234 C
.M. Nyachoti et al. Livestock Production Science 65 2000 229 –237
consumed by mucosal tissue of the small intestine sen et al., 1996. Per kg EBW, the wet weights of
and caecum, although values for the caecum mucosa colon and caecum ranged from 15.5 to 17.5 and 2.22
in the BCM- and BCM–ALF-fed pigs were numeri- to 2.94 g, respectively, which agrees closely with the
cally higher than in the CC-fed pigs Table 4. values 17.23 and 2.83 g, respectively reported by
Dietary treatment affected P , 0.05 the calculated Jørgensen et al. 1996 for pigs fed high fibre diets.
total amount of oxygen consumed by the muscularis The weights of the small intestine relative to EBW
tissue of the small intestine, colon and caecum were not affected by diet composition and were
Table 4. The muscularis tissue of all segments in much higher in the present study compared with the
the BCM–ALF-fed pigs consumed higher P . 0.05 values observed by Jørgensen et al. 1996 32.8 vs.
21
amounts of oxygen than in the CC-fed pigs. 16.2 g kg
EBW. This large difference in small intestine weight between studies may partly be
attributed to pig genotype effects. For example,
4. Discussion Quiniou and Noblet 1995 demonstrated larger
differences in weights of visceral organs between pig Previous research indicates that the liver and
genotypes fed similar diets and at a similar body PVDO account for 25 and 20 of whole animal
weight. The BCM and BCM–ALF diets, which had oxygen consumption, respectively, although they
relatively more fibre content than the CC diet, had represent only about 15 of body weight in growing
the greatest impact on the caecum and colon. The pigs Yen et al., 1989; Yen and Nienaber, 1992; Yen,
latter is most likely due to the distension and 1997. Feeding pigs diets that increase organ mass
lengthening of the hindgut where most of the fibrous will concomitantly lead to increased energy expendi-
feed components are digested via microbial fermen- ture in visceral organs as reported by Pond et al.
tation Pond et al., 1988; Jørgensen et al., 1996; ´
1988 and Jørgensen et al. 1996. It is unclear Rerat, 1996.
whether this response is partly mediated through In the present study, the impact of diet on the
changes in energy expenditure per unit of tissue development of the mucscularis and mucosa tissue of
mass. This information is important in determining if the intestines was also examined. The observed dry
measurements of only organ mass in future studies jejunal mucosa weight contributed to approximately
will be sufficient for predicting energy expenditure in 0.775 of the total jejunal dry weight; this value
visceral organs. agrees closely with values of 0.62–0.76 reported in
In previous studies it was established that endog- sheep fed concentrate-based diets Rompala and
enous gut nitrogen losses and rates of gut protein Hoagland, 1987; Finegan, 1996. The contribution of
synthesis in the colon were higher in pigs fed BCM mucosal dry weight to the total dry weight in the
than CC diets Nyachoti et al., 1997b; Nyachoti, colon of sheep range 0.55–0.61 reported by
1998. Because the same diets were used in the Finegan 1996 is somewhat larger than that seen in
current study, associations between these previously the present study. The observed trends in mucosal
measured aspects of nutrient metabolism and energy development are consisted with the effects of diet
expenditure in visceral organs could be established. composition on the site of digestion and nutrient
In the present study, all pigs were killed 1 h post absorption when pigs are fed the type of diets used in
´ feeding for measurement of oxygen uptake approxi-
the current experiment Rerat, 1996. The CC diet is mately 2 h after feeding; this is a time interval that
highly digestible at the ileal level Nyachoti et al., corresponds to the interval used in the protein
1997b and is likely to be associated with more synthesis study Nyachoti, 1998; Nyachoti et al.,
development of the mucosa in this segment of the 1998.
gut, thus facilitating nutrient absorption. Relatively, a In the current study, BCM- and BCM–ALF-fed
larger proportion of the BCM and BCM–ALF diets pigs had heavier visceral organs than CC-fed pigs.
is digested by microbial fermentation in the hind gut This is consistent with previous research suggesting
and specifically in the colon, which stimulated that feeding practical high fibre diets causes an
mucosal development in this segment of the gut ´
increase in visceral organ mass in rats, pigs and Pond et al., 1988; Jørgensen et al., 1996; Rerat,
sheep Kelly et al., 1993; Zhao et al., 1995; Jørgen- 1996.
C .M. Nyachoti et al. Livestock Production Science 65 2000 229 –237
235
The lack of diet composition effects on weight- current study is much higher than in a mature slow
specific oxygen consumption in mucosa tissues growing animal as as for those used in the sheep
observed in the present study is in good agreement studies.
with results of previous studies with their livestock Previous research Burrin et al., 1990; Kelly et al.,
species Burrin et al., 1990; Kelly et al., 1993; 1993; Finegan, 1996 with sheep has shown that total
Finegan, 1996. The higher weight-specific oxygen gut oxygen consumption is affected more by mass
consumption by the muscularis tissue of pigs fed the changes than by weight-specific oxygen consump-
BCM–ALF and BCM diets than in pigs fed the CC tion. The present data are in line with these observa-
diet is likely to be a reflection of the amount of tions, particularly with respect to total oxygen con-
undigested material that is moved through the sumption in the liver and colon. As discussed earlier,
digestive tract. Due to constraints on equipment, it the higher oxygen consumption in the muscularis
was not possible to measure oxygen consumption in tissue of the GIT segments of BCM- and BCM–
the muscularis tissue at the various locations in the ALF-fed pigs compared with the CC-fed pigs was
intestine. For calculating total oxygen consumption likely due to differences in the amount of effort
in the small intestine and colon, it was assumed that required to move digesta through the digestive tract.
weight-specific oxygen consumption was similar as An increased motor activity in the colons of pigs fed
that in the caecum muscularis which is in between diets with low digestibilities has been reported
the small intestine and the colon. However, total Fioramonti and Bueno, 1980.
calculated oxygen consumption in the various gut The higher total oxygen consumption by the colon
segments is rather insensitive to variation in weight- observed in the BCM- and BCM–ALF-fed pigs in
specific oxygen consumption in muscularis tissue. the present study Table 4 compared with the CC-
This is because of the relatively small contribution of fed pigs, and higher total oxygen consumption by the
muscularis tissue weight to total intestinal weight liver in BCM–ALF-fed pigs than in the two other
and the low weight-specific oxygen consumption in treatment groups, support earlier findings that feed-
muscularis tissue as compared with mucosa tissue. ing high fibre diets increases oxygen consumption by
Moreover, oxygen consumption was only measured visceral organs. Although diet composition did not
in one specific segment of the liver, small intestine, affect weight-specific oxygen consumption in viscer-
colon and caecum. Since the metabolic rate may al organs, total oxygen consumption was affected
differ between the segments of these tissues, relative, mainly because of diet effects on organ size. These
rather than absolute, differences in in vitro oxygen results suggest that feeding diets that increase organ
consumption between treatments should be consid- mass will also lead to increased energy expenditure
ered. by these organs. This increase in energy expenditure
To our knowledge, similar data on in vitro oxygen may be associated with increased protein synthesis
consumption in the intestine and liver are not rates in visceral organs and enhanced endogenous
available for pigs. Weight-specific in vitro oxygen gut nitrogen losses when pigs are fed diets that
consumption by mucosal tissue in the intestine of increase visceral organ mass Nyachoti et al. 1997b,
sheep fed either forage- or concentrate-based diets 1998. These observations indicate that employing
for 8 weeks was reported by Finegan 1996 to be feeding strategies that reduce visceral organ mass
7.56 vs. 6.42 in the jejunum, 4.79 vs. 4.74 in the can increase the efficiency of converting dietary
caecum and 5.77 vs. 3.66 ml g h in the colon, energy and protein into edible pork products.
respectively. The data obtained in the current study agrees closely with the results seen in the colon and
caecum but not in the jejunum. Species differences
5. Conclusion
