Are you seeing cases?
This spring we diagnosed rickets twice at the Dumfries centre and there were several other telephone enquiries about suspect cases.
Rickets is usually described as a condition of hill hoggs away wintered on good dairy grazing and is a consequence of Vitamin D deficiency at a time of fast growth triggered by improved nutrition. Rapid skeletal growth ensues but calcification of new bone is impaired leading to widening of growth plates. Stiffness, recumbency and carpal valgus can result, see picture below.
In the last few years we have also seen an atypical presentation affecting homebred, white faced ewe hoggs on two farms. In both cases the hoggs were in lamb and in one flock there was no history of away wintering. Clinical signs were restricted to a generalised stiffness with recumbency in a very small minority of affected animals. Response to treatment with a Vitamin D drench was good and there were no problems at lambing time.
Vitamin D is produced in the skin by photobiosynthesis. In sheep this is limited by the fleece and reduced by pigmentation of the hair. Dumfries lies at 55º N and at this latitude photobiosynthesis only occurs between mid-March and mid-September.
One possible reason for the apparent upswing in cases this spring was the mild winter which allowed continued grass growth. Sunshine hours during summer 2015 were around 50 hours below the 30 year average (1980 – 2010) but have been lower in the current decade. Summer 2016 was similar so animals may enter the winter period with comparable, lower Vitamin D reserves.
Prevention of rickets is by administration of a Vitamin D drench before hoggs move to wintering (e.g. Battle, Hayward and Bower Vitamin D3 drench). This can be repeated in early spring. Consideration could also be given to extending prophylaxis to breeding ewe hoggs.
Some useful references are supplied below:
Bonniwell, M.A., Smith, B.S., Spence, J.A., Wright, H. and Ferguson, D.A. (1988) Rickets associated with vitamin D deficiency in young sheep. Veterinary Record 122, 386 – 388
Mearns, R., Scholes, S.F.E., Wessels, M., Whitaker, K. and Strugnell, B. (2008) Rickets in sheep in northern England. Veterinary Record 163, 98 – 99