Energy balance of conjugated linoleic acid-treated pigs

The term conjugated linoleic acid (CLA) refers to a group of linoleic acid derivatives whose conjugated double-binding system begins at the carbon atom 8 to 11. This means that including the cis-trans geometry, 16 isomers are possible in theory. CLA occurs primarily in lipids of ruminants because polyunsaturated fatty acids can be converted to CLA in the rumen of these animals through the action of bacterial enzymes (Kepler et al. 1966). The most widely occurring isomer is C18 : 2 c 9, t 11, which is present in milk and dairy products in concentrations of 0.4–1.7% (Fritsche and Steinhart 1998). But CLA was also generated in the colon of rats fed a diet containing free linoleic acid (Chin et al. 1994b). In animal experiments CLA inhibits carcinogenesis and reduces the development of arteriosclerosis (Ip et al. 1994; Belury 1995; Jahreis and Bochmann 1998), and was found to have a specific influence on body composition. In experiments with mice, pigs and chicks a negative effect of CLA on the accumulation of body fat was observed (Pariza et al. 1996; Dugan et al. 1997; Park et al. 1997; West et al. 1998). The effective dose in those experimental diets was 0.5 to 1.5% CLA. In contrast, CLA may also act as a growth factor and increased daily weight gains of rats (Chin et al. 1994a). However, in these trials on changes in body composition the feed intake was not controlled and the observed effects may be due at least partially to differences in feed intake between the control group and the CLA animals. The objective of the present study was to investigate the influence of CLA on thermogenesis and energy balance in animals with an isoenergetic feed intake by using the methodology of the calorimetric balance technique. The animals used in the model were adult sows with a nutritional status approaching equilibrium.