Abstract
BackgroundPolled animals are valued in cattle industry because the absence of horns has a significant economic impact. However, some cattle are neither polled nor horned but have so-called scurs on their heads, which are corneous growths loosely attached to the skull. A better understanding of the genetic determinism of the scurs phenotype would help to fine map the polled locus. To date, only one study has attempted to map the scurs locus in cattle. Here, we have investigated the inheritance of the scurs phenotype in the French Charolais breed and examined whether the previously proposed localisation of the scurs locus on bovine chromosome 19 could be confirmed or not.ResultsOur results indicate that the inheritance pattern of the scurs phenotype in the French Charolais breed is autosomal recessive with complete penetrance in both sexes, which is different from what is reported for other breeds. The frequency of the scurs allele (Sc) reaches 69.9% in the French Charolais population. Eleven microsatellite markers on bovine chromosome 19 were genotyped in 267 offspring (33 half-sib and full-sib families). Both non-parametric and parametric linkage analyses suggest that in the French Charolais population the scurs locus may not map to the previously identified region. A new analysis of an Angus-Hereford and Hereford-Hereford pedigree published in 1978 enabled us to calculate the frequency of the Sc allele in the Hereford breed (89.4%) and to study the penetrance of this allele in males heterozygous for both polled and scurs loci (40%). This led us to revise the inheritance pattern of the scurs phenotype proposed for the Hereford breed and to suggest that allele Sc is not fully but partially dominant in double heterozygous males while it is always recessive in females. Crossbreeding involving the Charolais breed and other breeds gave results similar to those reported in the Hereford breed.ConclusionOur results suggest the existence of unknown genetics factors modifying the expression of the scurs locus in double heterozygous Hereford and Angus males. The specific inheritance pattern of the scurs locus in the French Charolais breed represents an opportunity to map this gene and to identify the molecular mechanisms regulating the growth of horns in cattle.
Highlights
Polled animals are valued in cattle industry because the absence of horns has a significant economic impact
Testing the inheritance patterns in French Charolais The most commonly accepted model of the inheritance of polled and scurs loci is presented in Table 1: nine genotypes corresponding to the three phenotypes constitute the horn and scurs inheritance model originally proposed by White and Ibsen [6] based on Galloway-Holstein crosses and revised by Long and Gregory [7] based on Angus, Hereford and Angus-Hereford crosses and Brem et al [8] based on observations in Fleckvieh
Revision of the previously proposed inheritance of the scurs phenotype Since our results suggest that the inheritance of the scurs phenotype in the French Charolais breed may differ from that in other breeds, we decided to revise the data set studied by Long and Gregory [7] in the light of our results
Summary
Polled animals are valued in cattle industry because the absence of horns has a significant economic impact. Absence of horns has a significant economic impact, since horns are a major cause of bruising and other injuries, which generate veterinarian costs and reduce the value of carcasses [1,2,3]. Removing horns of livestock not naturally polled, i.e. dehorning, is a general practice that remains a painful operation regardless of the method used [2,4,5]. It is usually perceived as only "treating the symptom and not the cause", since it must be repeated from generation to generation. Breeding polled cattle offers an adequate non-invasive and longterm means to dehorning
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