Feeding treated wheat straw to weanling pigs
What are the health benefits?
By Veronica I. Polniak and Dale W. Rozeboom
Dietary fiber has become an intriguing ingredient for gut development and health in the nursery pig diet. As the global population continues to expand, food security discussions are relevant for locations that face challenges raising livestock and cultivating feed. The potential for crop residues and fibrous byproducts is being explored as feed ingredients for swine as there is evidence of health benefits. However, additional processing is necessary to improve digestibility.
There are many processes or treatments such as chemical, thermal, enzymatic, alkaline or a combination thereof. Evidence indicates that applying a treatment process makes fibrous feedstuffs suitable supplements in the weaned pig diet. Research in the 1980s reported growing pigs fed 10% hydrolyzed straw meal improved the health, growth and efficiency of pig production.
For the farmer, understanding how fiber impacts gut health, at each phase of production, may be important. The effects of dietary fiber on inflammation in the gut have been studied. Interleukins and cytokines are produced in response to inflammation, infection or trauma. Pro-inflammatory cytokines like IL-6, IL-12, and TNF-α cause clinical signs of illness (fever or inflammation). The role of anti-inflammatory cytokines, like IL-10, is to inhibit the immune and inflammatory response produced by pro-inflammatory cytokines. These pro and anti-inflammatory cytokines work in conjunction with each other to regulate and balance the immune system.
There is evidence that weaned pigs fed 7.5% soluble dried distillers’ grain and observed an increase in IL-6 and IL-10 of ileal tissue, and feeding 5% corn bran increased anti-inflammatory cytokine, IL-10. Furthermore, dietary fiber research has highlighted intestinal health benefits in the weaned pig diet. The inclusion of 19% barley hulls in the diet increased villi length and enhanced intestinal lining enzyme activity, thereby altering gastric function and nutrient absorption capacity. These findings emphasize the role dietary fiber can play in enhancing gastrointestinal health.
The prospect of dietary fiber enhancing health led to three experiments at Michigan State University Swine Research Laboratory in 2018, 2020 and 2023. Weaned pigs were fed two dietary treatments: a control and 5% treated wheat straw. Diets were formulated as isocaloric and isonitrogenous using a commercially complex ingredient matrix. All animals were housed in a nursery room at the Michigan State University Swine Farm.
Samples collected were blood and intestinal segments (ileum and ascending colon) for laboratory analyses. To assess the immune response of young pigs fed dietary fiber, blood plasma was analyzed for IgA. Intestinal health was determined through histology and gene expression of IL-6, IL-10, IL-12 and TNF-α in ileal and colonic tissue. This work's objective was to determine if the treatment of wheat straw would provide health benefits to the immune system and intestinal immune parameters.
Experiments:In 2018, 108 crossbred (PIC 327 x Yorkshire) mixed sex pigs were weaned at 27 days and 8.5 kg body weight. In 2020, 192 crossbred (PIC 359 x Yorkshire) mixed sex pigs were weaned at 27 days and 8.4 kg body weight. In 2023, 20 crossbred (PIC 800 x Yorkshire) barrows were weaned at 27 days and 8.6 kg body weight.
To further understand the immune system and gut health of young pigs fed dietary fiber, a vaccine immune challenge was administered to every pig in the third week of the 2023 study. The vaccines used were Ingelvac CircoFLEX Porcine Circovirus Type 2 (1mL intramuscular) and Enterisol Lawsonia Intracellularis (2mL oral inoculation). Titers were determined for serum, weekly post vaccination, and at sacrifice for intestinal tissue to confirm pigs experienced an immune and gut challenge.
Findings:The nursery pig's immune response differed with the feeding of treated straw. In experiments 2018 and 2020, plasma IgA increased with 5% TWS in the diet, however, IgA did not differ in the 2023 study (Table 1). It was speculated that the vaccine-challenge called for a greater immune response that the TWS could not overcome.
A complex response was elicited in the gut of weaned pigs as apparent in morphology and gene expression (Tables 2 and 3). The experiment conducted in 2023, using immune-challenged pigs, resulted in greater muscle thickness and crypt depth for the 5% TWS treatment. The titer results for Lawsonia intracellularis in ileal and colonic tissue indicate the pigs fed 5% TWS were experiencing a greater intestinal response (Table 4); there is potential that the treatment provided a protective function by limiting the response to the gut.
When comparing gene expression across all three experiments, inconsistent results are observed between inflammatory cytokines in the ileum and ascending colon. In 2020, the expression of intestinal lining cytokines with the feeding of 5% TWS was dissimilar to those observed in the 2018 experiment. In 2020, a down-regulation of IL-10 (anti-inflammatory) was the only difference when comparing CON and 5% TWS treatments in the ascending colon. In the 2023 experiment, two differences in the ascending colon gene expression were identified, increases in the pro-inflammatory cytokines, TNF-α and IL-6 (P < 0.05).
An increase in these markers could be a result of the Lawsonia intracellularis vaccine-challenge because these markers participate in the healing processes when disease is present. The dissimilarities across all experiments could be a result of the differences between studies.
The 2023 experiment was the only experiment to use all barrows and implement an immune challenge. This study also fed weaned pigs for six weeks, versus a four-week period in the first two experiments. Another difference that may have impacted the studies was a difference in genetic line and sample size. This may explain some of the observed differences, but it is not definitive which factors are most relevant.
Dietary fiber impacts the expression of immune health markers throughout the body and gut of the young pig. The health benefits of dietary fiber in the diet depend on health status of the pig, leaving much to be learned about the inclusion of fibrous feedstuffs and treated crop residues in nursery rations.
*References available upon request
Polniak is a graduate student and Rozeboom is a retired faculty member, both in the Department of Animal Science, Michigan State University.
