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Manage Grazing to Beat Bloat
Grazing strategies that reduce the risks.

When it comes to beating bloat, Dr. Ann Clark has an impressive record. In 10 years of grazing research at the Elora Research Station near Guelph, Ontario, she has lost to bloat only one of the hundreds of weaned lambs, lightweight Holstein calves, bred dairy heifers, beef stockers and mature cows passing through intensively managed paddocks that are 40- to 80-percent white clover. And that lone animal was a steer that succumbed on the last day of a three-year trial!

What's more, the University of Guelph crop scientist seldom feeds any grain or hay in her work, and uses no bloat-control products. "We use grazing management to avoid the problem in the first place, rather than trying to control it after the fact," she says.

While bloat is most closely associated with alfalfa, it can also be a problem with white and red clovers. In New Zealand, perennial ryegrass is the primary culprit, especially when it is 3 to 4 inches tall, growing rapidly, and low in both dry matter and energy. "What makes bloat most frightening is that it seems to appear infrequently and quite unpredictably, perhaps once in 10 to 15 years," observes Clark. "But losses can be severe when it does crop up." One top Ontario producer she knows lost 18 Charolais steers one night in September while they were on alfalfa-reed canarygrass pasture that had been rotationally grazed by the same steers all summer.

There are many effective products on the market designed to prevent such nightmares. But most are relatively expensive, and you must ensure that each animal in the herd gets a sufficient dose every day, or sometimes even twice a day, cautions Clark. Some bloat preventatives may be administered by drenching, topdressing feed, metering into water systems, or in blocks or boluses.

"Getting enough into the animals on a routine and consistent basis is costly, whether for controlled release bolus systems or for daily handling," Clark notes. "Some products are less costly, but rely on voluntary intake. Individual animals vary in their timing and the amount they consume, which introduces a significant risk to these approaches. "That's why we rely on these general principles:"

Keep grazing intervals short. Clark keeps her grazing intervals to a maximum two to three days, because short grazing intervals reduce the range in forage quality that rumen microflora must cope with. Nutritional quality -- including crude protein content -- is highest in the middle to upper portion of the forage, she explains. Because stock graze from the tops down, the quality of the feed they ingest is highest at the beginning of -- and lowest at the end of -- a given paddock stay. So the shorter the interval, the more consistent the feed quality.

Entering paddocks when forages are 8 to 10 inches tall also reduces the range in quality between the top and bottom of the plants, compared with taller pastures. The percentage of white clover in Clark's stands increases through the grazing season, but these changes normally are gradual enough for the rumen microflora to adjust, she points out.

Leave reasonable residue. "In the research at Elora, the stock are obliged to graze down to 2 to 4 inches, depending on the trial," says Clark. "But any grazing below this height abruptly reduces both nutritional quality and intake." Leaving stock too long on a given sward creates a risky combination, warns Clark: Hungry animals with rumens challenged by abnormally low-quality feed. "This is the kind of animal that would be most likely to bloat when introduced into a fresh paddock," she observes.

Move stock late in the day. Clark rotates stock in the late afternoon or early evening, particularly late in the season when frosts are common. Carbohydrate levels in the new paddock are highest at this time, which helps to even out imbalances between energy and protein, she notes. "In addition, stock will enthusiastically graze off the youngest and most bloat-prone portions of the sward that same evening, before frost occurs," says Clark.

Mix Pasture Species. Use forage combinations that blend bloating and nonbloating tissues in the top of the canopy, suggests Clark. One reason alfalfa is so risky is that it tends to outgrow and overtop other species, especially in summer and early fall. Stock preferentially graze the youngest and most bloat-prone material in the uppermost portion of the plant before they reach the diluting layers of grass, stems and older herbage. Try mixing birdsfoot trefoil -- a nonbloating legume -- with the alfalfa. Their heights are similar and trefoil tends to be more palatable, so stock will ingest a better blend of bloating and nonbloating tissues, she explains.

White clover can grow laterally into winterkilled grass patches to form pure -- and sometimes lethal -- stands that stock will graze preferentially. Interseed highly palatable grasses -- such as perennial ryegrass or bluegrass -- or spray out the clover to avoid this risk. Keep less palatable grass species -- such as orchardgrass -- young and vegetative so that stock will consume them along with the clover.

"In sum, you can address bloat risk with purchased antibloating agents," says Clark. "But basic principles of grazing management may be equally effective in avoiding the problem in the first place. Keeping nutritional quality consistent is the key."

Balance Pain vs. Gain

Avoiding bloat requires a careful balancing act that weighs maximum production against bloat risk, says Michigan State University grazing specialist Ben Bartlett. "High-performance pastures have more bloat potential, so the challenge is to find a level of gain (production) vs pain (bloat risk) that you are willing to live with.

"It's tricky," he adds. "You want your paddocks small enough that the cattle can't get enough to eat by just topping the legumes. You need to force them to eat the middle third of the plant so that they get some stem. On the other hand, you don't want to let them get hungry, either.

"This is easy to recommend, but takes a lot of observation and pasture walking to get the job done," he cautions. Slowing the rotation can help prevent bloat because more of the plants are mature and have more fiber, he suggests. Feeding some dry hay is also an option. "But if they eat it, that means the pasture is too lush or the cattle are really hungry," he says. The extra fiber will also increase saliva flow, decreasing the frothing potential.

Bartlett also suggests moving cattle during times when they aren't likely to pig out, for example, around 10 a.m. when they tend to go out and lay down. "I really think that's why you hear it suggested to not move cattle until the dew is off," he says. "It's not so much the wet feed as the stock's behavior."

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