Scientifically Speaking …
By Matthew Wedzerai
POTENTIAL OF PLANT EXTRACTS IN COMBATING PRRS IN PIGS Researchers from the University of California have found great potential of plant extracts in enhancing the immune response and growth efficiency of weaned pigs infected with porcine reproductive and respiratory syndrome virus (PRRS).
PRRS is a major economically significant pathogen that has adversely impacted the global pig industry for decades. PRRS is characterised by abortion, premature birth, and high piglet mortality in sows, as well as pneumonia and mortality in weaned piglets and meat pigs. Studies show that our understanding of the virology, origin, and evolution of PRRS virus and the host’s immune response is limited. Adding to that, new mutations continually emerge during PRRS outbreaks. Such limited knowledge impedes development of effective methods to eradicate this virus. However, researchers are making efforts to have effective eradication strategies in place. Plant extracts (secondary plant metabolites) are effective feed additives in pig production due to several of their properties including antimicrobial, anti-inflammatory, and antiviral activity.
The study The researchers conducted two separate experiments to test the beneficial effects of garlic botanical extracted from garlic, turmeric oleoresin extracted from ginger, and capsicum oleoresin from pepper on PRRS-infected weaner piglets. The aim of the study was to determine how these three dietary plant extracts improve growth performance and immune response, and how they modulate gene expression of pigs infected with PRRS virus. The experimental diets were as follows: (1) control diet, no additive; (2) control diet plus 10 mg capsicum oleoresin/kg; (3) control diet plus 10 mg garlic botanical/ kg; (4) control diet plus 10 mg turmeric oleoresin/kg. All diets were challenged with PRRS virus.
Growth performance As expected, the researchers found that the PRRS virus significantly reduced growth rate, feed intake and gain:feed ratio, while the supplementation of plant extracts improved both growth and gain to feed ratio. In their study, the addition of capsicum oleoresin improved the growth of pigs by 11 %, while garlic botanical had a 17 % improvement, and turmeric oleoresin had the highest growth improvement of 32 %. The gain to feed ratio was 21 % better with the
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addition of capsicum oleoresin, 7 % with garlic botanical, and 38 % with turmeric oleoresin. Overall, turmeric oleoresin was more efficient in alleviating the negative effects of PRRS infection on growth of pigs.
Improving immune response The primary targets of the PRRS virus are immune cells, such as, alveolar macrophages, monocytes, and dendritic cells. Which means the PRRS infection can impair immune responses, increasing the risk of secondary infections by other pathogenic bacteria or viruses. The results of this study indicated that PRRS infection may directly or indirectly kill the alveolar macrophages or cause adverse alterations in their morphology and function. Because alveolar macrophages are crucial to the host against airborne pathogens, PRRS infection may potentially predispose pigs to secondary pulmonary infections. In this study, feeding the three plant extracts enhanced the
immune responses by increasing the proliferation of B cells and CD8+ T cells of PRRS-challenged pigs. The plant extracts also significantly reduced viral load, pro-inflammatory cytokines, and acute phase proteins, all pointing to a better immune response of piglets to the PRRS virus – suppressing inflammation and preventing possible secondary infections. “Although all three plant extracts modulate the immune responses of PRRS-infected pigs, the supplementation of garlic botanical affects the adaptive immunity of infected pigs more than the capsicum oleoresin and turmeric oleoresin, as is indicated by the greater number of B cells and CD8+ T cells”, said the researchers.
Modulation of gene expression From their first study, each plant extract differently affected growth efficiency and immune responses. Therefore, the objective of the second study was to characterize the effects and investigate the potential underlying mechanisms of plant extracts on gene expression of alveolar macrophages in weaned pigs experimentally infected with PRRS virus. Their results clearly showed that PRRS infection up-regulates the
expression of genes related to cell apoptosis, immune system process, and response to stimulus, but down-regulates the expression of genes involved in signalling transduction and innate immune response. The plant extracts of capsicum, garlic and turmeric differently regulated the expression of genes in alveolar macrophages of PRRSV-infected pigs but counteracted the effects of PRRS on gene expression. To be specific, the researchers found that PRRS infection reduced the expression of several genes related to the innate immune responses in alveolar macrophages, such as, CD46, DDX58, FCN2, MyD88, TLR4, and TLR8. Feeding capsicum oleoresin counteracted the effects of PRRS virus on A2M, CCL21, CCR2, CD3D, HSP70, HSP90AA1, and IL1A genes, while garlic botanical counteracted effects on C5, CCL21, HSP70, HSP90AA1, IFIT1, IFIT2, IL1A, MHC1, and PPBP genes, and turmeric oleoresin reversed the effects of PRRS virus on the expression of C5, CASP3, CASP8, CCL21, IFI30, IFIT2, IL1A, JAK2, PSMB10, and TLR8 genes.
Comment section is sponsored by Compound Feed Engineering Ltd
www.cfegroup.com
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