Introduction

Abstract

Bovine milk lipids exist naturally within colloidal suspensions of emulsified globules, each globule comprising a triacylglycerol (TAG) core enveloped by a tri-layer globule membrane (Lopez et al. 2011). In the cow, the control of size, composition, structure and secretion of native milk fat globules (MFG) is carried out by the cellular regulatory system of the mammary gland (Heid and Keenan 2005; Mather and Keenan 1998). The major physiological role of MFG is in delivering nutrition (particularly energy) and bioactive molecules to the suckling calf. Interestingly, these packages of energy have a wide diversity of size, ranging from 0.1 to 15 μm with a mean diameter of 4 μm (Walstra 1995; Michalski et al. 2001). From a physiological perspective, it is not known whether each size class has additional functions beyond the general role of energy delivery. In fact, there is a variation of the MFG size and size distribution within a single cow in a herd, among breeds and between seasons. They are also changed at various lactation stages and can be modified through feeding and milking times (Logan et al. 2014; Wiking et al. 2004, 2006; Carroll et al. 2006; Hurtaud et al. 2010).