Phalaris Disorders
Phalaris can contain several alkaloids which can be toxic to livestock under certain conditions. The alkaloids are thought to affect the heart, spinal cord and brain, with sheep being more commonly affected than cattle.
Alkaloid levels are highest under the following conditions: – Rapidly growing young plants – Following the break of a dry season – Warm temperatures – Plants growing in the shade – Early in the morning – On foggy or cloudy days
Such conditions are most likely to occur during autumn.
There are three types of phalaris poisoning:
Sudden Death – occurs within 24 hours of grazing phalaris.
Acute Nervous Disorder – becomes evident when sheep are disturbed. Signs include aimlessly walking, high stepping and a stiff gait. Convulsions may occur in severe cases.
Phalaris Staggers – characterised by incoordination and nervous signs which appear in sheep as excitability, tremors, twitches, head shakes, head nodding, leg weakness, leg stiffness, rocking, kneeling, buckling over and frequent falling, followed by vigorous struggling to get up again. Cattle display mild hind leg weakness, tremors and mild incoordination (particularly of the tongue), which may lead to loss of weight or failure to gain weight.
Prevention of Phalaris Staggers requires avoidance of grazing phalaris pastures when alkaloid levels are likely to be high. Allowing 2-3 weeks for the plant to produce a reasonable amount of dry matter before grazing, plus avoiding grazing with hungry stock are important control measures.
There is some evidence to suggest that oral administration of Cobalt will stimulate rumen microorganisms which break down the causative agents. This is unlikely to be practical in many cases, hence grazing management is the most suitable means of prevention.