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Description
Guajillo is a shrub to small tree in the legume family
(Leguminosae) with few or no prickles. Height of the plant
can be quite variable growing up to 15 feet tall. The leaf
arrangement is similar to that of mesquite leaves but slightly
smaller. Flowers are white to yellow, arranged in dense groups,
and sweet scented. The plant produces a typical bean type
legume fruit that is flattened and 4 to 6 times as long as
wide.
Distribution and Habitat
Guajillo grows on a variety of soil types but is
most prolific on ridges and shallow soils. It is mainly found
in the Rio Grande Plains and southwest Texas and less common
in the southern Edwards Plateau and Trans-Pecos regions. It
is also found extensively in northern Mexico.
Regions: 2, 6,
7, 10.
Toxic Agent
Sheep, goats and possibly cattle are poisoned by
guajillo. The leaves of the plant contain several "amphetamine-like"
sympathomimetic amines, principally N-methyl--phenethylamine
and tyramine. Over-consumption as might occur when complimentary
herbaceous forage is limited, may cause a condition in sheep
and goats known as "guajillo wobbles," which may be followed
by death. The lethal dose of plant material for sheep and
goats has not been determined. However, direct administration
of the amine extract from the plant at 0.4% of body weight
produced death in sheep. The toxic dosage is 15 times the
animal's weight in leaves and fruit consumed over several
months.
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Livestock Symptoms
Symptoms of guajillo poisoning include:
- "guajillo wobbles" or "limber leg" in sheep
and goats, an uncoordinated rubbery action in the rear legs,
although it may progress to the front legs as well
- downed animals remain alert with normal
appetite
- death
Leg dysfunction appears at first only
when animals are forced to move, but after several days
the incoordination becomes complete and the animal becomes
unable to rise and may die. These symptoms are generally
not apparent unless animals have been on an almost exclusive
diet of guajillo for at least 9 months. Losses are negligible
on ranges in good condition with a variety of forage plants.
But on poor ranges, and especially during drought, losses
may reach as high as 50 percent.
Other poisoning symptoms may be more subtle (sub-clinical).
Research in sheep, goats, and cattle has demonstrated
that some of the amine compounds in guajillo are capable
of illiciting release of excessive stress hormones. As
a result, certain reproductive functions can be suppressed
(i.e. normal release of reproductive hormones, display
of estrus, ovulation and testicular development). Lowered
pregnangy rates have been reported in nannies given N-methyl--phenethylamine
infussions daily during a 45 day breeding season.
Integrated Management Strategies
Historically, guajillo has been considered a
valuable browse plant that should not be grazed to the
exclusion of other range forage. Recent evidence suggests
that the plant has been over-rated as a forage since the
majority of the nitrogen contained in the plant is of
non-protein origin and the plant has a low digestibility
value. When poisoning occurs, supplemental feeding and
reduced stocking rates will lower the incidence of poisonings.
If possible, animals should be moved to a pasture containing
a greater variety of browse and especially herbaceous
forage when signs of illness first appear. Recovery of
affected animals is possible if placed on an adequate
ration. Guajillo is very difficult to control with herbicides
and no specific recommendations are available. Several
mechanical control methods are available that reduce populations.
Preferably, managers should not over-stock pastures, encouraging
grass growth and allowing animals alternatives to shrub
foliage.
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