Syndrome of arachnomelia in Simmental cattle

Abstract

Background: The syndrome of arachnomelia is an inherited malformation mainly of limbs, back and head in cattle. At present the arachnomelia syndrome has been well known mainly in Brown Swiss cattle. Nevertheless, the arachnomelia syndrome had been observed in the Hessian Simmental population during the decade 1964-1974. Recently, stillborn Simmental calves were observed having a morphology similar to the arachnomelia syndrome. The goal of this work was the characterization of the morphology and genealogy of the syndrome in Simmental to establish the basis for an effective management of the disease.

Results: The first pathologically confirmed arachnomelia syndrome-cases in the current Simmental population appeared in the year 2005. By 2007, an additional 140 calves with the arachnomelia syndrome were identified. The major pathological findings were malformed bones affecting the head, long bones of the legs and the vertebral column. It could be shown that, with the exception of two cases that were considered as phenocopies, all of the paternal and about two-third of the maternal pedigrees of the affected calves could be traced back to one common founder. Together with the data from experimental matings, the pedigree data support an autosomal recessive mutation being the etiology of the arachnomelia syndrome. The frequency of the mutation in the current population was estimated to be 3.32%.

Conclusion: We describe the repeated occurrence of the arachnomelia syndrome in Simmental calves. It resembles completely the same defect occurring in the Brown Swiss breed. The mutation became relatively widespread amongst the current population. Therefore, a control system has to be established and it is highly desirable to map the disease and develop a genetic test system.

Figure 1

Allelic frequency and number of confirmed cases of AS. The allelic frequency of the AS carriers in the living cows of the breeding population is shown per year (blue line). The lower line (red) shows the frequency estimation based on ROMEL and his progeny (including females, ignoring other carriers). The number of pathologically confirmed cases per year is shown by bars.

Figure 2

Extracted pedigree of AS affected calves. Part of the pedigree that shows the inheritance path of the AS mutation from SEMPER to the first 13 affected calves. Individuals that were most likely carriers of the AS mutation are shown in gray, males as square, females as oval, affected calves as rhomb.

Figure 3

An AS affected calf with typical pathological findings. A – Overview: Note dolichostenomelia, convexity of the frontal bone, and kyphosis. B – Sagittal section through the head: Severe deformation (dent forming, brachygnathia inferior, compression of cerebrellum). C – Cross sections of metacarpus (on the top) and -tarsus (at the bottom); sections of an unaffected calf as a control on the left. Note the dysplasia of the bone of the diaphysis. It is mainly due to a decreased diameter whereas the width of the substantia compacta is normal.

Figure 4

225-days old fetuses from experimental matings of obligate arachnomelia syndrome carriers. A, B – Normal 225-day fetus, overview and head. C, D – AS affected 225-day fetus, overview and head.