Analysis of Variation in cis-9, trans-11 Conjugated Linoleic Acid (CLA) in Milk Fat of Dairy Cows

• Published in: Journal of dairy science 2002-09, Vol.85 (9), p.2164-2172
• Main Authors: Peterson, D. G, Kelsey, J. A, Bauman, D. E
• Format: Article
• Language: English
• Subjects: Analysis of Variance; Animal productions; Animals; Biological and medical sciences; Cattle - metabolism; Diet; Fatty Acids - analysis; Female; Fundamental and applied biological sciences. Psychology; Lactation; Linoleic Acid - analysis; Lipids - analysis; Mammary Glands, Animal - enzymology; Milk - chemistry; Milk - enzymology; Rumen - metabolism; Stearoyl-CoA Desaturase - metabolism; Terrestrial animal productions; Vertebrates
• ISSN: 0022-0302; 1525-3198
• DOI: 10.3168/jds.S0022-0302(02)74295-1

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.