Rain Generates Springlike Pasture Regrowth this Fall
By Jennifer Stewart
Cooler temperatures and the return of rainfall after a hot, extremely dry summer has caused a springlike regrowth in pastures that can present some health risks for grazing cattle.
Lush growth in predominantly grass pastures can cause cattle to suffer grass tetany, a potentially fatal condition caused by a magnesium deficiency. Bloat, on the other hand is more of a concern in heavy-legume pastures.
"Generalities can be dangerous, but grass tetany is classically seen in the spring with older, lactating beef cows on lush, vegetative, grass pastures when nighttime temperatures are below 55 degrees," said Purdue Extension beef specialist Ron Lemenager. "These are the same conditions our fall calving herds are now experiencing, which makes them the most susceptible."
With the lack of rain for most of the summer, he said grasses have reduced magnesium uptake from the soil that is aggravated when soil profiles are high in potassium and nitrogen. Many producers fertilized pastures in the spring, and with the drought, there has been some nitrogen and potassium carryover.
"In addition, magnesium absorption in the animal is compromised when dietary potassium intake is high and sodium intake is low, which is a characteristic of lush, vegetative growth," Lemenager said.
Grass tetany is especially dangerous because the time from the first symptoms to coma and death can be as few as 2-3 hours, he said.
Symptoms include excitable and possibly aggressive behavior, muscle tremors and convulsions.
"Early detection and treatment is extremely important, but the ultimate goal is prevention," Lemenager said. "Producers should provide the cow herd with a vitamin-mineral supplement that is both palatable and contains higher magnesium concentrations - typically about 4 percent."
Bloat is a digestive disorder caused by the accumulation of gas in the rumen. Gas production is a normal result of rumen fermentation, but when the animal's ability to release the gases is impaired, pressure builds and bloat happens.
"Bloating usually occurs when hungry cattle are first turned onto legume pastures and usually follows a large meal soon after turnout," Lemenager said.
One of the first symptoms is a swollen abdomen. Cattle might also be lethargic or show signs of respiratory distress. Severe cases of bloat can cause death within 2-4 hours of onset because the swollen rumen prevents normal breathing.
Preventing bloat completely isn't possible, but Lemenager said there are management techniques to lower the risk. They include making sure cattle are full before first allowing them to graze, feeding dry grass hay or corn silage before turning animals out to pasture, delaying turnout until pastures are dry after dew or rain, monitoring animals every couple of hours for the first 6-8 hours after turnout, considering anti-bloat supplements (but they need to be included in the diet for at least a week before turnout onto a high legume containing pasture) and carefully selecting which legumes to plant when renovating pastures.
"Death from grass tetany and pasture bloat can occur quickly and it is often too late when producers first observe animals in distress," Lemenager said. "Benjamin Franklin once said an ounce of prevention is worth a pound of cure and that advice fits both grass tetany and pasture bloat. It is much easier and more cost-effective to proactively manage cattle to prevent these ailments than to treat them after they occur."
