Role of biohydrogenation intermediates in milk fat depression

Abstract

Role of biohydrogenation intermediates in milk fat depressionFat is the most variable constituent in milk and is reduced on low-fiber/high-concentrate diets or on rations containing lipid supplements rich in polyunsaturated fatty acids. The biohydrogenation theory attributes the causal mechanism underlying dietinduced milk fat depression (MFD) to changes in ruminal lipid metabolism leading to increased formation of specific biohydrogenation intermediates that exert anti-lipogenic effects. Trans-10, cis-12 conjugated linoleic acid (CLA) is the only intermediate shown unequivocally to inhibit milk fat synthesis. However, increases in ruminal trans-10, cis-12 CLA formation do not provide a universal explanation for the reductions in milk fat during diet-induced MFD, suggesting that other biohydrogenation intermediates may also be involved. Post-ruminal infusion experiments have provided tentative evidence that cis-10, trans-12 CLA and trans-9, cis-11 CLA also exert antilipogenic effects. Diet-induced MFD is consistently associated with an increase in milk fat trans-10 18:1 concentrations, but recent direct evidence offers little support for a role of this intermediate in the regulation of milk fat synthesis. Further research is required to characterize the structure and function of other biohydrogenation intermediates, as well as considering the contribution of more global changes in ruminal lipid metabolism to provide a more universal explanation of diet-induced MFD.

Role of trans fatty acids in the nutritional regulation of mammary lipogenesis in ruminants

“…Of all the hypotheses developed to explain diet-induced MFD, the biohydrogenation theory appears to be the most robust and offers a more convincing explanation for MFD over a wider range of diets. However, increases in ruminal outflow of trans-10, cis-12 CLA, do not explain the decreases in milk fat synthesis in all cases of diet-induced MFD, with the implication that additional biohydrogenation intermediates and/or mechanisms must be involved (Shingfield and Griinari, 2007).…”

“…A number of studies have been conducted to characterize the anti-lipogenic effects of trans-10, cis-12 CLA in lactating ruminants. Abomasal infusions of relatively pure preparations supplying between 1.25 and 14.0 g/day over 4-or 5-day periods have established that trans-10, cis-12 CLA decreases milk fat synthesis in a dose-dependent curvi-linear manner in the lactating cow (de Veth et al, 2004;Shingfield and Griinari, 2007). Administration of 1.25 to 5.0 g of trans-10, cis-12 CLA/day typically results in similar decreases in the output of preformed fatty acids and fatty acids synthesized de novo, often in the absence of changes in milk fat SCD product and precursor concentration ratios.…”

“…Investigations with lactating ruminants, experiments with animal models and cultured adipocytes have provided an insight into the structural components associated with anti-lipogenic activity. Available data indicate that for a fatty acid to exhibit anti-lipogenic activity several structural features are required: (i) free carboxyl group on the first carbon atom; (ii) cis-trans or trans-cis conjugated double bond system; and (iii) trans or cis double bond on carbon 10 relative to the carboxyl group (Park et al, 2004;Shingfield and Griinari, 2007). There are also data indicating that monoenoic fatty acids with a cis or trans double bond on carbon 10 may alter LPL activity and lipolysis of TAG in fully differentiated 3T3-L1 adipocytes (Park et al, 2004).…”

“…Numerous reviews have considered the effect of nutrition on milk fat synthesis in ruminants (Bauman and Griinari, 2003;Chilliard et al, 2007;Shingfield and Griinari, 2007), whereas several appraisals have considered possible molecular mechanisms underlying diet-induced changes in mammary lipogenesis and fat secretion Bernard et al, 2008;Harvatine et al, 2009a). In the following sections, the role of TFA formed during ruminal metabolism of dietary unsaturated fatty acids, lipogenic precursor supply and products of intermediary metabolism on milk fat secretion are examined.…”

“…Even though certain attributes of a diet are important in the establishment of MFD, there is considerable interaction between the composition of the basal diet, amount and source of dietary lipid supplement and feeding frequency Shingfield and Griinari, 2007).…”