T. W. Scott

Protection of dietary polyunsaturated fatty acids against microbial hydrogenation in ruminants

Polyunsaturated fatty acids are normally hydrogenated by microorganisms in the rumen. Because of this hydrogenation ruminant triglycerides contain very low proportions of polyunsaturated fatty acids. A new process is described whereby polyunsaturated oil droplets are protected from ruminal hydrogenation by encapsulation with formaldehyde-treated protein. The formaldehyde-treated protein resists breakdown in the rumen thereby protecting the fatty acids against microbial hydrogenation. When these protected oils are fed to ruminants the formaldehydeprotein complex is hydrolyzed in the acidic conditions of the abomasum and the fatty acids are absorbed from the small intestine. This results in substantial changes in the triglycerides of plasma, milk and depot fats, in which the proportion of polyunsaturated fatty acids is increased from 2–5% to 20–30%. These effects are observed in the plasma and milk within 24–48 hr of feeding while a longer period is necessary to alter the composition of sheep depot fat. The implications of these findings are discussed in relation to human and ruminant nutrition.

Incorporation of n−3 fatty acids of fish oil into tissue and serum lipids of ruminants

This study examines the biohydrogenation and utilization of the C20 and C22 polyenoic fatty acids in ruminants. Eicosapentaenoic (20∶5n−3) and docosahexaenoic (22∶6n−3) acids were not biohydrogenated to any significant extent by rumen microorganisms, whereas C18 polyenoic fatty acids were extensively hydrogenated. The feeding of protected fish oil increased the proportion of 20∶5 from 1% to 13–18% and 22∶6 from 2% to 7–9% in serum lipids and there were reductions in the proportion of stearic (18∶0) and linoleic (18∶2) acids. The proportion of 20∶5 in muscle phospholipids (PL) increased from 1.5% to 14.7% and 22∶6 from 1.0% to 4.2%; these acids were not incorporated into muscle or adipose tissue triacylglycerols (TAG). In the total PL of muscle, the incorporated 20∶5 and 22∶6 substituted primarily for oleic (18∶1) and/or linoleic (18∶2) acid, and there was no consistent change in the porportion of arachidonic (20∶4) acid.

Assessing the biological effectiveness of protected lipid supplements for ruminants

Techniques are described for assessing the effectiveness with which lipids may be protected against ruminal degradation. A simple in vitro test was developed using pancreatic lipase, and this test may have application in quality control of the commercial production of protected lipid supplements, as it is applicable to supplements containing polyunsaturated or saturated lipids. All the in vitro tests overestimate the actual in vivo biological effectiveness, and this is probably due to mastication and greater microbial activity in vivo than in vitro. The poor biological response of some protected lipid supplements is most probably due to the incomplete entrapment of lipid droplets in the protein matrix.

Effects of protected cyclopropene fatty acids on the composition of ruminant milk fat

Unsaturated fatty acids can be protected from ruminal hydrogenation, and, when fed to lactating ruminants, the constituent acids are incorporated into milk triacylglycerols. By this means, it has been possible to reduce the melting point of milk triglycerides and to make softer butter fat. This report shows that, by feeding small amounts of protected cyclopropene fatty acids, one is also able to make harder butter fat.Sterculia foetida seed oil, a rich source of cyclopropene fatty acids, was emulsified with casein and spray dried to yield a free flowing dry powder. When this material was treated with formaldehyde and fed to lactating goats (ca. 1 g cyclopropene fatty acids per day), there were substantial increases in the proportions of stearic acid and decreases in the proportions of oleic acid in milk fat. Similar results were obtained when the formaldehyde-treated supplements were fed to lactating cows (ca. 3 g cyclopropene fatty acids per day). The effect was considerably less apparent when theS. foetida seed oilcasein supplement was not treated with formaldehyde, suggesting that cyclopropene fatty acids are hydrogenated in the rumen as are other unsaturated fatty acids. The effect of feeding protected cyclopropene fatty acids on the stearic: oleic ratio in milk fat is probably due to cyclopropene-mediated inhibition of the mammary desaturase enzymes.

Effect of dietary fat supplementation on the composition and positional distribution of fatty acids in ruminant and porcine glycerides.

Dietary fats which were protected from ruminal metabolism were fed to ruminants, and the constituent fatty acids subsequently appeared in the glycerides of tissues and secretory products. These dietary fat induced alterations in tissue lipid composition were particularly apparent when the fat source was enriched with linoleic acid. Similarly, when pigs were fed linoleic-enriched fats, the linoleic acid was incorporated into the adipose tissue triglycerides. Stereospecific analyses were carried out on triglycerides from various tissues and secretory products obtained from animals fed control or linoleate-enriched diets. The analysis of adipose tissue triglycerides showed that linoleate and oleate were preferentially esterified to positions 2 and 3 (cattle and sheep), and positions 1 and 3 (pigs). Of the other major adipose tissue fatty acids, palmitate was preferentially esterified at position 1 (ruminants) and position 2 (pigs), and stearate was preferentially esterified at positions 1 and 3 (ruminants), and position 1 (pigs). Stereospecific analysis of high mol wt milk triglycerides showed that linoleate was either evenly distributed on all three positions (goats), or predominantly on position 3 (cows). Furthermore, the incorporation of this linoleate did not markedly alter the positional specificity of the other major milk triglyceride fatty acids. Of these fatty acids, the short and medium chain length acids (butyratelaurate) were mainly on position 3, myristate and palmitate on positions 1 and 2, and stearate and oleate evenly distributed. Thoracic duct lymph triglycerides from sheep tended to show preferential incorporation of linoleate at position 3, palmitate at position 2, and stearate at position 1 and 3; oleate, on the other hand, tended to be evenly distributed on all three positions of the lymph triglyceride. The stereospecific arrangement of fatty acids in sheep liver triglycerides was similar to that of lymph triglycerides, and this may reflect the uptake of intact or partially hydrolysed chylomicron and/or very low density lipoprotein triglycerides by the liver. There were also some analogies in the stereospecific arrangement of fatty acids on ruminant lymph and milk triglycerides and this may reflect an incomplete hydrolysis of chylomicron and/or very low density lipoprotein triglycerides prior to uptake by the mammary gland. An unusual feature of lymph from sheep fed linoleate was the presence of phospholipids which contained large amounts of linoleate in ca. equal proportion at both positions 1 and 2 of the phospholipid molecule.

Effect of dietary polyunsaturated pork on plasma lipids and sterol excretion in man.

Pork, enriched in linoleic acid content, was compared with conventional pork in the diet of three human subjects with respect to the plasma cholesterol concentration and the excretion in feces of neutral sterols and bile acids. Since the fatty acids in pork glyceride have an unusual positional distribution, the redistribution that might occur during the absorption and disposition of a fat meal was also studied. The plasma cholesterol was lower with polyunsaturated pork, the difference, 14 mg/100 ml plasma, being of the order expected from the change in polyunsaturated to saturated fatty acid ratio. On average, the excretion of neutral sterols was 57% greater with polyunsaturated than with conventional pork in all three subjects, and in this respect the results resembled the findings with polyunsaturated ruminant fats. During the absorption of pork fat, the high proportion of palmitate in the 2 position of lard triglyceride served as a useful marker, since human triglyceride carries mainly unsaturated fatty acids in that position. There were stepwise changes in the fatty acid composition at the 2 position of triglyceride as the fat was absorbed, transported through, and cleared from plasma, the palmitate being gradually replaced by oleate and linoleate. By contrast, the total fatty acid profile in the triglyceride changed relatively little, implying selective reacylation with palmitate at the 1 and/or 3 position. During the clearing of dietary triglyceride, the porcine triglyceride was thus converted to the form occurring in humans.

Effect of feeding protected lipids on fatty acid synthesis in ovine tissues.

The effects of including protected lipid supplements in the sheep diet have been studied by measuring the incorporation of [1-14C] acetate into tissue fatty acids in vivo and in vitro. Supplementing the diet with protected lipid significantly (P<0.05) depressed lipogenesis in adipose tissue both in vivo and in vitro. However, when protected lipids of different fatty acid composition were given to lambs, the protected safflower oil supplement containing high levels of linoleic acid was the only treatment to cause a significant (P<0.05) depression in fatty acid synthesis in adipose tissue, the major site of lipogenesis in the sheep. Larger adipose cells in the lipid-supplemented sheep indicate that these sheep were fatter than those receiving the basal diet. Therefore, supplemented wethers deposited more fat than sheep receiving the basal diet and this fat was derived from the supplement rather than from de novo synthesis.

Effect of feeding protected cholesterol on ruminant milk fat secretion

Feeding 1–2 g/day of cholesterol protected against ruminal hydrogenation caused a 20–30% drop in the secretion of milk fat by goats and cows. The effect was observed with goats fed conventional rations or with goats and cows fed rations supplemented with protected lipids, but was not observed with cows fed conventional rations, or when unprotected cholesterol and protected β-sitosterol was fed to these animals. The results suggest that this depression in milk fat is due to a decreased uptake of plasma triacylglycerol fatty acids by the mammary gland, induced by dietary cholesterol.