Evidence that leptin genotype is associated with fertility, growth, and milk production in Holstein cows.

This study investigated associations between single nucleotide polymorphisms (SNP) in the leptin, leptin receptor, and neuropeptide Y (NPY) genes with growth, milk production, and fertility traits. Holstein Friesian heifers from 19 UK dairy farms were recruited at birth, providing an initial population of 509. Animals were monitored until they either reached the end of their second lactation or were culled. Size (weight, height, length, girth) was measured at 1, 6, and 15 mo to assess growth traits. Heifer fertility was assessed by recording age at service, age at conception, age at first calving, and number of services. Cow fertility was assessed by recording days from calving to service and conception, services per conception, percentage of animals in calf at 100 d after calving and the calving interval in each lactation. Milk production was recorded as days in milk, total milk per lactation, 305-d yield, milk per day, and peak yield. Mixed model analyses revealed that leptin SNP were associated with early skeletal growth (height, A1457G; length, A59V), fertility (UASMS1, UASMS2, A1457G, A59V) and milk production (A59V). The leptin receptor SNP (T945M) was only weakly associated with milk per day and days to first service. The NPY SNP (NPY1) was associated with the prevalence of the animal being in calf 100 d after calving and 305-d milk yield in the first lactation. The association of leptin SNP with fertility traits in heifers, in addition to lactating cows, suggests that some effects on fertility are direct and not necessarily mediated via altered tissue mobilization. In accord with this, other work has shown that leptin can affect oocyte quality and early embryo development. These results support the use of leptin SNP to inform marker-assisted selection in dairy cows.