Effect of an Immunomodulatory Feed Additive in Mitigating the Stress Responses in Lactating Dairy Cows to a High Concentrate Diet Challenge

Dairy cows are often exposed to multiple stressors in a lactation-cycle, with sub-acuteruminal acidosis (SARA) a frequent example of nutritional stress. SARA affects ruminal and intestinalequilibrium resulting in dysbiosis with localized and systemic inflammation impacting animal healthand productivity. OmniGen-AF (OMN, Phibro Animal Health Corporation, Teaneck, NJ, USA) isa feed product recognized for modulating innate immune function, especially during periods ofstress. The objective of this study was to determine the effects of OMN in lactating dairy cowsfed a high-starch, low-fiber diet. Twenty-four blocked cows were assigned to control or treatment(55 g/d). After the additive adaptation (49 d) cows were fed the challenge diet (28 d). Milk, ruminationand pH were continuously recorded; components, rumen fluid, and blood were taken in multipletime-point and analyzed. Results showed that the challenge decreased the rumination, shiftedruminal fluid composition, decreased milk production and the components, and slightly increasedthe time below pH 5.5, with no differences between groups. The treatment produced greater rumenbutyrate and lower lactate, prompter regeneration of red blood cells, increase of neutrophils, lowerparaoxonase, gamma-glutamyl-transferase, andβ-hydroxybutyrate, with no differences on othertested inflammatory markers. Results show that OMN helps modulating some of the metabolic andimmunological responses to SARA.