Abstract
A new undesirable genetic factor, neuropathy with splayed forelimbs (JNS), has been identified recently in the Jersey breed. Calves affected with JNS are unable to stand on splayed forelimbs that exhibit significant extensor rigidity and excessive lateral abduction at birth. Affected calves generally are alert at birth but exhibit neurologic symptoms, including spasticity of head and neck and convulsive behavior. Other symptoms reported include dislocated shoulders, congenital craniofacial anomalies, and degenerative myelopathy. Inheritance of an undesirable genetic factor was determined from a study of 16 affected calves reported by Jersey breeders across the United States. All of their pedigrees traced back on both paternal and maternal sides to a common ancestor born in 1995. Genotypes revealed that JNS is attributable to a specific haplotype on Bos taurus autosome 6. Currently 8.2% of the genotyped US Jersey population are carriers of the haplotype. Sequencing of the region of shared homozygosity revealed missense variant rs1116058914 at base 60,158,901 of the ARS-UCD1.2 reference map as the most concordant with the genetic condition and the most likely cause. The single-base G to A substitution is in the coding region of the last exon of UCHL1, which is conserved across species. Mutations in humans and gene knockouts in mice cause similar recessive symptoms and muscular degeneration. Since December 2020, carrier status has been tracked using the identified haplotype and reported for all 459,784 genotyped Jersey animals. With random mating, about 2,200 affected calves per year with losses of about $250,000 would result from the 1.3 million US Jersey cows in the national population. Selection and mating programs can reduce numbers of JNS-affected births using either the haplotype status or a direct gene test in the future. Breeders should report calf abnormalities to their breed association to help discover new defects such as JNS.
Highlights
Genomic testing of the Jersey breed has allowed accurate and inexpensive tracking of both deleterious and beneficial haplotypes for economically important traits
The genotypes of known limber legs (LL) carriers did not include the same haplotype attributed to Jersey neuropathy with splayed forelimbs (JNS)
The genetic variants associated with LL and JNS were located on 2 different chromosomes
Summary
Genomic testing of the Jersey breed has allowed accurate and inexpensive tracking of both deleterious and beneficial haplotypes for economically important traits. For recessive defects identified before the availability of genomic testing, such as limber legs (LL) and recto-vaginal constriction discovered in the Jersey breed in the 1970s and 1980s (Lamb et al, 1976; Leipold et al, 1990), carriers are labeled to reduce their use. Many other recessive or dominant conditions are tracked using genomic tools as reported in other breeds (Nicolas and Hobbs, 2014; Cole et al, 2020). The condition was named Jersey neuropathy with splayed forelimbs (JNS) because affected calves are unable to stand on splayed forelimbs that exhibit significant extensor rigidity and excessive lateral abduction at birth (Figure 1). Affected calves generally were alert at birth but exhibited neurologic symptoms, including spasticity of head and neck and convulsive behavior. The objective of this study was to determine the genetic basis for JNS
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