Genetic Conditions

Genomics and genotyping have allowed discovery of genetic variants on the bovine genome that are causal to the expression of specific phenotypic features. In some cases, this is a desired expression. In other cases, it is detrimental or even lethal. Multiple genetic variants have been identified in specific dairy breeds. 

Official documentation from the breed associations and Council of Dairy Cattle Breeding contains codes that clarify the carrier status of the bull for these genetic variants.

“Recessives” are the variants that are only expressed when the individual carries two copies of the gene. These will only occur when a mating has taken place between two parents that are either affected or carriers of the variant. This can be prevented through avoiding mating of two carriers. 

Because there have been different versions of DNA microarrays (chips) used to genotype animals over the years, not all chips contain the actual genetic variant. In that case, and when the exact variant is still unknown, a haplotype (larger strand of DNA bases that are inherited together) is used to identify the carriers or affected animals.  

Below is a summation of the official genetic variants and haplotypes commonly reported by the Council for Dairy Cattle Breeding. Individual bull studs could also test and report variants that are not on this list.

Haplotype codeDescription
AH1Ayrshire haplotype affecting fertility
AH2Ayrshire haplotype affecting fertility
ARecessiveSyndrome of arachnomelia and arthrogryposis (SAA; spiderleg)
A*RecessiveSyndrome of arachnomelia and arthrogryposis (SAA) through DNA marker testing
TATested free of SAA
DRecessiveSpinal dysmyelination (SDM)
RecessiveSpinal dysmyelination (SDM) through DNA marker testing
TDTested free of SDM
MRecessiveSpinal muscular atrophy (SMA) through affected offspring or gene test
M*RecessiveSMA through DNA marker testing
TMTested free of SMA
WRecessiveWeaver syndrome (bovine progressive degenerative myeloencephalopathy)
W*RecessiveWeaver syndrome through affected offspring
TWTested free of Weaver syndrome
Haplotype codeDescription
BH2Brown Swiss haplotype affecting stillbirth
BHPBrown Swiss haplotype for polledness
BHDBrown Swiss haplotype for SDM
BHMBrown Swiss haplotype for SMA
BHWBrown Swiss haplotype for Weaver syndrome
BH14Brown Swiss haplotype causing early pregnancy loss
LLRecessiveLimber leg
RVCRecessiveRectovaginal constriction
Haplotype codeDescription
JH1First Jersey haplotype affecting fertility
JHPJersey haplotype for polledness
JNSJersey Neuropathy with Splayed Forelimbs
BLRecessiveBovine leukocyte adhesion deficiency (BLAD)
TLTested free of BLAD
CVRecessiveComplex vertebral malformation (CVM)
TVTested free of CVM
Deficiency of uridine monophosphate synthase (DUMPS)
TDTested free of DUMPS
MFRecessiveMulefoot (syndactylism)
TMTested free of mulefoot
PCDominantTested heterozygous polled
PODominantObserved polled
PPDominantTested homozygous polled
TPDominantTested free of the polled condition (horned)
RCRecessiveRed hair color
B/RRecessiveBlack/red hair color
TRTested free of red hair color
TYTested free of brachyspina
CDRecessiveCholesterol deficiency
TCTested free of cholesterol deficiency
DR1DominantTested Heterozygous for Dominant Red
DR2DominantTested Homozygous for Dominant Red
Haplotype codeDescription
HH0Holstein haplotype Associated with Brachyspina
HH1First Holstein haplotype affecting fertility
HH2Second Holstein haplotype affecting fertility
HH3Third Holstein haplotype affecting fertility
HH4Fourth Holstein haplotype affecting fertility
HH5Fifth Holstein haplotype affecting fertility
HH6Sixth Holstein haplotype affecting fertility
HHBHolstein haplotype for BLAD
HHCHolstein haplotype for CVM
HHDHolstein haplotype for DUMPS
HHMHolstein haplotype for Mulefoot
HHPHolstein haplotype for Polled mutation
HHRHolstein haplotype for Red mutation
HDRHolstein haplotype for Dominant Red
HBRHolstein haplotype for Black/Red color
HCDHolstein haplotype for Cholesterol deficiency

Source: Council on Dairy Cattle Breeding