The following is an extract from the NT Ag Note May 2010 - "Birdsville Disease". Gracie*, A. Brown* and P. Saville, Biosecurity and Product Integrity

Birdsville disease is a toxic condition of horses caused by eating Birdsville indigo (Indigofera linnaei).

Indigofera is a low, spreading plant with a thick taproot that enables it to withstand drought conditions and respond rapidly to rainfall. It has numerous thin woody stems that form a mat up to 1.5 m across. In the higher rainfall areas, the weed displays a more erect habit, uncommonly growing to a height of 30 to 45 cm. The leaves are fern-like and consist of seven to nine wedge-shaped leaflets 3 to 6 mm long that tend to fold upwards along the midrib. Flowers are very small and occur in dense clusters in the forks of the leaves. They are red in colour turning blue as the leaves dry out. Seed pods are grey, very narrow, sharply pointed at the tip and contain two cube-shaped seeds that are separated by a partition. The pods are about 6 mm long.

Symptoms

Affected horses may show a variety of signs, including general weakness and nervousness, particularly depression, incoordination, shivering, twitching and swaying. Uncoordination and general weakness are more evident when the animal is, or has been, under physical stress and may be quite hazardous to the rider. As the toxic effects are often permanent, a degree of incoordination will remain after access to the plant is denied. The first signs of poisoning observed in horses at rest are loss of appetite and depression. Bad breath may be noticed. Signs may develop after only 10 days of feeding on indigofera. Protracted cases exhibit weight loss and toe-dragging, which results in a characteristic wear of the front of the hoof. Continual ingestion of the plant will result in death. In some cases the disease may be diagnosed without seeing the horses but by observing their tracks. Toe-drag marks are distinctive and may be continuous.

 The Arginine Horse Block

Analysis ("Dry Matter" Basis)

Size 
 Salt
 Crude Protein
 Total Protein
 Phosphorus
 Calcium
18kg block
20.0%
22.4%
22.4%
0.7%
6.9%

Directions for Use:    Allow free access by stock.

Feeding Rates:         Required rate is 200grams per head per day.