A result of record warm weather in New Zealand

Mild winter likely cause of cow deaths

Mild weather affecting swede crops could be behind the mystery illness killing Southland cows, a major forage crops supplier says.

the Southland Times,

15 September, 2014

Dairy cows have died while eating swede crops in Southland, prompting DairyNZ to issue an advisory.

PGG Wrightson Seeds, which supplies forage brassica products in New Zealand, has investigated the issue and believes Southland's mild winter this year is to blame.

Anecdotal comments indicated a similar "swede poisoning" occurred in Southland 45 years ago but this event had caught everyone by surprise.

"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," PGW Seeds general manager David Green said.

With extra swede leaf material available because of the unusually mild winter, it appeared some cows had consumed more leaf and less bulb than normal, Green said.

"Consuming more leaf, less bulb and less supplementary feeds during wet August conditions has combined to amplify risk factors that can cause liver disease."

While the company does not yet know the full extent of the problem, it understands between 30 and 50 farms and hundreds of cows are affected.

Most of the farms were in central and lowland Southland and the illnesses ranged from mild photosensitivity, increased susceptibility to infections and liver damage, through to death.

Initial reports from veterinary advisors suggested glucosinolate toxicity was the cause of the illness, Green said.

Glucosinolates are natural components occurring in many pungent plants, especially brassicas.

While small amounts are believed to be healthy, the use of glucosinolate-containing crops as a primary food source for animals could have negative effects.

Mild weather in Southland over winter meant there was more leaf and the bulb of the swede was less palatable, leading to higher ingestion of glucosinolates through the leaves, which contained much greater concentrations.

The main crop associated with the issue is the cultivar HT Swede, used widely throughout the lower South Island, but at least one other swede variety is involved.

There have been no reports of problems in other parts of the country with HT Swede, which means the weather and environmental conditions in Southland are likely to blame.

PGW Seeds was consulting with affected farmers, rural retail representatives and other rural professionals, Green said.

It has also been talking with DairyNZ and has engaged specialist veterinary advice, as well as producing a communication to retailers and resource material for vets.

Farmers noticing any signs or symptoms in their cows should immediately contact their vet for advice.

SYMPTOMS

• Weight loss. Down-cows that are unresponsive to normal metabolic intervention.
• Photosensitivity. Signs of this include: - cows seeking shade (if available) - reddening of the udder and skin damage to white skin areas - restlessness shown by skin twitching; flicking of ears and tail; irritability; and stomping.
• If symptoms appeared, animals should be removed from crop if possible and shade should be provided for any animal showing signs of photosensitivity.