Livestock Research for Rural Development 15 (1) 2003

Citation of this paper

N balance studies in young Mong Cai and Large White pigs fed high fibre diets based on wheat bran 

J Ly, Chhay Ty and Pok Samkol 

The Ecological Farm, University of Tropical Agriculture Foundation
Chamcar Daung, Dangkor District, PO Box 2423
, Phnom Penh 3, Cambodia


A total of 16 castrate male pigs [Mong Cai (MC) or Large White (LW)] with an average weight of 20 kg were used in a random two-block design to study N utilization from a high fibre diet consisting of wheat bran as the major dietary component (68% in dry basis). Daily feed consumption was 40 g DM/kg body weight and crude protein (Nx6.25) of the diet was 18% in DM.  

There was no effect of genotype on total tract digestibility for DM, organic matter, crude fibre and NDF but MC pigs digested  less N than LW animals. Faecal pH values were lower and short chain fatty acids and ammonia tended toward a higher output in MC pigs than in LW.  N retention was lower in MC than in LW pigs when expressed as a proportion of live weight or of N intake.  This trend was not apparent for N retention as proportion of N digested..

The results from the present experiment suggest that the N requirement of Mong Cai pigs may be lower than what is recommended for "improved" genotypes selected for lean meat production.  

Key words:  Genotype, Large White, Mong Cai, N balance,  pigs 


Experimental evidence has been accumulated suggesting that the scheme of N utilization in Mong Cai pigs is somewhat different from that observed in improved pig genotypes selected for lean meat traits (Bun Tean 2002; Nguyen Thi Thuy and Ly 2002; Chiv Phiny et al 2002). The Mong Cai breed has probably originated in the Red River basin, in North Vietnam (Molenat and Tran 1991), and its population size is considerable in Indochina, mainly in Vietnam.  

A somewhat similar trend in N utilization has been observed in another Asian breed, the Meishan pigs from China, when compared to European Large White animals (Février et al 1990; Guohai et al 1990, cited by Aumaitre et al 1992; Kemp et al 1991). This could explain the apparent lower efficiency of N utilization by Mong Cai (and similar unselected genotypes) for protein accretion for growth purposes, when rations are formulated according to the needs of "improved" breeds. Such improved genotypes, which been selected for a high protein to fat ratio, are usually fed to express the maximum potential of growth of lean body mass.  In Europe, Whittemore et al (2001) have recently directed attention towards the relationship between the nutrient requirements by the pig, and the effective use of these nutrients. 

The aim of the present experiment was to obtain additional information about the characteristics of some digestive processes and N balance in Mong Cai  as compared to Large White pigs, kept in a common environment, in terms of feeding management and high air temperature. 

Materials and Methods 

Eight Mong Cai and eight Large White castrate male pigs, with an average weight of 20 kg,  were allocated in a random two-block design to study N utilization from a high fibre diet consisting of wheat bran as the major dietary component. The Mong Cai pigs were of Vietnamese origin (from Thu Duc, near Ho Chi Minh City) and the Large White pigs were of commercial origin, locally available in the Phnom Penh market. Both types of animals had been born from parents raised in the University pig herd, at the Ecological Farm. 

The diet was composed (% DM basis) of wheat bran 68.0,  maize bran 20.0, dried fresh water fish 10, vitamin and mineral premix 2.0. The vitamin and mineral supplementation was according to NRC (1998) recommendations. Details of the chemical composition of the ingredients and the diet are in Table 1. Daily feed intake was adjusted to 40 g/kg of live body weight, which was close to ad libitum based on previous observations. The daily feed allowance was given in a meal form twice daily (7:00 and 13:00 h) in equal quantities. Fresh water was available through drinking nipples.  

Table 1. Characteristics of the ingredients and the diet (in per cent, dry basis)


Wheat bran

Maize bran

Dried fresh water fish

Vitamin, mineral supp.


Dry matter












Organic matter






Crude fibre












Ether extract


















Gross energy, KJ/g DM1






WHC, g/g DM2






1 Estimated according to Nehring and Haenlein (1973)
Water holding capacity analyzed following Tsaras et al (1998). See text

The animals had a five-day adaptation to the diets. During the adaptation period, feed consumption was adjusted to a level with no feed refusals. Thereafter, quantitative collection of faeces, urine and any feed residue were made during another five days. During the entire 10-day period, the animals were housed individually in metabolism crates designed for quantitative collection of faeces and urine separately. These crates were in an open stable without walls. Urine was collected in covered plastic buckets, under enough H2SO4 solution to keep the liquid at pH below 4. 

The DM content of feeds and faeces was determined according to Undersander et al (1993) by microwave radiation until constant weight, and N in feeds, faeces and urine was as indicated by the A0AC (1990) the wet oxidation Kjeldahl procedure. The content of cell walls (NDF) in the samples was determined according to Van Soest et al (1991). The gross energy value of feed ingredients and the diet was calculated according to the Nehring and Haenlein (1973) formula.  Water holding capacity of feed ingredients was determined by the filtration technique described by Tsaras et al (1998) as adapted by Ly (2003), by using during five minutes a gentle vacuum originated from a commercial dust aspirator connected to a vacuum flask. 

The pH value in fresh faeces was determined with a glass electrode fitted to a digital pH meter. In addition, faecal concentrations of short chain fatty acids (SCFA) and NH3 were estimated in fresh faecal material filtered through three sheets of cotton after suspending the samples in distilled water (1:4 by weight). The samples were mixed in the ratio of 1:1 (by volume) with a saturated solution of MgSO4 in H2SO4 and the resulting acid product of steam distillation titrated, following the method outlined by the standard procedure of Pennington (1952; quoted by Ly 1986).  In this particular case, an aliquot of the faecal filtered slurry was steam distilled  after mixing with NaOH 40% in the ratio 1:5 (by volume) as recommended in the standard Kjeldahl procedure,  and then titrated by the acid-base method. 

The indicators of daily faecal output were calculated as described by Ly et al (1998). All analyses were conducted in duplicate. 

Means between treatments were compared by the standard t-test (Steel and Torrie 1980) following ANOVA analysis using the Minitab program software (Ryan et al 1992). Regression analysis was employed in the required cases. 



Average air temperature during  the trial was 35.0 ± 3.5oC as measured every day at 12:00 hours. The animals did not show any symptom of discomfort at any moment and feed refusals were minimal, perhaps due to the fact that a rather low consumption of feed was selected during the experiment (the level had been fixed according to recorded intakes by the Mong Cai pigs, which is less than has been observed in Large White pigs of the same live weight). The pigs were always in positive live weight balance, with an average daily gain during the ten-day period of 200 ± 35 g/day.

Digestive indices 

There was no effect of genotype on faecal excretion of fresh material and water, the values of which were high as expected from the high water holding capacity of the diet (Table 2).  The Large White pigs had a higher faecal pH than Mong Cai animals. On the other hand, faecal concentration and output of metabolites tended to be higher (a trend for NH3 (P<0.10) and higher for SCFA (P<0.05) in the Mong Cai than in the Large White pigs. There was a great variability in the faecal indices, which implies that large numbers of animals would be needed to demonstrate that the observed differences represented a true effect of breed.

Table 2. Faecal characteristics in Mong Cai and Large White young pigs


 SE ±

Mong Cai

Large White

Number of animals




Faecal characteristics





DM, %




SCFA, mmol/100 g DM




NH3, mmol/100 g DM




Faecal output per kg DM intake

Fresh material, g




DM, g




Water, g




SCFA, mmol




NH3, mmol




+ P<0.10;  * P<0.05;  *** P<0.001

In previous experiments, faecal output of SCFA and ammonia appeared to be inversely proportional to pH values in faeces from Mong Cai pigs ((Ly and Pok Samkol 2001; Ly 2003), and this phenomenum appeared to hold true for faecal SCFA and pH (P<0.08) on one hand, and for faecal ammonia and pH (P<0.04) on the other hand. At the same time a straight, negative relationship has previously been found between faecal output of these types of metabolites and organic matter digestibility (Ly 2003). A similar significant relationship (Table 3) was observed in the current study, which appeared to be stronger for ammonia than for SCFA output, and on the other hand, stronger for Large White than for Mong Cai pigs. 

Table 3.  Linear interdependence between faecal output of SCFA and ammonia (y, mmol/kg DM intake) and organic matter digestibility (x, %) in Mong Cai and Large White pigs








Faecal SCFA output






Mong Cai





- 0.362


Large White





- 0.999









Faecal ammonia output






Mong Cai





- 0.669


Large White





- 0.998







- 0.628


Since it has been revealed that bacterial metabolism in pig's faeces is similar to that occurring in the terminal part of the gastrointestinal tract in this species (Williams et al 1998; Bauer et al 2001), it is possible to think that there exists certain influence, other than the dietary effect, on microbial activity in the large intestine of the pig due to the nature of the genotype under examination. In fact, Bruininx et al (2002) observed a noticeable influence of piglet genotype on SCFA and ammonia concentration in large intestinal digesta. An increase in microbial activity in caecum and colon of Mong Cai pigs, through a shift of bacterial balance to enhance the cellulolytic bacteria population (Varel et al 1984; Varel 1987), could support an increase in degradation of the fibrous fractions of the diet, as data from the present experiment could indicate. As it is well known, the large intestine of the pig is the main site of the alimentary canal for fibre degradation (Bach Knudsen and Jorgensen 2001).  An increase in activity of the large intestinal microbiota could occur too in organs susceptible to be further anatomically adapted to room bulky feeds (Low 1985, 1993; Kyriazakis and Emmans 1995). 

There was no significant influence of breed on DM and organic matter digestibility (Table 4), which was relatively high, in spite of a high NDF content in the diet that could in turn negatively affect digestive indices, as it has been claimed elsewhere (Fernández and Jorgensen 1986; Close 1993; Le Goff et al 2002). Digestibility of NDF and crude fibre were relatively high too in both breeds taking into account the highly fibrous nature of the rations, with a very slight inclination, although not significant (P>0.10) for Mong Cai pigs to better digest several fibre fractions as compared to the Large White animals. In this connection, it has been found that total tract digestibility of hemicellulose and cellulose is not higher than 45 and 35% respectively for wheat bran in Large White pigs (Chabeauti 1991; Chabeauti et al 1991). 

Table 4. Total tract digestibility in Mong Cai and Large White young pigs



SE ±

Mong Cai

Large White

Number of animals




Total tract digestibility, %





Organic matter




Crude fibre








There are conflicting results concerning fibre fraction utilization by local pigs from the Far East of Asia. Aumaitre et al (1992) did not find differences between improved European on one hand and Chinese breeds on the other in digestive capacity for utilization of dietary fibre.  In a previous experiment with Mong Cai pigs (Nguyen Thi Thuy and Ly 2002), it was observed a non significant improvement of NDF digestibility as compared to Large White animals. 

Balance of N 

Several indices of N balance indicated that Mong Cai utilized less dietary N than Large White pigs (Table 5). There was a similar mean daily N intake in both breeds, but Mong Cai showed a high variability for this index.  Faecal excretion of N was higher (P<0.05) in Mong Cai animals than in the Large White, and this phenomenum determined a significantly higher digestibility (P<0.01) for pigs of the Large White breed. These results are in accordance with others comparing these two same genotypes (Nguyen Thi Thuy and Ly 2002). 

Table 5. N balance  in Mong Cai and Large White young pigs



SE ±

Mong Cai

Large White

Number of animals




N balance, g/day








Excretion in faeces








Digestibility, %




Excretion in urine




Total excretion
















+ P<0.10;  * P<0.05;  ** P<0.01

It was found that 40.8% of total N excretion was via faeces in the Mong Cai pigs whereas the same index was only 33.8% in the Large White animals (Figure 1). As it can be clearly deduced, urine was the main route of N elimination in both breeds eating a highly fibrous diet. 

A trend was found for total excretion of N to be higher in the Mong Cai animals when this index was compared to that of Large White pigs. In consequence, animals from the Large White genotype had a significantly higher N retention in terms of the daily total amount retained (P<0.05) or related to the N intake in percentage (P<0.01). N retention in Mong Cai pigs (6.7 g/day) accounted for 83.6% of the same index for Large White pigs (7.9 g/day). This same trend was not apparent for N retention expressed as percentage of digested N (P<0.26) between both genotypes studied. However, the efficiency of utilization of digested N accounted for 93.7% in compared values for Mong Cai and Large White pigs.

Results concerning the effect of genotype on N balance are in accordance with other previous studies (Bun Tean 2002; Chiv Phiny et al 2002) indicating a lower N utilization by Mong Cai pigs as compared to other improved breeds. The data from the current investigation are in accordance too with a similar trend previously observed with Meishan pigs as compared to Large White (Février et al 1990; Kemp et al 1991), or with Jiaxing pigs if compared to Jiaxing x Landrace animals (Guohai et al 1990; cited by Aumaitre et al 1992). 


Results from the present experiment support the hypothesis that N requirement of Mong Cai pigs must probably be lower than that recommended for certain improved genotypes for lean meat. 

More research is needed in order to clarify the pattern of microbial digestion of N in the large intestine of pigs fed high levels of fibrous materials, with emphasis on the nature of the pig's genotype and the botanical origin of the dietary fibre. 


This publication is an output from a collaborative research work carried out by members of the staff of the University of Tropical Agriculture Foundation, Cambodia, and the Swine Research Institute at Havana.

Thanks are given to the MEKARN project (supported by SIDA-SAREC of Sweden), for partial funding of the current investigation. The authors are grateful to Dr. Claude Février, formerly from the Swine Research Station at INRA, Rennes, for his support in literature search and comments.


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Received 19 November 2002; Accepted 12 December 2002


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