As tempting as it might be to turn the cows out on the spring grass and in the warm weather, don’t do it too abruptly, says Alberta livestock and forage specialist Grant Lastiwka.
The consequences could be deadly if cattle develop grass tetany or bloat.
Organisms in the rumen have been dealing with winter feed and won’t be able to handle a sudden switch to the pasture, where the grass doesn’t provide the same nutrients.
“A rumen takes time to adjust,” Lastiwka said.
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In the case of grass tetany, or staggers, the problem is the nutrient ratio.
The spring grass is low in available magnesium, high in potassium and high in nitrogen.
Pastures that have been fertilized often present a greater risk because the potassium and nitrogen tie up the magnesium.
Kristen Ritson-Bennett of Blue Rock Animal Nutrition said that inhibits magnesium absorption by the cattle.
“We counter that by feeding a high level of magnesium,” she said.
The best source, magnesium oxide, is unpalatable to cattle.
“So we use a more expensive source, magnesium sulfate, with flavouring agents,” she said.
A constant source of three percent magnesium offered in mineral provides good protection.
Symptoms of grass tetany are often not seen until a cow is found dead, but mild cases include decreased milk yield and a nervous animal. In more serious cases, the animal can stop grazing, appear unusually alert and uncomfortable and may stagger and then convulse.
Lastiwka said providing minerals even before cattle are turned out can prepare the rumen for the new feed.
Another strategy is to stockpile perennial forage from the previous year. The cattle graze a combination of a feed that would be more similar in quality to what they were eating all winter while introducing green feed at the bite zone.
“This would allow for a smoother transition,” he said.
Lastiwka stockpiles forage on his own operation, where he begins calving May 25.
Older cows often seem to have more trouble with magnesium deficiency than younger cows, and grass tetany typically develops in early lactation.
Getting the cattle out on the mixed feed with good trace and macro minerals prevents problems, he said. Plus, pasture productivity is improved because the stockpiled grass catches snow and protects the lead tillers of the new growth.
Ritson-Bennett said high sodium levels in water can make free-choice mineral challenging, but lactating cows will seek it out.
Pastures with legumes present less risk of grass tetany but could cause bloat.
Lastiwka said producers who move to incorporate more legumes in pastures and cocktail cover crops should be aware of bloat, particularly later in the grazing season after the annual crops in the mix have been grazed off.
Making sure animals are full when they are first turned into a spring pasture helps, as does feeding grain before turnout.
Bloat is less likely to develop on dry forage.
