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Toxic Plants and Herd Animals

Apr 15, 2016

By Aaron Agnew


For the past few weeks my focus has been on specific animals, goats, sheep, etc… For this week’s article I thought I’d discuss a topic that is relevant to any herd animal, the potential for a herd to consume toxic plants. 

While most animals will not consume a toxic plant if their food supply is sufficient, the potential is still there and, I think, it makes for an interesting topic.  In doing my research for this article I was surprised to find that many plants which are safe for human consumption are not always safe for ruminants.  One example is the plant commonly referred to as “lambsquarters”.

Lambsquarters was introduced to the Americas by Europeans centuries ago and it has not only found its new home to be acceptable, it has become so prolific that most people consider it to be a weed.  Its potential toxicity to herd animals has to do with its being a “nitrate accumulator”.  According to the University of Vermont Extension Service, “[s}ymptoms of labored breathing and rapid, weak pulse appear within one to four hours after consumption. Advanced symptoms include muscle tremors, general weakness, prostrate position and death.”  This plant will not always be toxic.  The amount of nitrate stored in the plant seems to be the deciding factor.  For a list of plants in Vermont that are toxic to livestock click here

So, what to do?  First, if you believe one of your animals, or multiple ones, have consumed a toxic plant call a veterinarian immediately.  However, prevention is the best tool!  As previously stated, most animals will not consume toxic plants unless their normal food supply is not enough to keep them from being overly hungry.  Most toxic plants have a bitter, or nasty flavor and an animal will not continue to eat them after the first bite.  So, in short, make sure your animals have plenty to eat.  Keeping fence lines clear of brush and encroaching plants can also help ensure that your herd does not come into contact with a toxic plant. 

Worth mentioning also is a condition called “grass tetany”.  “Grass tetany, sometimes called grass staggers or hypomagnesaemia, is a metabolic disorder of cattle related to a deficiency of magnesium (Mg).”  Grass tetany occurs when cattle or sheep return to pasture in the spring and the grasses they are eating do not provide enough magnesium.  Lactating cows are particularly susceptible. 

Signs of tetany can range from increased irritability for the animal, to muscle switching, to leg paddling (“lying on their side with stiff outstretched legs that thrash backwards and forwards”).  Treatment in severe cases should be turned over to a veterinarian who can inject Mg intravenously to help restore appropriate levels.  In cases that are not so severe, or simply in prevention, you can provide magnesium lick blocks, or a magnesium supplement with the animals feed. 

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