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Dietary influence on organ size and in vitro oxygen
consumption by visceral organs of growing pigs
1
*
C.M. Nyachoti, C.F.M. de Lange , B.W. McBride, S. Leeson, H. Schulze
Department of Animal and Poultry Science, University of Guelph, Guelph, Ontario, Canada N1G 2 W1
Received 3 June 1999; received in revised form 20 October 1999; accepted 10 December 1999
Abstract
Although visceral organs represent only about 15% of the pig’s body weight, they account for about 45% of whole body oxygen consumption. The effect of diet on organ mass and in vitro oxygen consumption by some visceral organs was investigated in a study using 15 Yorkshire male castrates (18.961.5 kg initial body weight). Diets were based on casein-corn starch (CC), barley-canola meal (BCM) or barley-canola meal–alfalfa meal (BCM-ALF) and formulated to contain 0.088 MJ digestible energy (DE) per gram of crude protein. Pigs were fed at 2.6 times maintenance DE requirements twice daily for 3 weeks, then every 3 h for 3 days prior to tissue sampling. One h after feeding, pigs were killed and samples of the liver, jejunum, colon and caecum taken immediately. In vitro oxygen uptake was determined polarographically using an oxygen electrode. Per kg empty body weight (EBW), weight of the small intestine did not differ (P.0.10) between treatments. Per
kg EBW, weights of liver, colon and caecum were higher (P,0.05) in BCM- and BCM–ALF-fed pigs than in CC-fed pigs. Weight-specific oxygen consumption by the liver tissue and intestinal mucosa was not influenced by diet (P.0.10).
However, weight-specific oxygen consumption was higher (P,0.05) in the caecum muscularis of pigs fed BCM- and BCM–ALF than in the CC-fed pigs. Per kg of EBW, total oxygen uptake by the colon of BCM- and BCM–ALF-fed pigs was higher (P,0.001) than in CC-fed pigs. The values for oxygen consumption by the liver in CC- and BCM-fed pigs were similar (P.0.10) and lower than those in the BCM–ALF-fed-pigs. In conclusion, changes in diet composition alter energy
expenditure in the liver and intestinal tissue. This appears largely mediated via effects on organ size and not via weight-specific oxygen consumption. 2000 Elsevier Science B.V. All rights reserved.
Keywords: Pigs; Visceral organs; Oxygen consumption; Diet composition
1. Introduction
Although visceral organs represent only about 15% of body weight, they are reported to account for a large proportion of total body energy expenditure
*Corresponding author. Tel.:11-519-824-4120, ext. 6477; fax: in farm animals (Gill et al., 1989; Yen et al., 1989; 11-519-836-9873.
Huntington, 1990; Yen, 1997). For instance, Yen
E-mail address: [email protected] (C.F.M. de Lange).
1 (1997) estimated the contribution of portal
vein-Present address: Finnfeeds International Ltd, P.O. Box 777,
Marlborough, Wiltshire, SN8 1XN, UK. drained organs (PVDO) and the liver to whole
animal oxygen consumption to be about 25 and 20%, castrates with an average initial body weight of respectively, in the growing pig. Two processes, 18.961.5 kg were obtained from the University of
4 1
namely Na / K pumping and protein turnover, are Guelph Arkell Swine Research farm for use in the known to be responsible for the high energy expendi- study. They were housed in individual pens with ture by gut tissues and the liver (Lobley, 1988; Kelly slatted plastic flooring in a temperature-controlled and McBride, 1989; McBride and Kelly, 1990). room (20–228C) and allowed to adapt to their new
Studies with ruminant animals show that these environment and diets for a minimum of 3 weeks processes are influenced by feeding level and diet before measurement of in vitro oxygen consumption composition (Burrin et al., 1990; Kelly et al., 1993; in selected organs.
Finegan, 1996). Diets that are high in fibre or other Three diets, based on either CC, BCM or BCM– anti-nutritional factors are also known to increase the ALF, were used in this experiment (Table 1). The amount of endogenous gut nitrogen losses in pigs diets were formulated to meet or exceed require-(Butts et al., 1993; Boisen and Moughan, 1996; ments for vitamins and minerals (NRC, 1998) and to Nyachoti et al., 1997a). The latter may also be contain a similar digestible energy to crude protein related to energy expenditure in gut tissues. ratio (0.88 MJ DE per percentage point of diet crude Diet composition, and in particular dietary fibre protein) based on ingredient compositions according content, influences the mass of visceral organs. The to NRC (1998). Unfortunately, the digestible energy effects of diet on energy expenditure in visceral to analyzed crude protein ratio differed between diets organs may be mediated through effects in visceral (0.83, 0.99 and 0.97 for the three diets, respectively). organ mass or energy expenditure per unit of tissue The latter can likely be attributed to the lower than mass. For example, Pond et al. (1988) and Jørgensen anticipated protein level in the barley used in the et al. (1996) showed that feeding high fibre diets BCM and BCM–ALF diets. Pigs were given their increased visceral organs mass and intestinal length daily feed allowance in two equal amounts (at 0800 relative to empty body weight (EBW) compared and 2000 h) and intake was restricted to 2.6 times the with those fed low fibre diets. However, in these maintenance energy requirement (ARC, 1981). Dur-studies, effects on energy expenditure per unit of ing the last 3 days prior to tissue sampling time, the tissue mass were not determined. feeding schedule was changed to feeding every 3 h The present study was undertaken to determine in so as to minimize fluctuations in nutrient metabolism vitro oxygen consumption by visceral organs in in visceral organs (Lobley et al., 1992).
growing pigs fed diets based on casein-corn starch
(CC) and barley-canola meal (BCM), known to 2.2. General conduct of the study induce low or high endogenous gut nitrogen losses,
respectively (Nyachoti et al., 1997b). A third, more Five pigs were randomly assigned to each of the extreme diet, based on BCM–alfalfa (BCM–ALF), three diets. For the measurement of in vitro oxygen was included in the present study to accentuate the consumption, three pigs were killed per day for 5 influence of diet on gut metabolism. The effect of consecutive days by an intra-cardiac injection of a 10 diet on organ weights was also assessed. ml dose of sodium pentobarbitone (Euthanal; 300 mg / ml). On each day, one pig from each treatment was picked at random and killed 1 h after feeding. A
Table 1
21
Formulation (g kg ), calculated DE content and analyzed composition of the experimental diets (as fed basis)
Ingredient Diet
Casein-corn Barley-canola Barley-canola
starch meal meal1alfalfa meal
Alfalfa meal – – 300
Barley – 609.5 440
Canola meal – 225 100
Casein 213.2 – –
Corn starch 590.8 – –
Sucrose 100 100 100
Limestone 6 12 –
Dicalcium
phosphate 24 7.5 14
Fat (A / V blend) 35 35 35
Iodized salt 5 5 5
a
Vitamin premix 5 5 5
b
Mineral premix 1 1 1
Alfafloc 20 – –
Calculated DE (MJ / Kg) 16.4 13.4 12.5
Analyzed composition
Dry matter 955.3 913.6 928.0
Crude protein 198.7 133.1 120.9
Crude fibre 20.9 59.9 123.0
ADF 29.4 80.8 154.6
NDF 31.6 192.8 213.7
a 21
Vitamin premix supplied (mg kg of finished feed): retinyl palmitate56.6; cholecalciferol50.03; all-rac-a-tocopherol543.0; menadione53.0; choline chloride5600.0; pantothenic acid518.0; riboflavin56.0; folic acid52.4; nicotinamide530.0; thiamin51.8; pyridoxine51.8; biotin50.24; cyanocobalamin50.03.
b 21
Mineral premix supplied (mg kg of finished feed): Cu515.0; Zn5100.0; Fe5100.0; Mn520.0; I50.3; Se50.3.
(15–30 mg fresh weight) of liver (thin slices), intact each gut segment was dissected, blotted and then mucosa (from each gut segment) and muscularis weighed before scraping off the mucosal tissue using (from caecum only) were dissected out under 310 a microscope slide. The mucosa and muscularis
magnification, blotted dry and weighed. Samples tissues were weighed separately prior to determining were then placed in 4 ml of M199 medium (Sigma DM contents by oven drying at 1008C for 12 h
Chemicals, St. Louis, MO, USA; medium contained (AOAC, 1990). The latter values were used in Earlies salts, L-glutamine and HEPES buffer) and calculating the total dry weight of mucosa and
oxygen consumption was measured. The tissues were muscularis, respectively, in the gut segments. The maintained at pH 7.4 and 378C during the measure- rest of the liver and segments of the gut were cleaned
ment of oxygen uptake for 10 min (Kelly et al., of digesta and weighed. 1993). In vitro oxygen uptake was measured
polaro-graphically using a Clark-style oxygen electrode 2.3. Calculations and statistical analysis (Yellow Springs Instruments Inc., Yellow Springs,
consump-tion determined in the caecum muscularis was were obtained, differences between means were assumed to be the same as that in the muscularis of compared using Duncan’s multiple range test (Steel the small intestine and colon for the purposes of and Torrie, 1980). Treatment means were considered calculating total oxygen consumption (Finegan, significantly different at P,0.05.
1996). For calculating EBW, it was assumed that gut fill in the CC-, BCM- and BCM–ALF-fed pigs was
3, 5 and 8.2% of BW, respectively (Mohn and de 3. Results
Lange, unpublished observations; Jørgensen et al.,
1996). Relative organ weights (g / kg EBW) were All pigs appeared healthy and readily consumed calculated by dividing the weight of each organ by all their feed throughout the experiment. The CC-EBW. The data were subjected to analysis of vari- and BCM-fed pigs had similar body weights and ance using the general linear models procedure of the EBW at the end of the study and were heavier Statistical Analysis System (1985) with diet as the (P,0.01) compared with those fed the BCM–ALF
source of variation. When significant diet effects diet (Table 2). With the exception of the small
Table 2
Body weight and visceral organ weight of growing pigs fed casein-corn starch-(CC), barley-canola meal-(BCM) or barley-canola meal–alfalfa meal (BCM–ALF)-based diets
e
Item Diet S.E.M.
CC BCM BCM–ALF
Initial body weight (kg) 18.6 19.6 18.4 0.66
a a b
Final body weight (kg) 27.28 27.2 24.32 0.49
a a b
Empty body weight (kg) 26.46 25.84 22.44 0.46
21 c
Wet organ weights(g kg empty body weight)
a b b
Dry organ weights(g kg empty body weight)
a a,b b
Dry weight-mucosa(g kg empty body weight)
Small intestine 4.29 3.96 4.78 0.36
a b b
Colon 0.64 1.16 1.24 0.08
Caecum 0.11 0.12 0.16 0.06
21 c
Dry weight-muscularis(g kg empty body weight)
a a b
Small intestine 1.14 1.17 1.45 0.09
Colon 1.36 1.55 1.75 0.14
Caecum 0.31 0.32 0.38 0.03
a,b
Means in the same row with different superscripts differ (P,0.05).
c
Assumed contribution of gut fill to body weight: 3, 5 and 8.2% for the CC-, BCM- and BCM–ALF-fed pigs, respectively (Mohn and de Lange, unpublished observations; Jørgensen et al., 1996).
d
Gastrointestinal tract; excludes the stomach.
e
Table 3
intestine, the BCM- and BCM–ALF-fed pigs had
In vitro weight-specific oxygen consumption (ml / g DM / h) by the
heavier (P,0.05) visceral organs relative to EBW
liver and gastrointestinal tract mucosa and muscularis tissues in
compared with those fed the CC diet (Table 2). On a growing pigs fed casein-corn starch-(CC), barley-canola meal-DM basis, the effect of diet on the relative weights (BCM) or barley-canola meal–alfalfa meal (BCM–ALF)-based
of visceral organs was significant only in the liver diets
a
(P,0.05) and colon (P,0.01). However,
numeri-Tissue Diet S.E.M.
cally, it was larger in the small intestine, caecum and
CC BCM BCM–ALF
total gut of BCM–ALF-fed pigs than CC-fed pigs.
Liver 3.63 3.31 3.84 0.24
The mucosal tissue in the colon of BCM- and BCM–ALF-fed pigs was heavier (P,0.01) than in
Mucosal tissue
the CC-fed pigs (Table 2). In the caecum, there was Jejunum 12.72 12.25 12.77 0.58 a tendency (P,0.067) towards heavier mucosal Colon 5.63 7.13 6.77 0.83
Caecum 6.00 6.56 5.70 0.64
tissue in BCM–ALF-fed pigs compared with CC-fed pigs. In the muscularis tissue, diet was significant
Muscularis tissue
(P,0.05) only in the small intestine; muscularis b c c
Caecum 1.28 2.26 2.49 0.29
tissue was heavier in the BCM–ALF-fed pigs than in
a
Pooled standard error of the mean (N55).
BCM- and CC-fed pigs, both of which were similar. b,c
Means in the same row with different superscripts differ
The relative contribution of mucosa to the total dry (P,0.05). weight of the gut segments was influenced by diet in
the jejunum (P,0.05) and colon (P,0.01), but not
in the caecum (P.0.10). The dry mucosa weight
represented (mean6S.E.) 0.79560.008, Table 4
0.77260.005 and 0.76860.009 of the total dry Total in vitro oxygen consumption (ml / h / kg empty body weight) by the visceral organs and gastrointestinal mucosa and muscularis
weight of the jejunum in CC-, BCM- and BCM–
tissues in growing pigs fed casein-cornstarch-(CC), barley canola
ALF-fed pigs, respectively. These respective values
meal-(BCM) or barley-canola meal–alfalfa meal
(BCM–ALF)-were 0.32260.031, 0.43160.013 and 0.41660.007 a
based diets
in the colon. In the caecum, the dry mucosa weight b
Tissue Diet S.E.M.
as a proportion of the total dry caecum weight
CC BCM BCM–ALF
averaged 0.28560.022 across treatments.
c c d
Dietary treatment did not influence weight-specific Liver 19.66 18.99 24.30 1.38 Small intestine 60.88 47.89 64.02 8.8
oxygen consumption in the liver or mucosal tissue of
c d d
Colon 5.29 11.77 12.41 0.96
jejunum, colon and caecum (P.0.10, Table 3).
Caecum 1.18 1.70 2.09 0.27
Weight-specific respiration in the muscularis tissue
Total GIT 66.3 61.4 79.2 9.8
was higher (P,0.05) in the BCM- and
BCM–ALF-fed pigs, compared with the CC-BCM–ALF-fed pigs (Table 3). Mucosal tissue
Small intestine 55.55 49.33 61.04 4.13
Per kg of EBW, total oxygen consumption was
c d d
Colon 3.47 8.12 8.29 0.65
affected by dietary treatment in the liver (P,0.05)
Caecum 0.66 0.87 0.90 0.07
and colon (P,0.001), and was numerically higher
in the caecum and total gut of BCM- and BCM– Muscularis tissue
c c,d d
ALF-fed pigs compared with CC-fed pigs (Table 4). Small intestine 1.45 2.7 d 3.47 0.39
c d
Colon 1.82 3.65 4.19 0.44
Total oxygen consumption by the liver in CC- and
c c,d d
Caecum 0.41 0.7 0.91 0.11
BCM-fed pigs were similar (P.0.10) and lower
a
(P,0.05) than in the BCM–ALF-fed-pigs. Total Assumed contribution of gut fill to body weight: 3, 5 and 8.2% for the CC-, BCM- and BCM–ALF-fed pigs, respectively
oxygen consumption by the mucosal tissue of the
(Mohn and de Lange, unpublished observations; Jørgensen et al.,
colon was lower (P,0.05) in the CC-fed pigs than
1996).
in the BCM- and BCM–ALF-fed pigs, which in turn b
Pooled standard error of the mean (N55).
c,d
were similar (P.0.10). Diet composition had no Means in the same row with different superscripts differ
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
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
and differences in the stage of development and
mechanisms of thermogenesis in selected tissues. Proc. Nutr.
effects on the organ mass. Such effects may lead to a
Soc. 48, 185–198.
substantial increase in the already disproportional
Kelly, J.M., Southorn, B.G., Kelly, C.E., Milligan, L.P., McBride,
contribution of these organs to whole body energy B.W., 1993. Quantification of in vitro and in vivo energy expenditure, thus reducing the efficiency of convert- metabolism of the gastrointestinal tract of fed or fasted sheep.
Can. J. Anim. Sci. 73, 855–868.
ing dietary energy into edible pork products.
Lobley, G.E., 1988. Protein turnover and energy metabolism in animals: interactions in leanness and obesity. In: Leclerq, B., Whitehead, C.C. (Eds.), Leanness in Domestic Birds. Genetic, Metabolic and Hormonal Aspects. Butterworths Co INRA, pp. Acknowledgements
331–361.
Lobley, G.E., Harris, P.M., Skene, P.A., Brown, D.S., Milne, E.,
We thank Linda Trouten-Radford, Manfred Hansel Calder, A.G., Anderson, S.E., Garlick, P.J., Nevison, I., Con-and Kim Coudenys for their excellent technical nell, A., 1992. Responses in tissue protein synthesis to sub- and supra-maintenance intake in ruminant lambs: comparison of
assistance. Financial support was provided by
Fin-large dose and continuous infusion techniques. Br. J. Nutr. 68,
nfeeds International, Marlborough, UK and the
Natu-373–388.
ral Sciences and Engineering Research Council of McBride, B.W., Kelly, J.M., 1990. Energy cost of absorption and
Canada. metabolism in the ruminant gastrointestinal tract and liver: a
review. J. Anim. Sci. 68, 2997–3010.
NRC, 1998. Nutrient Requirements of Swine, 9th Edition. Nation-al Academy Press, Washington, DC.
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