Growth hormone induced alterations of leptin serum concentrations in dairy cows as measured by a novel enzyme immunoassay

The present knowledge on the interrelationship between leptin and the somatotropic axis in livestock, in particular the effects of growth hormone (GH) treatment, on leptin secretion is inconsistent. We therefore aimed to characterise GH-induced alterations of blood leptin concentrations in dairy cows and first developed and validated a competitive enzyme immunoassay (EIA). The assay is valid in cattle, sheep, goat, pig and in horses. Lactating cows were injected once with 500 mg depot-formulated bovine GH and blood samples were drawn every second day 2 weeks before and 4 weeks after the GH injections and were assayed for leptin and for insulin-like growth factor-1 (IGF-1). Leptin concentrations were decreased in response to the GH treatment solely in pregnant cows (p < 0.05), whereas IGF-1 concentrations were increased independently of pregnancy status. In conclusion, the response of leptin blood concentrations towards GH treatment in lactating cows might depend from endocrine and metabolic cues related to pregnancy.