Abstract
Under the present intensive rearing conditions, calves face a series of stressors and multiple pathogens often necessitating antimicrobial use. Multiple feed additives are currently explored for their ability to prevent disease and limit the use of antimicrobials. Supplementation of the polyunsaturated long chain n-3 fatty acids eicosapentaenoic (EPA) and docohexaenoic (DHA) from marine origin has been proposed as a strategy to improve immune function and prevent excessive inflammation reactions. The aim of this randomized clinical trial was to explore the effects of n-3 fatty acids (PUFAs) used as feed supplement on health, production and immune variables in a veal calf setting. One hundred-seventy calves were randomly assigned to 3 treatment groups: microalgae (MA, n = 57, 2.5 g DHA/animal/day), fish oil (FO, n = 57, 2.5 g EPA + DHA/animal/day)] and a control group (CON, n = 56). Average daily gain (ADG), bodyweight at 12 weeks on feed and slaughter weight were determined. Health monitoring consisted of recording of clinical signs and repeated thoracic ultrasonography. After 5, 8 and 11 weeks of supplementation, the function of neutrophils, monocytes and peripheral blood mononuclear cells (PBMCs) was evaluated ex vivo by measuring reactive oxygen species (ROS) production by neutrophils and monocytes and proliferation of and cytokine release by PBMCs. Under the field conditions of this study, dietary supplementation of MA and FO showed very limited immunomodulatory effects. Feeding MA led to increased ROS production by neutrophils, Estimate (E) = 0.38, Standard Error (SE) = 0.14; P < 0.05, compared to the control calves after 5 weeks of in-feed supplementation. FO reduced IL-6 secretion E= -0.29, SE= 0.11; P < 0.05 compared to MA treated animals after 11 weeks on feed. Health and production variables were unaffected by treatments. The doses of EPA and DHA used in this study did not cause immunomodulatory changes in highly stressed calves to such an extent that this led to better health or growth of animals.