Understanding green grass for cattle

Even though the weather has improved significantly over the past couple of weeks, were still a few weeks away from getting heavily involved in crop seeding.

What we are starting to see is grass greening so I thought that I would once again borrow information from Rachel Endecott our MSU Extension beef specialist in regards to green grass and cattle.

We havent had much of a winter in most of Montana in 2015. With many signs and symptoms of an early spring, grass tetany is probably a timely topic. Grass tetany is a metabolic disease of cattle associated with grazing lush, green pasture. The condition is caused by low blood concentrations of magnesium, which is a required mineral for cattle. When pastures are growing rapidly in the spring, grass may not contain adequate amounts of magnesium to meet requirements.

High potassium and crude protein concentrations found in rapidly growing forage complicate the grass tetany issue, because they can both interfere with the absorption of magnesium from the rumen. Magnesium requirements increase during lactation, so lactating cows have increased risk of developing grass tetany, and the risk increases as milk production increases.

Low calcium intake combined with inadequate magnesium intake can result in more severe cases of grass tetany. Stress, storms or other conditions that result in cattle being off feed for 24 to 48 hours may decrease blood magnesium levels and cause grass tetany in several cows in a herd at one time.

Signs of grass tetany could include finding dead cattle with evidence they may have struggled. Symptoms in live cattle could include convulsions, weakness, disorientation or aggressive behavior. Testing for grass tetany can be accomplished by collecting a blood sample in live animals, although care must be taken. Life-threatening convulsions can be caused by simply running the animals through the chute to collect a sample. Blood concentrations of magnesium return to normal after death, but magnesium concentrations of fluid from the eye or cerebrospinal fluid do not change near death and are good sources for testing for grass tetany in animals found dead.

Prevention of grass tetany is the key to successfully managing this condition. Achieving increased calcium and magnesium consumption through supplementation is the main goal. Daily intake of magnesium is important, as grass tetany can occur within 48 hours when blood magnesium concentrations are too low. This can be accomplished in several ways, from salt-mineral mixes to molasses-based lick tubs, all of which are available in high-mag formulations at your local feed store. Supplying additional magnesium during the early growing season can help your operation avoid losses from grass tetany.

Just how good is that lush green grass? Dont forget that lush pasture can be 70-80 percent water. This results in a dilution of the other nutrients in the forage and means that cows may not be able to meet their dry matter intake requirements with green grass alone. For example, a 1,400-pound cow consuming 2.5 percent of her body weight on a dry matter basis would need 35 pounds of dry feed per day. If the forage she were consuming contains 70 percent water, she would have to eat about 116 pounds of that fresh forage in order to get 35 pounds of dry matter. In other words, it might not be time to put up the hay processor or bale feeders just yet.

As always, if you have questions, feel free to give me a call at 406-433-1206 or send an email to timothy.fine@montana.edu.

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Understanding green grass for cattle