Feeding high concentrates to high producing animals usually change the rumen environment and compromises the productivity of ruminants. Different feed additives are used to prevent the occurrence of sub-acute ruminal acidosis, among these additives, buffers are commonly used. The aim of this meta-analysis was to investigate the effects of buffer supplementation on milk yield and composition in dairy cows. PubMed, Scopus, Web of Science and Google Scholar databases were searched from 1969 to 2020. A total of 86, 91, 94, 85, 27 and 34 trials were included to buffer supplementation effects on dry matter intake (DMI), milk yield (MY), fat, crude protein (CP), solid not fat (SNF) and lactose, respectively. The magnitude of the effect (effect size) was assessed using standardized mean differences (SMD) for continuous results, between the buffer supplementation addition and control treatments. The addition of buffer supplementation had no significant effect on DMI (SMD=-0.002, P=0.16), MY (SMD=0.001, P=0.99), CP (SMD=-0.002, P=0.34) and SNF (SMD=0.006, P=0.32), respectively. Milk yield increased in the group receiving the buffer supplementation in comparison with the control group. The percentage of fat (SMD=-0.185, P=0.001) significantly decreased in the control group compared to the group receiving the buffer. The dietary buffers significantly increased the content of lactose (SMD=0.008, P=0.014) in dairy cows’ milk. This meta-analysis indicated that buffer supplementation improved milk yield and composition in dairy cows. پرونده مقاله

Heat stress is a major cause of growth retardation and one of the most significant stressors that affect poultry, especially in hot parts of the world. This meta-analysis aimed to evaluate the effect of organic selenium supplementation on antioxidant enzymes and the performance of broiler chickens in heat-stress conditions. From 2003 to 2022, the Scopus, PubMed, Web of Science, and Google Scholar databases were searched. A total of 49, 43, 48, 19, and 27 trials were included to evaluate organic Se effects on feed intake (FI), average daily gain (ADG), feed conversion ratio (FCR), superoxide dismutase (SOD), and glutathione peroxidase (GPX) respectively. The use of organic Se supplementation had no significant effect on ADG (SMD=-0.009, 95% CI -0.105 to +0.086, I2=67.28, P=0.85), FI (SMD=-0.092, 95% CI -0.392 to +0.208, I2=58.53, P=0.548) and FCR (SMD=0.003, 95% CI -0.006 to +0.013, I2=62.89, P=0.47) in the pooled standardized mean difference random effect model. A low concentration of GPX was found in the control group (P=0.000, I2=86.32) in comparison to organic Se supplemented broilers. On the other hand, when the random model was applied to GPX studies, there was much heterogeneity. The standard mean differences of SOD were significantly higher (P<0.041, 95 CI 0.000 to +0.006, I2=0.71) in the treatment receiving Se supplementation. In conclusion, this meta-analysis shows that adding organic Se did not significantly affect on performance, but significantly increased the concentration of SOD and GPX in broilers under heat stress. پرونده مقاله