‘Software disease’ — The hazards of plastic, net wrap and twines

Animal Health: Ingestion of plastics has become a common killer

Despite its size, wads of net wrap such as this one can be easy to miss in a full rumen if you are not looking for it.

Cattle, especially young ones, are curious and chew on anything within reach. They may eat baling twines, plastic bags and other debris that ends up in their pen or pasture. The strange material may taste or smell interesting, so the animals chomp it down. Sometimes they accidentally ingest foreign objects in their feed. Cattle eat hurriedly and don’t bother to chew their feed very much the first time around. Every year a few cattle die mysteriously — often after a slow decline with loss of weight and diarrhea — and the owner and veterinarian may be clueless about the cause of death unless the animal is opened up to find the material plugging the GI tract.

For example, Colorado Springs veterinarian Dr. Gary McIntyre was called out to a ranch to check a steer that was slowly wasting away with watery diarrhea and getting weaker each day. The steer was a little bloated and wasn’t eating much, but drank a lot of water. His temperature was normal, heart and lungs seemed fine. He didn’t have hardware, and none of the fecal or blood tests that were taken showed any indication of disease. The steer finally died and Dr. McIntyre did a necropsy — and discovered denim pants plugging up the stomach.

Ingestion of various materials (usually plastic) has become a common killer today because cattle have access to more litter. The pasture or pen may be next to a highway where litter from passing cars blows over the countryside. If cattle are within a mile of dumpsters, construction sites, or a housing subdivision’s garbage that may blow over the fields, they may encounter various objects to chew on. Plastic bags, party balloons, weather balloons and other “fallout” from human activity may end up inside cattle, and there’s no way to remove the blockage without surgery. Without knowing the problem, very few veterinarians perform exploratory surgery. The result is a quiet, slow, painful death, with no definitive symptoms.

Small pieces of material may go on through and you never know the animal ate it. If it’s a large blockage, however, the animal may stop passing manure, and stop eating. The GI tract is “full” so there’s no room for more feed. A partial blockage leads to diarrhea, since only the liquid contents of the gut can make it through. This leads to suspicion of diseases like coccidiosis, salmonella, BVD, E. coli, Johne’s disease, liver flukes or other parasites, but there is no treatment for “plastic disease.” The best prevention is to pick up every piece of garbage you find in your pastures, including old hay twines, and never re-bale broken bales without first removing the twines.

Net wrap and twines

A growing number of cattle producers are discovering the risks for cattle when leaving net wrap or twine on big bales of hay/straw when feeding, or using a bale processor to chop forage as it is being fed. Dustin McCullen, a rancher near Dixon, Montana, noticed a cow losing weight, with diarrhea. She got to the point that he shot her as the most humane thing to do, then had his veterinarian, Dr. Beth Blevins, do a post-mortem examination.

“A few years ago we started noticing an occasional cow start wasting away, with little or no appetite. They went downhill fast once they started losing weight. We’d lose about one cow per year. We first noticed it about eight years ago, after we bought a new baler that used net wrap on the big round bales,” says McCullen.

“The cows lost weight quickly and we’d end up shooting them because we didn’t want them starving to death or getting too weak to stand up. We couldn’t figure it out. Then we heard about one of our neighbours having troubles and finding the rumen full of net wrap. I’d been suspecting something like this, so the next case we saw, we asked our vet to do a post-mortem. Sure enough, the rumen had a big wad of net wrap in it.”

With some of the first cases, he thought it might be hardware. “We’d put magnets in these cows and give them antibiotics, but nothing helped. These cows were starving to death in spite of lots of feed available. The rumen was full — with the net wrap and impaired digestion — so they couldn’t eat very much,” says McCullen.

“We wondered about Johne’s disease but we hadn’t bought any outside cattle. After we found the net wrap in the cow our vet cut open, we suspect that’s what was killing the other cows.” The wad of net wrap removed from the rumen was huge, and tangled amongst the hay in one big mess.

“In the past we often put straw bales in a round bale feeder, and to keep it from shattering and being wasted we’d leave the net wrap on and come back the next day and take it out of the empty feeder. I think sometimes the cows would get hold of that net wrap and eat it,” he says.

“When our vet posted that cow, this was the first case she’d seen, but she thought most people don’t check. They might have a cow or two that wasted away and they never know what the problem was. In our experience there has been no reason for the weight loss; it might be a four-year-old cow, or a 14-year-old cow. The symptoms are similar to Johne’s (but young cows don’t show symptoms, if they have Johne’s) and hardware, but after dragging that big wad of net wrap out of this cow we are certain that’s what happened to the other cows,” he says. They all declined in flesh and eventually had to be euthanized.

“When bales are frozen and we roll them out for the cows, it can be nearly impossible to take the net wrap off. We just leave it on the outside round and come back and get it later after the cows have eaten the hay. That’s probably when we have the most trouble — when the net wrap or twine is stuck to those bales and you have to leave it on there,” says McCullen.

“We didn’t seem to have that much trouble with twine. Perhaps it’s possible for a piece of twine to go all the way through the cow, whereas the big wad of net wrap can’t make it through.” It might depend on how much twine the cow ate, and whether it breaks apart going through the stomachs.

Beth Blevins, the veterinarian who did the necropsy on McCullen’s cow, says cattle may keep ingesting more pieces of net wrap and it gets all tangled together as a bigger wad, making it even harder for it to pass on through. Diagnosis is difficult in the living cow because the wad of net wrap would not be detectable with ultrasound. “It would look just like part of the rumen contents, mixed in with all the hay and feed,” she says.

The plastic doesn’t seem to break down in the rumen. “I don’t know how long this wad was in her gut, but it looked just like fresh net wrap — except that it had changed to a darker color. It didn’t break down at all. The rumen has bacteria for fermentation digestion, but it doesn’t have the acid that’s in the abomasum (true stomach). The acid might break it down, but the net wrap stayed in the rumen,” says Blevins.

John Campbell, head of the department of large animal clinical sciences, Western College of Veterinary Medicine in Sask­atchewan, has seen producers lose cows that ingested net wrap left on the bales or chopped up by a processor.

“I’m starting to believe this is a bigger problem than we thought. A few years ago I did a herd investigation in which a fairly well managed cow-calf herd had six cows die in two days. The local veterinarian asked me to come by, and I was able to necropsy two cows that had recently died. The cows were close to calving and in reasonable body condition,” Campbell says.

“The rumens were very large and full of feed and I found large amounts of plastic net wrap occluding the outflow. The producer had used a bale processor but did not remove net wrap when processing bales. I believe the cows ingested large pieces of net wrap and it may not have been an issue until they were heavily pregnant. Once the fetus got large enough to restrict abdominal space, the rumen became occluded and huge, and these cows died of what appeared to be suffocation.”

“The herd I investigated had multiple cows that died within a few days of each other, possibly because they were heavily pregnant. The full rumen and large uterus may have put too much pressure on the lungs. In other instances net wrap may become entangled with all the food material and create blockage at the exit into the intestine. This creates a slower demise, with the cow losing weight for a period of time.”

The ingested material may be small amounts of chopped up net wrap, or a large piece left on a bale — or not chopped up by the processor. “Perhaps the blades are dull, or the net wrap gets wound around them, or sometimes the processor just shoots that wrap out in one big piece and doesn’t chop it up. In this particular instance it was obvious that the processor was not chopping up the wrap,” says Campbell.

“I think sometimes the ingested pieces don’t affect cattle as much when they are not pregnant. There is enough room in the rumen for a fair amount of foreign matter to roll around without obstructing anything. But once a cow gets heavily pregnant with a big fetus pushing against the rumen, this makes it more difficult for the material to move around in there. It may get wedged in the wrong spot. It might suddenly obstruct the outflow and in some cases it might completely block the outlet and food can’t go on through the tract.” These cows can’t eat much and waste away.

“The pregnant cows I observed were in good shape, however, and dying suddenly. Their rumens were full of feed, and they had a big calf in them, and when they lay down with pressure on their lungs, they essentially suffocated. One of the cows I opened up had just started to calve. The calf’s legs were entering the birth canal. She may have laid down to calve and couldn’t breathe adequately because of the full rumen,” says Campbell.

“The rumens of the cows I opened up were gigantic. It took a lot of time to wade through all the feed material in the rumen to find the net wrap. It would be easy to miss if you weren’t looking for it, even though these were really big wads,” he says.

“I don’t know how common this problem is, or how often we’re missing it. For that producer who lost the six cows, you wouldn’t know whether he’d have 10 more cows die, or no more cows die. Certainly you could look for and diagnosis this condition in the heavily pregnant cow if you saw a cow that was really full on the left side and palpated her rumen and it was hard and impacted, rather than full of gas,” says Campbell.

“You could do a rumenotomy — open up the rumen and search for the foreign material. It wouldn’t be an easy job, with all the food material, but it would be something a person could try.” It might be a chance to save the cow.

“It would be an extensive surgery because you’d be pulling material out of that rumen for quite a while before you could get it all out. A lot of that stuff was hard and dry, and packed tightly, in the cows I opened up. It would take some time,” he says.

In this particular instance the bale processor had not chopped the net wrap up into little pieces like you’d expect it to. “It seemed to wrap around and then shoot it out in a big wad now and then,” he says. You often see big pieces lying out in the field after the cows have eaten the hay. It might be wise to gather it up or take it off the bales before feeding them, but that can be a challenge — if moisture has frozen the net wrap to the bales. It can be almost impossible to get it all off.

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