Valerate-based feed additives for weanling piglets
Anti-inflammatory nature warranted investigation on potential to promote piglet health postweaning.
By Lauren Kovanda
The postweaning period is arguably the most critical in the life cycle of commercially produced pigs. Multiple risk factors influence the capacity for piglets to thrive during this time. Pigs are exposed to external sources of stress and pathogens including Enterotoxigenic Escherichia coli (ETEC). Meanwhile pigs undergo stark transition in diet and are physiologically underdeveloped in terms of immune and intestinal function.
In order to support the health of piglets, antimicrobials were previously administered at subtherapeutic doses in feed—a practice which has since been limited in efforts to combat development of antimicrobial resistance. Sustaining animal welfare and productivity requires incorporation of alternative strategies in our farming practices.
Dr. Yanhong Liu at UC Davis has been delving into the potential benefits of including non-antibiotic feed additives in swine diets to address the most prevalent disease encountered in weaned pigs: Postweaning diarrhea caused by ETEC. Many naturally sourced compounds are under investigation for their antimicrobial and anti-inflammatory properties which render them useful as supplements for swine diets.
Among different types of feed additives including botanicals and probiotics, short chain fatty acid-based compounds are a promising dietary supplement. Scientists across various disciplines have uncovered the important roles of short chain fatty acids that are produced naturally by the microbes present in the gut, especially in the large intestine. However, to address the affliction of the small intestine by ETEC infection, feeding these metabolites directly has been a topic of research in Liu’s lab over the past number of years.
The most naturally abundant short chain fatty acids in the intestine are butyrate, propionate, and acetate. Valerate is another short chain fatty acid that, until recently, has not been studied in the context of its effects when used as a feed additive. Initial experiments revealed the ability of valerate based compounds, including glyceride forms of valerate, to directly inhibit the growth of ETEC. This led to further studies using intestinal cells derived from pigs, where anti-inflammatory effects were identified.
Inflammation associated with stress or disease has an energy cost, meaning there is reduced energy directed toward growth. Additionally, in the worst of cases, severe inflammation can cause death. As such, the anti-inflammatory nature of valerate warranted further investigation on its potential to promote the health of piglets postweaning.
After attaining preliminary evidence demonstrating the anti-inflammatory effects of valerate, two studies were conducted using weanling piglets challenged with ETEC. The first study established an appropriate inclusion rate of valerate monoglycerides while piglets were coinfected with ETEC F4 and ETEC F18, the two most prominent strains present on swine farms. Results indicated that at a 0.1% inclusion rate, butyrate glycerides along with valerate glycerides reduced blood markers of inflammation and frequency of severe diarrhea when compared with pigs fed a control diet without feed-additives. Butyrate-based feed additives have been shown previously to improve disease resistance in pigs, however this pilot established for the first time that feeding valerate glycerides had similar impacts.
The next study was a larger scale trial which tested an additional inclusion rate of valerate monoglycerides (0.075% and 0.1%), as well as 0.1% inclusion of valerate triglycerides. The glyceride forms of short chain fatty acids are ideal for application as feed additives due to their liquid form and pleasant odor. This study demonstrated the capacity of valerate, especially in triglyceride form, to alleviate the negative effects of ETEC infection in weaned piglets. Valerate triglycerides reduced frequency of severe diarrhea in piglets over the entire trial period. In addition, the shedding of the pathogen was monitored, and on the seventh day after infection, pigs on the valerate triglyceride diet exhibited reduced fecal shedding. This is important when it comes to reducing the transfer of the pathogen between individuals.
Diarrhea is linked to the inflammatory response, so it was not surprising to find that inflammatory marker, TNF-α, was lower in blood of pigs fed valerate triglycerides at various points throughout the trial period.
When looking at the intestines, the gene expression of TNF-α was reduced in pigs fed the monoglycerides of valerate. Further examination of intestinal gene expression showed that the tight junction protein, ZO1 was upregulated compared to pigs fed the control diet in pigs fed triglycerides of valerate. This protein is important in maintaining gut barrier function which counters the excessive loss of water during diarrhea.
These experiments established that valerate glycerides may serve as a useful feed additive for weaned piglets. The data amassed shows that these supplements may reduce the severity of postweaning diarrhea in piglets associated with both ETEC F4 and/or ETEC F18.
Although an anti-inflammatory effect is evidenced by the results of these studies, further research is needed to understand exactly how valerate interacts with the intestinal environment and impacts intestinal physiology. Various factors should be explored including the availability of valerate in different glyceride forms via enzymatic activity, and the specific pathways and receptors involved in the observed responses.
These studies were led by Lauren Kovanda under the supervision of Yanhong Liu at the Department of Animal Science of the University of California, Davis. The first full text article is available: Lauren Kovanda, Jungjae Park, Sangwoo Park, Kwangwook Kim, Xunde Li, Yanhong Liu, Dietary butyrate and valerate glycerides impact diarrhea severity and immune response of weaned piglets under ETEC F4-ETEC F18 coinfection conditions, Journal of Animal Science, Volume 101, 2023, skad401, https://doi.org/10.1093/jas/skad401.
Kovanda is a PhD candidate at the University of California-Davis.