title: Analysis of variation in cis-9, trans-11 conjugated linoleic acid (CLA) in milk fat of dairy cows.
abstract: Conjugated linoleic acid (CLA) is a fatty acid with numerous putative health benefits and is a natural component of ruminant-derived food products. An intermediate in rumen biohydrogenation is cis-9, trans-11 CLA, the major CLA isomer in milk fat. However, the major source of cis-9, trans-11 CLA in milk is endogenous synthesis by delta 9-desaturase conversion of trans-11 C18:1, another rumen biohydrogenation intermediate. The desaturase indices serve as a proxy for delta 9-desaturase activity and are calculated from the ratios of fatty acid pairs that represent product/substrate for this enzyme. This study analyzed individual animal variation in milk fat content of cis-9, trans-11 CLA and in desaturase indices in milk fat. Thirty lactating Holstein cows were allocated to one of three treatment groups: one received a standard total mixed ration, one received a diet that produced an elevated milk fat content of CLA, and a third treatment group was alternated between these diets at 3-wk intervals over the 12-wk study. There was a two- to threefold variation among individuals on the same diet for both milk fat content of CLA and desaturase indices in milk fat. This hierarchy was maintained to a large extent over the 12-wk study even in the variable treatment group that alternated between the two diets. Within the variable diet treatment, some animals consistently had a substantial response in milk fat content of CLA to dietary shifts, whereas other cows had little or no response. We conclude that while diet is a major determinant of the CLA content in milk fat, individual animal differences also have a substantial effect. The variation among individuals includes differences related to both rumen biohydrogenation and delta 9-desaturase activity in the mammary gland.
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D002417:Cattle / Q000378:metabolism*; D004032:Diet; D005227:Fatty Acids / Q000032:analysis; D005260:Female; D007774:Lactation; D019787:Linoleic Acid / Q000032:analysis*; D008055:Lipids / Q000032:analysis; D008321:Mammary Glands, Animal / Q000201:enzymology; D008892:Milk / Q000737:chemistry* / Q000201:enzymology; D012417:Rumen / Q000378:metabolism; D013230:Stearoyl-CoA Desaturase / Q000378:metabolism
chemical_list: D005227:Fatty Acids; D008055:Lipids; D019787:Linoleic Acid; D013230:Stearoyl-CoA Desaturase