Hydrops foetalis in dwarf calves associated with twinning

Hydrops fetalis associated with pulmonary hypoplasia in Dexter calves

The occurrence of severe fetal dystocia due to hydrops fetalis associated with pulmonary aplasia in two male and pulmonary hypoplasia in one female Australian Dexter fetuses from two herds is described. Obstetrical intervention by caesarean section was required for delivery of the fetuses, with mortalities in one dam and the 3 calves. Clinical, pathological and genetic features are tabulated to assist in distinguishing pulmonary hypoplasia-associated hydrops fetalis from the more prevalent disorder of chondrodysplasia in Dexter cattle. Anasarca and complete absence or presence of only rudimentary lung tissue in a large thoracic cavity clearly distinguishes this entity from the lesions of Dexter chondrodysplasia that include severe micromelia and abundant lung tissue in a small thoracic cavity with shortened spine and rib cage. Pedigree information suggested that Dexter hydrops may be transmitted in an autosomal recessive manner.

Inheritance of proportionate dwarfism in Angus cattle

OBJECTIVE

To determine the mode of inheritance of congenital proportionate dwarfism in Angus and Angus crossbred cattle, initially detected in two commercial beef herds in northern New South Wales.

DESIGN

Matings of normal carrier sires to unrelated cows of diverse breeds, and of one carrier sire to his unaffected daughters. An unrelated Piedmontese bull was also mated to unaffected daughters of the carrier sires.

PROCEDURE

Two carrier Angus bulls and nine unaffected daughters, all of whom were completely indistinguishable from normal animals, were purchased for controlled breeding studies under known nutritional and disease conditions. Affected and carrier individuals were examined for the presence of obvious chromosomal abnormalities.

RESULTS

Angus dwarfism has been successfully reproduced under controlled experimental conditions over successive years using unrelated dams and is undoubtedly heritable. The high frequency of occurrence of affected individuals (23/61 = 0.38 +/- .06) among the progeny of matings of the Angus sires to unrelated females of diverse breeding is not compatible with recessive inheritance, because of the negligible frequency of proportionate dwarfism in the breeds of the dams. Both paternal and maternal transmission of the defect was demonstrated, so that imprinting in the strict sense of a gene that is only expressed when received from the male parent appears not to be involved. Tested individuals showed no evidence of gross chromosomal abnormality. Dominant autosomal inheritance with incomplete penetrance was indicated by the lack of expression of the defective gene in the two Angus sires and in three unaffected daughters who produced dwarf calves from matings to the Piedmontese bull.

CONCLUSIONS

The mode of inheritance is that of a single autosomal dominant gene with a penetrance coefficient of 0.75 +/- 0.12, estimated from the observed incidence of 23/61 affected offspring of the two carrier Angus bulls mated to unrelated dams. Simple genetic models involving either (i) an unstable mutant which changes at high frequency to the expressed dominant dwarfing allele during gametogenesis, or (ii) a dominant allele with penetrance determined by an unlinked modifying locus, are shown to be compatible with the experimental data. Both models indicate that penetrance of the dwarfing gene may possibly be higher in matings involving carrier daughters of the two Angus bulls.

Chondrodysplasia in Australian Dexter cattle

OBJECTIVE

To describe the occurrence of chondrodysplasia in Australian Dexter cattle.

DESIGN

A pathological and genetic case report.

PROCEDURE

Congenital lethal chondrodysplasia was studied in two female Dexter foetuses aborted mid to late gestation. Clinicopathological findings including histological changes in limb bones, and analysis of pedigree information were evaluated.

RESULTS

Characteristic features of congenital lethal chondrodysplasia (Dexter bulldog) include abortion, disproportionate dwarfism, a short vertebral column, marked micromelia, a relatively large head with retruded muzzle, cleft palate and protruding tongue and a large abdominal hernia. Histological changes in limb bones are consistent with failure of endochondral ossification. Dexter chondrodysplasia is considered to be inherited in an incompletely dominant manner with the homozygous form producing the congenital lethal condition. A preliminary minimum estimate of heterozygote frequency is 19% within the registered Australian Dexter herd, based on analysis of the contribution of three obligate heterozygotes whose semen has been widely used by artificial insemination in Australia.

CONCLUSION

Dexter chondrodysplasia is present in Australian cattle and further cases of the homozygous form, congenital lethal chondrodysplasia, are likely to occur.

RECOMMENDATION

It is requested that spleen and liver tissue from bulldog foetuses and blood from their parents be collected to assist research into Dexter chondrodysplasia.

Foetal anasarca in Awassi sheep

Two anasarcous foetuses of Awassi sheep are described. The foetuses were removed from the dams by caesarean section because of dystocia due to failure of cervical dilation. Uterine incision was made in situ because uteri were so distended they could not be brought out from the site of incision. Large quantities of uterine fluids and abnormal thick placentas were found. One foetus weighed about 7 kg and the other 13 kg. The foetal heads were deformed: the upper jaw was prognathic and the left ear of the small foetus was cystic. Necropsy revealed subcutaneous musculature was soft and flabby and abdominal and thoracic cavities contained serosanguinous fluid. Histopathological examination revealed that only the larger foetus had focal aggregates of basophilic nucleated red blood cells and scattered megakaryocytes in the liver. We conclude that anasarca can occur in Awassi sheep, with and without associated extramedullary haematopoiesis.