WESTERN PRODUCER — Producers are reminded to be careful this winter when choosing alternative or new feeds and are urged to test their feed
What could kill eight cows within 10 minutes?
That is one mystery the Western College of Veterinary Medicine’s disease investigation unit faced last winter.
Dr. John Campbell, a long-time professor and head of the unit, said he had never seen a situation like that.
“It was a bunch of cows dying suddenly in a cow-calf herd where the producer got a new delivery of some flax screenings,” he said during an October Saskatchewan Agriculture webinar.
The screenings had come from a local seed grower, and Campbell said the producer fed six pails to 40 cows.
“Within five minutes it was pretty obvious something was wrong. A lot of these cows began to show clinical signs. They went down, weak in their back legs, twitching their eyelids.
“Within 10 minutes there’s eight cows dead. There’s not a lot of things that can kill cows that quickly,” he said.
The local veterinarian sampled the animals but found nothing in the tissues.
Campbell said the kidneys, brains and lungs were severely congested, which would indicate acute circulatory failure and pulmonary emphysema.
But testing also showed the cows were extremely deficient in copper. Normal liver copper is 25 to 150 parts per million, but these cows were between 1.56 and 2.10 p.p.m.
Copper is necessary for iron metabolism and that severe deficiency was a key factor in the conclusion.
“What we think the diagnosis on this case was is cyanide toxicity. There’s a number of plants that can accumulate large quantities of cyanogenic compounds, sometimes called prussic acid…and flax is one of those,” he said.
When the plant cells rupture and release cyanogenic glucoside, it converts to hydrocyanic acid. This can be exacerbated when plants are stressed and Campbell said the significant drought and frost last year could be those stressors.
The hydrocyanic acid is absorbed into the blood stream, which prevents oxygen from being released from the hemoglobin, he said, and the animals essentially die from asphyxiation.
Although there is no conclusive diagnostic test, Campbell said the combination of severe copper deficiency and cyanide toxicity seem likely.
“It is pretty clear cut that there’s not too many other things that could kill cows quite that quickly,” he said.
Another case last winter involved flax but this situation involved flax straw.
A herd of 500 cows was fed a ration of about 40 pounds of flax and canary straw and nine lb. of barley.
The local veterinarian was called to examine a down cow with an enlarged abdomen and off her feed. She was treated with mineral oil and meloxicam but found the next day with a prolapsed uterus.
Campbell said the necropsy showed the cause of death as uterine prolapse, but the rumen and abomasum were filled with ingested fibre and enlarged.
“It’s ruminal impaction,” he said. “Even though the cow died from uterine prolapse, there were pretty clear signs of ruminal impaction.”
He said cows can handle only 1.5 percent of their body weight in straw, and flax straw should be a maximum of 10 lb. per head per day.
The third example from last winter came from a 50-head commercial herd being fed mixed grass hay, including slough hay with cattails, and greenfeed.
The local veterinarian said the herd was well managed yet a series of sudden deaths raised alarm bells.
Sixteen head died over three weeks in January and February: five between Jan. 1 and Feb. 5; and 11 between Feb. 5 and Feb. 28, with six occurring Feb. 5-6.
All were sudden deaths, with blood coming from the vulva, rectum and nose of some of the animals.
There was no evidence of blackleg, and some concern about anthrax, but those tests were negative. There was some evidence of liver necrosis and mild pericarditis.
All possibilities were examined, but when more cows died, an entire animal was sent to the lab.
Campbell said it was clear that the cow was in bad body condition. The spine, hips and ribs could be seen and inside there was no fat on any organs. The bones indicated emaciation and starvation.
“This cow for sure was emaciation and inadequate energy, but were the rest?” Campbell said.
He said the case is confusing and shows that investigators can get on the wrong track looking for anthrax and other possible causes.
Campbell also said the unit still doesn’t know what caused cases of low birthweight calves a couple of years ago.
Both calves and cows were low on manganese but that may or may not have been the reason.
He said it is an in-utero issue, but there is no good explanation beyond that.
A new syndrome identified in calves is also believed to be caused in-utero.
Liver necrosis has been seen at both Prairie Diagnostic Services and the University of Calgary veterinary college.
Affected calves show clinical signs within the first week of life. They are weak and poor doing, and sometimes show signs of neurological disease before dying. The cows appear normal and Campbell said some herds have seen substantial losses.
There are “quite dramatic lesions” on the livers and Campbell said it’s likely this is happening in-utero but no further explanations have been found.
There have been no identified commonalities among affected herds, feed doesn’t appear to be the reason, and no specific bacteria or viruses have been singled out.
Producers are reminded to be careful this winter when choosing alternative or new feeds and are urged to test their feed.