Dose-response relationship in dairy ewes fed a rumen unprotected CLA supplement

Establishment of dose response relationships between dietary CLA and milk fat inhibition permits to customize CIA supplementation to specific milk fat production targets. The present study evaluated the performance, milk composition, and FA profile of dairy ewes fed 10, 15 or 30 g/d of a rumen unprotected CIA supplement and the time course for recovery from milk fat depression. Supplemental lipids consisted of calcium salts of fatty (CSFA) and rumen unprotected CIA methyl ester. Twenty-nine primiparous Lacaune were randomly allotted to 1 of 4 treatments: Control: 30 g of CSFA (n=7); CLA1: 20 g of CSFA plus 10 g of CIA (n=7); CLA2: 10 g of CSFA plus 20 g of CIA (n=7); and CIA3: 30 g of CIA (n=8). The study lasted 35 d (7 d adaptation, 21 d treatment 7 d recovery). During the recovery period, all animals received the Control treatment. The CIA doses tested did not affect milk yield, milk protein content and secretion, or SCC (P > 0.05). Incremental CIA doses reduced milk fat content and secretion in a linear manner. Identical linear response was observed in milk fat concentration of fatty acids <= C16 (decrease) and > C16 (increase) when CIA dose increased from 0 to 30 g/d. The transfer efficiency from diet to milk did not differ between CIA doses (P > 0.05). Incremental doses of rumen unprotected CIA methyl ester increased trans-10, cis-12 CIA incorporation into milk fat and the pattern for CIA-induced milk fat decrease was driven by the supply of trans-10, cis-12 CIA to the mammary gland. (C) 2013 Elsevier B.V. All rights reserved.