so flats often have lower counts than the slopes above them.
A useful system is to use warm slopes as an indicator site and sample it regularly. When spore counts start to rise, check other paddocks to find the pattern over the farm. Do not assume that the dangerous paddocks will be the same every year. For example in a very warm dry year, wet flat paddocks, usually safe, may be dangerous.
To collect a pasture sample from a paddock; using scissors cut a handful of pasture leaves down to the level the animals are grazing (for cattle this is usually about 2cm), from at least 5 different places about 10 metres apart. There is some variation in spore numbers in an apparently even paddock, particularly if the grass is long and tufty, and collection from several places averages out this variation. Do not select for any particular pasture species unless you want to know the different contamination levels between for example Ryegrass and Clover. Try not to include soil as this can make the spore counting very difficult. Avoid parts of the paddock sheltered by trees or hedges and try to sample from an area of even slope. Take separate samples if you want to know spore numbers from under hedges or on different aspects. If you sample the site regularly, always follow the same route across it.
We require 200 grams of grass sample to run the test; this is roughly a bread bag full of grass. It needs to be processed the same day as it is cut, but will keep overnight in the fridge if you obtain the sample in the evening and can get it to your local clinic by the following morning.
Spore numbers can rise in the absence of rain if the weather is humid, particularly late in the season. Spore numbers do not always rise immediately after rain and their peak may occur up to a week after the last rainfall. Also it is not safe to assume that two or three frosts will reduce spore numbers to a safe level.
The ‘spore/g of pasture’ level which will cause clinical facial eczema is affected by the length of time that spore numbers stay high, the depth to which the pasture is grazed, and also the amount of sub-clinical liver damage already present in an animal from previous low doses of toxin. This damage may have occurred in a previous season.
Spore counts ≥ 100,000 spores/gram of pasture are highly dangerous in the short term.
Spore counts ≥ 40,000 spores/gram of pasture are dangerous with chronic exposure.
We do monitor several farms, which gives a very general picture of the toxic levels in your area. However, due to the variation possible, it is still a good idea to get a sample from your farm tested, once local levels become dangerous.
Once spore levels become ‘dangerous’ animals need to be given some form of preventative zinc treatment or moved to ‘safer’ grazing.
Spore counts can rise very rapidly, all susceptible animals should receive treatment. Remember animals that had a bolus in February may well need a further treatment four to six weeks later. We always see cases later in the season in animals that did not receive a second bolus. Administering zinc boluses is a highly skilled procedure and when done incorrectly can result in serious damage, infections and even deaths. We have highly trained technicians and handling facilities available to help you. Contact your local clinic to book.
For the latest spore counts in your area visit: https://www.anexafvc.co.nz/news-item/facial-eczema-watch-spore-counts or sign up for weekly emails at https://www.anexafvc.co.nz/newsletters
To learn how to collect a grass sample, contact your local clinic or click here https://www.anexafvc.co.nz/sheepfactsheets/how-to-collect-a-grass-sample-for-spore-count-testing