Effects of Spirulina platensis on Growth Performance, Carcass Traits, Cecal Microflora and Immune Response of Broiler Chickens Under Heat Stress and Comparing It with Vitamin E

Introduction: Due to genetic selection, today's strains exhibit higher metabolic activity, resulting in increased heat production and reduced heat resistance. This can negatively impact their immune system and production performance (Havenstein et al. 1994).Thaxton et al. (1968) showed that high ambient temperature can have a negative effect on the immune responses of broiler chickens. In recent years, in order to improve the health of chicken meat consumers, the production of broiler chickens without the use of antibiotics has been proposed, and the ban on the use of antibiotics has been issued by the European Union in 1999 (Youssef et al., 2016). For this reason, today there is a tendency to use alternative sources. Algae and microalgae are of the natural substances whose beneficial effects have received much attention in recent years. Spirulina platensis (SP) is a filamentous blue-green microalgae (cyanobacteria) generally regarded as prebiotic and source of high quality protein, minerals, essential fatty acids, essential amino acids, pigments and phenolic acids. Many studies have shown that Spirulina has antioxidant, immunomodulatory, anti-inflammatory, antiviral, and antimicrobial activity in various experimental animals (Hajati and Zaghari 2019).Materials and Methods: A total of 360 one-day old male broiler chickens (Ross 308 strain) were allocated to 6 treatments, 6 replicates and 10 birds each replicate in a completely randomized design. The experimental treatments included different levels of Spirulina platensis microalgae powder: 0 (Control), 0.25, 0.50, 0.75, and 1.0 percent Spirulina platensis powder, and one treatment included Vitamin E at the level of 150 g/ton feed. The basal diet was based on corn0soybean meal and all the diets were isocaloric and isonitrogenous and used for 42 days in diets. During the experiment, the feed consumption and weight gain of the chickens were measured weekly and the feed conversion ratio was calculated for each week and period.On 42 d of experiment, 2 birds from each replicate were randomly selected, humoral immune response was evaluated and then killed after weighing, carcass components and internal organs were weighed and their weight was calculated as a percentage of live weight. In order to evaluate the humoral immune system, the antibody titer produced against SRBC was measured using the hemagglutination method. In the end of experiment, the microbial population of the cecum was counted. All the data were analyzed in the form of a completely random design by SAS software and with the GLM procedure, and the comparison of means was done with Tukey's test.Results and Discussion: Results showed that the use of different levels of SP had no significant effect on the amount of feed intake during the whole period (P<0.05), but in finisher period, using %1 SP could improve body weight gain and feed efficiency of the broilers compared to control group (P<0.05). Breast yield of the chickens was affected by the level of dietary Spirulina, and it improved at the levels of 0.5, 0.75, and 1.0 percent SP usage compared to control and vitamin E groups (P<0.01). The relative weight of abdominal fat decreased in the birds fed with SP at the levels of 0.75 and 1.0 percent compared to control group (P<0.01). There was no difference among total count, ceca Lactobacillus and E. Coli in the chickens of different experimental groups (P>0.05). The response of humoral immune system was higher in all four levels of SP and also vitamin E compared to control treatment. Chickens which consumed Spirulina at the level of 1 percent had the highest level of antibody titer. Mustafa et al. (2021) by achieving a growth performance similar to the present research, stated that the effect of SP on the intestinal microbial population, such as the increase of Lactobacillus and the decrease of Escherichia coli, has improved the performance of the birds under heat stress conditions. According to the reports on the effects of heat stress on digestive enzymes (Sahin et al., 2002) and the efforts of previous researchers to overcome the adverse effects of heat stress on digestive enzymes by using phytogenic compounds (Khosravinia et al., 2016), the researchers of the present study believe that the improvement of the mucous tissue and intestinal immune system and perhaps the increase in the secretion of digestive enzymes are the most important factors for improving the performance of birds in heat stress conditions.Conclusion: Under heat stress condition, using 1 percent Spirulina platensis microalgae in broiler chickens’ diet could improve both humoral immune system and growth performance.