Influence of a supplement containing conjugated linoleic acidon dairy performance, milk fatty acid composition, and adiposetissue reactivity to lipolytic challenge in mid-lactation goats

The objective of this work was to evaluate the effect ofthe supplementation of conjugated linoleic acid (CLA;4.5 g of cis-9,trans-11 C18:2 and 4.5 g of trans-10,cis-12C18:2) on milk performance, milk fatty acid (FA) composition,and adipose tissue reactivity in dairy goats feda high-concentrate diet based on corn silage. Twentyfourmultiparous dairy goats in early to mid lactationwere used in a 10-wk trial, with a 3-wk adaptation tothe experimental total mixed ration that contained cornsilage (35%, dry matter basis), beet pulp (20%), barley(15%), and a commercial concentrate (30%). Goatswere randomly allocated to 2 experimental groups andthey were fed 45 g/d of a lipid supplement (either CLAor Ca salts of palm oil added on top of the total mixedration). Individual milk production and compositionwere recorded weekly, and milk FA composition wasanalyzed in wk 2, 5, and 6. In the last week of the trial,an isoproterenol challenge was performed for 12 goatsbefore morning feeding. The CLA supplementation hadno effect on dry matter intake (DMI), body weight(BW), milk yield, milk protein content, and lactoseyield and content, but it significantly decreased milkfat yield and content by 18 and 15%, respectively. Thedecrease in milk fat yield was related to a lower secretionof FA synthesized de novo, of the medium-chainFA, and to a lesser extent of the long-chain FA thatare taken up from the peripheral circulation. The CLAsupplementation decreased the proportion of the sumof C16:0 and C16:1 and the sum of total cis C18:1, andit increased the proportions of the sum of long-chain(C >16) and the sum of iso FA without modificationof the total trans C18:1 and the sum of FA synthesizedde novo (C <16). During the first 25 min relative toisoproterenol injection, the maximal concentrations,the increases above basal concentration, the changes inarea under the curve, and the total area under the curve for glucose and nonesterified FA were not affected byCLA treatment. In conclusion, CLA supplementationassociated with a high-concentrate diet based on cornsilage resulted in decreased milk fat yield, increasednet energy balance, and it did not affect the sensitivityof the adipose tissue to lipolytic challenge in lactatinggoats