Leptin in bovine plasma, colostrum and milk during the first month of lactation

The objective of this study was to determine leptin content in bovine colostrum and mature milk during the first month of lactation, and their possible relation with plasma leptin. Five multiparous Holstein dairy cows homogenous for parity and mean production in the previous lactation were used. Colostrum and milk yield and composition were measured on day 0, 10, 20, and 30 of lactation. Blood samples were collected on day 0, 10, and 20 post-calving. Plasma, skim colostrum and skim milk were analysed for leptin content using a commercial multi-species leptin RIA kit. Leptin concentration was 56% lower in mature milk than in colostrum (13.90 vs. 6.14 microg/l; P<.01), while no significant differences were observed during the first month of lactation (5.88, 6.16, 6.38 microg/l on day 10, 20 and 30, respectively). Leptin daily secretion in mature milk was 21% lower than in colostrum (220.0 microg/d vs. 173.2 microg/d; P<.01). Plasma leptin at calving was 2.64 microg/l, decreasing by 18% during post-partum (2.17 microg/l; P<.05). Although, both plasma and milk leptin concentrations showed a similar decreasing time trend during the first month of lactation, colostrum and milk showed a higher leptin level than plasma, suggesting that transfer of leptin from the blood account only partially for its milk content.