The effect of different levels of selenium-enriched probiotics on the growth performance and Blood parameters of suckling calves

Minerals play a crucial role in maintaining the characteristics of the rumen environment in cattle, enhancing the fermentation process. Selenium, a rare yet essential mineral, is particularly important for improving immunity and reducing the incidence of certain diseases. By contributing to the structure of the enzyme glutathione peroxidase, selenium is vital for the antioxidant system. This study aimed to compare the effects of selenium-enriched probiotic supplements on the growth performance, feed intake, hematological parameters, and health status of suckling calves. For this purpose, a total of 80 newly born Holstein calves (35±1 kg) were selected immediately after birth and before the first milk feeding. They were randomly assigned to four treatment groups. Each treatment group received one of the following diets randomly: the first group served as the control group and received a starter without selenium supplementation. The second, third, and fourth groups received probiotics enriched with selenium at concentrations of 0.15, 0.30, and 0.45 ppm, respectively (SE0.15, SE0.3, and SE0.45). The feeding period, based on the dairy farming schedule and the feeding period for each treatment, was considered 75 days mixed in the starter. Throughout the experimental period, growth-related parameters such as average weight gain, height, average daily dry matter intake, as well as the health condition of the calves were evaluated by evaluating the health of the calves using the Wisconsin scoring index were recorded. The results of this experiment indicated that the SE0.45 treatment, which received a starter supplemented with 0.45 ppm selenium-enriched probiotic, exhibited a higher average weight compared to the control group (linear and quadratic, P<0.05). The experiment also demonstrated that selenium supplementation led to an improvement in average feed intake during the trial period, with SE0.45 treatment showing the best performance compared to the control group (linear and quadratic, P<0.05). According to the reported results in Table 7, the blood albumin concentration in the selenium-supplemented treatment groups was higher than that in the control group (linear, quadratic, and cubic, P<0.05). Additionally, the average concentration of glutathione peroxidase in the selenium-receiving treatment groups was higher than in the control group (linear, P<0.05). The results of this experiment indicated that adding selenium-enriched probiotics at levels of 0.30 and 0.45 ppm to the diet of suckling calves resulted in an increase in average height at the end of the experimental period compared to the control group (linear and quadratic, P<0.05). The daily height gain of the calves in the selenium-receiving groups was higher than the control group before weaning (linear, quadratic, and cubic, P<0.05). Microbial culture results of fecal samples indicated that the total bacterial count in the 0.45 ppm selenium-supplemented group was lower than that in the control group (linear, P<0.05). However, the population of Lactobacillus species in this treatment group was higher than in the control group (linear and quadratic, P<0.05). The addition of selenium to the diet of suckling calves not only affected height and weight gain but also improved the antioxidant system in the blood and enhanced the intestinal microflora conditions of the calves. Based on the regression results obtained, the optimal selenium supplement dose in the diet of suckling calves until weaning was calculated to be between 0.11 to 0.41 ppm. The average optimal doses obtained for all significant traits are equivalent with 0.3 ppm on selenium in the supplement.