Factors influencing the structure and function of the small intestine in the weaned pig: a review

Alterations in piglet small intestinal structure at weaning

Under commercial conditions, weaning of piglets is associated with social, environmental and dietary stress. Consequently, small-intestinal barrier and absorptive functions deteriorate within a short time after weaning. Most studies that have assessed small-intestinal permeability in pigs after weaning used either Ussing chambers or orally administered marker probes. Paracellular barrier function and active absorption decrease when pigs are weaned at 3 weeks of age or earlier. However, when weaned at 4 weeks of age or later, the barrier function is less affected, and active absorption is not affected or is increased. Weaning stress is a critical factor in relation to the compromised paracellular barrier function after weaning. Adequate feed intake levels after weaning prevent the loss of the intestinal barrier function. Transcellular transport of macromolecules and passive transcellular absorption decrease after weaning. This may reflect a natural intestinal maturation process that is enhanced by the weaning process and prevents the pig from an antigen overload. It seems that passive and active absorption after weaning adapt accurately to the new environment when pigs are weaned after 3 weeks of age. However, when weaned at 3 weeks of age or earlier, the decrease in active absorption indicates that pigs are unable to sufficiently adapt to the new environment. To improve weaning strategies, future studies should distinguish whether the effect of feed intake on barrier function can be directed to a lack of a specific nutrient, i.e. energy or protein.

/pdf/intestinal-barrier-function-and-absorption-in-pigs-after-10qs2x0yel.pdf

Intestinal barrier function and absorption in pigs after weaning: a review

The aims of the present study were (a) to maintain the structure and function of the small intestine of the piglet after weaning, and (b) to compare the capacity in vivo of sucking and weaned piglets to digest oral boluses of lactose and sucrose and absorb their monosaccharide products. Piglets were fed on cows' whole milk ad libitum every 2 h for 5 d after weaning. Physiological doses of lactose plus fructose (treatment LAC+FRU) and sucrose plus galactose (treatment SUC+GAL) were administered on day 27 of lactation and on the fifth day after weaning, after which time piglets were killed. Villus height and crypt depth were maintained (P > 0.05) by feeding cows' milk after weaning. The areas under the curves (AUC) for galactose and glucose, adjusted for live weight and plasma volume, increased (P < 0.05) after weaning. Despite the enhancement of gut function after weaning, the galactose index (GalI:AUC for galactose ingested as lactose divided by the AUC for the same dose of galactose ingested as the monosaccharide) and fructose index (FruI: AUC for fructose ingested as sucrose divided by the AUC for the same dose of fructose ingested as the monosaccharide), which are indices of digestive and absorptive efficiency, both decreased after weaning. This apparent anomaly may be reconciled by increased growth, and hence surface area, of the small intestine between weaning and slaughter such that 'total' digestion and absorption most probably increased despite apparent decreases in GalI and FruI. Positive correlations (P < 0.05) between villus height and GalI are consistent with the maximum activity of lactase occurring more apically along the villus. Significant linear relationships (P < 0.05) were recorded between villus height at the proximal jejunum and adjusted AUC for galactose and glucose following treatment LAC+FRU, and between villus height at the proximal jejunum and adjusted glucose AUC following treatment SUC+GAL. These relationships suggest that maximum digestion and absorption occurs at increasing distances along the crypt:villus axis in the weaned pig.

https://researchrepository.murdoch.edu.au/2803/1/maintenance_of_villus_height_and_crypt_depth.pdf

Maintenance of villus height and crypt depth, and enhancement of disaccharide digestion and monosaccharide absorption, in piglets fed on cows' whole milk after weaning

Thirty-two piglets weaned at 28 days of age were used to test the hypothesis that maintenance of nutrition after weaning would prevent the normal decline in villous height and increase in crypt depth and hence preserve the structure and function of the small intestine. Piglets were allocated to one of four treatments at weaning: (1) control group killed at weaning; (2) piglets offered a dry starter diet ad libitum; (3) piglets offered ewes' fresh milk; and (4) piglets offered ewes' fresh milk plus 20 g t-glutamine per I. Piglets in treatments (3) and (4) were offered ewes' fresh milk every 2 h in a feeding schedule that increased from 1·2 I per piglet on the 1st day after weaning to 2·4 I on days 4 and 5. On the 5th day all piglets were killed and samples of small intestine were taken for histological and biochemical examination. Feeding ewes' milk or ewes' milk plus 20 g L-glutamine per I maintained (P > 0·05) villous height and crypt depth compared with piglets killed at weaning. In contrast, piglets given a dry starter diet had shorter villi (P 0·05) in their intestinal mucosa. Piglets given the starter diet proportionately grew from 0·49 to 0·62 more slowly (P 0·05), but consumed proportionately 0·30 less energy (P 0·05). Significant correlations existed between voluntary food intake and villous height at the proximal jejunum for piglets given the starter diet and ewes' milk (P < 0·05 and P = 0·073, respectively). In turn, villous height was significantly correlated (r = 0·78 to 0·87, P < 0·05) with the rate of body-weight gain after weaning in these two groups. For piglets offered ewes' milk plus glutamine, an increase in DM intake was associated only with increases in crypt depth (P < 0·01). These data show that the structure and function of the small intestine can be preserved when a milk diet is given after weaning, and suggest an association between food intake and villous height in determining post-weaning weight gain.

/pdf/maintenance-of-villous-height-and-crypt-depth-in-piglets-by-4cko2k3vsm.pdf

Maintenance of villous height and crypt depth in piglets by providing continuous nutrition after weaning

The relationship between structure and the ability of piglet intestine to transport alanine has been determined during the first few weeks of postnatal life. Villus length halved without change in crypt depth during the 3rd week of postnatal life. A similar shortening of villi, accompanied by an increase in crypt depth, took place when 2-week-old piglets were weaned on to a solid diet. Weaning piglets at 3 weeks increased crypt depth without causing further shortening of villi. Alanine transport was shown, by quantitative autoradiography, to be largely confined to enterocytes in the region of the villus tip. The way in which this transport function developed was analysed further by fitting logistic growth curves to measurements of intra-enterocyte alanine concentration. The ability of enterocytes to transport alanine occurred earlier and alanine was accumulated to higher concentrations in enterocytes studied in 21- compared with 15-day-old unweaned piglets. Weaning piglets on day15 or 21 and measuring alanine transport 5 days later produced a pattern of development similar to that reported previously for adult animals. Transport of alanine throughout postnatal development showed sodium dependency. Effects of alanine on intestinal short-circuit current of weaned piglets were again similar to those recorded in adult animals. These results are discussed in terms of intestinal adaptation to a changing environment and in relation to the ‘notional capacity’ of a pig villus to transport amino acids during the early postnatal period of development.

M. W. Smith

Papers

Effect of postnatal development and weaning upon the capacity of pig intestinal villi to transport alanine