About Green Feed Rickets
Green feed rickets occurs mainly in unshorn lambs and weaners that are deficient in Vitamin D, particularly in overcast weather on lush ryegrass pasture or cereal crops such as oats. Rapidly growing ram lambs are most at risk. Vitamin D controls phosphorus and calcium absorption from the intestine and to and from the bones.
Ewes can supply sufficient Vitamin D in their milk for the first 4-6 weeks of a lamb's life - after that the lamb is on its own. Vitamin D is produced in the body when exposed to sunlight or UV radiation. Vitamin D is also available in various oils (fish particularly) and sun-cured hay. Vitamin D is stored in the animal's fat so an adult animal is less susceptible compared to younger classes simply due to higher fat reserves.
In Tasmania and parts of southern Victoria there is often insufficient sunlight for Vitamin D production. Sheep with black pigmented skins or long wool receive less sun exposure than white skinned and short wooled sheep. The problem thus also occurs in shedded sheep for the same reason. Some cereal crops may also contain a rachinogenic factor (something that specifically prevents Vitamin D working).
SignsCommonly seen as an abnormally high incidence of broken legs, backs etc
Ill-thrift in lambs and weaners; stiffness, shifting lameness, hunched back and rickets. Rickets is the enlarged joints, bow legs or knock knees or lumps along the rib cage where the ribs join the rib cartilage. Loose teeth and tooth rot may also be due to rickets.
Milk fever in lactating ewes may also be due to Vitamin D deficiency.
Blood tests may be misleading. Diagnosis is usually made at post mortem and by analysing the bone ash of a foot bone.
Provision of good quality sun-cured
hay is the simplest prevention and treatment.
There are injectable and oral Vitamin D supplements also available. Consult your veterinarian regarding the best options for diagnosis and treatment.