The PCR procedures reported here represent a significant improvement in reliability and accuracy over previous published methods. Utilisation of these PCR/restriction enzyme based assays will facilitate precise selection against the 1057deltaTA and 1783T alleles, and consequently reduce the incidence of generalised glycogenosis in registered and commercial Brahman herds.

The clinical, pathological and biochemical findings of a study of 30 Poll Hereford, Hereford, Poll Hereford cross or Hereford cross calves affected with branched chain ketoacid dehydrogenase (BCKAD) complex deficiency or maple syrup urine disease (MSUD) are presented. In breeding studies, 6 of 21 calves from obligate heterozygote matings were affected with MSUD, suggesting the disease is inherited in an autosomal recessive manner. Calves were clinically affected from birth, but there were variations in the subsequent course of progressive deterioration of central nervous system function. Concentrations of the branched chain amino acids and keto acids were elevated in pre-suckle plasma and cerebellar water content was higher in affected calves. Activity of BCKAD complex was minimal in fibroblasts cultured from an affected calf. Spongiform encephalopathy and elevated ratios of the branched to straight chain amino acids in formalin fixed cerebral tissue were found in a stillborn foetus and a 3-month-old Hereford calf. These findings suggest the disease occurs prenatally and that a delayed form may exist.

Estimates of branched chain amino acid concentrations in plasma and, or, serum, urine, cerebrospinal fluid, formalin-fixed cerebral tissue and the associated formalin, provided evidence for a diagnosis of branched chain keto acid decarboxylase deficiency in five polled Hereford calves. The similarity of the clinical signs of dullness, recumbency and opisthotonos, and the observation of severe status spongiosus within the central nervous system, indicated that this condition had probably affected seven other newborn calves. It is suggested that this condition is analogous to branched chain keto acid decarboxylase deficiency or maple syrup urine disease of children.

Thirty-four newborn polled Hereford and polled Hereford cross calves affected with a condition previously described as neuraxial oedema and six normal calves were examined. None of the affected calves were seen to stand after birth and when first examined the calves were in lateral recumbency, with extension and crossing of the hindlimbs. All the affected calves were bright and alert, could lift their heads and apparently could see and hear. When the calves were encouraged to stand spontaneous and stimulus-responsive myoclonic extensor spasms, with whole body rigidity, were consistently observed. Thirty-two of the affected calves had macroscopic lesions in the coxae. No significant pathological or biochemical lesions were observed in the central nervous system of any of the calves. The water content of the cerebellum did not differ between normal and affected calves. As oedema of the central nervous system is not a feature of this condition it is more appropriate to describe it as inherited congenital myoclonus.

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