Introduction
Alfalfa is recognized as one of the most nutritious forages
available and is widely used as conserved forage (ex, hay,
silage) in the diets of beef and dairy cattle. However, the
utilization of alfalfa by grazing beef cattle has been limited
due to its propensity to cause pasture bloat. Ruminants are
unique in their ability to readily digest the cell wall
components of forages and it is this ability that gives them a
competitive advantage over other meat producing animals. Thus,
to be sustainable in the future, forages must be a major
component of any ruminant production system. Alfalfa is one of
the few forages that is capable of sustaining levels of
production that are comparable to those achieved in the feedlot.
Grazing of pure alfalfa stands has the potential to more than
double the net farm income generated from mixed grass-legume
pastures and under irrigation production yields of 1371 pounds
of beef per acre have been reported. However, pasture bloat
continues to impede the widespread adoption of alfalfa grazing
systems, although, numerous technologies are presently being
tested for bloat prevention. Agronomic strategies such as the
co-cropping of bloat safe legumes (ex, sainfoin, birdsfoot
trefoil) with alfalfa and wilting of the alfalfa prior to
consumption are being explored for their ability to provide
additional bloat protection. Although many of these technologies
can reduce the risk of bloat, none of them can guarantee bloat
safe grazing of alfalfa under the management conditions.
The Plant
Alfalfa has an initial rate of ruminal digestion that is five to
ten times greater than that of most grasses. The rapid microbial
colonization and digestion of alfalfa reduces particle size and
increases the passage of digesta from the rumen, enabling the
animal to consume greater quantities of forage. Whereas this
rapid digestion and particle size reduction is responsible for
the high productivity of cattle on alfalfa pasture, it also is
in part responsible for bloat. Bloat risk is highest when
alfalfa is in vegetative to early bloom stages of growth. As
alfalfa enters into the full bloom or post bloom stages, soluble
protein levels decrease, plant cell walls thicken, lignin
content increases and the rate of digestion of alfalfa in the
rumen decreases. Consequently, many experienced producers do not
allow their cattle to graze alfalfa until it is in full bloom. Soluble protein levels may also be higher in the plant early in
the day and this may be why many experienced producers recommend
that cattle be turned into alfalfa pastures after the morning
dew is off the alfalfa. Other strategies of bloat prevention
such as wilting of alfalfa also lower soluble protein levels in
the alfalfa and reduce bloat risk. Although one might think that
the same effect would be achieved after a good fall frost,
freezing can rupture plant cell walls and increase the release
of soluble protein in the plant. Thus, the notion that alfalfa
is bloat-safe after a frost is a fallacy. It is likely that the
risk of bloat in frozen alfalfa decreases with time as proteins
complex with carbohydrate in a manner similar to that achieved
with wilting or drying. However, as many a dairy farmer can
attest to, cattle can still bloat on alfalfa hay, and long term
frozen alfalfa should be considered bloat reduced, not bloat
safe.
The Animal
Proper management of the animal is just as pivotal to bloat
prevention as management of the plant. Although there are few
experiments to prove the concept, most experienced producers
would agree that cattle must learn to graze alfalfa. In our
experience, cattle that have not grazed alfalfa will invariably
consume most of the other forages (ex, grasses, dandelions)
that are present in pasture. This may result in a false sense of
security as cattle will seldom bloat while these alternative
forages remain in the stand. However, as these forages become
depleted, the risk of bloat increases and such a scenario is
often responsible for bloat outbreaks two to three days after
animals have been moved to a new pasture. Uniform and regular
intake is the key to managing animals on alfalfa pastures.
Cattle should never be introduced to an alfalfa pasture until
they have been fed to satiety. Providing cattle with a mixture
of good quality alfalfa-grass hay can provide the rumen fill
that is necessary to prevent overconsumption of fresh alfalfa
when cattle are first introduced to the pasture. High stocking
densities increase competition for the alfalfa and reduce the
likelihood of any one animal selectively grazing only the top
portion of the plant. Once introduced, every effort should be
made to maintain the herd on alfalfa pasture. Animals will often
experience mild bloat when they are first introduced to alfalfa,
but this condition can often be treated by simply keeping the
animal walking until the gas dissipates. Removing the animals
from the pasture and reintroducing them at a later date often
only increases the risk of bloat, unless the initial grazing
attempt was made in the bud or pre-bud stage of growth. If
rotational grazing is used, care should be taken to ensure that
the initial paddock is not over grazed to the point that animals
are hungry when they are introduced into a fresh paddock.
Management of cattle on alfalfa pasture is a dynamic art and
must be done with an appreciation of the factors that can cause
fluctuation in the intake of alfalfa. Environmental factors that
interrupt regular grazing bouts on alfalfa pasture such as
storms, exceptionally hot weather or biting flies can alter
intake patterns and increase the risk of bloat. During these
periods of high risk, animals should be observed for symptoms of
bloat more often as these conditions often lead to multiple
bloats or bloat storms. Cattle generally have three to four
grazing bouts per day on alfalfa pastures. Major bouts tend to
occur shortly after sunrise and early in the evening. Bloat
usually occurs an hour to one and a half hours after a major
grazing bout. Consequently, familiarity with the grazing
patterns of the cattle can enable producers to adjust their
management practices to observe the animals during times of
greatest bloat risk.
Conclusion
Although several technologies have been developed to reduce the
risk of bloat, it is highly unlikely that any of these will
completely eliminate the occurrence of bloat on alfalfa pasture.
Increased management and the risk of bloat can be seen as the
cost that is associated with the high levels of productivity and
associated profitability that are possible with grazing alfalfa.
As with production of cattle in a feedlot, producers will only
be comfortable with grazing alfalfa if they are prepared to
adopt the concept of an acceptable level of death loss.
Knowledge of the interactions between the animal, plant and
environment factors that lead to bloat is the key to profitable
grazing alfalfa with minimal death loss. Bloat prevention
technologies can be coupled with management to allow one to have
a sounder night's sleep.
Common Sense Management in Alfalfa Grazing
-
Never move cattle in the morning. 2 to 5 pm is better.
-
Moving during rain is not as dangerous as about
two days after
a rain when it is hot. Alfalfa is growing rapidly and high risk.
-
Have
"escape" pastures, the ability to exit from alfalfa if
conditions for grazing are very poor.
-
Once alfalfa has reached 15% to 20% bloom the risk of grazing
drops substantially.
-
Understand that even if you waste 50% of alfalfa it is still
better than grass as it outproduces grass by that much and
fixes nitrogen.
-
Do not graze each paddock right to nothing before moving.
This will create bigger swings in nutrition and a greater risk
for cattle to bloat. You would not have cattle on 20 lbs barley,
drop them down to 5 lbs (ie, grazing down to roots) and then
back up to 20 lbs.
-
Monitor grazing of the cattle.
Observe what they are eating
and see if they are mixing their alfalfa with grass.
-
Employ haying of your paddocks ahead if need be, in case
things get too rank.
-
Be careful during early fall frosts; cell walls are broken
by freezing and make alfalfa highly digestible. As a rule, two
weeks after a strong killing frost alfalfa is safe to graze.
-
CRC bolus – rumensin to prevent bloat.
-
Continuous grazing can present more danger as after
two to three
weeks of grazing within a pasture alfalfa starts to regrow.
-
Alfasure liquid bloat product is 100% effective in
preventing bloat and can be used during risk periods. If water
source is controlled it works well. Alfasure or Dioctol can also be used to relieve bloat
in animals.
Prepared by:
John Popp
Manitoba Agriculture, Food and Rural Initiatives
Tim McAllister
Agriculture and Agri-Food Canada
Walter Majak
Agriculture and Agri-Food Canada
Bjorn Berg
Alberta Agriculture, Food and Rural Development
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