Urea poisoning has been confirmed as the cause of last week's deaths of 122 cows on a south Taranaki dairy farm.
The cows were in a herd of 600 owned by 2007 Taranaki Sharemilkers of the Year Chris and Catherine Cook.
There were still some unknowns around the deaths, Taranaki Veterinary Centre chief executive Stephen Hopkinson, of Hawera, said. "But urea is the cause. The farmers were using a urea tank [to fill their water troughs]."
"We know it was urea and we know the level because it was shown in the testing. The Cooks say the tank was rinsed," Hopkinson said, declining to reveal details of the tests.
He could not say whether the urea was absorbed by the plastic of the Donaghys container the Cooks were using, whether some had not dissolved, or whether it had settled out of the solution and remained after rinsing.
Hopkinson said the cows would have absorbed the urea quickly because it was in a liquid.
Urea could be fed at a certain level to cows which converted it into protein, but there was no treatment for urea poisoning.
Farmers such as the Cooks who use a Donaghys product called LessN receive a plastic mixing tank - which is less absorbent than stainless steel.
LessN is a pasture boost added to a urea solution, a recent innovation in urea application.
Donaghys managing director Jeremy Silva said the confirmation of urea poisoning as the cause of the deaths showed they were not related to LessN itself.
The company's calculations showed almost 20kg of urea residue would have to have been in the 5000-litre tank to poison 122 cows, which would have had to drink the entire contents, or more than 40 litres each.
"This sort of amount does not seem likely if rinsing was reasonable and especially if the rinsing was followed by draining the rinsing water out," Silva said.
If the cows had had no access to water before the troughs were filled, sudden gorging might have exacerbated their reaction to urea. "'Every farmer will want to know what has happened on this farm," he said.
Massey University toxicologist Kathy Parton said cows would show signs of toxicity 30 minutes to an hour after ingesting excess urea.
Meanwhile, Hopkinson is warning farmers against multiple use of containers in the wake of the deaths. For example, he said teat spray in a detergent bottle would be neutralised.
- Taranaki Daily News
Is it time for authorities to introduce tougher penalties for poaching?Related story: Booby traps for poachers cost farmers