Diet‐dependent occurrence of CLA isomers in rumen and duodenal digesta of slaughtered bulls

This study examined the effects of linolenic acid‐rich vs. linoleic acid‐rich feeding system on the occurrence of individual CLA isomers in the rumen and duodenum digesta of German Holstein and German Simmental bulls using Ag⁺‐HPLC/DAD. The diet affected the biosynthesis of individual CLA isomers in the rumen of the bulls of both breeds. The isomer t‐11,c‐13 CLA was detected as the most abundant isomer in the rumen of linolenic acid‐rich diet‐fed bulls, up to six times higher compared to linoleic acid‐rich diet‐fed bulls. However, the main isomer in muscle lipid, c‐9,t‐11 CLA, was produced to a low extent in the rumen of linolenic acid‐rich diet‐fed bulls compared to higher concentrations of this isomer in the rumen of linoleic acid‐rich diet‐fed bulls. The isomers t‐7,c‐9 CLA and t‐8,c‐10 CLA were not present in the rumen samples of bulls fed both diets; however, abundant t‐7,c‐9 CLA was identified in the duodenum. The CLA isomers t‐12,t‐14 CLA and t‐11,t‐13 CLA were identified as the main t,t CLA isomers in the rumen, and were significantly enhanced in the rumen of linolenic acid‐rich diet‐fed compared to linoleic acid‐rich diet‐fed bulls. In contrast to c‐9,t‐11 CLA, the t,t CLA isomers seem to be biosynthesized predominantly in the rumen, further transported via the duodenum and finally deposited in the tissue lipids mainly in linolenic acid‐rich diet‐fed bulls. This was shown earlier for muscle and subcutaneous fat samples from the same animal experiment.