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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
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.
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.
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:"
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
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.
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.
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.
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.
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
"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.
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."
©1997 Committee for
Sustainable Farm Publishing
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