(Dr. Dan Thomson): Hey folks, welcome to DocTalk. We are going to have a great show today. We’ve got Dr. Deon van der Merwe who is a toxicologist here at Kansas State University and we are going to talk about different toxic plants that are out in your pasture, some of the problems they can cause whether it’s putting up hay or over grazing pastures and ways that you can prevent your cows from running into those toxic plants.
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(Dr. Dan) Welcome to the show. (Dr. Deon) Thank you very much. (Dr. Dan) Folks, this is Dr. Deon van der Merwe who is the head of the toxicology section here at the Veterinary Diagnostic Laboratory at Kansas State University’s College of Veterinary Medicine and Dr. Deon you see a lot of cases. You see a lot of different things around, and I wanted to bring you on the show to talk to people about toxicology and generally toxic plants out in our pastures; there’s quite a few. (Dr. Deon) Yes. It’s actually quite surprising how many poisonous plants that are in Kansas. (Dr. Dan) [laughs]. (Dr. Deon) We don’t necessarily think of Kansas as the world’s most diverse place in terms of plant life but if you start counting the number of species and you use as your definition whether poisonous plant is plants that have been reported to have caused poisoning, there are about 140 species of poisonous plants in Kansas. (Dr. Dan) [laughs]. And they’re present all the time. (Dr. Deon) Yes. That’s the other thing that people sometimes find surprising. These plants are in just about every pasture in Kansas. You’ll have a hard time finding a pasture that does not contain any poisonous plants. So the question really becomes, when do they cause problems, because they obviously don’t always cause problems. So understanding those conditions under which the poisonous plants become a risk is really the key. (Dr. Dan) So they’re there and different environmental conditions either have them more prevalent or help the animals select them, something to that nature, and then we start to see their issues. (Dr. Deon) Yes. There are a few reasons why this is a fact. So one of the big ones is that most poisonous plants are not that attractive to animals to eat them, so especially grazing animals like cattle, they are adapted to living in an environment that has poisonous plants in it. So there are certain compounds that are produced by the plants that the animals can detect. And if they detect that then they will move on and eat something else. So when we see most of the problems is when they don’t have something else to move on to. So, for example, you have a severely overgrazed area then the plants that are nontoxic are more attractive to the animals can be consumed to the extent that they have no choice left but to eat whatever is there… (Dr. Dan) Right. (Dr. Deon) …which could be the poisonous plants. And then, of course, there’re quite a few other factors as well like drought for example. It can change the physiology of the plant in such a way that it starts to build up compounds that are going to be toxic. So a good example of that is nitrate. Nitrate is always present in most plants. They use it as a basic building block for making proteins and other molecules in the plant. But under certain conditions like drought the nitrate can build up so the concentration in the plant can start to exceed the threshold where it becomes poisonous to cattle. (Dr. Dan) So overgrazing, drought, sometimes we have to understand they’re always there and either our own poor management or potentially some of the environmental conditions will get us there. We’re going to take a break. (Dr. Deon) Yes. (Dr. Dan) And then we’ll come back, we’re going to talk more with Dr. Deon van der Merwe about toxicology and the toxic plants out there in your pastures.
(Dr. Dan Thomson) Hey folks, welcome back to DocTalk. Dr. Dan Thomson here with Dr. Deon van der Merwe and we are talking about toxicology; plants, pastures, gardens, different things around your farm that you might not know that it was toxic, that could be toxic, either to your cattle or to yourself through your cattle. When we left, and during the break, we talked about some different subjects, but one of the things was about people that not only manage the forage that’s in the pasture but then they are going to make hay. What are some of the things that people need to be concerned about or at least have an awareness about when they’re putting up hay? (Dr. Deon van der Merwe) One of the things that, of course, is going to play a role is what are the plants that are being incorporated into the hay. So, when you make hay and you store it for a while and then you present it to animals, maybe during the winter time, there is going to be much less of selective feeding on that material. So, if you incorporate poisonous plants in the pasture, even though the animals will typically avoid those plants if it’s growing in the pasture in a fresh state, when the plant is dried out and mixed with other things in the hay then they are more likely to actually consume that material. If it is a plant that contains toxins that tend to persist, a good example of toxins like that would be alkaloids, so the alkaloid containing plants, if that material gets into hay, that hay will become poisonous and will stay poisonous for a very long time. So, even if you use that next year it will still be a risk. Another thing that can be risk here is the physiological state of the plant when you make the hay. This is another good example where nitrate is a factor. So, if you have those conditions, let’s say you have a drought condition and the plant has accumulated a dangerous level of nitrate, if you cut the plant at that stage and make a hay the nitrate will be preserved in the hay and the hay will be poisonous to animals, even many months or even years later. However, if that plant remains in the pasture and growing conditions get better, so the drought gets broken and it starts growing again, then the plant will actually consume the nitrate and it will become safe again. So, by way of making hay you actually preserve the toxicity of the material. (Dr. Dan) Some of the places where you have one cutting of hay or maybe two cuttings of hay, some of the brawn pastures and different things like that, it might behoove you if you’re going through a draughty time period to wait a little bit longer than normal, just based on the nitrates. Can you test the hay before you put it up then, on nitrate levels? (Dr. Deon) Yes, you certainly can. If you have those conditions that you expect can lead to nitrate poisoning, like drought conditions as well as plants that grow in very highly fertilized soil, so old fields and things like that, areas where you might have distributed manure, those are all risk factors that will make it more likely. So if you have conditions like that, highly fertilized soil, drought conditions, then you should test before you make hay. (Dr. Dan) Cool. Well, let’s take a break. When we come back we’ve got some fun ones to talk about, things that people probably don’t think about when they think about toxicology and their cattle. Thanks for watching DocTalk, more on toxicology after this.
(Dr. Dan Thomson) Hey folks, thanks for watching DocTalk and I’m here with Dr. Deon van der Merwe and we are talking about toxicology because he is an expert in toxicology and works here as the leader of our toxicology group at the Kansas State Veterinary Diagnostic Laboratory located in the college veterinary medicine. Some of the things, the first one that we talked about, you said spring frost and some of the poison hemlock issues. (Dr. Deon van der Merwe) Yes. That’s one of the interesting things that we run into on occasion here in Kansas. Poison hemlock is a fairly common plant especially in the center to the eastern parts of the state. Around Manhattan and to the east of Manhattan it’s quite common. It doesn’t cause poisoning every year even though in some years it just grows everywhere it seems. It doesn’t seem to cause a lot of poisoning. However, when we have late frost in the spring, typically around middle to end of March, that is when the poison hemlock sometimes would be the only green thing that has started growing, so the grass is still brown down and the only green thing in the pasture would be the poison hemlock. However, they are going to be producing compounds that the cattle find offensive. However, when they get frosted and you get ice crystals that form in the cells, the ice crystals will actually damage the plant cells to the extent that those volatile compounds that cause the aversion in the cattle, those don’t stay around in the cells anymore because of the damage to the cells. After that frost for a period of about two to three weeks, those plants are extremely dangerous because now they are less able to induce the aversion in cattle but they are still the only greenish things around. (Dr. Dan) Folks, when we talk about aversion, some plants will get a post-ingestive feedback or a negative post-ingestive feedback that after the cow eats something, they don’t feel so good. That would then train the cow to not continue to eat that plant and when you get this frost it knocks out those compounds that send those signals, so they just eat the heck out of it. (Dr. Deon) All right. That’s actually an important principle. The fact that you can have animals essentially get trained on what plants that are safe and which are not. When you have animals that get transported from one area to another, and especially if they are hungry at the time that they get offloaded, that is when we often see plant poisoning because then they tend to just eat whatever is there. They are not trained to know which plants are dangerous. (Dr. Dan) So if you are shipping cattle or buying cattle from out of the western parts of the United States and bringing them east or something in the southeast and bringing them west, you might want to do something to kind of control or curb that appetite as you turn them out. (Dr. Deon) That’s right. I think at least what you should do is make sure they have adequate safe feed readily available at the time of offloading. Don’t just send them directly into a strange pasture. (Dr. Dan) Some hay and make sure you nitrate it before you make the hay. There are a lot of things going on here but let’s take a break and when we come back let’s talk about the white snakeroot and the yew plants. I think those are pretty cool things. Folks, Dr. Deon van der Merwe and he’s toxicologist here at Kansas State University and we are glad to have him here on the show. More after these messages.
(Dr. Dan Thomson) Hey folks, welcome back to the show. Dr. Dan here with Dr. Deon van der Merwe, who is a toxicologist at the Kansas State University Diagnostic Lab located at the College of Veterinary Medicine. We have a couple of fun ones here to talk about that people probably don’t recognize, the yew bush. (Dr. Deon van der Merwe) So, yew is a fairly commonly used garden plant here in Kansas. It’s an evergreen. It tends to be quite robust and nothing wants to eat it because it’s very poisonous. Unfortunately, it is one of those plants that is very, very toxic to cattle but cattle don’t have an inherit aversion to it so if they get over it, they will often eat it. One of the poisonings that we see, unfortunately quite commonly in Kansas, is when people trim the yew bushes or take them out and then that material gets thrown out in a way that cattle can get access to it. It really takes a very surprisingly small amount of plant material to kill an adult cow. Just a few twigs are enough to kill a large bovine. It is very toxic, very potent. A small amount is quite poisonous and it kills quickly. (Dr. Dan) If you’ve got cows and if you’ve got evergreen bushes around make sure that it’s not a yew bush, and if it is, don’t throw the trimmings over in the pasture with the cows. (Dr. Deon) For sure. Very dangerous. (Dr. Dan) The other one, because we wanted to make sure we got to this one, was the white snakeroot. (Dr. Deon) Right. The white snakeroot is a little shrub with tiny white clusters of flowers that grows on it. Towards the middle to the end of the summer you will see the white flowers. This time of year, early summer, you’ll see just the green leafy material. It’s a plant that grows at the edges of forests. Typically you don’t see it inside pastures themselves but if a pasture butts up to a forested area you tend to see them at those forest edges because it’s a plant that’s adapted to the intermediate light level. It can’t really stay or live effectively under a deep shade in the forest and there’s too much sun out in the pasture, but when you get that in between area that’s where they grow. So, if you have that condition and dairy cattle get to those plants, they will consume it and then the milk will become poisonous. (Dr. Dan) To us? (Dr. Deon) To us as well as to calves. Anything that consumes the milk will actually be at risk of getting poisoned. (Dr. Dan) So, beef cows that consume it could give it to their calves and cause poison. (Dr. Deon) Exactly. That is possible, for sure. (Dr. Dan) But you said that there was a famous… (Dr. Deon) An infamous, I should say. (Dr. Dan) …infamous case. (Dr. Deon) Right, the infamous case of Abraham Lincoln’s mother. This was, of course, back in the early 1800s when people were not familiar with the problem and what it was caused by, it was known as “milk fever” at that stage because they knew that this was a problem associated with milk but they didn’t know why. Later, of coarse, people figured it out that this disease was caused by this compound from the white snakeroot excreted into the milk. Unfortunately, Abraham Lincoln’s mother actually died when he was just a kid. He was about 10 years old when his mother died from this. (Dr. Dan) Well, we could go on and on. We’ve got to have you back on the show. Thanks a million for being with us today. (Dr. Deon) You’re very welcome. (Dr. Dan) Folks, thanks for watching DocTalk. If you want to know more about what we do, you can find us on the web at http://www.doctalktv.com. Remember to always work with your local veterinarian. Thanks for watching us today, I’m Dr. Dan Thomson and I’ll see you down the road.
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