فهرست مطالب فرخ نظمی

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).

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 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.

Under heat stress condition, using 1 percent Spirulina platensis microalgae in broiler chickens’ diet could improve both humoral immune system and growth performance.

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. Several studies have demonstrated the growth-promoting effects of spirulina platensis on broiler chickens. Jamil et al., (2015) showed that feeding 0.2, 0.4, or 0.8 percent spirulina increased weight gain and linearly decreased feed conversion ratio (FCR) of broiler chickens. Similar results were reported by Shanmugapriya et al., (2015). They reported that feeding 1% of spirulina platensis to broiler chicks caused to improve growth performance. As well as growth performances, treatment with S. platensis was reported to increase the carcass percentage and ready-to-cook yields of broiler chicks in the studies of Raju et al. (2004), Kaoud (2012) and Holman & Malau-Aduli (2013). The cecum plays an important role in preventing colonization of pathogens and detoxifying harmful substances (Jorgensen et al., 1996), therefore may play an important role in improving nutrients absorption and better performance. A previous study in broiler chickens also concluded that intestinal microbial-including cecum is highly associated with the production performance of broiler chickens (Jeong and Kim, 2014). Park et al., (2018) indicated that broiler chickens fed a Spirulina supplemented diet led to higher cecal Lactobacillus concentration, but had no effect on the number of coliform bacteria. Some other studies suggest that microalgae have potential antibacterial, antiviral, and antifungal activities. de Mule et al., (1996) observed that methanolic and aqueous extracts of Spirulina inhibited the growth of Candida albicans whereas Lactococcus lactis was promoted by the extract, with growth increasing from 7.5 to 14.7%.

Three hundred one-day- old male Ross 308 broiler chicks were assigned to 5 dietary treatments with 6 replicates and 10 birds each in a completely randomized design. Dried Spirulina Platensis (SP) powder provided from Pars Jolbak Co. in Shiraz, Iran and after chemical analysis was used in diets. All experimental diets were corn soybean based and formulated to reach ROSS 308 broiler chicken requirements. Dietary treatments were 0 (control), 0.25, 0.5,0.75 and 1 % Spirulina Platensis (SP). All diets were isocaloric and isonitrogenous and were fed to birds during 6 weeks. The average daily feed intake (FI) and weight gain (WG) were measured for each group and feed conversion ratio was calculated. Daily mortality was weighed, recorded and used to correct the feed conversion ratio. Daily FI was determined from the difference between supplied and residual feed in each pen and was adjusted for mortality. At the end of the experiment, two birds per each replicate (similar to cage average weight) were selected. The birds were killed by cervical dislocation. Breast, thigh, pancreas, abdominal fat and liver were removed, weighed and expressed as a percentage of live weight at 42 d of age. At the end of experiment, cecal samples collected from each bird. One gram of cecal sample from viable counts of bacteria in the cecal samples were conducted by plating serial 10-fold dilutions onto Lactobacilli MRS agar plates and MacConkey agar plates to isolate Lactobacillus spp. and coliform bacteria, respectively. The lactobacilli agar plates were then incubated for 24-72 h at 37◦C under anaerobic conditions. After the incubation periods, colonies of the respective bacteria were counted and expressed as the logarithm of colony-forming units per gram (log10 CFU/g). All data analyzed by ANOVA using the GLM procedure described by the SAS Institute (2009). Tukey test was used to determine the significant differences between the treatment means.

The results showed that feed intake of birds was not influenced by SP supplementation during the whole period, but weight gain of birds fed diets containing 1 % SP, was increased (P<0.05) and feed conversion ratio was decreased significantly (P<0.05) as compared as control birds. Similar to our results, Park et al., (2018) showed that up to 1% SP in broiler diets, did not affect the feed consumption of broiler chickens. They showed that increasing dietary SP from 0 to 1 %, caused to increase in weight gain during total period. Shanmugapriya et al., (2015) reported that feeding 1% of spirulina platensis to broiler chicks caused to improve growth performance.The mechanism of action of Spirulina has not been clearly established, but previous studies have reported that dietary supplementation of Spirulina has positive effects on growth performance in poultry. Carcass yield and breast relative weight in chickens fed more than 0.5 % SP were significantly increased (P<0.05), but abdominal fat, liver and thigh relative weight were not affected. Similar to our results, increase in carcass percentage and ready-to-cook yields of broiler chicks were reported in the studies of Raju et al. (2004), Kaoud (2012) and Holman & Malau-Aduli (2013). In present study, the chickens fed more than 0.5% SP had lower cecal E.Coli concentration and nonsignificant increase in Lactobacillus concentration. Similarly, Park et al., (2018) indicated that broiler chickens fed a Spirulina supplemented diet led to higher cecal Lactobacillus concentration. Regard to previous study which concluded that intestinal microbial-including cecum is highly associated with the production performance of broiler chickens (Jeong and Kim, 2014), therefore in our study, the better performance of chickens fed higher than 0.5% SP may be associated with decrease in cecal E.Coli Concentration.Conclusion It is concluded that dietary supplementation of broiler diets with 1% Spirulina platensis, could improve the growth performance, carcass yield and cecal microbial population of broiler chickens at 42 day of age.Keywords: Prebiotic, Feed Conversion ratio, Carcass yield, Escherichia coli, Algae