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African Journal of Pig Farming ISSN 2375-0731 Vol. 3 (8), pp. 001-006, August, 2015. Available online at 
www.internationalscholarsjournals.org © International Scholars Journals 

 

Author(s) retain the copyright of this article. 

 

Full Length Research Paper 

 

The effect of glutamine supplement on small intestinal 
morphology and xylose absorptive ability of weaned 

piglets 

 
C. B. Hsu1, 2, H. J. Huang1, C. H. Wang1 H. T. Yen3 and B. Yu2* 

 
1
Kaohsiung Animal Propagation Station, Livestock Research Institute, COA, 372 Tungang Road, Laupi Village, Neipu, 

Pingtung 912, Taiwan, R.O.C 
2
Department of Animal Science, National Chung Hsing University, 250 Kuo Kuang Road, Taichung 402, Taiwan, R.O.C 

3
Animal Technology Institute Taiwan, P.O. box 23, Chunan, Miaoli 350, Taiwan, R.O.C 

 
Accepted 05 February, 2015 

 
The purpose of this study is to demonstrate the effects of glutamine (Gln) supplement on small intestinal 
morphology, xylose absorptive and growth performance of weaned piglets. Forty eight piglets weaned at 28 ± 2 
days of age were randomly allotted to three treatment groups. A basal corn-soybean diet was formulated to 
contain 20.3% protein and 3450 kcal DE/kg diet. Glutamine was supplemented to the basal diet at 0% (control), 
1% (Gln 1%) and 2% (Gln 2%). Pigs were fed experimental diets for three weeks. The results showed that the 
villous height of the Gln groups tended higher than the control group in duodenum and jejunum (P < 0.1). 
Glutamine supplementation increased plasma net xylose absorptive concentration from 0.78 to 1.20 and 0.95 to 
1.23 in Gln 1% and Gln 2% group, respectively, which were better than the control group (0.86 to 0.97) in day 7 to 
14 after weaning. Growth performance was not significantly affected by Gln supplement; however, average daily 
gain was approximately improved from 21 to 28% by Gln supplement compared to the control group during 21 
days of experimental period. In summary, the results suggested that dietary supplementation of Gln could be 
beneficial in small intestinal villous morphology and xylose absorptive capacity, and could have a slight 
contribution to the average daily gain of weaned piglets. 

 
Key words: Glutamine, growth performance, intestinal morphology, weaned piglets.

 
INTRODUCTION 

 
Inadequate nutrient intake after weaning often causes 
damage to the intestinal villi resulting in poor growth of 
weanling pigs (van Beers-Schreurs et al., 1998). Amino 
mucosa. One of them, glutamine (Gln) is an essential  
 
 
 
*Corresponding author.  E-mail:  byu@dragon.nchu.edu.tw. Tel: 
+886-4-22860799. Fax: +886-4-22860265. 

 
Abbreviations: Gln, Glutamine; P5C, proline 5-carboxylate; 
DE, digestible energy; CP, crude protein; SI, small intestine;  
PBS, phosphate buffered saline;; EDTA, 
ethylenediaminetetraacetic acid;; TPN, total parenteral nutrition; 
IgA, immunoglobulin A; VH, villous height; CD, crypt depth; BW, 
body weight; ADG, average daily gain; ADFI, average daily feed 
intake. 

 
 
 

 
acids provide the major energy source for the intestinal 
precursor for the synthesis of proteins as well as 
purine/pyrimidine nucleotides. Moreover, it can be used 
as an energy source to support rapidly, the differentiation 
and proliferation of intestinal epithelial cells (Newsholme 
et al., 2003; Wu et al., 1996) and activated lymphocytes 
cells (Wu et al., 1995). Therefore, Gln is the most abun-
dant free amino acid found in the blood of animals and in 
the milk of sows (Wu and Knabe, 1994).  

At normal intakes, dietary Gln is metabolized by the 
small intestine and essentially, all Gln within the body is 
synthesized de novo through the action of glutamine 
synthetase. The major sites of net Gln synthesis are lung, 
adipose tissue, and skeletal muscle and under some 
conditions, the liver. The intestine expresses proline 5-
carboxylate (P5C) synthase, which means that proline is 



 

Table 1. The composition of basal diet.  
    

 Ingredient (%)  Basal diet 

 Maize, dent yellow  49.05 

 Soybean meal, 44 of CP  23.70 

 Dried skim milk  16.0 

 Whey  5.0 

 Soybean oil  1.0 

 Dicalcium phosphate  1.60 

 Limestone, pulverized  0.80 

 Salt  0.50 

 Vitamin premix 
1
  0.10 

 Mineral premix
2
  0.15 

 Choline chloride, 50  0.10 

 Maize starch  2.0 

 Glutamine  0 

 Calculated values  

 Crude protein  20.3 

 Calcium  1.01 

 Total phosphorus  0.77 

 Lysine  1.17 
 

1
Supplied per kg of diet: Vitamin A, 6,000 IU; vitamin D3, 800 

IU; vitamin E, 20 mg; vitamin K3, 4 mg; vitamin B2, 4 mg; 

vitamin B6, 1 mg; vitamin B12, 0.02 mg; niacin, 30 mg; calcium 
pantothenate, 16 mg; folic acid, 0.6 mg; biotin, 0.01 mg; choline 

chloride, 50 mg. 
2
Supplied per kg of diet: Fe (FeSO4.H2O), 140 

mg; Cu (CuSO4.5H2O), 7 mg; Mn (MnSO4.H2O), 20 mg; Zn 

(ZnO), 120 mg; I (KIO3), 0.45 mg. 

 

an end product of intestinal Gln catabolism (Wu et al., 
1995).  

Previous studies have shown that Gln is a conditionally-
essential amino acid under weaning period as well as 
stressful conditions such as injury and infection 
(Newsholme, 2001). Yi et al. (2005) showed that Gln is 
beneficial for maintaining muscular Gln concentrations 
and normalizes lymphocyte function of Escherichia coli-
challenged weaned pigs. Furthermore, due to the effect 
of Gln on regulation of systemic inflammation, it had been 
thought that it could be applied potentially to inflammatory 
diseases (Singleton and Wischmeyer, 2008). However, 
the endogenous Gln is insufficient and consequently, 
animals need to increase their requirement (Hall et al., 
1996). Therefore, the aim of this study is to investigate 
the effects of dietary glutamine supplementation on small 
intestinal villous morphology/structure, xylose absorptive 
ability and growth performance of weaned piglets. 

 

MATERIALS AND METHODS 
 
Animals and diets 

 
The animal feeding protocol of this research was approved by the 
Animal Care and Use Committee of Kaohsiung propagation station, 
Livestock Research Institute, Council of Agriculture. Forty-eight 
crossbred pigs (Landrace × Yorkshire × Duroc) weaned at 28 ± 2 

 
 
 
 

 
days of age were obtained from 10 litters, and littermates were 

randomly allotted to 12 pens for three dietary treatments according 
to weight and sex. Same sex was allotted to each pen. The treatments 

consisted of a control group (C), control diet supplemented with 

glutamine in replace of maize starch for 1% (Gln 1%) and 2% (Gln 2%). 

The control diet (Table 1) was based on maize-soybean meal with 

digestible energy (DE) 3450 kcal/kg, crude protein (CP) 20.3%, and 

lysine 1.17% according to the standards of NRC (1998). During the 21 

days of experimental period, pigs were housed in a traditional nursery 

room with wire-floored pens. Meal feed and nipple water were provided 

ad libitum. The individual pig weight, pen feed consumption, and pen 

feed efficiency (gain/feed) were recorded weekly. 
 

 

Small intestinal morphology observation 

 
Four pigs from each treatment (one pig per pen as duplicate) were 
sacrificed on day 14 post-weaning. Pigs were anaesthetized by 
halothane inhalation. Following intestinalectomy, the small intestine 
(SI) was removed and the length was determined; the positions at 
10, 50, and 90% of the length of the SI were located at duodenum, 
jejunum and ileum, respectively. A 4 cm segments was taken from 
each portion for histological measurement. These samples were 
first rinsed with 0.1 M phosphate buffered saline (PBS) at pH 7.2, 
and then fixed with 10% neutral formaldehyde. After 24 h, the 

samples were removed from the fixative, cut into 1 cm
2
 sections 

(two per location) and stored in fresh fixative. Then, they were 
embedded in paraffin, sectioned at 6 µm thickness and stained with 
hematoxylin as well as eosin for a light microscopy examination. 
The villous height (VH) and crypt depth (CD) were measured based 
on 15 apparently intact villi from each section according to Yu and 
Chiou (1997). Another 4 cm samples were taken from jejunum and 
ileum for morphological observation using a scanning electronic 
microscope according to the method of Yu and Chiou (1997). The 
gut samples were fixed in 10% buffered neutral formaldehyde, then 
rinsed in PBS 3 times and placed in 1% osmium tetraoxide 
overnight. They were rinsed again in PBS for 4 times. The samples 
were gradually dehydrated by increasing alcohol concentrations 
from 50 to 100%. They were then dehydrated, mounted on 
aluminum stubs, coated with gold for 30 min, and subsequently 
placed in the scanning electronic microscope (HITACHI S-300) for 
scanning. 

 

Xylose absorption ability 

 
On day 7 and 14 post weaning, eight pigs of each treatment group 
(2 pigs per pen) were carried to measure the ability of active 
absorption of small intestine. Before the procedure, the pig fasted 
for 16 h, and then fed 10% D-xylose (Sigma Chemical Inc, USA) 
solution at a dose of 1 ml/kg body weight by gavages. Blood 
samples (6 ml) were withdrawn through anterior vena cava with 
tubes containing ethylenediaminetetraacetic acid (EDTA) pre and 
post 1 h gavages. Plasma was obtained by centrifuging at 1500 g 
for 15 min and was stored at -20°C until analyzed for D-xylose 
concentration according to the procedures of Trinder (1975). The 
ability of absorption was determined by measuring the difference of 
xylose concentration in plasma between pre and post feeding of 
xylose. Another twelve pigs were randomly selected from the same 
herd at 28 day of age and their xylose absorption was measured as 
a reference data. 

 

Statistical analysis 

 
Data was analyzed by analysis of variance (ANOVA) using the 
General Linear Model (GLM) procedure of the Statistical Analysis 



  
 
 

 

Table 2. Effect of supplementing glutamine on the intestinal morphology of weaned pigs
1
. 

 

Item Control Gln 1% Gln 2% SE Contrast (C vs. Gln) 

Duodenum      

Villus hight,µm 282 345 332 23 0.069 

Crypt depth,µm 266 282 260 32 0.914 

VH/CD 1.06 1.21 1.27 0.20 0.941 

Jejunum      

Villus hight,µm 306 377 397 33 0.068 

Crypt depth,µm 202 242 211 16 0.236 

VH/CD 1.52 1.56 1.84 0.19 0.634 

Ileum      

Villus hight,µm 260 349 302 33 0.121 

Crypt depth,µm 193 192 196 21 0.964 

VH/CD 1.34 1.64 1.54 0.17 0.601 
 

1
Each value represents the mean of 4 pigs. VH, Villous height; CD, crypt depth.  

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Figure 1. The scanning electron micrographs of the jejunal (A, B, C) and ileal (D, E, F) villi from control and glutamine supplement  
groups of pigs at 14 days postweaning. Control group (A and D); Gln 1% group (B and E); and Gln 2% group (C and F). The boxed 
areas showed erosion of surface epithelium at the apex of the villi in control group. 

 

 

System (SAS) programs (1999). Duncan’s new multiple range test 
was applied for comparing the differences among treatments. The 
orthogonal contrasts were performed to compare the glutamine 
treatment effect. The difference was considered to be significant at 
P < 0.05, and P < 0.10 was considered as a trend. 
 

 

RESULTS 
 
Intestinal morphology 
 
The morphology of the duodenum, jejunum and ileum at 

 
 

 

day 14 of the experiment is shown in Table 2. The results 
showed that glutamine supplement groups numerically 
improved the villus height of duodenum and jejunum 
when compared to the control (P < 0.1). Whereas, there 
were no difference between 1 and 2% Gln supplement 
groups. Figure 1 shows the scanning electron micro-
graphs of the jejunal (Figures 1A, B and C) and ileal 
(Figures 1D, E and F) villi from the control and glutamine 
supplement groups, respectively. In general, blunted and 
folded villi were observed in most pigs (Figures 1B, C, E 
and F). Damaged villi with erosion of surface epithelium 



 
 
 

 
Table 3. Effect of supplementing glutamine on the plasma xylose concentration (mmol/L) of 

weaned pigs
1
. 

 

Item Control Gln 1% Gln 2% SE 

Day 7     

Preoral conc. 0.15 0.15 0.12 0.01 

Postoral conc. 1.01 0.93 1.06 0.22 

Net absorptive conc. 0.86 0.78 0.95 0.22 

Day 14     

Preoral conc. 0.16 0.09 0.14 0.02 

Postoral conc. 1.13 1.29 1.37 0.23 

Net absorptive conc. 0.97 1.20 1.23 0.22 
 

1
 Each value represents the mean of 8 pigs.

 

 

 

Table 4. Effect of supplementing glutamine on the growth performance of weaned pigs
1
 

 

Item  Control Gln 1% Gln 2% SE 

Average BW (kg)     

Initial  6.66 6.69 6.67 0.22 

7 day (12)
1
  7.26 7.28 7.37 0.24 

14 day (12)  8.28 8.50 8.35 0.35 

21 day (8)  9.78 10.35 10.36 0.58 

ADG (kg/head)     

0 to 7 day  0.09 0.09 0.10 0.02 

8 to 14 day  0.13 0.17 0.14 0.03 

15 to 21 day  0.20 0.24 0.26 0.03 

0 to 21 day  0.14 0.17 0.18 0.02 

ADFI (kg/head)     

0 to 7 day  0.23 0.19 0.22 0.04 

8 to 14 day  0.24 0.28 0.31 0.05 

15 to 21 day  0.33 0.30 0.34 0.05 

0 to 21 day  0.26 0.24 0.28 0.03 

Gain/Feed     

0 to 7 day  0.41 0.45 0.44 0.08 

8 to 14 day  0.53 0.60 0.46 0.12 

15 to 21 day  0.67 0.80 0.76 0.09 

0 to 21 day  0.54 0.63 0.64 0.05 
 

1
Values are presented as means with the numbers of piglets given in parentheses. BW, Body 

weight; ADG, average daily gain; ADFI, average daily feed intake. 
 

 

at the apex of the villi were detected in some pigs from 
the control group (Figures 1A and D). The integrity of 
intestinal morphology was better in the glutamine supple-
mentation groups than in the control group. 
 

 

Absorption of xylose 

 

Table 3 shows plasma xylose concentration of the three 
treatments. The average plasma xylose concentration at 
weaning was 0.17 mmol/L (data not shown). Glutamine 
supplementation increased plasma net xylose absorptive 

 
 

 

concentration from 0.78 to 1.20 and 0.95 to 1.23 in 1 and 
2% Gln group, respectively, which were better than the 
control group (0.86 to 0.97) in day 7 to 14 after weaning. 
 

 

Growth performance 

 

The growth performance is presented in Table 4. No 
significant differences in average daily gain (ADG), daily 
feed intake and gain/feed were observed regardless of 
the treatment group. However, ADG was numerically 
improved (P > 0.05) 30 and 8% by Gln 1% and Gln 2% 



 
 
 

 

compared to the control from d 8 to 14 of the experi-
mental period (P > 0.05) and 20 and 30%, respectively, 
from day 15 to 21. Overall, ADG was improved 21 to 28  
% approximately by glutamine supplement compared to 
the control group during 21 days of experimental period. 
 

 

DISCUSSION 

 

Weaning of piglets is known to be associated with gross 
changes in small intestinal morphology and structure 
such as villous atrophy, decreased villous height and 
increased crypt depth that will decrease the intestinal 
active absorption (van Beers-Schreurs et al., 1998). If the 
intestinal villous atrophy could be prevented, it would 
improve nutrient digestion and absorption and growth gap 
of weaned piglets (Pluske et al., 1997).  

In the present study, glutamine supplementation showed 

a trend of improving villous heights of the duodenum and 
jejunum at day 14 of the weaning period (P < 0.1) and 
activation absorptive ability of xylose. The results agreed 
with the findings of Wu et al. (1996) as well as the 
previous research that glutamine or glutamine-dipeptide 
supplementation to total parenteral nutrition (TPN) 
solution prevented gut atrophy in humans and rats 
(Schroder et al., 1995). Liu et al. (2002) suggested that 
the jejunal atrophy was prevented by 1.0% glutamine 
supplementation during the first week post-weaning 
piglets. Yu et al. (2002) also suggested that a combi-
nation of 1.0% of glutamine and 1000 ppm of nucleotide 
in diet could improve feed intake and intestinal villus 
height. The reasons being that glutamine facilitated the 
survival and proliferation of intestinal mucosal cells and 
that glutathione synthesis from glutamine maintains the 
mucosal integrity and defenses. Another explanation 
could be the glutamine-dependent protein expression of 
intestinal epithelial tight junction barrier and cellular 
localization in Caco-2 cell monolayers (Liu et al., 2002; 
Wu et al., 1996). This mechanism may similarly relate to 
glutamine-mediated modulation of intestinal barrier 
function in stressed animals and humans (Li et al., 2004; 
DeMarco et al., 2003). Furthermore, enteral glutamine 
can stimulate the mucosal protein synthesis and preserve 
the paracellular permeability (Coeffier et al., 2003; Le 
Bacquer et al., 2003) that will be helpful for maintaining 
the epithelial barrier function. Our study indicated that the 
villi of the control pigs were damaged to some extent 
possibly due to inadequate nutrient intake and it may 
result in increase rate of cell turnover as well as 
decreasing villi height. The present study showed that the 
intestine xylose absorptive ability improved from day 7 to 
14 after weanling in both Gln supplement groups when 
compared to the control group. Therefore, glutamine 
supplementation provided a beneficial environment for 
the proliferation of enterocytes, preventing intestinal 
atrophy and activation absorptive function.  

Currently, glutamine supplementation had no significant 

  
 
 
 

 

improvement on the performance of piglets; however, it 
numerically improved 21 to 28% of ADG compared to the 
control group during 21 days of experimental period. Zou 
et al. (2006) found that pigs supplemented with 1% 
glutamine had a 12% lower feed/gain ratio during the first 
ten days after weaning and had a 27.8% higher ADG 
during day 11 to 20 post-weaning. Wu et al. (1996) had 
reported that 0.2 to 1.0% glutamine supplementation did 
not have any significant effects on the daily feed intake, 
ADG, and gain/feed during the first week post weaning, 
but the gain/feed of pigs supplemented with 1% gluta-
mine was 25% higher than the control pigs during the 
second week of post-weaning. Lee et al. (2003) also 
found that 1.5% glutamine supplementation did not affect 
the feed intake, ADG, and gain/feed of pigs weaned on 
21 days of age, but the small intestinal development and 
bile immunoglobulin A (IgA) production were improved. 
Similar results were also reported by Bartell and Batal 
(2007) in chicken, their results showed 1% Gln could 
improve growth performance, facilitate the health of GI 
tract, and increase the concentrations of sera IgG and 
IgA. In the study of Yi et al. (2005), they indicated that 
2.0% glutamine supplementation on pigs weaned at 17 
days of age did not affect growth performance during 11 
days of feeding, but glutamine supplementation had 
beneficial effects on alleviating growth depression of E. 
coli K88+-challenged weaned pigs, through maintaining 
intestinal morphology and function. Focusing on glutamine 

supplementation for growth performance in weaned 
piglets, Zou et al. (2006) explained the importance of 
glutamine on energy source for enterocytes, the neces-
sary precursor for DNA and protein synthesis, and the 
biological regulating function of glutamine metabolite. 
Recently, research on molecular mechanisms had revealed 
the findings that dietary glutamine supplement would 
increase intestinal expression (120 to 140%) of genes 
that is necessary for cell growth and removal of oxidants 
(Wang et al., 2008). However, the reason growth perfor-
mance could not be consistently improved by glutamine 
might result from the fact that it may not be affected by 
glutamine alone, but with other uncertain environmental 
factors. Therefore, from the results obtained, it is sug-
gested that glutamine supplementation for weaned piglets 
seemed to lack the significant improving effects on 
growth performance, but posses positive and improving 
efficacy for the maintenance of the intestinal villous 
morphology and function.  

In conclusion, dietary supplementation of glutamine could 
be beneficial to small intestinal villous morphology, xylose 
absorptive capacity and slightly contribute to the average 
daily gain of weaned piglets. 
 

 

ACKNOWLEDGEMENTS 

 
The authors would like to thank the Council of Agriculture 
of the Republic of China for supporting the research and 



 
 
 

 

the Ajinomoto Co. Inc. (Yokyo, Japan) for their generous 
gift of L-glutamine. The authors also appreciate Dr. T. K. 
Chung for his help to revise the manuscript. 
 

 
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