Enrichment of (n-3) fatty acids of suckling rats by maternal dietary menhaden oil

Dietary linseed oil in the maternal diet affects immunoglobulins, tissue fatty acid composition and expression of lipid metabolism-related genes in piglets

This experiment investigated the effects of supplementing the maternal diet with linseed oil (LSO) and soya bean oil (SBO) on immunoglobulins, the fatty acid composition and hepatic expression of lipid metabolism-related genes in piglets. Multiparous sows (twenty-four per diet) were fed on diets containing a supplement of either SBO or LSO during last week of gestation and lactation. The results indicated that supplementation of maternal diet with LSO could improve the weaning weight of piglets and average daily gain (ADG) (p < 0.05). The concentration of immunoglobulin G (IgG) and immunoglobulin A (IgA) was enhanced in sow plasma, colostrum and milk by the addition of LSO (p < 0.05). In addition, the concentration of 18: 3n-3 fatty acids was higher in the milk of LSO sows. Meanwhile, maternal supplementation with LSO increased the levels of plasma IgG, IgA and the tissues n-3 polyunsaturated fatty acid (PUFA) in piglets (p < 0.05). Correspondingly, the mRNA expression levels of hepatic ∆5-desaturase (D5D) and ∆6-desaturase (D6D) were higher, and fatty acid synthase (FAS) was lower in piglets from LSO-fed sows when compared with that in the SBO group. In conclusion, LSO supplementation of the maternal diet increases immunoglobulins, modifies the fatty acid composition and affects the gene of D5D and D6D expression of piglets.

Supplementation with fish oil as a source of n-3 fatty acids does not downregulate mammary lipogenesis in lactating mice

The very long chain n-3 (ω-3) polyunsaturated fatty acids (VLCn3PUFAs) are potent regulators of hepatic lipid synthesis, but their effect on lipid synthesis in the lactating mammary gland is less well investigated. The objective of the present study was to examine effects of fish oil (FO) supplementation on mammary lipogenesis and the expression of lipogenic genes in mammary and hepatic tissues of lactating mice. Beginning on day 6 of lactation and continuing for 7 d, female C57BL/6J mice (n = 8/diet) were fed 1 of 3 dietary treatments: a 5%-fat diet containing mainly saturated fatty acids (FAs) (low-fat control) or 2 10%-fat diets, 1 enriched with FO as a source of VLCn3PUFAs and the other enriched with a safflower/palm oil mixture (high-fat control) as a source of oleic acid. Mammary lipogenic capacity, measured by (14)C-glucose incorporation into FAs by mammary explants, was similar among treatments, and there were no treatment effects on the proportion of de novo synthesized FAs in milk fat or on litter weight gain, a proxy for milk energy secretion. Also, there were no treatment effects on mammary mRNA abundance for key lipogenic enzymes and proteins involved in the regulation of milk lipid synthesis. In contrast, there was a treatment effect on hepatic lipogenesis, with FO resulting in a decrease of ~50% in hepatic lipid content and a similar downregulation of lipogenic gene expression compared with the 2 control diets. Overall, there were tissue-specific differences in dietary VLCn3PUFA effects on lipid synthesis with no observed effects for mammary lipogenic variables but marked reductions occurring in hepatic lipogenesis.

Linseed oil in the maternal diet increases long chain-PUFA status of the foetus and the newborn during the suckling period in pigs

Linseed oil, being rich in 18 : 3n-3, represents an alternative source of n-3 PUFA in the maternal diet. However, little is known about the effect of this oil on the long chain n-3 PUFA composition of offspring, which are required for normal growth and maturation of numerous organs. The main objective of the experiment was therefore to investigate fatty acid composition of tissues from sows at the end of gestation and from piglets during the first week of postnatal life in response to maternal dietary linseed oil intake. Sows received either a lard (LAR)-based diet or a linseed oil (LSO)-based diet during gestation and lactation. Fatty acid composition was evaluated in sow plasma, placenta and milk, and in different tissues of piglets on days 0, 3, 7, 21 and 32. The LSO diet increased the proportions of n-3 PUFA and especially 22 : 6n-3 in the placenta. The carcass of LSO piglets at birth contained greater proportions of 20 : 5n-3, 22 : 5n-3 and 22 : 6n-3. The LSO sow milk exhibited greater proportions of 18 : 3n-3 compared with the LAR sow milk. The piglets suckling LSO sows had greater proportions of 18 : 3n-3, 20 : 5n-3 and 22 : 5n-3 in plasma and carcass. The proportions of 22 : 5n-3 and 22 : 6n-3 were greater in the brain of LSO piglets than in that of LAR piglets during the suckling period. In conclusion, LSO in the maternal diet during gestation and lactation increases 22 : 6n-3 concentrations in the placenta and in the foetus carcass, and it maintains 22 : 6n-3 concentrations in the brain during the first week of postnatal life.

The comparative roles of polyunsaturated fatty acids in pig neonatal development

The present review focuses on the importance of polyunsaturated fatty acid (PUFA) provision for the normal development of the pig neonate. The review describes first the selected fatty acid composition of a range of porcine tissues including nervous tissues, muscle and adipose tissues, reproductive organs and immune-responsive organs and/or cells. The importance of PUFA to the functioning of the immune system of the neonate is considered briefly and is followed by an in-depth consideration of the sources of PUFA for the neonatal pig. The effects of different categories or specific types of fatty acid (i.e. non-essential, linoleic, α-linolenic, long-chain n-6 and n-3 PUFA) on various indices of pig neonatal growth are reviewed. The importance of n-3 PUFA supply to the fetal and early neonatal pig is underlined and evidence is presented for more attention to be given to the amounts available from maternal sources. Based on the material reviewed, recommendations are made on the dietary intake of PUFA in the gestating pig.

Uptake of 13C-tracer arachidonate and gamma-linolenate by the brain and liver of the suckling rat observed using 13C-NMR

Arachidonic acid (AA; 20:4n-6) is one of the principal components of the phosphoglycerides in neural cell membranes. During the critical period of postnatal development in mammals, AA is supplied preformed, directly from the milk or derived from precursor fatty acids such as gamma-linolenic acid (GLA; 18:3n-6). In this study, 13C-NMR spectroscopy was applied to investigate the incorporation of [1-(13)C]AA and [3-(13)C]GLA into liver and brain lipids of 7-15-day-old rats. The main objective was to establish the importance of dietary GLA for tissue AA accretion relative to the contribution from preformed dietary AA. [1-(13)C]AA and [3-(13)C]GLA were injected into the stomach of 7-day-old rats as a mixture. 13C-NMR spectroscopy of lipid extracts revealed incorporation of [1-(13)C]AA and [5-(13)C]AA (the latter derived from metabolism of the injected [3-(13)C]GLA) into phosphoglycerides and triacylglycerols. Preformed AA was 10 (liver)-17 (brain) times more efficient in contributing to tissue AA than AA derived from precursor GLA. In separate experiments, NMR spectroscopy was used to assess uptake of [1-(13)C]AA directly in living rats and intact organs. Results showed that intact liver and brain contain an appreciable amount of NMR-detectable lipids. The in vivo/in vitro information obtained from organs provided details on the mobility and turnover of tissue lipids.

Dietary menhaden and corn oils and the red blood cell membrane lipid composition and fluidity in hyper- and normocholesterolemic miniature swine

Fatty acids in the diet are readily incorporated into lipids in various tissues. However, it is not clear whether all tissues have the same level of incorporation. Second, (n-6) unsaturated fatty acids increase the fluidity of membranes, but this has not been shown for (n-3) fatty acids. In this study, we measured the incorporation of (n-6) and (n-3) fatty acids into erythrocyte membrane lipids and studied their effects on the fluidity of erythrocyte membranes. One group of female miniature swine was made hypercholesterolemic by feeding the swine cholesterol and lard for 2 mo; the other group served as controls and was fed a stock diet. Both groups were then fed either corn oil or menhaden oil or a mixture of the two for 23 additional weeks. Blood was collected at 0, 2, 4, 12 and 23 wk after initialization of the experimental diets, and fatty acid composition of phospholipids was assessed. Membrane phospholipids of pigs fed menhaden oil had elevated (n-3) fatty acids (20:5 and 22:6), and lower 18:2 than those fed corn oil. There was no difference in 20:4 content. The fatty acid changes occurred as early as 2 wk after consumption of the corn oil or menhaden oil in pigs previously fed a stock diet, but it took longer in pigs previously fed lard + cholesterol, indicating residual effects of pretreatment. Menhaden oil increased anisotropy (indicating decreased fluidity) more than corn oil for the nonpolar probe diphenylhexatriene (DPH) at earlier time points, but not at 23 wk. Erythrocyte membrane fluidity was significantly related to membrane polyunsaturate content, with (n-6) fatty acids having a greater influence than (n-3) fatty acids. A comparison of the present red blood cell fatty acid compositions with brain synaptosome fatty acid compositions for the same animals showed poor correlations for some of the fatty acids. There was no significant direct relationship between docosahexaenoate (DHA) concentrations in erythrocyte membranes with DHA concentrations in brain synaptosomes from cerebellum, forebrain and caudate nucleus.

Modification of milk formula to enhance accretion of long-chain n-6 and n-3 polyunsaturated fatty acids in artificially reared infant rats

Artificially reared infant rats were used to determine the effects of long-chain polyunsaturated fatty acid (LCPUFA) supplementation on blood and tissue concentrations of arachidonic acid (AA) and docosahexaenoic acid (DHA). Beginning at 7 d of age, infant rats were fed for 10 d with rat milk formulas supplemented with AA at 0, 0.5 and 1.0%, or supplemented with DHA at 0, 0.5 and 1.0% of total fatty acid. The supplementation of AA increased accretion of the fatty acid in tissue and blood phospholipids with a maximum increase of 9% in brain, 15% in liver, 25% in erythrocytes, and 43% in plasma above the values of unsupplemented infant rats. Rat milk formula containing 1.0% of AA had no added benefits over that containing 0.5% of AA. The supplementation of DHA increased phospholipid DHA by a maximum of 24% in brain, 87% in liver, 54% in erythrocytes, and 360% in plasma above the unsupplemented control. The increase in tissue and blood DHA was concentration-dependent on formula fatty acid. Brain phosphatidylcholine and phosphatidylethanolamine were similarly enriched with AA and DHA by supplementation of the corresponding fatty acids. In general the observed increase of AA was accompanied by a decrease in 16:0, 18:1 n-9, and/or 18:2n-6, whereas the increased DHA was associated with a reduction of 18:1n-9, 18:2n-6, and/or 20:4n-6. Clearly, infant rats were more responsive to DHA than AA supplementation, suggesting a great potential of dietary manipulation to alter tissue DHA concentrations. However, the supplementation of DHA significantly decreased tissue and blood AA/DHA ratios (wt%/wt%), whereas there was little or no change in the ratio by AA supplementation. Although the physiological implications of the levels of AA and DHA, and AA/DHA ratios achieved under the present experimental conditions are not readily known, the findings suggest that artificial rearing could provide a suitable model to investigate LCPUFA requirements using various sources of AA and DHA in rats.

Interaction of n-3 long-chain polyunsaturated fatty acids with n-6 fatty acids in suckled rat pups

The addition of long-chain polyunsaturated fatty acids (LCP: C20, and C22) to infant formula may permit fatty acid accretion rates similar to breast-fed infants, and may have long-term outcome benefits, such as improved visual acuity and cognitive development. Although fish oil may provide a source of n-3 LCP, sources of n-6 LCP have been more difficult to identify. The present study evaluates the effects of n-3 and n-6 LCP derived from single-cell oils on liver, plasma, and brain fatty acid levels in a neonatal animal model. Newborn rat pups were suckled for 14 d by dams receiving diets containing n-3 LCP alone or combinations of n-3 LCP and increasing doses of linoleic acid (18:2n-6) or arachidonic acid (20:4n-6). Dietary groups received 2% n-3 LCP and 1, 2, or 5% of either 18:2n-6 or 20:4n-6. The 20:4n-6 source also contained modest levels of 18:2n-6. At the termination of the study, liver, plasma, and brain were obtained from the rat pups and the phospholipid fatty acid profiles determined. The results indicate complex interactions of n-3 and n-6 fatty acids. Groups receiving dietary 20:4n-6 incorporated higher levels of n-6 LCP into tissues than did the groups receiving 18:2n-6. The brain was relatively resistant to changes in fatty acid composition compared with the liver and plasma. As expected, tissue n-3 LCP levels were reciprocally related to n-6 levels. The present results document that single-cell LCP oils are bioavailable in a neonatal animal model. The use of 20:4n-6 is a more effective means of supporting n-6 status than the use of 18:2n-6. These results may have implications for the addition of LCP to infant formula.

Modifying the n-3 fatty acid content of the maternal diet to determine the requirements of the fetal and suckling rat

During perinatal development, docosahexaenoic acid (22:6n-3) accumulates extensively in membrane phospholipids of the nervous system. To evaluate the n-3 fatty acid requirements of fetal and suckling rats, we investigated the accumulation of 22:6n-3 in the brain and liver of pup rats from birth to day 14 postpartum when their dams received increasing amounts of dietary 18:3n-3 (from 5 to 800 mg/100 g diet) during the pregnancy-lactation period. The fatty acid composition of brain and liver phospholipids of pups, as well as that of dam's milk, was determined. At birth, 22:6n-3 increased regularly to reach the highest level when the maternal diet contained 800 mg 18:3n-3/100 g. On days 7 and 14 postpartum, brain 22:6n-3 plateaued at a maternal dietary supply of 200 mg/100 g. Docosapentaenoic acid (22:5n-6) had the opposite temporal pattern. The unusually high concentration of eicosapentaenoic acid (20:5n-3) in liver and dam's milk observed at the highest 18:3n-3 intake suggests an excessive dietary supply of this fatty acid. All these data suggest that the n-3 fatty acid requirements of the pregnant rat are around 400 mg 18:3n-3 and those of the lactating rat at 200 mg (i.e., 0.9 and 0.45% of dietary energy, respectively). The values of 18:3n-3 and 22:6n-3 milk content which allowed brain 22:6n-3 to reach a plateau value in suckling pups were 1% of total fatty acids and 0.9% (colostrum) to 0.2% (mature milk), respectively. These levels are similar to those recommended for infant formulas.

Effect of maternal dietary arachidonic or linoleic acid on rat pup fatty acid profiles

Rapidly growing neonatal mammals accrete relatively large quantities of long chain (> or = C20) polyunsaturated fatty acids (LCP) in membrane phospholipids. We have examined accumulation of omega 6 LCP in suckling neonatal rat pups during the first 14 d of life when their dams received essential fatty acids in the form of triglycerides containing linoleic acid or arachidonic acid. Dietary levels of these fatty acids were either 1 or 5% of total dietary fatty acids. The fatty acid profile of pup stomach contents (composed solely of the dams' milk) and plasma lipids, as well as liver and brain phospholipids, were determined. Stomach linoleic and arachidonic acid levels reflected the diet of the dams. Pup plasma and liver arachidonic acid levels increased progressively from the group receiving 1% linoleic acid to 5% linoleic acid and from 1% arachidonic acid to 5% arachidonic acid. Interestingly, brain phosphatidylethanolamine and phosphatidylcholine arachidonic acid levels were more stable than plasma or liver levels. These results suggest that the brain may be capable of either selective transport of omega 6 LCP or chain elongation/desaturation of linoleic acid. These data indicate that care must be exercised when adding LCP to infant formula since widely divergent accretion rates of arachidonic acid may occur in various tissues.

Maternal dietary fish oil enriches docosahexaenoate levels in brain subcellular fractions of offspring

Prompted by the speculated essentiality of docosahexaenoic acid (DHA) for neural development, this study was undertaken to investigate the incorporation of (n-3) fatty acids in the maternal diet into various phospholipids of infant rat brain subcellular fractions: microsomes (Ms), synaptosomes (Sy), myelin (My), and mitochondria (Mt). Two groups of infant rats were nourished by dams fed diets containing 20% of either corn oil (CO) or menhaden oil (MO) from 2 until 12 days of age. DHA but not eicosapentaenoic acid (EPA) was distributed to all subcellular fractions of infant rats in the CO group. The levels of DHA were higher in Ms and Mt than Sy and My, and higher in phosphatidylethanolamine (PE) and phosphatidylserine (PS) than phosphatidylcholine (PC) and phosphatidylinositol (PI). The MO feeding enriched DHA in PE of all subcellular fractions, PS of all subcellular fractions, except My, PC of Sy, My and Mt, and PI of My. EPA was enriched in phospholipids in all subcellular fractions, except mitochondrial PS of the MO group. In the MO group, the ratios of EPA/DHA, ranging from 0.01 to 0.85, in all subcellular phospholipids were markedly lower than that found in the mother's milk (i.e., 1.5), suggesting an ability to elongate and desaturate EPA to DHA and/or disproportional uptake of the fatty acids by the brain. In PE of all subcellular fractions, the increased levels of DHA and EPA, with a concomitant reduction of arachidonic and/or linoleic acid, yielded higher ratios of total (n-3)/(n-6) fatty acids in the MO than the CO group. The inclusion of preformed DHA and EPA in the maternal diet provides an effective means to enrich these fatty acids in developing brains.

The effects of dietary fish oil on alveolar type II cell fatty acids and lung surfactant phospholipids

The purpose of this study was to determine the responsiveness of alveolar type II cells to dietary fish oil and the consequent effects on alveolar and lung surfactant. Rats were fed a corn oil or a fish oil diet for four weeks. Dietary n-3 fatty acids were readily incorporated into the type II cell phospholipids as indicated by higher levels of eicosapentaenoic acid (2.77 +/- 0.10%) and docosahexaenoic acid (1.63 +/- 0.10%) in the group receiving the fish oil diet. The elevated levels of n-3 fatty acids were accompanied by concomitant reduction in arachidonic acid and linoleic acid. Neither eicosapentaenoic acid nor docosahexaenoic acid was incorporated into type II cell triacylglycerols. Feeding a fish oil containing diet increased surfactant phospholipids, particularly 1,2-disaturated acyl phosphatidylcholines in whole lung compared to a corn oil diet. However, the amount of surfactant found in the alveolus was not different between the two diet treatment groups. The results suggest that dietary n-3 fatty acids stimulate synthesis and/or inhibit degradation of lung surfactant without altering surfactant secretion in alveoli.

Changes in plasma and erythrocyte fatty acids in patients fed enteral formulas containing different fats

Critically ill hospital patients were fed enteral formulas containing different fat substrates. Seven patients received formula X, which contained 28 g of structured triglycerides and menhaden oil to provide 7.6 g of medium-chain fatty acids, 2.5 g linoleic acid, 1.3 g eicosapentaenoic acid, and 0.4 g docosahexaenoic acid per 1000 mL of formula. Six patients received formula Y consisting of 36.8 g of medium-chain triglycerides and corn and soy oils providing 14.3 g medium-chain fatty acids and 11.7 g linoleic acid per 1000 mL. Feeding of formula X increased plasma total phospholipid levels of eicosapentaenoic acid on days 7 and 14 and docosahexaenoic acid levels on day 14. Plasma levels of linoleic acid were reduced in formula-X-fed in comparison to formula-Y-fed patients, whereas arachidonic acid was maintained in both groups during feeding. As a result of these changes, the patients receiving formula X had decreased ratios of arachidonic acid:eicosapentaenoic acid in plasma. Formula Y feeding did not alter eicosapentaenoic acid and docosahexaenoic acid levels in the plasma. In the erythrocyte, formula X feeding resulted in a threefold increase in eicosapentaenoic acid from mean baseline levels of 0.4 +/- 0.4% to a mean value of 1.2 +/- 0.9% at day 7. The formula X feeding decreased linoleic acid levels on days 7 and 14, whereas levels of arachidonic acid and docosahexaenoic acid remained constant. Formula Y feeding did not affect any of the parameters measured for erythrocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of dietary sources of fat on lipid synthesis in mink (Mustela vison) mammary tissue

1. The fatty acid composition of the triglyceride fraction of mink milk sampled during mid-lactation (day 28 post partum) from two nursing mink was compared to that of plasma samples and to the fatty acid composition of the feed rations used. 2. Chemical analysis of the triglyceride composition of mink milk demonstrated only minute concentrations of fatty acids with a chain length below C14. 3. The saturated C16:0- and C18:0-unit fatty acids in mink milk made up for 24-40% of the total amount of fatty acids extracted, the remainder being represented by mono and polyunsaturated long-chain (C16-C24) fatty acids. 4. Preliminary in vitro experiments proved the incorporation of 14C-labelled glucose, acetate or palmitate into triacylglycerols in cultures of mink mammary tissue to be linear for at least 2 hr. 5. The in vitro capacity for de novo fatty acid synthesis in mink mammary tissue using 14C-labelled glucose or acetate was low, i.e. ranging from 0.096-0.109 nmol/g (fresh tissue)/min, and amounted to only about 5% of that obtained in the case of [14C]palmitic acid incubation. 6. Following 14C-labelled acetic or palmitic acid incubation of mink mammary tissue neither desaturation nor chain elongation was observed. 7. In response to long-term feeding on rations with two different sources of animal fat (F = fish oil or L = lard) the influence of compositional changes in dietary neutral lipids on the fatty acid composition of the lipids of mink milk is discussed.

Do essential fatty acids play a role in brain and behavioral development?

The membrane phospholipids of the brain contain high levels of polyunsaturated fatty acids (PUFA), particularly arachidonic acid, 20:4n-6 and docosahexaenoic acid, 22:6n-3. These long-chain PUFA are synthesized from their respective essential fatty acid (EFA) precursors, linoleic acid, 18:2n-6 and linolenic acid, 18:3n-3. Although the necessity of n-6 fatty acids for optimum growth has been established, a similar requirement for those of the n-3 family is less clear. The rapid accumulation of the long-chain n-3 PUFA in the brain during prenatal and preweaning development suggests that the provision of n-3 fatty acids to the developing brain may be necessary for normal growth and functional development. The intent of this review is to assess the experimental work which addresses this question, most of which has been conducted on rodents. The emphasis will be on studies which measure behavioral outcomes, and particular attention will be paid to methodological issues which affect the interpretation of these data. An integration of the research findings will be presented and discussed in light of possible implications for therapeutic interventions.

Fatty acid profiles of brain phospholipid subclasses of rats fed n − 3 polyunsaturated fatty acids of marine or vegetable origin. A two generation study

The effects of dietary n - 3 polyunsaturated fatty acids (PUFA) on fatty acid profiles of rat brain phospholipid subclasses as well as on heart phosphatidylethanolamine through two generations were examined: Three groups of rats were fed 20 weight% fat diets in which approx. 30% of the fatty acids were polyunsaturated, either 17% linoleic acid + 13% C20(-) + C22 polyunsaturates from fish oil or 17% linoleic + 13% alpha-linolenic acid from linseed oil or 30% linoleic acid. The rats of the two generations were killed as adults at 18 weeks of age. The results demonstrated that fish oil was a better source than alpha-linolenic acid for incorporation of n - 3 PUFA into the examined phospholipids. This was seen both in brain and heart tissue and in both generations of rats. In the brain phosphatidylethanolamine (PE) and phosphatidylserine (PS) similar fatty acid profiles were found in 1st and 2nd generation, but fish oil was more efficient than 18:3(n - 3) in increasing the levels of 22:6(n - 3), 20:5(n - 3), 22:5(n - 3) and reducing 20:4(n - 6) and 22:5(n - 6). Fatty acid profiles of phosphatidylinositol (PI), phosphatidylinositol-4-phosphate (PIP) and phosphatidylinositol-4,5-bisphosphate (PIP2) were affected by dietary fats. In PIP and PIP2 of 2nd generation rats 20:4(n - 6) was reduced from 36 to 29% following fish oil intake, whereas alpha-linolenic acid had no effects. The cholesterol/phospholipid ratio was not affected in the brain, neither was the degree of unsaturation of the phospholipids. In heart PE the highest levels of 20:5(n - 3)(2%) and 22:6(n - 3) (36%) were observed following fish oil intake. However, in rats fed alpha-linolenic acid a considerable increase in the level of 22:6(n - 3) was observed from the 1st (21%) to the 2nd generation (26%).

The effects of dietary n-3/n-6 ratio on brain development in the mouse: a dose response study with long-chain n-3 fatty acids

This study examines the effects of the ratio of n-3/n-6 fatty acids (FA) on brain development in mice when long-chain n-3 FA are supplied in the diet. From conception until 12 days after birth, B6D2F1 mice were fed liquid diets, each providing 10% of energy from olive oil, and a further 10% from different combinations of free FA concentrates derived from safflower oil (18:2n-6), and fish oil (20:5n-3 and 22:6n-3). The range of dietary n-3/n-6 ratios was 0, 0.25, 0.5, 1.0, 2.0 and 4.0, with an n-6 content of greater than 1.5% of energy in all diets, and similar levels of total polyunsaturated fatty acids (PUFA). In an additional group of ratio 0.5, 18:2n-6 was partially replaced by its delta 6 desaturation product, 18:3n-6. Biochemical analyses were conducted on 12-day-old pup brains, as well as on samples of maternal milk. No obvious effects on overall pup growth and development were observed, apart from a smaller litter size at ratio 1. Co-variance analysis indicated that increasing the n-3/n-6 ratio was associated with slightly smaller brains, relative to body weight. We found that 18:2n-6 and 20:5n-3 were the predominant n-6 and n-3 FA in the milk; in the brain these were 20:4n-6 and 22:6n-3, respectively. Increasing dietary n-3/n-6 ratios generally resulted in an increase in n-3 FA, with a corresponding decrease in n-6 FA.(ABSTRACT TRUNCATED AT 250 WORDS)