Effect of dietary fish oil on biohydrogenation of fatty acids and milk fatty acid content in cows

Abstract

Mechanisms underlying milk fat conjugated linoleic acid (CLA) responses to supplements of fish oil were investigated using five lactating cows each fitted with a rumen cannula in a simple experiment consisting of two consecutive 14-day experimental periods. During the first period cows were offered 18 kg dry matter (DM) per day of a basal (B) diet formulated from grass silage and a cereal based-concentrate (0·6 : 0·4; forage : concentrate ratio, on a DM basis) followed by the same diet supplemented with 250 g fish oil per day (FO) in the second period. The flow of non-esterified fatty acids leaving the rumen was measured using the omasal sampling technique in combination with a triple indigestible marker method based on Li-Co-EDTA, Yb-acetate and Cr-mordanted straw. Fish oil decreased DM intake and milk yield, but had no effect on milk constituent content. Milk fat trans-11 C18:1, total trans-C18 : 1, cis-9 trans-11 CLA, total CLA, C18 : 2(n-6) and total C18 : 2content were increased in response to fish oil from 1·80, 4·51, 0·39, 0·56, 0·90 and 1·41 to 9·39, 14·39, 1·66, 1·85, 1·25 and 4·00 g/100 g total fatty acids, respectively. Increases in the cis-9, trans-11 isomer accounted for proportionately 0·89 of the CLA response to fish oil. Furthermore, fish oil decreased the flow of C18 : 0(283 and 47 g/day for B and FO, respectively) and increased that of trans-C18 : 1fatty acids entering the omasal canal (38 and 182 g/day). Omasal flows of trans-C18 : 1acids with double bonds in positions from delta-4 to -15 inclusive were enhanced, but the effects were isomer dependent and primarily associated with an increase in trans-11 C18 : 1 leaving the rumen (17·1 and 121·1 g/day for B and FO, respectively). Fish oil had no effect on total (4·36 and 3·50 g/day) or cis-9, trans-11 CLA (2·86 and 2·08 g/day) entering the omasal canal. Flows of cis-9, trans-11 CLA were lower than the secretion of this isomer in milk. Comparison with the transfer of the trans-9, trans-11 isomer synthesized in the rumen suggested that proportionately 0·66 and 0·97 of cis-9, trans-11 CLA was derived from endogenous conversion of trans-11 C18 : 1in the mammary gland for B and FO, respectively. It is concluded that fish oil enhances milk fat cis-9, trans-11 CLA content in response to increased supply of trans-11 C18:1that arises from an inhibition of trans-C18 : 1reduction in the rumen.

Metabolism of polyunsaturated fatty acids and their toxicity to the microflora of the rumen

“…The source of these is not known, either biochemically or microbiologically, nor are their likely effects on health. For example trans-11,cis-13-18:2, trans-7,cis-9-18:2 and trans-11,trans-13-18:2 were the next most abundant CLA isomers found in milk in the Shingfield et al (2003) study. None of the cultures tested here formed trans-11,cis-13-18:2, trans-7,cis-9-18:2 or trans-11,trans-13-18:2; it is possible they are formed from cis-9,trans-11-CLA by species other than Butyrivibrio.…”

“…Thus, as C. proteoclasticum is related closely to Butyrivibrio (Kopečný et al 2003;van de Vossenberg and Joblin 2003), these results are in agreement with the original results of Polan et al (1964), who investigated more than 20 strains of ruminal bacteria. The most abundant CLA isomer usually found in milk is cis-9,trans-11-18:2 (Offer et al 2001;Shingfield et al 2003). The cis-9,trans-11 isomer is generally considered to be the main health-promoting CLA for human consumption (Pariza 2004).…”

“…Many isomers of C18:2 other than cis-9,trans-11-18:2 appear in digesta and milk too (Shingfield et al 2003). The source of these is not known, either biochemically or microbiologically, nor are their likely effects on health.…”

“…None of the cultures tested here formed trans-11,cis-13-18:2, trans-7,cis-9-18:2 or trans-11,trans-13-18:2; it is possible they are formed from cis-9,trans-11-CLA by species other than Butyrivibrio. The trans-10,cis-12 isomer is usually present at low concentrations in digesta and milk (Offer et al 2001;Shingfield et al 2003), yet it, or its derived trans-10-18:1 biohydrogenation product, can accumulate under certain dietary circumstances, causing milk fat depression, which can be an important problem in the dairy industry (Griinari and Bauman 1999). No isomerisation of LA to the trans-10,cis-12-CLA isomer was found in any of the bacteria investigated here.…”

“…Major advances have been made in achieving the desired changes in fatty acid content of meat and milk experimentally, via dietary manipulation in ruminants, generally by adding oils containing unsaturated fatty acids to the diet (Jenkins 1994;Offer et al 2001;Scollan et al 2001;Shingfield et al 2003). Often, benefits can be attributed directly to the oils which were added to the diet escaping the rumen without being hydrogenated by ruminal microorganisms.…”