2.10. Estimation of atherogenicity and desaturase indexes The mammary gland of ruminants has substantial D9-desaturase activity, enzyme which can be measured indirectly by comparing the product: substrate ratio of certain fatty acids. Therefore, C14:1/C14:1 + C14:0 ratio is the best indicator of this activity because all C14:0 in milk fat come from de novo synthesis in the mammary gland (Lock et al., 2005). CLA desaturase index was estimated by the following formula: CLA desaturase = cis-9, trans-11/(cis-9, trans-11 + trans-11-C18:1). Other parameter that has biological interest is the atherogenicity index (AI), which characterizes the atherogenicity of dietary fat, by using AI