A rigid lamb syndrome in sheep in Rhodesia
Rudert, C.P.; Lawrence, J.A.; Foggin, C.; Barlow, R.M.
Veterinary Record 102(17): 374-377
1978
ISSN/ISBN: 0042-4900 PMID: 565556 Document Number: 131522
The syndrome was first seen in Rhodesia in 1971 in experimental sheep and occurred again in 1972, 1973 and 1976. The sheep were pregnant Dorper ewes grazing on heavily fertilized star grass (Cynodon aethiopicus). In 1971, 24 ewes used for an investigation of goitre in autumn-born lambs, with free access to a salt lick containing P, traces of I, Cu and Co, gave birth to lambs of which 2 were born rigid and died within 48 h. Goitrous lambs were not affected. In 1972 in other experiments on the occurrence of goitre, salt licks containing P, S and I were used and 6 ewes gave birth to rigid lambs, 2 of which were goitrous. Two rigid lambs survived, and were hand fed for 3 weeks and then killed. In 1973, experiments were on giving vitamins E and Se to 81 ewes with 81 controls. Of 24 rigid lambs born, 19 were in the control group and there were 17 stillbirths of which 14 were in the control group and may have been caused by the rigid lamb syndrome. In 1976, 56 rigid lambs were born to 4 groups of 30 Dorper ewes grazing star grass given no S or 72, 96 or 120 kg/ha. Of lambs born, 27% were rigid in the control group and 60 to 70% in the other groups. In 1974 and 1975 no rigid lamb was born although many of the same ewes and rams were used as in previous years. Rigid lambs occurred on 3 other farms also in Dorper ewes grazing star grass and there were indications that lambs have also been affected in other areas. To date it has not been possible to induce the rigid lamb syndrome and its occurrence has always been sporadic and unpredictable. The clinical findings are given; rigidity was seen at birth, which was often prolonged and difficult, and some rigid lambs were stillborn. Affected lambs were usually smaller than normal, mean 2.7 kg, against 3.3 kg. Most rigid lambs died within 48 h of birth, but a few survived for 3 weeks and one for 9 weeks. There was however no change in rigidity during this period. Pathological findings are given. Lesions were confined to the neuromuscular system. In brief, it seemed that the development of the rigid lamb syndrome may involve arrest of myelination coupled with widespread neuronal degeneration. Possible factors involved in the aetiology are discussed, such as nitrate, cyanide, S, Cu, Se and vitamin E. It is suggested that an infectious cause, possibly viral, is possible. Hereditary causes are not considered likely.