Effects of different levels of conjugated linoleic acid (CLA) in post- molting diet of laying hens on production performance, immune response and some blood biochemical parameters

Recently, there has been increased research on isomers of conjugated linoleic acid. Conjugated linoleic acid (CLA) is a mixture of several geometrical and positional conjugated isomers of linoleic acid (LA, C18:2) which involve a double bond at positions 8 and 10, 9 and 11, 10 and 12 or 11 and 1, but the c-9, t-11 and t-10, c-12 isomers are physiologically important. CLA is produced in the rumen as a result of incomplete bio-hydrogenation of Linoleic acid. When bio-hydrogenation is incomplete, CLA can escape the rumen and be absorbed through the gastrointestinal tract, thereby providing the peripheral tissues with various isomers of CLA. Due to production of CLA isomers in ruminant’s rumen, ruminant products, such as milk and meat are main CLA sources in human diets (Chin et al., 1992). CLA has been reported to have anticarcinogenic, hypocholesterolemic, and antiartherogenic effects in laboratory animals. Some reports showed positive effects of CLA isomers on egg production, egg quality, immune response, antioxidant status and gene expression in laying hens. It has been documented that layer hens meet some oxidative attacks during force molting (Siegel 1980), therefore, the aim of this study was to evaluate the effect of different levels of conjugated linoleic acid (CLA) on egg production performance, some blood biochemical parameters and immune response of laying hens in post-molting phase. Material and In this experiment, sixty W-36 White leghorn laying hens in post-molting phase (78 week) were assigned to 3 treatments with 5 replications and 4 birds each based on completely randomized design. The purity of CLA source used in this study was above 90% with mixture of 50% c9-t11 and 50% c10-t12 isomers. Experimental diets were 1) Control diet (basal diet containing 0% CLA), 2) basal diet+0. 25% pure CLA and 3) basal diet+0.5% pure CLA and after adaptation period, diets were fed for 4 weeks. Egg production, egg weight, feed consumption, egg mass and feed conversion ratio were recorded weekly. In the end of experiment, two birds from each replicate close to cage average weight, was selected, blood samples were collected from the wing and serum separated. Total antioxidant capacity (TAC), total cholesterol, triglyceride and high density lipoprotein (HDL) cholesterol and low density lipoprotein (LDL) were measured using analytical kits. Another bird per replicate with average cage weight selected, after injection of vaccine in breast muscle, two weeks later, immune response was measured based on Hemagglutination-Inhibition (HI) Test. All data were analyzed by ANOVA using the procedure described by the SAS Institute (2009). Tukey test was used to determine the significant differences between treatment means. Results showed that egg production rate and egg mass of birds fed 0.5 % CLA were significantly higher than birds fed control diet or diet containing 0.25 % CLA during whole experimental period, but egg weight and feed consumption were not affected by dietary CLA level. Also feed conversion ratio of birds fed 0.5 % CLA was significantly (P<0.05) lower than control birds or those fed diet containing 0.25 % CLA. Ahn et al. (1991) reported improvement in egg production of layer hens fed 1.5 % CLA but Cherian et al. (2007) reported that egg production and egg mass of laying hens were unaffected by incorporating 0.25% CLA during the peak production period. Also Bolukbasi and Erhan (2004) reported no significant effect of 1% CLA in laying hens diet on the rate of egg production. Total cholesterol, HDL, LDL and VLDL in blood serum of birds were not affected by dietary CLA (P>0.05) in present study, but serum triglyceride decreased significantly with increase CLA level (P<0.05). Similarly, Munday et al. (1999) reported that mice fed CLA had lower serum triglyceride. The beneficial effects of CLA might be related to the fact that CLA decreases the activity of lipoprotein lipase (Park et al., 1997). Ha et al. (1990) reported that CLA is an effective antioxidant, more potent than a-tocopherol and almost as effective as butylated hydroxytolune (BHT), but total antioxidant capacity in blood serum of birds in present study were not affected by dietary CLA (P>0.05). It is concluded that use of 0.5% CLA in post-molting diet of laying hens improved immune system and egg production performance and decreased blood serum triglyceride of birds.