04-12-2008 - Congenital cataract in calves
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Congenital cataract in calvesCaroline E. Manser1
1 Stone Lane, Meldreth, Royston, Hertfordshire SG8 6NZ
SIR, - I was interested to read the letter from Ms S. Hurley (VR, November 8, 2008, vol 163, p 579) about congenitally blind Holstein-Friesian calves. Having spoken to the author, it seems the condition is very similar to congenital nuclear cataract, which I studied during the 1970s. Surveys of large groups of Friesians and Friesian crosses at that time showed an incidence of the condition of 3·7 per cent. In some herds at certain times of the year, over 25 per cent of calves were born with a degree of cataract. Typically, calves came from high-producing dairy herds with no apparent intercurrent disease. Affected herds were widespread but clusters were found in Devon, Dorset and the East Midlands (Ashton and others 1977, Clay 1977).
Genetic studies showed a slight predisposition to cataract in certain Friesian lines, but the incidence in Friesian crosses was the same as in purebreds. There was a marked seasonal variation, with most affected calves born in the summer and cows calving for the second or third time being most likely to produce a calf with cataracts. A metabolic cause was postulated but metabolic profiles did not indicate what exactly, and neither were any toxic causes found (Ashton and others 1977, Clay 1977).
Fortunately, the cataracts only affected the centre (nucleus) of the lens, which is formed during the first three months of gestation. Therefore, affected animals were not completely blind, and as the eyes grew, the proportion of the cataract decreased so that vision potentially improved.
ASHTON, N., BARNETT, K. C., CLAY, C. E. & CLEGG, F. G. C. (1977) Congenital nuclear cataract in cattle. Veterinary Record 100,505 -508[Medline]
CLAY, C. E. (1977) A study of congenital nuclear cataract in cattle. PhD thesis, University of Cambridge
Related articles in The Veterinary Record:
- Blind but healthy calves
- S. Hurley
The Veterinary Record 2008 163: 579. [Full Text]