Sources of variation in biopeptides and IgG levels in goat milk

For the importance of goat milk in human nutrition, we evaluated milk content of some bioactive compounds and the effect of time of milking and milk treatment on their concentration. Twenty-four Saanen goats were studied from day 18 to day 46 of lactation. Samples of the bulk milk were taken weekly from morning and evening milkings. An aliquot for each sample was centrifuged (skim milk). Another aliquot was sonicated before centrifugation. Both aliquots were analyzed for insulin, IGF-1 and IgG. No difference was observed between morning and evening milking for insulin. IGF-1 was higher in morning than in evening milk (20.3 vs. 15.7 ng/ml, P=0.06). By contrast, IgG level was higher in evening milk (252 vs. 92.2 ng/ml, P<0.05). No difference was observed between skim and sonicated-centrifuged milk for the mean level of IGF-1 and IgG, but mean insulin level was higher in sonicated-centrifuged milk (1.80 vs. 0.72 ng/ml, P<0.001).