Effects of a novel feed additive on clinical symptoms and the nasal and cecal microbiome in nursery pigs challenged with PRRSV and Streptococcus suis.

Porcine reproductive and respiratory syndrome virus (PRRSV) is a major endemic disease in swine, causing significant economic losses to the pork industry. PRRSV infection predisposes pigs to secondary infections, leading to a costly and challenging respiratory disease complex. Effective mitigation strategies are needed to reduce negative impacts of PRRSV on swine health and productivity. This study evaluated the efficacy of a novel feed additive (EP) containing a blend of activated medium-chain fatty acids, phytogenic compounds, and probiotics in PRRSV viral load, clinical symptoms, lung lesions, and nasal and cecal microbiome in nursery pigs experimentally co-challenged with PRRSV and Streptococcus suis. Twenty-six weaned pigs were randomly assigned to three groups: 1) non-challenged fed a control diet (Unchallenged), 2) PRRSV and S. suis co-challenged fed a control diet (Challenged), and 3) PRRSV and S. suis co-challenged fed control diet supplemented with 0.4% EP (Challenged + EP). Pigs were fed their respective diets for 29 days and were monitored for respiratory distress symptoms. On days 10 and 21, subsets of pigs were euthanized and necropsied to evaluate lung lesions, quantify viral load in the lung and serum, and characterize the nasal and cecal microbiome. Challenged pigs showed increased viral loads at days 10 and 21, respiratory distress score, and lung lesion score at day 21, and reduced overall weight gain (P < 0.05) compared to the Unchallenged pigs. The Challenged pigs supplemented with EP had lower PRRS viral load in both serum and lung (day 21; P < 0.05) and tended to have a reduced percentage of lungs affected by pneumonia lesions (day 21; P < 0.10) compared to the Challenged group. The Challenged pigs were enriched with nasal opportunistic bacteria, including Streptococcus, Trueperella, Mycoplasma, Actinobacillus, and Pasteurella (LDA score > 3; P < 0.05). However, EP supplementation reduced the abundance of these bacteria and Klebsiella (LDA score > 3; P < 0.05). Both Unchallenged and Challenged + EP pigs were dominated with cecal Prevotella and Blautia (LDA score > 4; P < 0.05). The Challenged + EP group also demonstrated an enrichment in Blautia and Negativibacillus in both nasal and cecal microbiome. In conclusion, dietary supplementation with EP reduced PRRSV infection severity and decreased enrichment of opportunistic bacteria during co-infection.