INTERACTIVE EFFECT OF DIETARY FIBRE AND IMMUNE CHALLENGE ON THREONINE REQUIREMENT AND INTESTINAL BARRIER FUNCTION IN GROWING PIGS
Date
2020-01-15
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
Type
Thesis
Degree Level
Doctoral
Abstract
High dietary fibre (DF) and immune system stimulation (ISS) are thought to limit amino acid
availability for protein deposition (PD) and growth in pigs. Fibre and threonine (Thr) may also
play an important role in intestinal barrier function. Therefore, this thesis evaluated the
independent and combined effects of high DF and immune challenge [Salmonella typhimurium
and systemic E. coli lipopolysaccharide (LPS)] on the Thr requirement for PD and growth in pigs,
and on the interactive effects of DF, Thr supply and immune challenge on intestinal barrier
function. A nitrogen-balance study estimated 0.68% and 0.78% standardized ileal digestible (SID)
Thr required to maximize PD in pigs fed low fibre (LF) and high fibre (HF) diets, respectively
when systemic ISS was not present. When systemic ISS was present, SID Thr requirement for PD
was estimated at 0.76% and 0.72% for pigs fed the LF and HF diets, respectively. Therefore, HF
and ISS independently, but not additively, increased the Thr requirement to maximize PD. A
subsequent growth performance study using the same HF diet estimated Thr required to maximize
average daily gain (ADG) at 0.76% and 0.80% SID Thr using the linear and curvilinear breakpoint
model respectively. In a third study, supplementing Thr to meet the requirement for HF and
systemic ISS, resulted in a numerically lower ADG in the HF-fed and Salmonella-challenged pigs,
compared to the LF-fed and Salmonella-challenged pigs. This suggested that Thr supply to meet
HF and ISS was not sufficient to maintain ADG during an enteric immune challenge and therefore,
indicates an additive effect of HF and enteric immune challenge on Thr requirement. Finally,
systemic ISS increased lactulose recovery in LF fed pigs but not in HF fed pigs, suggesting that
feeding HF had a protective effect against loss of intestinal barrier integrity. This effect appears to
be partly associated with mucus secretion in the gut, as HF increased fecal mucin output and ileal
intestinal goblet cell numbers and tended to increase MUC2 gene expression in the ileum. The
non-additive effect of systemic ISS and HF on PD is consistent with the LPS induced loss of barrier
function in the LF fed pigs which contributed to increased Thr requirement for PD. Indeed, no loss
of barrier function was observed when systemic ISS and HF were combined, hence no further
increase in Thr requirement was observed. In contrast, we postulate that an enteric immune
challenge and HF diet resulted in a higher magnitude of impact on gut mucosal protein dynamics
that exceeded the gut mucosal protein response to the effect of HF alone, resulting in increased
Thr utilization to support mucosal protein synthesis and thereby increasing dietary Thr requirement
for growth. In summary, results indicate that immune challenge and high DF will increase Thr requirement for growth, but DF will have beneficial effects on improving intestinal barrier function in pigs.
Description
Keywords
Threonine, pigs, barrier function, Salmonella, fibre,
Citation
Degree
Doctor of Philosophy (Ph.D.)
Department
Animal and Poultry Science
Program
Animal Science