The article you wrote in August about Chinaberry trees being toxic parallels an issue I have had with acorns. Three years ago, I lost some young heifers, poisoned by acorns. This past December I lost three mature cows with the same issue. My vet told me he knew of no other ranch that had had similar losses. I checked with my county Extension agent, and he said the same thing. How can I be the only person with this issue when our county has so many oak trees?
We have had this question several times in the past, and I've never felt I answered it as well as it needed to be answered. It seems to be such a random occurrence that defies an absolute answer. I've seen it many times over my 39 years in practice. Some of my own cows will forage acorns in the fall when I rotate pastures, and I have never had a problem. So why sometimes, and why some operations, and not others?
Let's first look at what is poisoning these animals. The toxins involved are tannins. Buds, young leaves and fresh acorns contain the highest levels of tannins. Levels of tannins also vary with species of oak, time of year, and even year to year. They do their damage in the lining of the digestive system, leading to ulcers in the mouth, stomach and intestines. They are broken down in the rumen to other toxins, that are absorbed and can severely damages kidneys and blood vessels. Affected cattle often go off feed, have dark, tarry stools, stand "tucked up," have ventral edema and kidney failure. Often the first sign of a problem are dead cattle. Treatment involves supportive care, but I have had little success especially if the kidneys are failing.
These types of poisonings are often linked to storms where trees are blown down, or large numbers of acorns blow off the trees. Hungry cattle, often those in poor body condition, are more prone to problems. Some in the field of veterinary medicine and research believe these leaves, buds and acorns are less than 50% of the diet cattle are going to be okay. Clearly, that makes good nutrition important. Another very pragmatic approach is to limit the herd access to pastures with lots of oak trees in the spring and early fall.
In the diet, there are some things cattle producers can do to help protect their animals from tannins. Hydrated lime and protein seem to provide some protection. The following supplemental feed has been used to prevent problems: cottonseed or soybean meal (1040#), dehydrated alfalfa meal (600#), molasses (160#) and hydrated lime (200#).
The first two ingredients in that formula can be tweaked, but molasses is essential to keep the hydrated lime from separating out. Cattle should be slowly adapted to this feed and would need to consume about 4 pounds per day, per head.
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