Effects of Conjugated Linoleic Acid (CLA) in Post- molting Diet of Laying Hens on Egg Production Performance and Egg Quality during Different Storage Times

CLA is a mixture of several geometrical and positional conjugated isomers of linoleic acid (C 18:2 cis-9, cis-12). Ruminant products, such as milk, meat, and cheese, are major CLA sources in human diets, but foods obtained from non-ruminants, contain much less CLA. Some reports showed positive effects of CLA on production performance of layer hens. Egg internal quality traits may be depressed during storage, but incorporation of CLA, may increase the permeability of the yolk membrane due to the cis-trans arrangements of CLA, therefore ion movement between the yolks and albumen through the yolk membrane, restrict some changes in egg internal quality traits, therefore an experiment was conducted to evaluate the effects of different levels of CLA in post-molting phase of laying hens on production performance and egg quality in different storage times and temperatures.
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. During the experiment, hens were provided feed and water ad-libitum. Egg production, egg weight, feed consumption, egg mass and feed conversion ratio were recorded weekly and reported as total period. Every two weeks, internal and external quality traits such as albumen percent, yolk percent, albumen pH, yolk pH, Haugh unit, yolk height, yolk Roche scale, yolk index, egg size, egg surface, specific gravity, shell strength, shell percent and thickness were evaluated. The eggs from treatments having best production performance (0.5 %) collected and stored in different temperatures (4 and 27° C) and duration times (1 day, 1 week and 1 month after production) then evaluated their internal quality. Results showed that egg production performance and egg mass of birds fed 0.5 % CLA was significantly higher than control or those fed 0.25 % during whole experimental period, but egg weight and feed consumption were not affected significantly by dietary CLA level and feed conversion ratio of birds fed 0.5 % CLA was significantly (P<0.05) lower than control or those fed 0.25 %. In the end of experiment, the internal egg quality traits such as albumen percent, yolk percent, albumen pH, yolk pH, Haugh unit, yolk height, yolk Roche scale, yolk index were not affected by dietary CLA levels (P>0.05). Also the external egg quality traits such as egg size, egg surface, specific gravity, shell strength, shell percent and thickness were not affected significantly. Results of egg quality traits during different times and temperatures showed that main effects of CLA levels, storage times and storage temperatures were significant (P<0.05) on most important egg internal quality traits such as Haugh unit and pH of albumen. Interaction effects of CLA levels with storage times and temperatures were significant (P<0.05) and in eggs kept within higher temperatures and longer times, albumen pH of eggs for birds fed 0.5 % CLA, were lower compared to albumen pH of eggs for birds fed control diet containing 0 % CLA. These results indicate that ion movement between the yolks and albumen through the yolk membrane in eggs from hens fed 0.5 % CLA was greater than that in the control eggs and caused to restrict pH increase during storage. It is speculated that the incorporation of CLA, most of which was in the trans form, could have increased the permeability of yolk membrane because of the cis-trans arrangements of CLA, which would have increased membrane fluidity and sizes of space between the fatty acid chains of phospholipids that constitute the membrane bilayer. It is concluded that use of 0.5 % CLA in post-molting diet of laying hens improved egg production performance of birds and restricted luctuations in pH and Haugh unit changes of eggs keep during high storage temperatures and duration times, therefore it is suggested to adding 0.5 % pure CLA in post-molted laying hen diets.