The Effect of Adding Thyme and Oregano Extracts and a Probiotic on Meat Quality and Tibia Bone in Broilers after a Feed Restriction Period

Background: Feed restriction is a method to control problems caused by rapid growth in the broiler industry.After the feed restriction period, the use of growth promoters can be a suitable option to compensate for the effects of the restriction.The use of antibiotics as growth promoters has been limited due to the increase in antibiotic resistance in recent decades.Therefore, it seems that the use of plant extracts, such as thyme and oregano, is a suitable and low-complication alternative to antibiotics due to their antibacterial, antifungal, anti-coccidial, anti-inflammatory, and microbial flora modulation properties.The use of herbal additives and growth promoters is a strategy to strengthen the compensatory growth phenomenon in broilers.Meat and bone quality in broiler chickens are economic traits.This study aimed to investigate the effects of using thyme, oregano, thyme-oregano, and a probiotic on meat quality and tibia bone status in broiler chickens after a feed restriction period.Methods: A total of 480 one-day-old Ross-308 male broiler chickens were used in the current study.This experiment was conducted as a factorial experiment (25) in a completely randomized design including two feeding methods (full feed and restricted) and four types of additives (thyme extract, 300 g/ton of basal diet; oregano extract, 300 g/ton of basal diet; an equal weight ratio of thyme + oregano extract, 300 g/ton of basal diet; probiotic protoxin, 250 g/ton of basal diet) along with control diets (without additives).In the first step, chickens were divided into two separate experimental groups.The first group was fed freely as a control group, but the quantitative restriction was applied in the second group from the age of 8-14 days for 7 days (25% less than the control group).After the end of the restriction period, herbal additives and the probiotic were added to the diet of both groups.Acidity, water holding capacity, oxidative stability, peroxide index, and color were the factors used to measure meat quality.For the sensory evaluation of the meat, the right side of the breast from each replication after preparation was cooked at 170 C in an electric oven for 40-45 minutes, depending on the weight of the samples.The evaluated traits in the experiment included smell, taste, crispness, juiciness, and general acceptability.To determine the ash, calcium, and phosphorus contents of the tibia bone in different treatments, two samples were selected from each replicate; their left tibia bone was separated and defatted by an autoclave at the end of the period.In the next step, after preparing the samples, the percentages of ash, calcium, and phosphorus were determined by the atomic absorption method.Data were analyzed statistically using the GLM procedure in SAS 9.1 software.Results: Based on the results, acidity and meat redness (a*) in the feed-restricted group were higher than in free-feeding chickens, and the TBA index in the free-feeding method was higher than in the restricted group (P 0.05).The water holding capacity of the carcass in the treatment without an additive was lower than in the treatments that received the additive (P 0.05).Moreover, carcass acidity was the lowest in the probiotic-receiving group and the highest in the group without additives (P 0.05).The peroxide index in the treatment without additives was higher than in the others (P 0.05).The combination of thyme and oregano significantly increased the lightness of the breast meat compared to the other additives.The overall