Research and Reviews: Dairy 2001

Special Circular 182-01

Factors Affecting the Production of Conjugated Linoleic Acid in Dairy Cows

Conclusions

1. The formation of CLA in the rumen is affected by amount of substrate (for example, LA) available. Generally, more substrate should result in more production of CLA, but under some circumstances, especially when LA is continuously fed, most of it will be BH into stearic acid.
2. Factors affecting ruminal fermentation, and especially those affecting ruminal BH, play an important role in regulating the production of CLA in the rumen. For example, feeding conditions that result in a reduced ruminal pH generally should increase the production of CLA.
3. Feeding fat sources high in unsaturated FA is an effective way to increase CLA production in the rumen because they not only provide substrate for formation of CLA and but also inhibit ruminal BH to facilitate the formation of CLA. Fish oil may have more direct effects on BH than vegetable oils.
4. Increasing solid passage rate also may contribute to increased productions of CLA in the rumen. However, the contribution may not be easily detected due to two reasons: First, it usually takes a very short time for CLA to be hydrogenated to VA. Secondly, under normal feeding conditions, the increase in passage rate is usually minor.
5. The CLA concentration in milk fat could be subject to very large variations, possibly because of the variation in activity of mammary D9-desaturase.
6. Endogenous synthesis may account for more CLA secretion in milk than the formation of CLA during ruminal BH. Therefore, feeding practices which increase duodenal flow of VA should accordingly increase CLA formation in milk.