I occasionally get involved in unusual disease outbreaks in cattle herds as part of my job at the Western College of Veterinary Medicine. This particular case took place in a well managed cow-calf operation in Saskatchewan.
The herd had experienced the sudden death of a number of pregnant cows that were close to calving. The cows were all in good body condition and appeared to be fed appropriately throughout the winter feeding period. In each case, the cow had died overnight and no symptoms had been noted before death.
We were able to do post-mortem examinations on two cows that had died recently.
The main abnormality that we noticed was a large rumen, which was packed full of feed material. When we examined the rumen contents in detail, we were able to find a large mass of bale net wrap that the cow had eaten and that appeared to have obstructed the outflow of the rumen.
Net wrap has become a more common way of holding large bales together. I expect there is a lot of variation in how producers manage these types of bales when feeding them.
Some producers attempt to remove the net wrap or plastic twine before feeding the bale or processing it, while others hope the bale processor chops the net wrap into small enough fragments.
The producer I worked with was relying on the bale processor to shred the net wrap, and clearly it was not doing that adequately.
The net wrap was being shot out of the bale processor as a large wad of material.
Cows are curious creatures and we’ve all seen cows chewing on pieces of twine. They will often continue chewing and swallow this material, which will then enter their rumen.
The newer plastic net wrap or plastic twine will not be digested within the rumen. It will remain intact.
Small pieces will move through the digestive tract and be passed in the manure. However, these large pieces of material probably remain in the rumen because they can’t be passed into the smaller areas of the digestive tract.
It is not unusual to find bits of plastic twine in the rumen of an animal when we perform post-mortems, but the animals I was working with were obviously obstructed by this large mass of plastic material.
The plastic material can probably circulate in the rumen and may be unlikely to cause obstruction on its own.
However, these cows were heavily pregnant and their fetuses took up more room in the abdomen as they grew in size.
The large calf’s presence in the abdomen made it more difficult for the large mass of plastic to move around in the rumen and it eventually obstructed the outflow of the rumen.
The cows continued to eat, and their rumens filled up with a large amount of feed material. In this case, it was hay.
My theory is that these cows laid down at night and the combination of a large calf and a huge rumen full of feed caused severe pressure on their diaphragm and lungs, causing them to suffocate and die suddenly.
It may have been compounded by lying down on a slope so that there was more pressure on the lungs.
Other sufferers of rumen impaction and obstruction may sometimes take longer to die as they gradually lose weight because of the inability to move material out of the rumen into the rest of the digestive tract.
However, all the cows in this case died suddenly and were still in good body condition.
These obstructed cows would be difficult to identify other than having a full rumen.
There is no data on how common this condition is, and perhaps this is just one unusual circumstance. However, I expect that this may be more common than we realize.
The newer plastic twine material does not break down in the rumen and can potentially cause an obstruction.
The net wrap may be more likely to be ingested in large enough segments to actually block the outflow of the rumen.
This was certainly a devastating blow to this producer when these healthy cows in good condition with full-term calves all died suddenly.
Producers who use net wrap on their bales may want to consider removing it or at least making sure their bale processor is doing a good job of shredding the net wrap into small segments.
John Campbell is head of Large Animal Clinical Sciences at the University of Saskatchewan’s Western College of Veterinary Medicine.