Purpose This study aimed to evaluate the antioxidative effects of methanolic and aqueous extracts of Dalbergia sissoo and Aegle marmelos on the oxidative stress index (OSI) in diarrheic calves affected by colibacillosis in the Bikaner region of Rajasthan, India. Methods A total of 32 colibacillosis-infected calves were randomly assigned to four treatment groups (n = 8 per group) to assess the efficacy of different extract-based regimens. The experimental groups received either methanolic or aqueous extracts of Aegle marmelos unripe fruit (150 mg/kg body weight, twice daily for five days) or Dalbergia sissoo leaves (1000 mg/kg body weight, twice daily for five days). Additionally, eight clinically healthy calves served as a control group. Polymerase chain reaction (PCR) analysis was performed to confirm colibacillosis. Statistical analysis revealed a significant reduction (p <.05) in OSI values between pre-treatment and post-treatment (days 3 and 6) and across all treatment groups over time. Results The findings of this study indicate that methanolic and aqueous extracts of Dalbergia sissoo and Aegle marmelos exhibit potent antioxidative properties. These extracts significantly reduce oxidative stress in colibacillosis-affected calves. Conclusion The observed antioxidative effects suggest that Dalbergia sissoo and Aegle marmelos extracts may serve as potential natural therapeutic agents for managing oxidative stress in diarrheic calves.