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Abstract
Six genetically related Shorthorn calves were affected with the tibial hemimelia syndrome. The lesions included bilaterally malformed or absent tibia and abdominal hernia in all animals, a long shaggy haircoat, retained testicles in males, and meningocele in three animals. The malformations were similar to those described previously in Galloway calves. Pedigree analysis demonstrated a mechanism by which a recessive allele in a homozygous state could be responsible for the disorder. The condition in these calves was considered the result of a recurrence of a genetic mutation affecting a putative hemimelia locus.
Key words: Cattle; congenital disorder; hemimelia; hereditary disease; meningocele; musculoskeletal system; skull; tibia; ventral hernia.
A syndrome of multiple congenital anomalies, including tibial hemimelia, abdominal hernia, and cranial defects, has been described initially in a beef calf of unspecified breed7 and later in Galloway cattle.5 Both tibias were shortened, malformed, or absent, there was cranioschisis involving the frontal bone leading in most cases to formation of one or two meningoceles, and a large defect in the ventral abdominal midline was associated with abdominal hernia. Additional lesions also included reproductive system anomalies (nonfusion of Müllerian ducts in females, bilateral cryptorchidism in males), internal hydrocephalus, and sometimes nonfusion of the pelvic symphysis. Pedigree analysis and breeding trials in the Galloway cattle indicated that this combination of anomalies was inherited as a simple autosomal recessive trait.3 It was estimated at the time that 1–2% of purebred Galloway calves born between 1965 and 1975 were affected, originating from 47% of the herds.6 Here, we describe a similar syndrome observed in Shorthorn cattle.
Six purebred Shorthorn calves were examined shortly after birth. All six were born between February and August 1999. The pathologic findings are summarized in Table 1. Calf 1 was female, from a herd of purebred Shorthorn cattle in Quebec, Canada. It was examined by a field veterinarian, who observed two meningoceles on either side of the forehead, a large abdominal hernia, and hind legs that appeared flaccid and shortened. The hair coat was long and curly. The animal was alert but unable to stand. It was euthanatized, and no necropsy was performed.
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Calf 3 was a female from the same farm and was sent to the pathology service of the Faculté de Médecine Vétérinaire of the Université de Montréal. The animal was alert with a suckle reflex and attempted but was unable to stand. It had a long and curly hair coat, and abdominal viscera were herniated through a 20-cm-long defect in the caudal abdominal wall on the ventral midline. The hind limbs were shortened, and both had complete absence of the tibia, confirmed by radiographs (Fig. 1). The distal femoral epiphyses bore only a single large rounded condyle (Fig. 2). The patellae were absent. The ilia were shortened and malformed, and the acetabular cavities were shallow. No abnormality was noted in the skull bones. The brain showed hydrocephalus, with moderate dilation of all ventricular chambers. On the roof of both lateral ventricles, two to four rounded sessile nodules up to 1.5 cm in diameter extended from the neuropil into the ventricular lumina; histologically, these nodules consisted of gray matter of normal appearance, without an ependymal covering.
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Past experience with this disorder in Galloway cattle and with other recessive traits suggests that numerous carriers may be present in the North American Shorthorn cattle population. Other affected calves might have appeared previously but were unreported because they were considered isolated cases, without an apparent hereditary basis. The appearance of multiple cases within a short time period made possible the investigation and discovery of familial relationships that revealed the probable hereditary basis behind these defects. The sudden occurrence of the syndrome in multiple animals within a period of a few months on three different farms could have been due to linebreeding and high inbreeding coefficients in those herds.
The similarity of the affected Shorthorn phenotype to the Galloway phenotype suggests that the same gene locus may be mutated. The common ancestral Shorthorn sire is not known to be related to the historic carriers in the Galloway breed. Because mutation rates are estimated in the range of 104–106 per generation, one might expect mutations to recur at regular intervals and similar mutations to occur independently in separate breeding populations. However, recurrent mutations are not often documented in the veterinary literature. Syndactyly is a recent example of a mutation of the same gene that emerged in two independently bred cattle populations. Crossbreeding trials demonstrated the mutation to be allelic, but the phenotypes were distinct, suggesting unique mutations.4 Similarly, the appearance of the tibial hemimelia syndrome in purebred Shorthorns 20 years after its identification in Galloways is most likely due to recurrence of a similar mutation. It is not clear how a single mutation could lead to concurrent anomalous development of skull, pelvic, and hind limb bones, abdominal wall, brain, reproductive system, and hair. Perhaps the mutation affects a homeobox gene disrupting fetal development in a generalized fashion. The minor differences in phenotype with the Galloways (variability in tibial anomalies, presence of pelvic anomalies and long haircoat, lower frequency of meningocele) suggest that the mutation is unique or that different modifying genes are present in the Shorthorns.
Reasonable medical certainty allows this syndrome to be considered a simple autosomal recessive trait until substantial evidence to the contrary is presented. The recessive inheritance must be considered when counseling owners of affected calves, and control programs should be encouraged by national Shorthorn cattle breed registries.
Acknowledgments
We are indebted to Dr. Denys Turgeon for pathologic examination of one animal and Dr. Ted Burnside for help with pedigree analysis.
References
This article has been cited by other articles:
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  I. Szczerbal, T. Stefaniak, A. Dubiel, J. Siembieda, W. Nizanski, and M. Switonski Chromosome instability in a calf with amelia of thoracic limbs. Vet. Pathol., September 1, 2006; 43(5): 789 - 792. [Abstract] [Full Text] [PDF]
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