In Vitro and In Vivo Antiviral Activity of a Modified Medium-Chain Fatty Acid Against Porcine Reproductive and Respiratory Syndrome Virus

Porcine reproductive and respiratory syndrome virus (PRRSV) causes significant economic losses in the global swine industry, partly because current vaccination strategies offer limited protection against heterologous viral strains. Since modified medium-chain fatty acids (mMCFA) offer enhanced structural stability and antimicrobial properties compared with unmodified MCFA, we evaluated a proprietary mMCFA blend (D-Strike, Devenish Nutrition) against PRRSV in vitro and in vivo. In vitro efficacy was assessed using TCID50 assays on MARC-145 cells and a viability qPCR (V-qPCR). At 1:1000, 1:2000, and 1:5000 dilutions, the mMCFA inactivated >4 logs (99.99%) of the virus within 5 min of exposure. The results of V-qPCR were also compatible with those obtained by cell culture assays. For the in vivo study, 40 weaned male piglets were assigned to four dietary treatments: negative control (group A), PRRSV-challenge control (group B), 0.2% D-Strike (group C), and 0.4% D-Strike (group D). Pigs in groups B, C, and D were challenged intranasally with virulent PRRSV. The results demonstrated that dietary mMCFA reduced clinical signs, attenuated a febrile response, and decreased the severity of lung lesions. Some responses appeared more pronounced at the 0.4% inclusion level than at 0.2%, although a formal dose–response analysis was not statistically significant for most outcome measures. The sera from the 0.4% D-Strike group showed 65% lower PRRSV than the positive control, although this difference was not statistically significant. In addition, this group had 0% mortality as compared to 20% in the positive control group. Feed efficiency also improved in D-Strike-fed pigs. These findings indicate that mMCFA shows promise as a feed additive for mitigating PRRSV infection, although the in vivo antiviral effects require confirmation in larger studies.