Genetic variation in Japanese Holstein cattle for EBL development

Area of Science:

• Veterinary Genetics
• Animal Breeding
• Disease Epidemiology

Background:

• Bovine leukemia virus (BLV) infection is rising in Japanese dairy farms, causing enzootic bovine leukosis (EBL).
• Previous observations noted familial tendencies in tumor development post-BLV infection.
• A genetic component influencing cattle susceptibility to EBL was hypothesized.

Purpose of the Study:

• To investigate the genetic basis of EBL susceptibility in Holstein cattle.
• To identify specific sire lines associated with varying EBL development rates.

Main Methods:

• Analysis of 6,022 Holstein cattle postmortem records (2004-2015) from 226 farms.
• Integration of pedigree, epidemiological, and BLV infection data.
• Statistical association analysis between sire/paternal grandsire information and EBL development; heritability calculation; proviral load (PVL) analysis.

Main Results:

• Identified statistically significant associations between specific sires/paternal grandsires and EBL development.
• Calculated the heritability of EBL development as 0.19.
• No significant differences in proviral loads (PVLs) were found among progeny of identified sires/paternal grandsires.

Conclusions:

• EBL development in this Holstein population is influenced by genetic factors independent of PVL levels.
• Genetic improvement for reduced EBL incidence is feasible in cattle, even with ongoing BLV infection.
• Selective breeding strategies can be employed to mitigate EBL risk in dairy herds.