Milk fat depression

Considerable variation among cows (Kinsella, 1972 Kelsey et al., 2003) and breeds (DePeters et al., 1995) in the extent of stearic acid desaturation and in mRNA expression (Taniguchi et al., 2004) has been observed. SCD mRNA expression is down-regulated by trans-10, cis-12 Ci8 2 (Choi et al., 2000), which is formed in the rumen in small amounts when milk fat-depressing diets are fed (Bauman and Griinari, 2003). 

Peterson, D.G., Matitashvili, E.A., Bauman, D.E. 2003. Diet-induced milk fat depression in dairy cows results in increased nans-10, cis-12 CLA in milk fat and coordinate suppression of mRNA abundance for mammary enzymes involved in milk fat synthesis. J. Nutr. 133, 3098-3102. 

Piperova, L.S., Teter, B.B., Bruckental, I., Sampugna, J., Mills, S.E., Yurawecz, M.P., Fritsche, J., Ku, K., Erdman, R.A. 2000. Mammary lipogenic enzyme activity, irons fatty acids and conjugated linoleic acids are altered in lactating dairy cows fed a milk fat-depressing diet. J. Nutr. 130, 2568-2574. 

Trans-10, cis-12 CLA is another CLA isomer in milk fat which can affect lipid metabolism. It is generally present at low concentrations in milk fat (typically <0.2% of CLA) under some dietary conditions, a portion of the rumen biohydrogenation shifts to produce more of this isomer, although it is still only a minor portion of total CLA. These dietary conditions are associated with milk fat depression and as little as 2 g/d of tram-10, cis-12 leaving the rumen will reduce milk fat synthesis by 20%. Because of the potency and specificity of this CLA isomer, it is being developed as a dairy management tool to allow for a controlled reduction in milk fat output. 

Figure 3.5. Generalized scheme of ruminal biohydrogenation of linoleic acid under normal conditions (solid line) and during diet-induced milk fat depression (dotted line). Adapted from Griinari and Bauman (1999).

Griinari, J.M., Bauman, D.E. 2003. Update on theories of diet-induced milk fat depression and potential applications. In Recent Advances in Animal Nutrition 2003 (P.C. Garnsworthy,... 

K. V.V. 1998. tra j-octadecenoic acids and milk fat depression in lactating dairy cows. J. Dairy Sci. 81, 1251-1261. 

Griinari, J. M., Bauman, D. E. (2006). Milk fat depression concepts, mechanism and management application. In K. Sejrsen, T. Hvelplund, M. O. Nielsen (Eds.), Ruminant physiology digestion, metabolism and impact nutrition on gene expression, immunology and stress (pp. 389-417). Amsterdam, Netherlands Wageningen Academic Publishers. 

Griinari, J. M., Chouinard, P. Y., Bauman, D. E. (1997). Trans fatty acid hypothesis of milk fat depression revised. In Proceedings of the Cornell nutrition conference for feed manufacturers (pp. 208-216). Ithaca, NY Cornell University. 

Piperova, L.S., B.B. Teter, I. Bruckental, J. Sampugna, S.E. Mills, M.P Yurawecz, J. Fritsche, K. Ku, and R.A. Erdman. Mammary Lipogenic Enzyme Activity, Trans Fatty Acids and Conjugated Linoleic Acids are Altered in Lactating Dairy Cows Fed a Milk Fat-depressing Diet./. Nutr. 130 2568-2574 (2000). 

Salts and Formaldehyde-Protected Conjugated Linoleic Acid in Inducing Milk Fat Depression. 88 1685-1693 (2005). 

Erdman, R. (1996) Milk Fat Depression Some New Insights, Proc. Tri-State Dairy Nutr. Conf, pp. 1-16, Fort Wayne, IN. 

Peterson, D.G., Matitashvih, E.A., and Bauman, D.E. (2002) Diet-Induced Milk Fat Depression in Dairy Cows Is Characterized by Increased Milk Fat Content of flO, cl2 CLA and Corresponding Reductions in Lipogenic Gene Expression, FASEB J. 16, A232 (Abstr.). 

The decrease of 4 0-14 0 and 16 0 concentrations in milk caused by CLA or soy oil supplementation (77) is consistent with the decrease reported by others (80). Because almost all milk 4 0-14 0 and about half of 16 0 is synthesized de novo by the mammary epithelial cells, these changes suggest that the mechanism of milk fat depression caused by CLA involves inhibition of de novo fatty acid synthesis, which cannot be attributed simply to the shortage of substrates for fatty acid synthesis because the addition of CLA to the diet did not change volatile fatty acid concentrations in the rumen. The possible mechanism of inhibition of fatty acid synthesis warrants further study, but it is likely related to inhibition of acetyl-CoA carboxylase because long-chain fatty acids inhibit activity of this enzyme (83) and expression of its gene (84). 

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