Congenital respiratory tract defects in lambs.

One hundred and forty-seven newborn lambs with congenital defects of the respiratory tract were examined during a 3-year investigation into the causes of perinatal lamb mortality. Respiratory defects were found in 3.3% of the 4,417 lambs examined and in one-third (36.6%) of the 401 congenitally malformed lambs. All the defects were secondary to other more extensive malformations. The upper respiratory tract was involved 3 times more than the lower tract. Males were involved more than females (4:3). The upper tract defects were harelip, cleft palate, atelorrhinia, arrhinia, proboscis, fused nostrils and choanal atresia. One of the facial clefts was a rare median harelip associated with cleft palate and fused nostrils. The lower tract defects were pulmonary agenesis, hypoplasia and duplication. The 2 most common defects were choanal atresia and secondary pulmonary hypoplasia. It was concluded that primary defects of the respiratory tract of sheep are rare and that secondary defects are relatively common.