Avoiding bloat on alfalfa pasture

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b. lOO ti NEW MEXICO COLLEGE OF AGRICULTURE AND MECHANIC AST'S ■.-■ "
AND AGRICULTURAL EXPERIMENT ST..TION   JO/' . •* \
Press Bulletin 1005
AVOIDING BLOAT ON ALFALFA PASTURE
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Dairymen have been reluctant to use legumes, either alfalfa or clover, for
pastures, because these plants tend to cause bloat in animals. Recent investigations
indicate that bloat results from insufficient belching and regurgitation. Some investigators believe that coarse, dry roughage causes a slight irritation in the rumen and thus stimulates regurgitation. Therefore, whenever th,e feed is succulent
and soft there will not be enough irritation to stimulate the required amount of
belching or regurgitation, and then bloat occurs. This theory of the cause of bloat
suggests two possible methods of prevention: (1) feeding dry hay in the pasture and
(2) pasturing only when the legume has attained considerable growth so that the
plants are more stemmy and less succulent.
Each of these methods has been successfully used during two pasture seasons,
1943 and 1944. The animals used were heifers from,12 to 18 months of age at the
beginning of the season. Approximately three-fourths of them were Holsteins and the
others were Jersey and Guernsey heifers. None of the heifers freshened or aborted
while on pasture. The animals were left on pasture day and night, with free access
to fresh water and salt.
In the first method, two.1-acre plots of alfalfa were pastured alternately to
allow for irrigation. Six animals were used throughout the se'ason of 150 days.
Every afternoon about 30 pounds of good quality dry alfalfa hay was put in the feed
rack in the pasture. This allowed approximately one-fourth to one-third as much hay
as the animals would eat in a dry lot. These animals failed to keep the alfalfa
grazed closely, and it was necessary to mow the plots each time the animals were
changed from one plot to the other. At no time during the season was there any sign
of bloat in any of the animals.
The second way of avoiding bloat is popularly called the "harvest method" of
pasturing. The animals are not turned on the field until the alfalfa is in the
early bloom stage, or about 3 to 6 days before it would be mowed for hay. A sufficient number of animals is then put on the field to complete the harvest in 6 to 8
days of grazing. The animals are then moved to harvest the next plot. This requires
four plots when irrigation water is available only once each week and when approximately 1 month is required to grow a cutting of hay.- For example, this week the
animals go on plot 1 and irrigation is applied to plot 2 and plot 4. This allows
plot 2 to be dried and ready for the anlnals next week. Then next week the animals
are moved to plot 2 and irrigation is applied.to plot 1 and plot 3. This method
requires tight ditch boxes to prevent leakage on plots not being irrigated while
other plots are being irrigated. The growth of the alfalfa at the beginning of the
season may be controlled by proper spacing of irrigations and by clipping the plots
so that each one will be ready to harvest at the proper time. The number of heifers
needed to harvest the crop can be closely approximated as follows: first, estimate
the yield in pounds of hay in that plot; second, divide that figure by 125 (which is
the approximate hay consumption per animal in seven days). If the estimate of yield
is accurate, then the calculated number of heifers will complete the harvest in 7
The harvest method has been used in three trials at the Experiment Station.
One trial in 1943 was on 5 acres of alfalfa which afforded 1,657 animal-days of pasture in addition to 6,944 pounds of hay. Approximately one-third of this hay was
cut at the beginning of the season to control the growth of alfalfa in the plots
and to make it conform to the sequence of the pasture schedule. Part of the hay