Relationship between fat globule size and chemical and fatty acid composition of cow's milk in mid lactation

The milk of 57 Italian Friesian cows in mid lactation was analysed in order to define the relationship between some qualitative milk parameters and the size of milk fat globules. The study focused on the morphometric evaluation of milk fat globules, chemical parameters and fatty acid composition of the milk. The results show that a prevalence of milk fat globules with a diameter < 6 mu m is positively correlated (P < 0.01) with the percentage of dry matter and lipids, whereas the greater presence of globules with a diameter < 6 mu m was associated (P < 0.01) with greater milk yield and a higher percentage of lactose, non-fat dry matter and ash. Regarding fatty acid composition, milk samples with a higher percentage of globules smaller than 6 wm in diameter contain more unsaturated fatty acids (P < 0.01), in particular C18:1, C18:2 and total CLA, while higher percentages of the larger fat globules indicated a prevalence of saturated fatty acids (P < 0.01). Based on these results, a diameter of 6 wm in fat globules may be considered a "threshold value" for the definition of various qualitative traits of cow's milk.