A new genetic defect in Holstein dairy cattle that can result in young calf death has been identified, German researchers announced at the 2015 Interbull Annual Meeting in July in Orlando, Fla.
The genetic defect – Haplotype for Cholesterol Deficiency – causes the calves to die if homozygous for HCD. The homozygous animals have no cholesterol and live only a few months.
The defective haplotype traces back to Maughlin Storm. Storm's sire and maternal grandsire do not carry HCD.
Unfortunately, the haplotype carrying the defect is difficult to track. To address this challenge, Animal Genomics and Improvement Laboratory, Canadian Dairy Network and VIT researchers are collaborating to more precisely trace HCD.
VIT is recording the genetic defect as CDH, rather than HCD. Their two-code system labels animals as IN for noncarrier and IV for suspect carrier.
In the United States, Canada, Italy and Great Britain, codes of zero, one, two, three and four have been proposed for reporting HCD. The codes and descriptions are:
1 = Non-carrier
2 = Carrier
3 = Homozygous
4 = Suspect carrier
5 = Suspect homozygous
According to Paul VanRaden, USDA AGIL research geneticist, and Dan Null, USDA-AGIL biological science lab technician, the earliest 11 homozygous U.S. females had no recorded breedings and no lactations.
None of the homozygous males entered an artificial insemination company or had any daughters, which is consistent with the calf loss hypothesis.
In Canada, HCD did not always cause early death. Some suspect homozygous females lived for two years.
VanRaden notes that calf death, caused by a genetic defect, typically creates a greater economic loss than most other haplotypes that cause early embryo loss. Even though calf survival has low heritability, the dairy cattle geneticist recommends avoiding recessive defects by using sound selection and mating programs.
For more specifics on HCD, refer to the technical note prepared by VanRaden and Null.
Source: Council on Dairy Cattle Breeding