AMERICAN ALOE (Agave americana) 'Garingboom'
By Dr Mackie Hobson BSc(Agric),BVSc

AMERICAN ALOE (Agave americana) ‘Garingboom’

Many Karoo farmers use American aloe ’Garingboom’ as a drought feed.

A study by Grootfontein  indicated that American aloe was able to satisfy 64% of the maintenance requirements of mature sheep, but that the best results were obtained at an inclusion level of 45% in maintenance diets with 55% lucerne. American aloe has a low protein (3-4%) content.

It must be remembered that American aloe contains oxalates which can be toxic in unadapted animals or fed excess amounts.

Why can American aloe be toxic?

The aloe contains soluble oxalates which leads to hypocalcaemia and can primarily affect the kidneys.

CLINICAL SIGNS

The clinical signs and treatment depend on whether the poisoning is acute (within hours) or chronic (days/weeks)

1. Hypocalcaemia -In acute poisoning( 2-6 hours after intake )

Unadapted animals eating excessive amounts of aloe leads to hypocalcaemia:

• Weakness
• Paresis to paralysis, semi-comatose.
• Milk fever signs- head pulled back over shoulder
• Bradycardia (slow heart rate)
• Death

2. Kidney failure – In Chronic poisoning (days/weeks )

This is due to blockage and damage of tubuli of the kidneys by Ca-oxolate crystals.

• Unable to produce urine and animal becomes ureamic.

3. Calcium deficiency –Chronic adapted animals (weeks/months)

 In adapted animals, excessive amounts of oxalates are absorbed and not all oxalates are detoxified in the rumen. Calcium deficiency resulting in:

• Bone abnormality,
• Poor milk production and - poor growth.
• Kidney- and bladder stones .
• Gastrointestinal stasis

4. Lamness (stiffness).

The primary cause of the condition is an acid-overload resulting from large intakes of American aloe, which has a relatively low pH (approximately 4,3). Affected animals suggested some resemblance to the "stiffness" syndrome seen in ruminants suffering from a grain-overload.

POST MORTEM FINDINGS:

1. Acute Hypocalcaemia:

 Nothing significant, - haemorrhages.

2. Kidney failure -Nephrosis and Uraemia:

• Ascites, hydrothorax, perirenal and subcutaneous oedema
• Kidneys pale, oedematous, swollen
• Ammonia and urea odour (uraemia).
• Haemorrhages in different organs.
• Oedema and haemorrhages in the rumen.

PREVENTION

• Avoid sudden exposure to American aloe (oxalate-containing plants) or intake of large quantities
• Avoid American aloe (oxalate-containing plants) as the only food
• Feed Ca2+ in the form of dicalcium phosphate as a lick (25% or more with salt) or mixed in the supplementary feed.
• Adding slaked lime

TREATMENT:

In acute cases can be effective

• Ca-boro gluconate by slow i/v injection or subcutaneous injection gives good results and animals may recover

In Kidney failure

• Treatment of little value and is irreversible.

Lameness/stiffness cases

• A similar approach to that used to overcome the problem of grain overload and subsequent acidosis, and which led to the "alkali-ionophore" treatment of grain (chocolate grain). Chopped American aloe treated similarly by adding half a percent of lime to can prevent the condition.

Dr Mackie Hobson (SAMGA)

REFERENCE:

Botha, C.J. (Christoffel Jacobus); Venter, Elna; University of Pretoria. Faculty of Veterinary Science. Dept. of Paraclinical Sciences. Section Pharmacology and Toxicology

Hoon, Grootfontein Agricultural College, 1994