An experiment was conducted to evaluate the effect of using thyme (Thymus vulgaris L; TH) or citric acid;(CA) either alone or in combination (at level 0.2 % of each) to improve the utilization of the low protein low energy broiler diets (LPLE), containing 4% lower protein and 200 Kcal /Kg lower energy than those of control diets at starter, grower and finisher periods. Control diets contained 21, 19 and 18% CP and 2988, 3083 and 3176 kcal ME/kg diet at starter, grower and finisher periods, respectively. It was supplied with required nutrients to satisfy the recommended requirements of Cobb broilers.
A total number of 180, seven days-old of unsexed Cobb broiler chicks were distributed into 6 treatments of 30 chicks each in three replicates.
Main results obtained can be summarized as follows:
-There were significant differences between values of weight gain in different growth periods while there were insignificant differences between values of feed conversion ratio except for total growth period (7-42d.).
-All over growth period, the LPLE diet decreased weight gain and degraded feed conversion ratio by 23.24 and 19.47% compared to control diet. In general, it seemed that addition of TH or CA either alone or in combination to the LPLE diet improved weight gain compared to LPLE diet and recorded the better feed conversion ratio compared to low protein (LP) or LPLE diet. The combination of such feed additives improved weight gain and feed conversion ratio by 10.46 and 10.13%, respectively compared to LPLE diet.
-There were insignificant differences between treatments for carcass characteristics and values of ash and nitrogen retention percentage. The LPLE diet decreased daily nitrogen excretion by 25.92% compared to control diet.
- The LPLE diet increased plasma globulin level by 32.75 % compared to control diet.
In conclusion, the addition of TH or CA either alone or in combination to LPLE broiler diet improved weight gain and feed conversion ratio, decreased plasma globulin and increased total plasma antioxidants capacity compared to LPLE broiler diet.