Dynamics of oxidative stress and immune responses in neonatal calves during diarrhea

Oxidative stress is the imbalanced redox status between oxidant production and their scavengers leading to intestinal physiological dysfunction. However, the role of systemic and local oxidative status during neonatal calf diarrhea is not known. This study assessed systemic (serum) and local (fecal) oxidative status when calves either naturally developed diarrhea or naturally recovered. Healthy calves were enrolled in the study at d 18 of age, and their health status was monitored from the enrollment. Based on their enteric health status on d 21 and 28, calves were grouped as continuous diarrhea from d 21 to 28 (n = 14), diarrhea at d 21 but recovered at d 28 (DH group, n = 19), healthy at d 21 but developed diarrhea at d 28 (HD group, n = 15), and healthy throughout the study (HH group, n = 16). Serum and fecal samples were collected at d 21 and 28 from all calves in the morning 2 h after feeding. Dynamics of oxidative stress indicators including reactive oxygen species (ROS), malondialdehyde (MDA), H₂O₂, 8-hydroxy-2'-deoxyguanosine (8-OHDG), glutathione peroxidase, superoxide dismutase, catalase (CAT), and total antioxidant capacity and inflammatory indicators TNF-α, IL-1β, IL-4, IL-6, IL-10, and IFN-γ were evaluated using serum samples. In addition, fecal oxidative stress indicators ROS and MDA were measured. Serum ROS, MDA, 8-OHDG, as well as fecal ROS and MDA, were higher, whereas serum CAT and H₂O₂ were lower in diarrheic calves than those of healthy calves. Serum ROS, MDA, and 8OHDG and fecal ROS and MDA increased in the HD group from d 21 to 28 as they developed diarrhea. In contrast, all these oxidative stress markers decreased in the DH group from d 21 to 28 as they recovered. However, serum H₂O₂ had an opposite changing trend, which became lower in the HD group and higher in the DH group at d 28. In conclusion, both systemic and local oxidative stress markers and cytokine profiles altered as calves moved from being healthy to having diarrhea or vice versa. Serum ROS, MDA, and 8-OHDG can be used to develop biomarkers to screen calves prone to enteric infections during the preweaning period.