Leptin distribution in goat milk fractions

The aims of this study were to determine the effects of morning vs. evening milking time on blood and milk leptin. Six lactating (120±12 DIM) Saanen goats were randomly selected for this experiment. On two subsequent milkings, blood and milk samples were collected and milk yield and composition measured. On plasma and whole sonicated milk and skim milk, leptin content were analyzed. Mean morning milk yield, fat, and protein were respectively, 1.36 kg/d, 3.84 %, 3.58 %, whereas on evening milking the same variable measured were 1.11 kg/d, 3.97 % and 3.57 %. Morning and evening whole sonicated milk leptin content and total secretion did not show significant differences (17.91 vs. 23.77 mg/l, and 24.33 vs. 24.32 mg/milking, respectively), but a wide range of variability was observed. Skim milk leptin was higher (P<.05) in morning milk than evening one (5.43 vs. 4.53 mg/l), without significant correlation to plasma leptin at correspondent sampling time (4.05 vs. 3.90 mg/l). Three main conclusions can be drawn: 1) no correlation was observed between milk and plasma leptin; 2) skim milk showed a higher leptin level than plasma, suggesting a possible mammary secretion; 3) of total leptin measured in milk, 57% was associated to fat fraction, remarking that milk sampling and handling procedures must be as accurate as possible.