Milk production responses of primiparous and multiparous dairy cows to dose of conjugated linoleic acid consumed in rumen inert form

Abstract

Conjugated linoleic acid (CLA) has the potential to be used as a dietary means of manipulating milk fat production of dairy cows to meet specified short-term targets, as in a supply-managed industry. An experiment was conducted to evaluate the dose-response to calcium salts of CLA fed as a top-dress on a corn- and alfalfa-based TMR. In two 5 × 5 Latin squares of 28-d periods, five primiparous and five multiparous cows were fed 0, 22, 45, 67 or 178 g d-1 CLA (29% trans-10, cis-12) as a calcium salt. Results from one multiparous cow on the 178 g d-1 treatment were removed from statistical analysis because milk production fell to 1.2 kg d-1 by the end of the period. On average, milk, lactose and protein yields increased at the lower doses of CLA and decreased to control levels at the highest dose. Milk fat yield declined progressively from 876 to 770, 689, 676 and 543 g d-1 on the five doses. Net energy balance of cows increased linearly from -1.5 Mcal d-1 on the control to 2.0 Mcal d-1 at 178 g d-1 CLA. The percentage depression in milk fat yield at different doses of trans-10, cis-12 CLA was described by the equation y = 54/(1 + 22.8/dose). Comparison with published literature suggested that feeding calcium salts of CLA was 30% as effective in depressing milk fat production as an abomasal infusion, due to rumen biohydrogenation and intestinal indigestibility.Key words: Milk composition, cattle, diet