BACKGROUND
in the year  <dig> a syndrome was described in the german and austrian simmental  population, that was pathologically similar to the arachnomelia syndrome in brown swiss cattle  <cit> .
the congenital arachnomelia syndrome  is mainly a malformation of the skeletal system in cattle that was initially described by rieck and schade  <cit>  in holstein friesian, red holstein and simmental.
the main pathological changes are skeletal malformations of the legs, the spinal column and the skull.
the legs are thinner and appear longer than normal  since the diameter of the diaphyses is reduced.
these long bones are more fragile and, in combination with stiffened joints, they tend to fracture during calving.
the fetlock joints are deformed, often stiffened and show hyperextension.
the malformation of the spinal column leads to kyphosis and scoliosis.
the skull malformations are characterized by a shortened lower jaw , convex rounding of the frontal bone leading to a marked stop  and rotation of the anterior cranium.
in some cases, additional malformations like hydrocephalus externus develop  <cit> .
since the report of rieck and schade  <cit>  no further cases were reported in simmental cattle, but in the 1980s the syndrome was dispersed in another breed, the european brown swiss cattle, by the use of american brown swiss sires  <cit> .
in brown swiss an autosomal recessive mode of inheritance was supposed and a control program based on the identification of carriers by pedigree analyses was established  <cit> .
recently, four cases of arachnomelia syndrome were reported in italy  <cit> .
in this study, we present the data of  <dig> pathologically confirmed cases of arachnomelia syndrome in simmental that were collected from october  <dig> to march  <dig>  we describe the pathological findings, the familial occurrence and an estimate of the frequency of the diseases allele in simmental cattle.
additional support for the mode of inheritance and the genetic basis of the arachnomelia syndrome is given by the result of experimental matings of obligate carriers.
RESULTS
as has not been reported again in simmental since its first description in the 1970s, more than thirteen years ago.
in autumn  <dig> a number of stillborn calves with similar malformations of the legs and head were recorded within the monitoring system of anomalies in simmental.
some of these calves were sent to the veterinary service laboratory for examination, and in december  <dig> the first  <dig> cases of as were pathologically confirmed.
subsequently, farmers and veterinarians had been encouraged to report cases by an information leaflet and various articles in local trade journals.
an increasing number of suspected cases was reported and an additional  <dig> affected calves were identified by pathological examination by june  <dig>
familial occurrence and case presentation of the syndrome of arachnomelia
the geographical origins of the cases were the southern part of germany and austria, reflecting the regional distribution of the simmental breed.
both sexes were equally represented in the  <dig>  affected calves.
the largest number of cases was registered in  <dig> .
in retrospect, it could be shown that the main reason for the rapid increase of cases in the years  <dig> and  <dig> was the high popularity of certain sires carrying the as mutation .
the latter two sires represent the key-nodes of the pedigree pathways of the mutation from the founder into the current population .
romel, for example, sired more than  <dig>  cows  <dig> to  <dig> years ago.
furthermore,  <dig> sons of romel born from  <dig> to  <dig> are registered and listed in the breeding database  <cit> .
these progeny were now mated to romel and sons or grandsons of egel and rexon resulting in a high probability for the occurrence of affected calves.
increasing awareness of the disease and abandoning of selling the semen from carriers led to a sharp drop of cases in  <dig>  the disease was successfully managed by efficient collaboration of the institute for animal breeding of the bavarian state research centre for agriculture , the landeskuratorium der erzeugerringe für tierische veredelung in bayern e.v , the bavarian animal health service  and breeding organizations.
pathological findings
calves under suspicion of the arachnomelia syndrome were sent to the pathology department of the tgd for macroscopic examination.
the observed major pathological findings were  facial deformation, including brachygnathia inferior and concave rounding of the maxilla forming a dent ;  abnormally thin diaphyses of the long bones  leading to frequent fractures of the metacarpus and metatarsus in the course of forced birth assistance .
the deformations of other bones of the legs were less apparent and the scapula was usually unaffected;  angular deformations of the distal parts of the legs characterized by bilateral stiff and hyperextended fetlocks with the extremity of the toe forward and parallel to the trunk of the body; and  defects of the vertebral column , but not of the ribs .
additionally, inconsistent pathological findings included cerebral herniation combined with a malformed foramen magnum, microphthalmia, and external and internal hydrocephalus.
the latter seem to develop secondarily, due to the enlarged foramen magnum.
histological examination of selected cases revealed the presence of hemorrhages at the osteochondral junction of the epiphysis and an abrupt transmission from chondral to osteogenic tissue.
cases never showed isolated malformations, e.g.
of the head or legs, but usually a combination of all pathological findings that are characteristic for the syndrome.
nevertheless, the degree of the lesions ranged from obvious spider-leg cases to moderate or mild changes, making a definite diagnosis difficult.
the latter cases  were excluded from the initial pedigree analyses.
meanwhile, an indirect gene test is available that has been developed at the institute for animal breeding of the bavarian state research centre for agriculture  and it could be shown that these cases are most probably not genetically affected .
carrier identification
two criteria were used for carrier identification.
the first was the presence of a calf that was diagnosed by pathological investigation.
in many cases more than one affected calf per sire was identified  <cit> .
some sires had only one affected calf, but a large number of risk-matings.
in these cases a second criterion, the statistical evaluation of risk-matings, was used to identify potential phenocopies.
for this purpose, the probability of observing only a single affected calf among a certain number of risk-matings of the sire in question was calculated.
risk-matings were defined as matings with direct progenies of identified as carriers.
the probability of observing an affected calf depends also on the probability that such a calf is reported to the lkv.
we assumed this probability to be 50%.
under these conditions, the probability of observing only one affected calf is lower than  <dig>  percent, if at least  <dig> risk-matings are given for a single sire.
in this case it is very likely that the single affected calf is a phenocopy.
in  <dig> and  <dig> this was the case for two sires used for artificial insemination that had no pedigree connection to semper .
experimental matings of obligate carriers
four out of seven cows that were known as carriers brought to the facilities of the itz were used for embryo transfer .
<dig> of the  <dig> recipients  were confirmed pregnant on day  <dig>  four of the  <dig> pregnant heifers  aborted between days  <dig> and  <dig> of pregnancy.
of the remaining  <dig> recipients,  <dig> were slaughtered on day  <dig>   <dig> on day  <dig>  and  <dig> animals on day  <dig> of pregnancy .
four fetuses  out of  <dig>  showed the typical pathological changes of the arachnomelia syndrome as described above .
all other fetuses showed no signs of as .
*day of slaughter or age of fetuses, respectively
male fetuses represented 76%  of pregnancies .
female weight , crown-rump length at day  <dig> and chest circumference at day  <dig> of normal fetuses were lower than that of male fetuses.
fetuses that were affected by the arachnomelia syndrome showed lower weight than normal fetuses.
the affected and the normal fetuses had similar crown-rump length, but the chest circumference of affected fetuses was higher than that of normal fetuses .
due to the small number of affected female fetuses, a comparison with unaffected animals for sex was not possible.
to compare unaffected and affected animals in total, the data were analyzed for statistical differences by the non parametric mann-whitney-test.
the only trait that was significantly different between unaffected and affected fetuses was the chest circumference .
the body weight of as affected calves was tendentially lower than that of normal calves.
since affected calves did not have different crown-rump-length and their chest circumference was even higher, this can best be explained by a reduced bone mass.
*p-value from the non parametric mann-whitney-test for differences between unaffected and affected fetuses
pedigree analysis and mode of inheritance
eight-generation pedigrees of all cases were extracted from the joint german and austria pedigree data and screened for common ancestors.
the pedigree of the majority of affected calves  could be traced back to one founder, semper , a sire born in  <dig>  6– <dig> generations before the affected calves were born .
most of the affected calves inherited the as mutation via rexon or egel .
in  <dig> cases the maternal paths were not linked to the common pedigree .
one explanation would be the existence of additional, hereto unknown origins of the mutation.
this could happen if the as mutation is much more ancient and additional pedigree paths exist or if an independent mutation event happened leading to the same phenotype.
an alternative, more plausible explanation could be the occurrence of misparentages.
it is well known that in the pre parentage-test era, the frequency of false paternity, especially of the cows, was reasonable high .
therefore, there is a good chance of a false registry within 6– <dig> generations.
the pedigree connection to the founder semper  is given separately for the sire , and the cow  of the affected calve.
they were listed separately for the two main lines, rexon and egel, that are progeny from semper  and passed the mutation of the arachnomelia syndrome into the current population.
two maternal paths were not connected to semper but to senat, the sire of semper.
* both sires, egel and rexon, appear in the pedigree
†these two cases are considered as phenocopies
there is strong support for the assumption that the as is regulated by a single autosomal locus acting in a recessive manner.
first of all, the pedigree structure of the affected calves in simmental can best be explained by a recessive mode of inheritance.
the paternal branch of the pedigree could be traced back to one sire, semper, for all affected calves, the maternal branch in the majority of the cases.
inbreeding loops over a few generations are present in several pedigrees of affected calves, e.g.
cases p <dig> and p <dig> .
sex-dependent inheritance can obviously be excluded and a dominant mode with reduced penetrance seems to be unlikely.
secondly, the experimental matings resulted in  <dig> affected and  <dig> unaffected fetuses, a result that most closely resembles the expectation of a recessive mode of inheritance.
thirdly, the occurrence of cases corresponded well with the numbers expected under the assumption of a recessively acting mutation.
we tested this on the progeny of romel, the largest dataset available from one carrier.
we analyzed the period from the beginning of the recording system for malformations to may  <dig>  in that period  <dig>  calves were born that were sired by romel.
from these,  <dig> were considered as risk pairings, i.e.
the mother had a risk of  <dig>  to be a carrier  and  <dig> calves out of these were diagnosed as affected.
since it is expected that about 1/ <dig> to 1/ <dig> of the affected calves were recorded, this result is very close to the expected 1: <dig> ratio of affected to unaffected calves.
moreover, these findings are concordant with the historical description of the arachnomelia syndrome in simmental  <cit>  and the analyses of cases in brown swiss  <cit> .
finally, when applying linkage analyses using microsatellite markers, evaluations with a model assuming recessive autosomal inheritance gave the highest lod scores .
allelic frequency of carriers in the present simmental cow population
since the arachnomelia syndrome-allele was passed to the current population through two parental lines  and the main carriers are known, it is possible to estimate the frequency of the disease allele by an allele-counting method  <cit> .
the allelic frequency was calculated for all cows from the breeding population who were alive in june  <dig>  in  <dig>  percent of the pedigrees of  <dig>  cows an identified carrier was found and the probability that individual cows were carrier of the arachnomelia syndrome-allele was calculated.
e.g.
in  <dig>  and  <dig>  cases a known carrier appeared as sire and grandsire, respectively.
in these cases the probability of transmitting the allele is  <dig> and  <dig> percent, respectively, if no further carrier is present in the two generation pedigree.
the averaged rate of the arachnomelia syndrome carriers based on known carriers over all cows alive in bavarian simmental was  <dig>  percent.
using this approach, the frequency of carriers was calculated for each year  from  <dig> to  <dig> .
the calculations were done twice, considering all known carriers together, and also by using only romel as a carrier to show the numeric contribution of his progeny .
for these analyses, the sires that are designated to be non-carriers by the number of risk pairings without having a case or the indirect gene test are set as non-carrier.
therefore, these frequencies are slightly lower than the initial frequency estimate of  <dig>  percent.
CONCLUSIONS
the cases of malformed simmental calves presented here showed the same morphology described in the arachnomelia syndrome in brown swiss , even though there is a certain morphological variation from mild to severe malformations.
the main findings, brachygnathia inferior and convex frontal bone of the face, deformation of vertebrae, and dysplasia of the limbs, namely the diaphyses of metatarsus and -carpus and the fetlocks, can best be explained by irregularly developed bone structure at the corresponding locations.
without pathological examination it is difficult to distinguish the arachnomelia syndrome from other malformations of the limbs.
therefore, low numbers of cases in simmental probably passed unrecognized before  <dig>  in that year the allelic frequency of the disease in the cow population increased sharply because some sires that had been carriers of the mutation had become very popular 2– <dig> years before.
the identification of a common ancestor, the results from the experimental matings and the analyses of numbers of cases from risk matings strongly support the hypothesis of an autosomal recessively inherited disease.
furthermore, this assumption is concordant with the historical description of the syndrome in simmental and brown swiss.
the allelic frequency of the arachnomelia syndrome in the current population is well above  <dig> percent and a substantial number of progeny from known carriers with superior genetic merit shall be used as sires during the next years.
therefore, a control system has to be established and the arachnomelia syndrome-gene should be mapped as a prerequisite for the development of an indirect gene test for carrier identification.
the availability of pathologically well characterized cases from the field and from the et-generated full-sib families will be an excellent material for a genetic mapping procedure.

 in the year a syndrome was described in the german and austrian simmental population, that was pathologically similar to the arachnomelia syndrome in brown swiss cattle. the congenital arachnomelia syndrome is mainly a malformation of the skeletal system in cattle that was initially described by rieck and schade in holstein friesian, red holstein and simmental. the main pathological changes are skeletal malformations of the legs, the spinal column and the skull. the legs are thinner and appear longer than normal since the diameter of the diaphyses is reduced. these long bones are more fragile and, in combination with stiffened joints, they tend to fracture during calving. the fetlock joints are deformed, often stiffened and show hyperextension. the malformation of the spinal column leads to kyphosis and scoliosis. the skull malformations are characterized by a shortened lower jaw, convex rounding of the frontal bone leading to a marked stop and rotation of the anterior cranium. in some cases, additional malformations like hydrocephalus externus develop. since the report of rieck and schade no further cases were reported in simmental cattle, but in the 1980s the syndrome was dispersed in another breed, the european brown swiss cattle, by the use of american brown swiss sires. in brown swiss an autosomal recessive mode of inheritance was supposed and a control program based on the identification of carriers by pedigree analyses was established. recently, four cases of arachnomelia syndrome were reported in italy. in this study, we present the data of pathologically confirmed cases of arachnomelia syndrome in simmental that were collected from october to march we describe the pathological findings, the familial occurrence and an estimate of the frequency of the diseases allele in simmental cattle. additional support for the mode of inheritance and the genetic basis of the arachnomelia syndrome is given by the result of experimental matings of obligate carriers.  as has not been reported again in simmental since its first description in the 1970s, more than thirteen years ago. in autumn a number of stillborn calves with similar malformations of the legs and head were recorded within the monitoring system of anomalies in simmental. some of these calves were sent to the veterinary service laboratory for examination, and in december the first cases of as were pathologically confirmed. subsequently, farmers and veterinarians had been encouraged to report cases by an information leaflet and various articles in local trade journals. an increasing number of suspected cases was reported and an additional affected calves were identified by pathological examination by june familial occurrence and case presentation of the syndrome of arachnomelia the geographical origins of the cases were the southern part of germany and austria, reflecting the regional distribution of the simmental breed. both sexes were equally represented in the affected calves. the largest number of cases was registered in. in retrospect, it could be shown that the main reason for the rapid increase of cases in the years and was the high popularity of certain sires carrying the as mutation. the latter two sires represent the key-nodes of the pedigree pathways of the mutation from the founder into the current population. romel, for example, sired more than cows to years ago. furthermore, sons of romel born from to are registered and listed in the breeding database. these progeny were now mated to romel and sons or grandsons of egel and rexon resulting in a high probability for the occurrence of affected calves. increasing awareness of the disease and abandoning of selling the semen from carriers led to a sharp drop of cases in the disease was successfully managed by efficient collaboration of the institute for animal breeding of the bavarian state research centre for agriculture, the landeskuratorium der erzeugerringe für tierische veredelung in bayern e.v, the bavarian animal health service and breeding organizations. pathological findings calves under suspicion of the arachnomelia syndrome were sent to the pathology department of the tgd for macroscopic examination. the observed major pathological findings were facial deformation, including brachygnathia inferior and concave rounding of the maxilla forming a dent; abnormally thin diaphyses of the long bones leading to frequent fractures of the metacarpus and metatarsus in the course of forced birth assistance. the deformations of other bones of the legs were less apparent and the scapula was usually unaffected; angular deformations of the distal parts of the legs characterized by bilateral stiff and hyperextended fetlocks with the extremity of the toe forward and parallel to the trunk of the body; and defects of the vertebral column, but not of the ribs. additionally, inconsistent pathological findings included cerebral herniation combined with a malformed foramen magnum, microphthalmia, and external and internal hydrocephalus. the latter seem to develop secondarily, due to the enlarged foramen magnum. histological examination of selected cases revealed the presence of hemorrhages at the osteochondral junction of the epiphysis and an abrupt transmission from chondral to osteogenic tissue. cases never showed isolated malformations, e.g. of the head or legs, but usually a combination of all pathological findings that are characteristic for the syndrome. nevertheless, the degree of the lesions ranged from obvious spider-leg cases to moderate or mild changes, making a definite diagnosis difficult. the latter cases were excluded from the initial pedigree analyses. meanwhile, an indirect gene test is available that has been developed at the institute for animal breeding of the bavarian state research centre for agriculture and it could be shown that these cases are most probably not genetically affected. carrier identification two criteria were used for carrier identification. the first was the presence of a calf that was diagnosed by pathological investigation. in many cases more than one affected calf per sire was identified. some sires had only one affected calf, but a large number of risk-matings. in these cases a second criterion, the statistical evaluation of risk-matings, was used to identify potential phenocopies. for this purpose, the probability of observing only a single affected calf among a certain number of risk-matings of the sire in question was calculated. risk-matings were defined as matings with direct progenies of identified as carriers. the probability of observing an affected calf depends also on the probability that such a calf is reported to the lkv. we assumed this probability to be 50%. under these conditions, the probability of observing only one affected calf is lower than percent, if at least risk-matings are given for a single sire. in this case it is very likely that the single affected calf is a phenocopy. in and this was the case for two sires used for artificial insemination that had no pedigree connection to semper. experimental matings of obligate carriers four out of seven cows that were known as carriers brought to the facilities of the itz were used for embryo transfer. of the recipients were confirmed pregnant on day four of the pregnant heifers aborted between days and of pregnancy. of the remaining recipients, were slaughtered on day on day and animals on day of pregnancy. four fetuses out of showed the typical pathological changes of the arachnomelia syndrome as described above. all other fetuses showed no signs of as. *day of slaughter or age of fetuses, respectively male fetuses represented 76% of pregnancies. female weight, crown-rump length at day and chest circumference at day of normal fetuses were lower than that of male fetuses. fetuses that were affected by the arachnomelia syndrome showed lower weight than normal fetuses. the affected and the normal fetuses had similar crown-rump length, but the chest circumference of affected fetuses was higher than that of normal fetuses. due to the small number of affected female fetuses, a comparison with unaffected animals for sex was not possible. to compare unaffected and affected animals in total, the data were analyzed for statistical differences by the non parametric mann-whitney-test. the only trait that was significantly different between unaffected and affected fetuses was the chest circumference. the body weight of as affected calves was tendentially lower than that of normal calves. since affected calves did not have different crown-rump-length and their chest circumference was even higher, this can best be explained by a reduced bone mass. *p-value from the non parametric mann-whitney-test for differences between unaffected and affected fetuses pedigree analysis and mode of inheritance eight-generation pedigrees of all cases were extracted from the joint german and austria pedigree data and screened for common ancestors. the pedigree of the majority of affected calves could be traced back to one founder, semper, a sire born in 6– generations before the affected calves were born. most of the affected calves inherited the as mutation via rexon or egel. in cases the maternal paths were not linked to the common pedigree. one explanation would be the existence of additional, hereto unknown origins of the mutation. this could happen if the as mutation is much more ancient and additional pedigree paths exist or if an independent mutation event happened leading to the same phenotype. an alternative, more plausible explanation could be the occurrence of misparentages. it is well known that in the pre parentage-test era, the frequency of false paternity, especially of the cows, was reasonable high. therefore, there is a good chance of a false registry within 6– generations. the pedigree connection to the founder semper is given separately for the sire, and the cow of the affected calve. they were listed separately for the two main lines, rexon and egel, that are progeny from semper and passed the mutation of the arachnomelia syndrome into the current population. two maternal paths were not connected to semper but to senat, the sire of semper. * both sires, egel and rexon, appear in the pedigree †these two cases are considered as phenocopies there is strong support for the assumption that the as is regulated by a single autosomal locus acting in a recessive manner. first of all, the pedigree structure of the affected calves in simmental can best be explained by a recessive mode of inheritance. the paternal branch of the pedigree could be traced back to one sire, semper, for all affected calves, the maternal branch in the majority of the cases. inbreeding loops over a few generations are present in several pedigrees of affected calves, e.g. cases p and p. sex-dependent inheritance can obviously be excluded and a dominant mode with reduced penetrance seems to be unlikely. secondly, the experimental matings resulted in affected and unaffected fetuses, a result that most closely resembles the expectation of a recessive mode of inheritance. thirdly, the occurrence of cases corresponded well with the numbers expected under the assumption of a recessively acting mutation. we tested this on the progeny of romel, the largest dataset available from one carrier. we analyzed the period from the beginning of the recording system for malformations to may in that period calves were born that were sired by romel. from these, were considered as risk pairings, i.e. the mother had a risk of to be a carrier and calves out of these were diagnosed as affected. since it is expected that about 1/ to 1/ of the affected calves were recorded, this result is very close to the expected 1: ratio of affected to unaffected calves. moreover, these findings are concordant with the historical description of the arachnomelia syndrome in simmental and the analyses of cases in brown swiss. finally, when applying linkage analyses using microsatellite markers, evaluations with a model assuming recessive autosomal inheritance gave the highest lod scores. allelic frequency of carriers in the present simmental cow population since the arachnomelia syndrome-allele was passed to the current population through two parental lines and the main carriers are known, it is possible to estimate the frequency of the disease allele by an allele-counting method. the allelic frequency was calculated for all cows from the breeding population who were alive in june in percent of the pedigrees of cows an identified carrier was found and the probability that individual cows were carrier of the arachnomelia syndrome-allele was calculated. e.g. in and cases a known carrier appeared as sire and grandsire, respectively. in these cases the probability of transmitting the allele is and percent, respectively, if no further carrier is present in the two generation pedigree. the averaged rate of the arachnomelia syndrome carriers based on known carriers over all cows alive in bavarian simmental was percent. using this approach, the frequency of carriers was calculated for each year from to. the calculations were done twice, considering all known carriers together, and also by using only romel as a carrier to show the numeric contribution of his progeny. for these analyses, the sires that are designated to be non-carriers by the number of risk pairings without having a case or the indirect gene test are set as non-carrier. therefore, these frequencies are slightly lower than the initial frequency estimate of percent.  the cases of malformed simmental calves presented here showed the same morphology described in the arachnomelia syndrome in brown swiss, even though there is a certain morphological variation from mild to severe malformations. the main findings, brachygnathia inferior and convex frontal bone of the face, deformation of vertebrae, and dysplasia of the limbs, namely the diaphyses of metatarsus and -carpus and the fetlocks, can best be explained by irregularly developed bone structure at the corresponding locations. without pathological examination it is difficult to distinguish the arachnomelia syndrome from other malformations of the limbs. therefore, low numbers of cases in simmental probably passed unrecognized before in that year the allelic frequency of the disease in the cow population increased sharply because some sires that had been carriers of the mutation had become very popular 2– years before. the identification of a common ancestor, the results from the experimental matings and the analyses of numbers of cases from risk matings strongly support the hypothesis of an autosomal recessively inherited disease. furthermore, this assumption is concordant with the historical description of the syndrome in simmental and brown swiss. the allelic frequency of the arachnomelia syndrome in the current population is well above percent and a substantial number of progeny from known carriers with superior genetic merit shall be used as sires during the next years. therefore, a control system has to be established and the arachnomelia syndrome-gene should be mapped as a prerequisite for the development of an indirect gene test for carrier identification. the availability of pathologically well characterized cases from the field and from the et-generated full-sib families will be an excellent material for a genetic mapping procedure. 
the major pathological findings were malformed bones affecting the head, long bones of the legs and the vertebral column. the frequency of the mutation in the current population was estimated to be %. 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. 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– recently, stillborn simmental calves were observed having a morphology similar to the arachnomelia syndrome. the first pathologically confirmed arachnomelia syndrome-cases in the current simmental population appeared in the year by an additional calves with the arachnomelia syndrome were identified. together with the data from experimental matings, the pedigree data support an autosomal recessive mutation being the etiology of the arachnomelia syndrome. 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 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– 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.  the first pathologically confirmed arachnomelia syndrome-cases in the current simmental population appeared in the year by an additional 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 %.  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. 