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Background: A wide range of isomer-specific health benefits have been attributed to conjugated linoleic acids (CLAs). Little information is currently available on the influence of different feed components on the concentration of CLA isomers in ruminant-derived products. The aims of this study were to compare the effect of cereal mix or dried sugar beet pulp supplementations fed to grazing dairy cows on milk CLA isomeric distribution and to examine the monthly variation of CLA isomers during the grazing season., Results: The concentrations of the isomers t7c9, t10c12 and t10t12 were higher in milk from cows supplemented with cereals (P < or = 0.001). The milk of beet pulp-supplemented cows showed higher levels of the isomers t11c13 (P < or = 0.05), t9t11 (P < or = 0.001) and t7t9 (P < or = 0.01). Total CLA as well as seven other minor isomers were not significantly affected by the concentrate type. Monthly variations occurred extensively for almost all detected isomers. Total CLAs showed the highest values at the beginning of the grazing season and in autumn in coincidence with plant regrowth., Conclusion: These results show that even at low levels, supplement types can significantly influence the concentration of some CLA isomers in milk fat; an indication is given of the possibility to manipulate the animals' diet to change the CLA isomeric profile in ruminant-derived products.

Multiparous sows (n 17) were included in a controlled cross-over-study in order to investigate the influence of a natural source of conjugated linoleic acid (CLA) (alpine butter) on the milk fatty acid composition of lactating sows (as an animal model for lactating women) and on the growth performance of their progeny. The usual fat source of a standard lactation diet was replaced by either CLA-rich alpine butter or margarine (control diet). Compared with the margarine diet, feeding the alpine butter-supplemented diet increased (P 0.05) affected. Growth performance of the progeny was similar for both dietary treatments. In summary, the findings show that adding alpine butter to the diet does not provoke a milk fat depression and does not alter the composition of total SFA, MUFA and PUFA in sow milk but increases its CLA concentration.

Consumption of CLA by lactating women affects the composition of their milk, but the pattern of the different CLA isomers is still unknown. We determined the effects of short maternal supplementation with CLA-rich Alpine butter on the occurrence of FA and CLA isomers in human milk. In an open randomized controlled study with a two-period cross-over design, milk FA and CLA isomer concentrations were measured on postpartum days > or = 20 in two parallel groups of lactating women before, during, and after consumption of defined quantities of Alpine butter or margarine with comparable fat content (10 d of butter followed by 10 d of margarine for one group, and vice versa in the other). In the 16 women who completed the study (8/group), Alpine butter supplementation increased the C16 and C18 FA, the sum of saturated FA, the 18:1 trans FA, and the trans FA with CLA. The CLA isomer 18:2 c9,t11 increased by 49.7%. Significant increases were also found for the isomers t9,t11, t7,c9, t11,c13, and t8,c10 18:2. The remaining nine of the total 14 detectable isomers showed no changes, and concentrations were <5 mg/100 g fat. A breastfeeding mother can therefore modulate the FA/CLA supply of her child by consuming Alpine butter. Further studies will show whether human milk containing this FA and CLA isomer pattern acts as a functional food for newborns.

The concentrations of CLA isomers were determined by Ag+ -HPLC in the milk fat of cows fed a control diet consisting of hay ad libitum and 15 kg of fodder beets or this diet supplemented with oilseeds containing either high levels of oleic acid (rapeseed), linoleic acid (sunflower seed), or alphalinolenic acid (linseed). Highly significant (P < or = 0.001) correlations were found between the daily intakes of oleic acid and the concentration of the CLA isomer trans-7,cis-9 in milk fat; of linoleic acid and the CLA isomers trans-10,trans-12, trans-9,trans-11, trans-8,trans-10, trans-7,trans-9, trans-10,cis-12, cis-9,trans-11, trans-8,cis-10, and trans-7,cis-9; and of alpha-linolenic acid and the CLA isomers trans-12,trans-14, trans-11 ,trans-13, cis,trans/trans,cis-12,14, trans-11 ,cis-13, and cis-11 ,trans-13. CLA concentrations were also determined in the milk fat of cows grazing in the lowlands (600-650 m), the mountains (900-1210 m), and the highlands (1275-2120 m). The concentrations of many isomers were highest in milk fat from the highlands, but only three CLA isomers (cis-9,trans-11, trans-11 ,cis-13, and trans-8,cis-10) showed a nearly linear increase with elevation. Therefore, these three CLA isomers, and particularly the CLA isomer trans- 11,cis-13, the second-most important CLA in milk fat from cows grazing at the three altitudes, could be useful indicators of milk products of Alpine origin.

The uniqueness of ruminant milk lipids is based on their high concentration of CLA. Maximal CLA concentrations in milk lipids require optimal conditions of ruminal fermentation and substrate availability, conditions like those present in pasture-fed cows. Our previous work showed that farm management (indoor feeding vs. pasture feeding) markedly influenced the CLA concentration. In this study, the objective was to evaluate the influence of the farm management system as dependent on different locations. Milk samples from different locations (Thuringia and the Alps, representing diverse altitudes) were collected during the summer months and analyzed for FA profile and CLA isomer distribution. The proportion of PUFA and total CLA in milk fat was significantly lower in milk from indoor cows compared with the pasture cows in the Alps. The trans-11 18:1 in milk fat of Alpine cows was elevated, in contrast to lower values for trans-10 18:1. Milk from cows grazing pasture in the Alps was higher in EPA and lower in arachidonic acid than milk from indoor-fed cows. The proportion of cis,trans/trans,cis isomers of CLA was 10 times higher from the indoor cows than from the Alpine cows. In addition to the major isomer cis-9,trans-11, this difference also occurred for the trans-11,cis-13 isomer, which represented more than a fourth of the total CLA present in milk fat. This is the first report showing a special isomer distribution in the milk fat of cows living under very natural conditions. We hypothesize that the CLA isomer trans-11,cis-13 is formed in large quantity as a result of grazing mountain pasture, which is rich in alpha-linolenic acid.