Effects of the time of the switch from a saturated (tallow) to an unsaturated (sunflower oil) dietary fat source on performance, blood parameters and carcass characteristics of broiler chickens

This experiment carried out with 700 day old (Ross hybrid female) broiler chicks were randomly distributed into seven groups with five replicates of 20 birds each. For 6 weeks، the birds were fed ad libitum with diets including 5 percent fat (tallow or sunflower oil) and all diets were calculated to be isocaloric and isonitrogenous for two periods 1-21 and 22-42 days of chickens. In this experiment the tallow was replaced by sunflower oil weekly in diet as the first treatment (6 weeks diets including tallow)، the second treatment (5 weeks of training diet including tallow and last week diet including sunflower oil) and respectively until the seventh treatment (6 weeks training period of sunflower oil) consumed diets. The traits mean gain body weight، feed consumption، carcass characteristics and blood parameters were calculated، and the SAS General Linear Models (GLM) procedure was used for the statistical analysis of data. For 1-21 days period، the results did not indicate any significant differences between mean body weights due to dietary treatments. In 22-42 days period and the whole period of experiment، birds fed diets supplemented with sunflower oil did gain more weight compared to those fed diets supplemented with tallow (p<0. 05). Feed consumption was significantly higher for chicks fed with tallow-supplemented diets (p<0. 05). Chicks fed diets supplemented with sunflower oil had the best value for feed conversion ratio (P<0. 05). Carcass weight and relative weight of digestive tract organs (including: intestine، preventriculus، liver، gall bladder and gizzard) were not affected by the time of dietary fat replacement. There was statistically significant differences between dietary treatments based on abdominal fat pad percentage (p<0. 05). Chicks fed diets rich in tallow had significantly higher amounts of triglyceride and cholesterol in blood serum (p<0. 05).