More than 200 cows have died in Southland after munching through a crop of bitter swedes containing toxic levels of natural chemicals.
Farming and crop specialists say the mild winter is likely to blame for the deaths of 200 to 300 pregnant dairy cows in the region’s lowland farms over July and August.
Farm animals routinely eat swedes and other brassica crops to supplement their diet over the winter months.
But David Green of PGG Wrightson Seeds, which supplies seed for swede crops, says frosts are needed to sweeten the swede bulb and deter growth of leaves which contain nine times the levels of naturally-occurring glucosinolates.
“This year they didn’t get the frosts in the low land areas so the bulbs didn’t sweeten and the leaves grew more than we’ve ever seen before,” Mr Green told NZ Newswire.
“As a result the bulbs aren’t as palatable as usual so these dairy cows seem to have consumed the leaves instead and what we have are animal health issues beyond what we’ve ever seen before with swedes.”
Glucosinolates are found in all brassica crops. In warmer temperatures levels of the compound can spike to point they become toxic.
“Farmers have been using swedes for probably 100 years and we’ve never seen anything like this,” Mr Green said.
Beef cattle, sheep and deer, all which routinely graze on swedes in winter, were unaffected by the crop.
“And it’s only in this specific area, the low-lying parts of Southland, that we’ve had this problem.”
He said farmers would be replanting 100,000 hectares of swede crops across New Zealand as usual this November.
He urged any farmers with concerns that their animals could be affected to talk over other planting options with agricultural retailers.
“There are other options, kale and beet for instance, so we can avoid this type of thing happening again.”