Effects of Specific Fatty Acids

Incorporation of dietary unsaturated fat into milk fat by ruminants is low because of the efficient ruminal biohydrogenation process (Jenkins, 1993). Nevertheless, dietary fatty acids have profound effects on milk fat composition that have led to a prodigious amount of literature in the past 20 years (for reviews see Sutton, 1989 Grummer, 1991 Palmquist et al., 1993 Kennedy, 1996 Mansbridge and Blake, 1997 Chilliard et al., 2000, 2001). 

Acyl chain length (Ci6 vs Cis) influences the proportions of these in milk fat the effects of are more subtle because of compensation by reduced de novo synthesis of Ci6 o when long-chain fatty acids are supplemented in the diet. Palmitic acid was increased from 45% of milk fatty acids to 53% when a high (68%) Ci6 o supplement was added to a low-fat diet. 

Similarly, supplementing soy oil (90% Cis) increased the total Qg of milk fat from 25% to 60% of milk fatty acids. Yields of Q, to C14 were reduced by both supplements, whereas the yield of Ci6 o was increased by palm oil and reduced by soya oil (Banks et al., 1976) these effects are typical (Noble et al., 1969). Similarly, supplementing increasing amounts of coconut oil (high in Ci2 o and Ci4 o) increased the proportions of these in milk fat and reduced the proportions and yields of short-chain fatty acids and Ci6 o (Storry et al., 1971). 

Oleic acid was increased to 48% of total milk fatty acids by feeding oleamide as a rumen-protected source of oleic acid (Jenkins, 1998). The response was nearly linear up to 5% of supplement in the diet dry matter. Proportions of all de uovo-synthesized milk fatty acids, except butyric, were reduced (Jenkins, 1999). LaCount et al. (1994) abomasally infused fatty acids from canola or high oleic acid sunflower oil into lactating cows. The transfer of oleic acid to milk fat was linear (slope = 0.541 0 350 g infused/ day) the proportion of oleic acid in milk fat increased and proportions of all de novo-synthesized fatty acids, except C4 and C6 decreased. The proportion of Ci8 o also was unchanged. Linoleic acid from canola also was transferred linearly (slope = 0.527 0-90 g infused/day). These transfers from the intestine are nearly identical to that reported by Banks et al. (1976). Hagemeister et al. (1991) reported 42 to 57% transfer of abomasally-infused linolenic acid to milk fat. 

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Geller, D.P., Goodrum, J.W., 2004. Effects of specific fatty acid methyl esters on diesel fuel lubricity. Fuel 83, 2351-2356. 

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