Role of vitamin C on immune function under heat stress condition in dairy cows

Abstract

Objective: The aim of this study is to investigate the effect of seasonal change in thermal environment on leukocytes constituents and effects of vitamin C on immune response under heat stress conditions, in high and low producing dairy cows in Tunisia. Methodology: Three experiments were carried out into two different periods: Spring P1 and summer P2 using a randomized block design per level milk production, within 72 Holstein cows divided in 3 groups formed by 24 cows. In each group there is 12 high and 12 low producing cows. The first group was used as a control group during P1, second and third group were tested in P2 with same rations. Meanwhile, the third group is supplemented with VC in ration (20 g/100 kg live weight). Cow’s blood was sampled to determine plasma VC and cortisol concentration. Percentages of leukocyte relative to total counted cells were calculated. Peripheral blood mono-nuclear cell function was evaluated and stimulated with phytohemagglutinin and poke weed and finally, their response in terms of DNA synthesis and IgM secretion was measured. Results: As results, VC concentration in P1 for first group (2.97 and 2.96 mg L−1 in HPC and LPC, respectively) was higher relative to concentrations in P2 for second group (1.77 and 1.88 mg L−1 in HPC and LPC, respectively). Plasma VC concentration was effected by the period but not by level milk production (p>0.05). However, DNA synthesis in PBMC stimulated with mitogens in second group was decreased in heat stress period (p<0.001). Whereas the IgM secretion (p<0.001) and the plasma cortisol concentration (p<0.05) in the second group was higher compared to the control group. But, DNA synthesis in PBMC and plasma cortisol concentration returned to base line levels in presence of VC in ration of third group in hot temperature and IgM secretion in PBMC of the same group was significantly reduced with the same treatment. Conclusion: This study indicates that the effects of high environmental temperatures on the immune response depend on the plasma VC concentration and milk production potential. However, ration supplemented with VC in dairy cows play an important role in immune functions under heat stress condition.