CLA induced milk fat depression reduced dry matter intake and improved energy balance in dairy goats

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) kg milk/day, BW of 40 +/- 3.7 kg 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 (30 g/day of calcium salts of FA) or CLA [30 g/day of a rumen unprotected CIA 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, CIA decreased milk fat content and yield by 13.9 and 13.3%, respectively, and CIA treated goats consumed 6.5% less corn silage. The CIA treatment increased the concentration of both CIA 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 CIA, while long chain FA were increased. However, the daily secretion was lower for FA of all chain lengths in CIA treated goats. Glucose and insulin were not affected by treatment, while CIA treatment decreased non esterified FA by 22.2%. The CIA treatment improved calculated EB by 0.3 Mcal/day. Overall, CIA 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. (C) 2013 Elsevier B.V. All rights reserved.