Two cases of grazing sheep with abundance of trans octadeca fatty acids in milk fat

Within two groups of lactating Karakachan sheep, grazing mountain pastures in the Bulgarian Rhodope region, respectively one ewe produced milk containing extraordinarily high amounts of c9t11-C18:2 and t10-C18:1. The deviations from the group averages ranged up to about 20 standard deviations for the t10-C18:1 isomer in both cases. For one of the two sheep also t11-C18:1 proportion in total fatty acids was increased. Proportions of Cl 8:0 and c9-C18:1 were very low. As the deviating sheep did not receive any treatment differing from that of the other seven and nine animals of the respective groups, it is hypothesized that these changes are due to an inhibition of the terminal step of biohydrogenation in the rumen, possibly by ingestion of an unknown, effective plant species.