Phenotypic and genomic study of digital dermatitis in UK Holstein heifers

Digital dermatitis (DD) is a global infectious hoof disease causing lameness in cattle. The condition has been studied extensively in milking cows. The present study deployed data from repeated clinical examinations of young heifers to develop DD phenotypes reflecting the disease prevalence and progression. The newly defined traits were then subjected to single-step genome-wide association analyses to assess their genetic profile. Data were collected during four monthly clinical examinations of 921 Holstein heifers aged less than 15 months. The M-score system was used to assess hoof health, and four phenotypes were developed on each animal: two binary traits considering the presence or absence of DD within each examination (BINR) and across all examinations (BINA) and two disease progression traits (TP1 and TP2) throughout the examination period. The latter two phenotypes were derived on heifers that were healthy at first examination (n = 625). Pedigree and genome-wide genotypes were available on these animals. For each trait, the ten 1-Mb windows that explained the largest proportion of the total genetic variance were used to search for positional candidate genes. Functional enrichment analysis was carried out to determine the functional candidates.

All traits were significantly (P < 0.05) heritable with heritability estimates ranging from 0.22 for TP2 to 0.32 for BINA. Our findings revealed common genomic regions between traits distributed across eight chromosomes (7, 8, 11, 12, 13, 20, 23 and 24). Functional enrichment analysis revealed multiple candidate genes including DOCK2 and SRF that are known for involvement in immune response.

Results provide novel insights into the genetic mechanism for DD development and progression in young dairy heifers.