الفهرس 
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Abstract
Chapter-I: A total of 322 transitions dairy cows, belonged to seven studies from five papers, were used. The complete steps of the meta-analysis were performed according to the standard pathway of PRISMA. For this reason, a comprehensive meta-analysis was used to accomplish this mission. The effect model and I2 statistic were used to estimate the degree of heterogeneity. Forest plot and Beggs test was used. Estimated the effect size of chelated Cr on glucose, NEFA, and insulin outcomes during the three-time points (i.e. before, at, after calving) was no significant. The heterogeneity was not significant for all variables. Consequently, fixed-effects models were used for the analysis of such data. Furthermore, Beggꞌs test indicated no evidence of substantial publication bias for all parameters. meta-analysis of our study indicated that supplementing chelated Cr can provide a glucose tolerance effect by increasing the insulin response and decrease NEFA concentration, but not in a significant level. Chapter-II: The present study took place during the period between November 2019 to January 2020 on a commercial dairy herd located in a city of Bilqas, Dakahlia governorate. On the farm, there were ninety cows at different stages of lactation. Among all, thirty-six cows, at ~ 4 weeks, before the expected time of calving, were used in an observational field study. A blood sample was drained from each cow, at the day 28 days prior to the expected time of calving. The OSi was calculated as ROS/ SAC Cows that have high values of OSi were considered to have OS status; while those having low OSi were considered negative controls. For CBC also analyzed. Biochemically, serum concentration of ROS, and the calculated OSi were higher in positive group than those of negative controls but not in a significant value. The same pattern was occurred for SAC but in a diverse manner. Serum levels of MDA, NEFA, SAA, liver enzymes, globulin were significant higher in positive group than negative group. Chapter-III: Following the initial screening, cows with high level of redox status indices (n = 27) were furthermore used in a completely randomized design and were assigned. The first group received a CMM consisting of Zn (350 mg/cow/day), Mn (200mg/cow/day), Cu (125 mg/cow/day), Co (12mg/cow/day) added to the whole mixed ration (n = 9 cows). The second group received CMM as previously described plus 1g /cow/day Cr (n = 9 cows). The third group received no feed supplements and kept as positive control (n = 9 cows); while cows that have had low OSi were considered as negative controls (n = 9 cows). In the first and second group, the supplementations were continued for eight weeks. Blood samples were collected at the following time points: T-28, T-14, T 0, T+14 and T+28 of calving. Milk samples were also obtained from each cow for milk composition scan, SCC and milk yield. The findings demonstrated that supplementing a dairy cow with either CMM or with Cr has an equal positive effect on indices of energy metabolites, hepatorenal variables and somatic cell counts; while supplementing CMM/Cr could impact the redox status, potentiate energy metabolites, reduced inflammatory response and improve some erythrocytic indices. In conclusion, supplementing CMM/Cr can augment the redox potential in transition dairy cattle.