Incomplete reduction of branchial clefts in Mutton Merino lambs.

Congenital malformations of the branchial arches, clefts and grooves have not been previously reported in sheep. These defects may be due to infectious agents (especially viruses), toxins or genetic abnormalities. Defects were reported in two of a set of quadruplet lambs born prematurely to an eight-tooth Mutton Merino ewe. The lambs weighed between 2.0 kg and 2.5 kg; this is below the normal expected birth weight of 3.5 kg for quadruplet lambs, below which viability is compromised. The firstborn lamb was severely affected by bilateral oroauricular fistulae. The second lamb was unilaterally affected on the right, less severely than the first. The third lamb was normal and the fourth was mummified. The occurrence of another case in this small flock almost a decade earlier indicates that there could be genetic involvement.