Abstract The extent to which CLA supplements inhibit milk fat synthesis is highly dependent on the amount of trans-10, cis-12 CLA reaching the mammary gland. Secondary events such as changes in milk yield, dry matter intake (DMI), body weight (BW) and energy balance (EB) may also occur depending on the magnitude of milk fat depression. This study investigated the effects of feeding a rumen unprotected CLA methyl ester supplement on milk fat yield and fatty acid (FA) profile, yield of milk and other milk components, DMI and metabolic variables in dairy goats. Twenty primiparous, non-pregnant Toggenburg goats, paired by BW, days in milk (DIM) and milk yield (MY) [2.8±0.4 (mean±SEM)kgmilk/day, BW of 40±3.7kg and 75±3 days in milk] were used in a crossover design with 14 days treatment periods and a 6 days washout. Goats were randomly assigned to the following treatments: Control (30g/day of calcium salts of FA) or CLA [30g/day of a rumen unprotected CLA methyl ester supplement (29.9% trans-10, cis-12 CLA)]. There was no treatment effect on BW, milk yield, or milk protein and lactose content and yield. However, compared to Control, CLA decreased milk fat content and yield by 13.9 and 13.3%, respectively, and CLA treated goats consumed 6.5% less corn silage. The CLA treatment increased the concentration of both CLA isomers (cis-9, trans-11 and trans-10, cis-12) in milk fat. The concentration of short and medium chain milk FA (C16) was decreased by CLA, while long chain FA were increased. However, the daily secretion was lower for FA of all chain lengths in CLA treated goats. Glucose and insulin were not affected by treatment, while CLA treatment decreased non esterified FA by 22.2%. The CLA treatment improved calculated EB by 0.3Mcal/day. Overall, CLA methyl ester supplements are effective in causing milk fat depression in lactating dairy goats and improving EB, which may be used as a nutritional tool in some circumstances.