Transport of fatty acids within plasma lipoproteins in lactating and non‐lactating cows fed on fish oil and hydrogenated palm oil

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The dynamics of ruminal biohydrogenation pathways allow production of a wide range of positional and geometrical fatty acid (FA) isomers. These compounds are absorbed and incorporated into milk fat at varying concentrations (Shingfield et al., 2013). For example, two FA with putative human health benefits, C18:1 trans‐11 (vaccenic acid) and C18:2 cis‐9, trans‐11 (rumenic acid), are not usual components in the ruminant diet but are formed in the rumen. Transfer of these FA from the small intestine to the mammary gland and endogenous conversion of C18:1 trans‐11 to C18:2 cis‐9, trans‐11 are important if the objective was to increase their concentration in milk. Efficiency of transfer of dietary long‐chain FA to milk is low (Offer et al., 1999), possibly due to selective incorporation into certain plasma lipoprotein fractions which are ineffective in delivering FA into the mammary gland (Lock and Bauman, 2004). The plasma lipoprotein profile of ruminant animals is characterized by extremely low concentrations of chylomicrons, very low‐density lipoprotein (VLDL) and total triglycerides, whereas most plasma lipid is carried out by high‐density lipoprotein (HDL) (Stamey Lanier et al., 2013).
Secretion of C16:0 and long‐chain FA in milk is derived from the triacylglyceride fractions of circulating plasma lipoproteins (specially VLDL) and chylomicrons or plasma albumin bound non‐esterified FA which need to be accompanied by genetic determinants of FA transport in blood such as the gene expression of FA transport and binding proteins (i.e. FA transport proteins, long‐chain acyl‐CoA synthetases, FA‐binding proteins and the FA transporter/CD36) (Pélerin et al., 2014).
It has been demonstrated that alterations in the diet can affect the distribution and chemical composition of plasma lipoproteins in models such as in humans (Blair et al., 2016), and in animal models such as rabbits (Niimi et al., 2016), rats (Sawale et al., 2016), swine (Nichols et al., 2015) and chickens (Jensen et al., 2016). Also, it has been shown that the degree of saturation of dietary lipids can affect the chemical composition of plasma lipoproteins in steers (Scislowski et al., 2004a,b) and dairy cows (Offer et al., 2001).
Fish oil (FO) supplementation could be used not only as a dietary source of energy in dairy cow diets (Kupczyński et al., 2011) but also to modify the FA profile of milk and cheese. For example, FO can increase the concentration of C18:1 trans‐11, C20:5 n‐3 and C22:6 n‐3 in milk and cheese of dairy cows (Vargas‐Bello‐Pérez et al., 2015). Hydrogenated vegetable oils also are used to increase energy supply in diets of high‐producing dairy cows (Kargar et al., 2012) and can increase milk and fat yields (Schroeder et al., 2002). However, little is known about how FA are partitioned in lipoprotein fractions and transported in the blood of lactating and non‐lactating dairy cows. Moreover, we know that PUFA supplementation in dairy cows can provoke increases in plasma total lipids, cholesterol, TG, phospholipids (PL) and non‐esterified FA (Sterk et al., 2012), but we do not know how dietary lipids affect lipoprotein fractions in lactating dairy cows and whether those fractions differ in FA concentrations. In this study, as lactation can affect plasma lipoprotein concentrations (Palmquist, 1976), two trials were conducted (one with lactating and another with non‐lactating dairy cows) to elucidate which lipoprotein fractions are involved in bovine plasma transport of FA (especially long‐chain n‐3 and 18‐carbon intermediates) when diets included FO (as a source of PUFA) or a blend of FO and hydrogenated palm oil (as a source of saturated FA).
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