Adaptive changes in the GI tract after of brush-border digestive enzyme activity after Effects of colostrum and milk on GI function

R .J. Xu et al. Livestock Production Science 66 2000 95 –107 97 The small intestine also undergoes a dramatic weaning 940–694 mm, and then continued to tissue growth and functional change during the decline to approximately 50 of the pre-weaning immediate postnatal period Table 2. It was reported value 5 days after weaning. Villus height reduction is that the small intestine in piglets increased up to 70 suspected to be the result of an increased rate of cell in total tissue weight, 115 in mucosal tissue loss, which subsequently leads to increased crypt cell weight, 24 in length, 15 in diameter, 24 in production and increased crypt depth Pluske et al., crypt depth and 33 in villus height during the first 1997. Associated with the reduction in villus height postnatal day Xu et al., 1992b. During the same and the increase in crypt depth, the morphology of period, the intestinal brush border digestive enzyme the villi also change from long finger-like projections activity increased 80–200, although the specific before weaning to leaf- or tongue-like structures after activity per unit mucosal tissue mass did not change weaning Cera et al., 1988. The structural changes significantly Zhang et al., 1997. The intestinal in the small intestine vary along the intestinal tract absorption capacity remained unchanged during the and are affected by the age of weaning. The changes first day of life, although the specific absorption in the pig weaned at 14 days of age are more capacity per unit mucosal tissue mass decreased conspicuous than those weaned at 21 days of age, during this period Zhang et al., 1997. The decline and the reduction of villus height is more prominent of specific absorption capacity was unlikely due to at the proximal region while the increase in crypt losses of brush membrane transporters, but rather to depth is more prominent at the distal region of the a dilution effect resulting from transient retention of intestine Pluske et al., 1997. colostral protein in the epithelial cells Xu et al., Concomitant with the structural changes, there are 1992b. marked alterations in intestinal functions following A distinct feature of the newborn small intestine is weaning. Hampson and Kidder 1986 reported rapid its ability to absorb macromolecules and, during the reductions in the specific activities of lactase and first day of life, a large quantity of colostral protein, sucrase during the first 4–5 days after weaning. particularly immunoglobulins, are absorbed across Miller et al. 1986 reported that the specific ac- the brush border membrane and a considerable tivities of sucrase, lactase and isomaltase fell by at proportion of the protein is transiently retained in the least 50 during the first 5 days of after weaning in epithelial cells Burrin et al., 1992; Xu et al., 1992b. pigs weaned at 28 or 42 days of age. On the other The ability of macromolecule absorption diminishes hand, the activities of maltase and glucoamylase within 2 days of postnatal life and the phenomena is increased in response to weaning Kelly et al., 1991. called gut closure Westrom et al., 1984. Increases in these polysaccharidases are likely the result of substrate induction. Several studies have shown that the decrease in villus height and the loss

3. Adaptive changes in the GI tract after of brush-border digestive enzyme activity after

weaning weaning coincided with a reduction in intestinal absorption capacity for sugar and amino acids Ham- After weaning, the environment in the GI lumen pson and Smith, 1986; Miller et al., 1986; Nabuurs et changes drastically with the replacement of highly al., 1994, although some other studies failed to digestible milk by solid food, often of plant origin. detect a significant reduction in the ability of sugar Associated with this, the GI tract in weaned pigs absorption Kelly et al., 1991. undergoes a marked change in structure and func- tion, particularly at the region of the small intestine Pluske et al., 1997. The most obvious changes in

4. Effects of colostrum and milk on GI function

the structure of the small intestine following weaning are a reduction in villus height and an increase in The dramatic changes in the GI tract during the crypt depth. Hampson 1986 reported that, follow- immediate postnatal period is apparently related to ing weaning at 21 days after birth, villus height was the ingestion of colostrum while the changes during reduced to 75 of the pre-weaning value 1 day after the period after weaning likely relate, at least in part, 98 R .J. Xu et al. Livestock Production Science 66 2000 95 –107 to the withdrawal of milk. Laboratory studies have post-translational processing of intestinal lactase shown that tissue growth and functional changes in Burrin et al., 1994. Kelly et al. 1993 reported that the GI tract in newborn pigs would not occur if the colostrum feeding during the first 24 h of life in animals were prevented from suckling Widdowson newborn pigs enhanced intestinal epithelial cell et al., 1976. Compared with piglets fed with water maturation, as indicated by an increased sucrase or electrolyte solution, piglets fed with colostrum or activity and a decreased lactase activity at 1 week of milk had a greater protein synthesis rate in the small age. A study in our own laboratory further showed intestine and greater total mucosal brush border that colostrum feeding increased intestinal mucosal lactase and maltase activities at 6–24 h after birth digestive enzyme activities and that pre-hydrolysis of Burrin et al., 1992, 1994; Zhang et al., 1998. colostrum with trypsin eliminated the stimulatory Newborn piglets fed colostrum for 6 h showed an effect Wang and Xu, 1996 Fig. 1. The latter increase in the relative abundance of pro-lactase finding suggests that colostrum contains trypsin- protein and a decrease in the relative abundance of labile bioactive compounds which can modulate the mature form of the enzyme in the intestinal intestinal function in neonates following oral inges- mucosa, suggesting that feeding colostrum alters the tion. It has also been shown in both prenatal and Fig. 1. Total lactase, maltase, alkaline phosphatase and aminopeptidase activities in the small intestinal mucosa of newborn unsuckled piglets N and piglets bottle fed for 3 days with either trypsinized porcine colostrum TC or intact porcine colostrum C. Enzyme activity was expressed as mmoles of substrate hydrolyzed per minute. Significant differences between the corresponding mean values in bottle-fed groups and the newborn group are indicated by P , 0.05 or P , 0.01. Significant differences between the corresponding mean values in [ [[ the two bottle-fed groups are indicated by P , 0.05 or P , 0.01. Redrawn from Wang and Xu 1996. R .J. Xu et al. Livestock Production Science 66 2000 95 –107 99 Table 3 postnatal pigs that feeding colostrum enhanced in- Concentrations of EGF, IGF-I, IGF-II, insulin and TGF-b in testinal macromolecule absorption and onset of gut porcine colostrum and milk closure Westrom et al., 1985; Sangild et al., 1999. a a Colostrum Milk Reference Factors affecting GI structure and function after weaning are complex and multiple, possibly includ- EGF ng ml | 1500 150–250 Jaeger et al., 1987 b 5 NR Vaughan et al., 1992 ing pathogenic bacterial interactions, psychological IGF-I ng ml 70–350 4–14 Simmen et al., 1988 stress, transient hypersensitivity to food components 72–136 10–27 Donovan et al., 1994 and withdrawal of maternal milk Pluske et al., c 541 NR Xu et al., 1996 1997. At the time of weaning, maternal milk is IGF-II ng ml 165–291 11–50 Donovan et al., 1994 b b withdrawn abruptly and supplementation of sows’ Insulin ng ml 12.4 1.6–3.3 Jaeger et al., 1987 b b 10.8–18.2 1.2–5.5 Westrom et al., 1987 milk or colostrum to piglets during the first week b c 16.5 NR Wang and Xu, 1996 after weaning can prevent villus atrophy, diarrhoea c TGFib ng ml 9–12 ND Xu et al., 1999 and growth retardation Mosenthin, 1998; Nabuurs, a Colostrum as the mammary secretion during the first 3 days 1998. after parturition and milk as the mammary secretion thereafter. b Converted to ng ml from the original published values using conversion factors of 7.175 pmol mU and 5743 g mol for insulin

5. Growth factors in colostrum and milk