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SOUTHLAND FARMERS are being advised to keep a close watch on cows that have been grazing or are grazing on swede crops after reports of illness, and in some cases death, on dairy farms.
"The mild winter and lush growth of leaf material on brassica crops, especially swedes, has caused problems where dairy cows have been introduced onto the late winter swedes after wintering on other types of crops," David Green, PGG Wrightson Seeds (PGW Seeds) general manager seeds says.
PGW Seeds is the major supplier of forage brassica products in New Zealand.
"With extra swede leaf material available due to the unusually mild winter it appears some cows have consumed more leaf and less bulb than normal. Consuming more leaf, less bulb and less supplementary feeds during wet August conditions has combined to amplify risk factors that can cause liver disease.
"We don't have a total picture yet on the extent of the problem. We think between 30 and 50 farms are affected and the illnesses range from mild photosensitivity and liver damage right though to death. It is likely 100s of cows will have been affected."
Most of the affected farms are in central and lowland Southland.
"As soon as the incidents of sick animals were reported we began working closely with farmers, vets and suppliers to investigate the problem and explore solutions," Green says.
"Blood tests and post-mortem examinations of affected animals have shown signs of liver disease. Other signs have been photosensitivity and increased susceptibility to infections."
Initial reports from veterinary advisors suggest glucosinolate toxicity is the cause of the illness.
Glucosinolates are natural components occurring in many pungent plants, especially brassicas. Small amounts ingested by humans and animals are believed to contribute to the health promoting properties of cruciferous vegetables.
The use of glucosinolate-containing crops as a primary food source for animals can have negative effects however.
Mild weather conditions in Southland this season mean there is more leaf and the bulb of the swede is less palatable, leading to higher ingestion of glucosinolates. Leaves contain much greater concentrations of glucosinolates than bulbs.
Green says that PGW Seeds are consulting with affected farmers, rural retail representatives and engaging with other rural professionals.
"We have also been talking with DairyNZ and have engaged specialist veterinary advice. We have also produced a communication to retailers and resource material for vets."
He says the problem is consistent with issues that can occur with brassica feeding regimes, but these have been exacerbated by weather conditions in Southland this year.
"The cultivar HT Swede, supplied by PGW Seeds, is widely used throughout the lower South Island and consequently is the main crop associated with the issue in Southland."
He says there has been another swede cultivar associated with the issue but there have been no reports of problems in other parts of the country with HT Swede, supporting the view that a combination of the weather and other extenuating circumstances in Southland are behind the problem.
Farmers noticing any of the signs or symptoms in their cows should immediately contact their vet for expert advice.
If stock are grazing crops and show signs of photosensitivity they should be removed from the crop immediately and farmers should contact their vet. Cows that have grazed swede crops within the last 2-3 weeks and are now calving should be closely monitored. Calving and early lactation can cause stress on the liver and highlight clinical disease. If farmers have any concerns they are better not to graze the crops particularly now many crops are starting to flower. Flowering parts of the plant contain more glucosinolates than leaf or bulb.
What to look out for?
Cows can show signs of liver disease 3-7 days after starting to graze the crop. Some cows are showing signs up to 2-3 weeks after leaving the crop as cows calve down. Signs vary but can include sudden/excessive loss of body condition, going 'down' with apparent milk fever that is not responsive to standard milk fever treatments. Other signs reported include photosensitivity ('sunburn' on udders, teats and occasionally white areas of skin), and increased susceptibility to infections including metritis (infected uterus).
What to do if clinical signs appear?
Remove cows from the swede crop if signs of illness appear. Contact your veterinarian for advice regarding treatment of individual cows and for feeding and cow management strategies to support affected cows. If crops are 'bolting' with reproductive development, remove all cows from the crop.
PGW Seeds is continuing to work with veterinarians, rural retailer representatives and the farmers affected.
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