Saponins and grasses
In the videoare:
Tracy Routledge, Communications Officer and Narrator, Department of Agriculture and Food, Western Australia
Marion Seymour, Veterinary Officer, Department of Agriculture and Food, Western Australia, Moora
Geoff Moore, Research Officer, Department of Agriculture and Food, Western Australia
Ted Spadek, Chemist,ChemCentre WA
Transcript
Tracy:Sub-tropical perennial grasses have been widely sown as they can increase productivity on sandy soils while also providing year-round ground cover. However, a dark cloud has been looming in the distance with the occasional cases of secondary photosensitisation in stock grazing these pastures.
In this video, we investigate saponins in grasses and how to minimise the risk to stock.
Marion:In November 2008, we saw a cluster of cases of photosensitisation in livestock grazing perennial pastures. It was mainly weaner sheep that were involved but we did see the disease in one mob of young heifers. The percentage of the mobs affected varied from 5% to the whole mob showing signs of the disease.
The pastures these stock were grazing were perennial pastures. Some of them were newly-established pastures and others were well-established pastures that had been growing for well over five years. All the pastures had been sown to a mix of perennial grasses including Rhodes grass, Bambatsi and Gatton panic, setaria and signal grass.
The first thing you might notice with affected stock is that they might be out in the paddock trying to get into the shade. The affected stock have swollen faces and swollen ears and the swelling in the ears quite often makes the ears look droopy. The swelling is due to damage in the skin from a chemical which is activated by the sun.
After a few days, the swollen areas might become raw and scabby and they often lose the wool and hair from those affected places. The animals develop a yellow mucous membrane, and that can be easily seen around the membranes of the eye. And if you open the mouth and look at the gums, you'll see they are a yellow colour. Some affected stock may be unwilling to get up and, in a severe case, some stock may die.
Geoff:When there was another incident of photosensitisation in March 2009, it became important to work out exactly what is happening from both an animal welfare perspective and a natural resource management perspective. As the saying goes, 'bad news travels fast', and for all the benefits of perennial grasses, the sowing of the perennial grasses in the Northern Agricultural Region could stop overnight.
Tracy:Results from the post-mortem of livers from affected animals showed steroidal saponins were the cause of the photosensitisation. While an investigation of the pasture species in the paddock implicated panic grass and signal grass, as in the literature, it is reported both these species can contain saponins. On the other hand, Rhodes grass does not contain steroidal saponins.
The Department of Agriculture and Food WA secured funding through the Cattle Industry Compensation Fund in a joint project with the ChemCentre of WA. Pasture samples were collected at regular intervals throughout the year from existing replicated trials at Badgingarra Research Station, Wellstead in the south, and from so-called 'hot' paddocks, where grazing animals have been affected.
The sample analysis was undertaken at the ChemCentre of WA. Fortunately, a method for analysing saponins had been developed by the US Department of Agriculture.
Ted:As far as I know, we were the first to develop a procedure with the LC triple quad for the analysis of saponins within Australia. I think previous work was fairly rough and ready, going back quite a few years.
Tracy:The main equipment used is a so-called LCC.
Ted:The LC triple quad reads a liquid chromatograph. 'Triple quad' means that it has three stages of separation, so it allows you to be very sure of what you are seeing. Forensics particularly use it because the evidence will stand up in court.
Tracy:Analysis of saponins on the LCC has to fit around the heavy demand for testing for Kronic and other drugs of abuse.
Ted:Probably still at the rate of about 400 a week, down from 1,600 a week.
Geoff:The preliminary results show that signal grass contains high concentrations of steroidal saponins and appears to be the main contributor to the saponin content in perennial grass pastures.
At this stage, we believe that signal grass is the main pasture species responsible for the sporadic incidents of photosensitisation that have occurred. Panic grass can contain steroidal saponins, but at this stage, all of the samples have been below the threshold.
Marion:To reduce the risk of photosensitisation, it is important to be vigilant when grazing perennial pastures containing panic and signal grasses. The risk of photosensitisation is increased when the perennial grasses make up all, or most of the green feed-on-offer. There is a lower risk when the winter annuals are actively growing and make up most of the feed available to the stock.
Young stock are more susceptible to the photosensitisation than older stock, therefore by grazing in short, hard grazing intervals with adult stock, you're less likely to have a problem.
Most perennial pastures contain some Rhodes grass. It's important to graze your perennial pastures before the Rhodes grass becomes rank. Some of the cases of photosensitisation that we've seen have occurred in pastures with plenty of Rhodes grass, but because it's been allowed to go rank, the animals have actively seeked out the more palatable panic and signal grasses.
When stock are grazing perennial pastures, particularly in the high-risk periods, it is important to monitor them daily. Being able to detect signs of photosensitisation early will reduce any production losses associated with the disease.
If stock are affected by photosensitisation, it's important to move these stock off the pasture onto a paddock which contains plenty of shade and feed them some good quality hay. Avoid any green feed, and avoid high protein supplements, as they will initially make the problem worse.
It is important if you have animals affected by photosensitisation to report this to either your local vet or to the Department of Agriculture and Food, as research is ongoing and knowing about these cases as they occur will increase our knowledge of the disease and how to prevent it.
Tracy:To date, signal grass appears to be the main concern. But controlled pot experiments are being conducted to assess the impact of different stresses on saponin concentrations in the grasses. There is also regular sampling of panic grass and signal grass from a number of commercial paddocks in the Northern Agricultural Region, from Gingin, north to Binnu.
End of transcript
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