Adequate oral threonine is critical for mucin production and gut function in neonatal piglets

Abstract

In previous experiments, we found that the threonine requirement of neonatal piglets fed parenterally was 40% of that when fed intragastrically; we hypothesized that much of the oral supply of threonine is being used for mucin production. To investigate this hypothesis, intragastrically fed 2-day-old piglets were fed one of three treatments for 8 days: 1) a threonine-adequate diet (IG-A; 0.6 g threonine.kg(-1).day(-1) fed intragastrically); 2) a threonine-deficient diet (IG-D; 0.1 g threonine.kg(-1).day(-1) fed intragastrically); or 3) a threonine-deficient diet with adequate threonine delivered parenterally (IV-A; 0.5 g threonine.kg(-1).day(-1) fed parenterally plus 0.1 g threonine.kg(-1).day(-1) fed intragastrically). IG-D piglets experienced higher nitrogen excretion, higher plasma urea, and lower plasma threonine concentrations versus both of the other groups (P < 0.05), indicating profound threonine deficiency. Mucosal mass and total crude mucin content were lower in the colons of IG-D pigs (P < 0.05). Histopathological analysis showed lower numbers of acidic mucin-producing goblet cells in the duodenum and ileum of IG-D pigs. In IG-D pigs, acidic mucin subtypes were lower in the small intestine but higher in the colon, which corresponded with persistent diarrhea. The parenteral supply of threonine was adequate to maintain most outcome parameters, although IV-A pigs did have smaller colonic goblet cells with more acidic mucins compared with IG-A pigs. Overall, our results suggest that adequate dietary threonine was critical in the production of mucus and that a parenteral threonine supply can ameliorate most of the symptoms of oral threonine deficiency.

Intestinal development and growth performance of early-weaned piglets fed a low-threonine diet

“…In the present study, the level of dietary threonine supply modified neither daily weight gain nor feed efficiency. This lack of effect of threonine deficiency on growth was also observed in early-weaned piglets fed a diet supplying only 17% of threonine requirements for a short period of time (Law et al, 2007). This result was quite unexpected since several studies showed that low dietary threonine supply decreases growth of weaning piglets (Sewell et al, 1953;Adeola et al, 1994) and growing pigs (Le Floc'h et al, 1994;Schutte et al, 1997).…”

“…This can be related to the complexity in analysing mucin biology and characteristics. Total crude mucin content is reduced in the colon but not in the ileum of early-weaned piglets receiving 17% of threonine requirements for 1 week (Law et al, 2007). In adult rats fed 30% of threonine requirements for growth (Faure et al, 2005), mucins synthesis is impaired in the ileum and the colon.…”

“…An interesting observation is that villi atrophy induced by threonine deficiency was noticed only in the ileum. Law et al (2007) reported villi atrophy in the mid jejunum and the ileum of piglets receiving a diet strongly deficient in threonine (piglets received 17% of the requirements recommended by National Research Council (1998)) for 1 week. In our study, we may assume that enough dietary threonine was available for the proximal but not for the distal part of the intestine.…”

“…However, this indicator is not fully representative of mucin synthesis capacity and did not take into account the different types of mucins. Indeed, Law et al (2007) noticed reduction in the number of ileal goblet cells producing acidic mucins, which are more resistant to bacterial mucolytic activities and protect against microbial penetration and translocation.…”

“…Therefore, the high rate of threonine extraction by the intestine could not be explained by threonine oxidation through the TDG pathway. Otherwise threonine utilisation by the intestine is often associated with mucin synthesis (Faure et al, 2005;Law et al, 2007). Indeed, threonine was found in high concentrations in the ileal endogenous protein losses (Hess et al, 1999), particularly in mucins in which threonine represents 16% of total AAs (Lien et al, 1997).…”