Inheritance of spina bifida in Icelandic lambs

A congenital neural tube defect, spina bifida, detected in Icelandic sheep was examined and compared with similar defects reported in humans and other animals. Pedigree analysis of 29 affected lambs in two neighboring flocks showed that 27 of these cases from the sire's side and 25 from the dam's side, can be traced back to a ram (no. 1) that was one of the foundation sires of the flock at Skriduklaustur where most of the affected lambs were born. Among the exceptions, two on the sire's side and one on the dam's side can be traced back to ewe no. 323 used at Skriduklaustur; another three affected animals can be traced through the dam's side to ewe no. 35 also used at Skriduklaustur, and to ewes E1 and E301 used at Eyrarland farm. All of the four ewes appear to be related to ram no. 1, although information on their parentage is not available from the flock record. The occurrence and frequency of this condition in the two flocks indicate that spina bifida is transmitted as an autosomal recessive trait in Icelandic sheep.