Apparent digestibility (ileal and overall) of nutrients as evaluated with PVTC-cannulated or ileo-rectal anastomised pigs fed diets containing two indigestible markers

Livestock Production Science 62 (2000) 133–141 www.elsevier.com / locate / livprodsci

Apparent digestibility (ileal and overall) of nutrients as evaluated with PVTC-cannulated or ileo-rectal anastomised pigs fed diets containing two indigestible markers Y.-L. Yin a ,1 , J.D.G. McEvoy c , H. Schulze d , U. Hennig e , W.-B. Souffrant e , a,b , K.J. McCracken * a

Department of Agricultural and Environmental Science, The Queen’ s University of Belfast, Newforge Lane, Belfast BT9 5 PX, Northern Ireland, UK b Department of Agriculture for Northern Ireland, Newforge Lane, Belfast BT9 5 PX, UK c Veterinary Sciences, Department of Agriculture for Northern Ireland, Stoney Road, Belfast BT4 3 SD, Northern Ireland, UK d Finnfeeds International Ltd., Marlborough, Wiltshire SN8 1 AA, UK e ¨ ¨ die Biologie Landwirtschaftlicher Nutztiere, Forschungsbereich Ernahrungsphysiologie ‘‘ Oskar Kellner’’, Forschungsinstitut f ur Rostock, Germany Received 28 July 1998; received in revised form 3 February 1999; accepted 15 June 1999

Abstract The techniques of post-valve ‘‘T’’ caecal cannulation (PVTC) and ileo-rectal anastomosis (IRA) and the indigestible markers Cr 2 O 3 and TiO 2 for determination of ileal digestibility of nutrients were studied in this experiment. The results showed that the marker Cr 2 O 3 gave consistently lower ileal recovery and ileal apparent digestibility of nutrients. The average value of ileal recovery of Cr 2 O 3 measured with the IRA method was only 87%. A nearly 100% of ileal recovery of TiO 2 measured with the IRA method suggests that the use of TiO 2 as a marker may be a better choice for determination of ileal digestibility of nutrients when partial-sampling ileal digesta. The reason for the lower ileal recovery of Cr 2 O 3 may be due to the chemical analytical problems of Cr in excreta. The low recoveries of markers (TiO 2 67.8% and Cr 2 O 3 60.6%) and the high values for ileal digestibility of nutrients in the high fibre content diet based on wheat bran (WB) measured by the PVTC total collection method indicated that a quantitative collection of digesta had not been achieved and hence that it is necessary to use a marker for the PVTC method. However, the results from the present experiment showed that there is a high ileal recovery of TiO 2 (95–100%) for the low and medium fibre diets based on wheat (W), recombined wheat (flour plus bran plus middlings, WR) and wheat middlings (WM) measured by the PVTC method. The ileal digestibility of nutrients measured by PVTC (TiO 2 ) agreed well with the IRA method for all of the for measuring the ileal digestibility of nutrients in pigs.  2000 Elsevier Science B.V. All rights reserved. Keywords: Ileal digestibility; Indigestible markers; PVTC-cannulation; Ileo-rectal anastomised pigs

*Corresponding author. Corresponding address: Agricultural and Environmental Science Division, Agriculture and Food Science Centre, Newforge Lane, Belfast BT9 5PX, Northern Ireland, UK. Tel.: 1 44-1232-255-368; fax: 1 44-1232-662-007. E-mail address: [email protected] (K.J. McCracken) 1 Present address: Department of Animal Science, University of Manitoba, Winnipeg R3T 2N2, Canada. 0301-6226 / 00 / $ – see front matter  2000 Elsevier Science B.V. All rights reserved. PII: S0301-6226( 99 )00130-X

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1. Introduction Since the 1970s, many studies have been performed to estimate ileal digestibility using different methods for digesta collection. These have been reviewed by Sauer and Ozimek (1986), Fuller (1991) and Yin and McCracken (1996). The methods frequently applied for quantitative collection are reentrant cannulation, end-to-end ileorectal anastomosis (IRA) or the steered ileo-caecal valve (SICV) technique (Mroz et al., 1996). These methods are generally regarded as more accurate for measuring ileal digestibility of nutrients, since they involve the total collection of ileal digesta and it is unnecessary to use a marker, such as chromic oxide. However, the re-entrant cannulation technique poses problems in that it interrupts the transport of the normal migrating myoeletric complex which is necessary for normal digesta passage (Laplace, 1980; Low, 1982; Sauer and Ozimek, 1986; Fuller, 1991). This method is also generally associated with blockage of the cannula by coarsely ground or fibrous diets which prevents its use with many feed components. With the IRA method, normal functioning of the large intestine is obviously not maintained and this may have an influence on the water and mineral ¨ absorption and on growth (Kohler et al., 1991). However, Hennig et al. (1986, 1992) and Yin et al. (1993) reported that the loss of the function of the large intestine can be compensated by supplying the animal with large amounts of water, minerals and vitamins and Laplace et al. (1994) showed that the end-to end procedure was preferable to the end-to¨ side operation used by Kohler et al. (1991). There is ample evidence, therefore, that the IRA method can be used for measurement of ileal digestibility of dry matter, crude protein, energy and amino acids no simultaneous information on faecal digestibility is obtained. The SICV method appears to have some advantages but has not yet been widely tested and no direct comparisons with the IRA method are available since the use of the latter is prohibited in the Netherlands. Methods frequently applied for partial-sampling involving the use of a marker include the simple ileal ‘‘T’’ and post-valve ‘‘T’’ caecal cannulae (PVTC). Unlike the simple ileal ‘‘T’’ cannula method, with the PVTC technique the caecum is partially removed and replaced by the PVTC cannula, which is placed

opposite the ileo-caecal valve. Once the cannula is opened the valve protrudes into the cannula and digesta can be sampled as it leaves the ileum. Recent studies showed that PVTC has a number of advantages over the simple ‘‘T’’cannulation methods (van ¨ Leeuwen et al., 1991). Kohler et al. (1991) compared three different cannulation techniques and reported higher ileal Cr 2 O 3 recovery and digestibility values with the re-entrant techniques than with the PVTC or simple ileal ‘‘T’’ cannula. However, with all three methods Cr 2 O 3 recovery was less than 100%. The authors concluded that the results showed less variation with the PVTC cannula compared with the simple ileal ‘‘T’’ cannula. Therefore on this basis, and in view of the simplicity of handling, the PVTC cannula appears to be a good alternative to the other methods. The results from Yin et al. (1999) indicated that the post-valvular ‘‘T’’-caecum cannula method is a more precise and less labour intensive technique for ileal digestibility studies than the simple ileal ¨ ‘‘T’’ cannula. Furthermore Kohler et al. (1991) and Yin et al. (2000) suggested that the PVTC method is almost a quantitative collection method. However this aspect requires further investigation. The low recovery of markers in faeces reported by Mueller (1956), Moore (1957, 1959), Ishikawa (1966), Ishikawa and Sugimura (1973), Moughan et al. (1991), Greer (1992) and McClean (1993) is a major cause for concern. Barnicoat (1945), Moore (1957, 1959), McClean (1993) and Yin et al. (2000) suggested that this may be due to retention and / or absorption in the large intestine. Although chromic oxide is frequently used as a marker in pig digestibility studies, some authors have found that recoveries are variable, less than 100% and that this material may have carcinogenic properties (Mueller, 1956; Moore, 1957; Peddie et al., 1982; Jagger et al., 1992; Monaghan, 1996). Data from ileal digestibility studies have indicated that chromic oxide may move out of phase with digesta, ¨ particularly when fibrous diets are fed (Kohler et al., 1990). The problems encountered with Cr 2 O 3 led to its replacement by some workers with other markers, e.g., titanium dioxide and acid-insoluble ash (Jagger et al., 1992; McCarthy et al., 1974; Moughan et al., 1991; Njaa, 1961; van Leeuwen et al., 1996). Titanium dioxide has been used successfully as an indicator in digestibility studies with rats, chickens and pigs (Njaa, 1961; Peddie et al., 1982; Jagger et

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al., 1992). However, there is little information about the use of TiO 2 as a marker for determination of the ileal digestibility of nutrients in pigs. The present studies afforded the opportunity to (1) compare the use of Cr 2 O 3 and TiO 2 as indigestible markers, (2) compare the PVTC with the IRA method, (3) evaluate the PVTC method for quantitative collection of digesta, using wheat and its byproduct-based diets with a range of fibre content.

2. Materials and methods Two separate studies were conducted. In experiment 1, 12 Large White Landrace boars, approximately 26 kg, were fitted with post-valve ‘‘T’’ caecal cannulae (PVTC) according to the procedures of van Leeuwen et al. (1991). The pigs were randomly allocated, in a four-period crossover design to eight diets based on wheat (W), wheat plus middlings (WM), wheat plus bran (WB) or recombined wheat (flour plus bran plus middlings, WR) without or with xylanase addition. Each of the four main diets was mixed as a single batch and then divided for enzyme addition. The diets, which contained both TiO 2 and Cr 2 O 3 as indigestible markers, were cold-pelleted (3 mm die) and fed dry. This experiment was conducted at The Queen’s University of Belfast. After a 5-d adaptation period, faeces were collected for 7 d and ileal digesta were collected for 12 h (08:00–20:00 h) on the next two days. In experiment 2, 30 German Landrace barrows, approximately 15 kg, were subjected to an ileo-rectal anastomosis by the procedure described by Hennig et al. (1986). The experiment was conducted at Rostock. The six diets, based on W, WM and WB, of identical composition to those used in Belfast, were fed to five pigs per diet. Ileal digesta were collected for 5 d after a 7-d adaptation period. Samples of ileal digesta were pooled within period and pig for each dietary treatment and freeze–dried. TiO 2 was measured according to Leone (1973). Cr 2 O 3 was measured using the method of Saha and Gilbreath (1991) by atomic absorption spectrophotometry. Further details of the diet compositions and methods of analysis are given in a previous paper (Yin et al., 2000). Ileal recoveries of TiO 2 and Cr 2 O 3 , and ileal apparent digestibility (IAD) of dry matter (DM),

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crude protein (CP), energy and amino acids (AAs) were calculated for the two experiments. Ileal recovery of TiO 2 and Cr 2 O 3 and IAD of DM, CP, gross energy and amino acids measured with TiO 2 and Cr 2 O 3 were compared by Student’s t-test. In order to compare three methods (PVTC TiO 2 marker, PVTC Cr 2 O 3 marker and PVTC total collection), the 144 data values corresponding to 12 pigs 3 4 periods 3 3 methods were analysed using a split plot model with diets as the main plot factor and methods as the sub-plot factors. The analysis was carried out using the REML procedure of the Genstat 5 Committee (1993). Because of the differences in location, pig breed and statistical design no statistical comparison of the PVTC and IRA techniques was considered valid.

3. Results

3.1. Ileal recoveries of TiO2 and Cr2 O3 The ileal TiO 2 and Cr 2 O 3 recoveries for the experimental diets W, WR,WM and WB and the average values are given in Table 1. With both markers the recoveries measured with the PVTC method for diet WB were significantly (P , 0.001) lower than for the other diets, values for TiO 2 and Cr 2 O 3 being, respectively, 31 and 24 units less than those for diet W. The ileal recovery of TiO 2 for all of the tested diets measured with the IRA method and for diets W, WR and WM measured with the PVTC method were close to 100%, whereas recoveries of Cr 2 O 3 were 11 units lower (P , 0.001), for both the PVTC and IRA methods. As a consequence of the lower Cr 2 O 3 recovery, the average values for IAD of DM, CP, energy and AAs in the four diets measured with TiO 2 were significantly higher than with Cr 2 O 3 (Table 2).

3.2. Ileal apparent digestibility of nutrients measured with markers ( PVTC) and total collection ( PVTC and IRA) methods As illustrated in Table 3, apart from CP digestibility (P , 0.05), all diet 3 method interactions for DM, CP and energy were highly significant (P , 0.001). Apart from the numerically lower DM di-

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Table 1 Ileal recovery (%) of TiO 2 and Cr 2 O 3 Diet

W

WR

PVTC

TiO 2 Cr 2 O 3

99.9 a 84.9 a

94.9 a 87.4 a

IRA

TiO 2 Cr 2 O 3

98.8 84.3

ND ND

WM 95.5 a 82.8 a 101.1 88.7

WB

S.E.D.

P

Mean

67.8 b 60.6 b

4.92 4.69

, 0.001 , 0.001

89.7 79.0

95.2 86.8

2.70 2.39

NS NS

98.4 86.8

PVTC: Measured with PVTC total collection method. IRA: Measured with IRA method. a,b Values in the same row without a common superscript are significantly different (P , 0.05). ND: Not determined.

Table 2 Comparison of average values of ileal apparent digestibility of nutrients in diets W, WR, WM and WB measured with PVTC cannula and either TiO 2 or Cr 2 O 3

DM CP Energy Threonine Valine Cystine Methionine Isoleucine Leucine Tyrosine Phenylalanine Lysine Histidine Arginine Aspartic acid Serine Glutamic acid Proline Glycine Alanine Total AAs

TiO 2

Cr 2 O 3

S.E.D.

P

0.702 0.772 0.710 0.747 0.748 0.785 0.888 0.810 0.820 0.831 0.923 0.819 0.850 0.883 0.756 0.812 0.892 0.787 0.721 0.719 0.817

0.671 0.748 0.680 0.72 0.722 0.760 0.880 0.790 0.801 0.814 0.812 0.800 0.834 0.870 0.730 0.792 0.881 0.763 0.690 0.688 0.798

0.0095 0.0081 0.0084 0.0092 0.0074 0.0083 0.0039 0.0042 0.0052 0.0048 0.0199 0.0054 0.0055 0.0042 0.0091 0.0073 0.0036 0.0061 0.0086 0.0054 0.0061

, 0.001 , 0.001 , 0.001 , 0.001 , 0.001 , 0.001 , 0.05 , 0.001 , 0.001 , 0.001 , 0.001 , 0.001 , 0.001 , 0.001 , 0.001 , 0.001 , 0.001 , 0.001 , 0.001 , 0.001 , 0.001

gestibility for diet WM the results for PVTC using TiO 2 and for IRA were very similar, and, in line with the expected effects of fibre, values declined from diet W to diet WB. Similar to the results for the digestibility of DM, CP and energy, ileal apparent digestibilities of amino acids were also comparable between the PVTC (TiO 2 ) and IRA techniques, except for valine, phenylalanine and proline. Values for the DM, CP, gross energy and AA with PVTC using Cr 2 O 3 were lower than for the other methods. PVTC by total collection agreed well with the PVTC

(TiO 2 ) and IRA methods for W, WR and WM but the high fibre WB diet resulted in higher estimates of apparent digestibility by the total collection method.

4. Discussion

4.1. Comparison of Cr2 O3 and TiO2 as markers for determination of ileal apparent digestibility of nutrients Low faecal recoveries of Cr 2 O 3 and TiO 2 (ranging from 71 to 85%) in pigs have been often reported in the literature (Mueller, 1956; Moore, 1957, 1959; Ishikawa, 1966; Ishikawa and Sugimura, 1973; Moughan et al., 1991; Greer, 1992; McClean, 1993; Yin et al., 2000). The present results show that the ileal recoveries of TiO 2 and Cr 2 O 3 are much higher than those at the faecal level. For example, the ileal recoveries of TiO 2 and Cr 2 O 3, measured with the IRA method, were 12.6 and 5.3 percentage units higher, respectively, than the overall (faecal) recoveries of TiO 2 and Cr 2 O 3 observed by Yin et al. (2000). The nearly 100% ileal recovery of TiO 2 for the low fibre diets W, WR and the medium fibre diet WM obtained with the PVTC and IRA pigs indicates that the disappearance of TiO 2 observed by Greer (1992); McClean (1993) and Yin et al. (2000) did not occur at the ileal level. This suggests that the lower recovery of marker in faeces is due to marker retention, or absorption or both in the large intestine. The reasons for retention and absorption in the large intestine of pigs may be a combination of the long retention time (36 h) of digesta (Kidder and Manners, 1978), the complex and capacious structure of

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Table 3 Comparison of ileal apparent digestibility of DM, CP, gross energy and selected AAs measured either with markers (TiO 2 or Cr 2 O 3 ) using PVTC-cannula or by total collection (PVTC or IRA)

DM

CP

Gross energy

Threonine

Valine

Isoleucine

Leucine

Phenylalanine

Lysine

Histidine

Diet

TiO 2

Cr 2 O 3

PVTC

W WR WM WB

0.773 0.766 0.673 0.594

0.741 0.752 0.632 0.556

0.772 0.783 0.688 0.732

W WR WM WB

0.807 0.804 0.757 0.720

0.779 0.790 0.727 0.693

0.807 0.808 0.769 0.808

W WR WM WB

0.787 0.771 0.683 0.596

0.757 0.759 0.644 0.558

0.777 0.792 0.698 0.724

W WR WM WB

0.77 0.767 0.743 0.708

0.737 0.753 0.71 0.68

0.768 0.785 0.756 0.794

W WR WM WB

0.766 0.777 0.749 0.701

0.733 0.763 0.717 0.673

0.764 0.793 0.761 0.797

W WR WM WB

0.831 0.837 0.803 0.768

0.808 0.826 0.778 0.746

0.83 0.848 0.813 0.841

W WR WM WB

0.849 0.841 0.807 0.78

0.827 0.832 0.783 0.76

0.849 0.853 0.817 0.85

W WR WM WB

0.935 0.935 0.918 0.904

0.83 0.846 0.797 0.777

0.85 0.865 0.828 0.861

W WR WM WB

0.843 0.832 0.82 0.786

0.811 0.822 0.797 0.767

0.834 0.845 0.829 0.855

W WR WM WB

0.865 0.863 0.847 0.825

0.845 0.855 0.827 0.808

0.864 0.872 0.854 0.882

S.E.D.

0.0155

0.0311

0.0142

0.0128

0.0123

0.0093

0.0121

0.0068

0.0093

0.0075

Diet 3 method

P , 0.001

P , 0.05

P , 0.001

P , 0.001

P , 0.001

P , 0.001

P , 0.001

P , 0.001

P , 0.001

P , 0.001

IRAa 0.763 ND 0.624 0.597 0.811 ND 0.747 0.745 0.784 ND 0.656 0.601 0.764 ND 0.732 0.702 0.805 ND 0.769 0.756 0.843 ND 0.815 0.8 0.851 ND 0.82 0.807 0.876 ND 0.851 0.834 0.844 ND 0.833 0.807 0.869 ND 0.865 0.848

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138 Table 3. Continued

Tyrosine

Arginine

Aspartic acid

Serine

Glutamic acids

Proline

Glycine

Alanine

Total AAs

Diet

TiO 2

Cr 2 O 3

PVTC

W WR WM WB

0.849 0.853 0.833 0.789

0.828 0.844 0.813 0.771

0.849 0.863 0.841 0.856

W WR WM WB

0.887 0.882 0.886 0.876

0.871 0.875 0.871 0.865

0.887 0.89 0.89 0.917

W WR WM WB

0.777 0.779 0.751 0.716

0.746 0.765 0.72 0.689

0.776 0.796 0.764 0.807

W WR WM WB

0.834 0.837 0.8 0.779

0.81 0.827 0.775 0.757

0.833 0.849 0.81 0.85

W WR WM WB

0.909 0.908 0.879 0.873

0.897 0.902 0.863 0.861

0.908 0.915 0.885 0.913

W WR WM WB

0.768 0.881 0.763 0.709

0.731 0.874 0.733 0.683

0.83 0.732 0.763 0.77

W WR WM WB

0.749 0.742 0.717 0.675

0.712 0.726 0.679 0.644

0.745 0.761 0.73 0.782

W WR WM WB

0.737 0.75 0.719 0.666

0.7 0.734 0.683 0.635

0.735 0.769 0.732 0.773

W WR WM WB

0.833 0.851 0.808 0.783

0.81 0.846 0.784 0.764

0.832 0.856 0.817 0.854

S.E.D.

0.0082

0.0062

0.012

0.009

0.0066

0.0247

0.0157

0.0144

0.0091

Diet 3 method

P , 0.001

P , 0.001

P , 0.001

P , 0.001

P , 0.001

P , 0.001

P , 0.001

P , 0.001

P , 0.001

IRAa 0.851 ND 0.858 0.834 0.908 ND 0.901 0.895 0.799 ND 0.769 0.75 0.836 ND 0.801 0.786 0.912 ND 0.873 0.879 0.891 ND 0.858 0.854 0.784 ND 0.74 0.732 0.77 ND 0.741 0.714 0.856 ND 0.825 0.814

a

IRA not included in statistical analysis, since the experimental design was different from the PVTC experiment. ND: Not determined.

the large intestine (Barnicoat, 1945; Moore, 1957; 1959) and the high specific gravity of TiO 2 and Cr 2 O 3 (Lide and Frederikse, 1995). In common with the studies of McCarthy et al. (1974), Moughan et al. (1991), Jagger et al. (1992)

and Monaghan (1996) the present results highlight the problems of use of Cr 2 O 3 as a marker. Mean values of the ileal recovery of Cr 2 O 3 measured with the IRA method was only 87% in this study. Consequently the ileal digestibility of DM, CP,

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energy and total AA measured with Cr 2 O 3 were respectively 4.6, 3.2, 4.4 and 2.4% lower than those measured with TiO 2 (Table 2). Jagger et al. (1992) found that the ileal digestibilities of N and AAs measured with Cr 2 O 3 were significantly lower (N, 6.7% and the average value of 11 AAs, 6.1%) than those measured with TiO 2 , when both markers were added to a barley and wheat based diet fed to growing and finishing pigs. Furthermore, the results of Jagger et al. (1992) and of this experiment show that the standard errors associated with apparent ileal digestibility values calculated using each marker were lower with TiO 2 than with Cr 2 O 3. This is somewhat surprising in that the level of incorporation of Cr 2 O 3 was higher than for TiO 2. At these low levels it would be possible for problems to arise due to lack of homogeneity of mixing. However, the low standard errors obtained with TiO 2 would suggest that diet mixing was not a problem. The primary reason for the low recovery and variable results from Cr 2 O 3 may be related to analytical problems arising mainly from interference by other minerals present in the sample (Williams et al., 1962; Saha and Gilbreath, 1991). For example, Williams et al. (1962) found a 12% decrease in Cr recovery when phosphate (PO 4 ) was added to the solution of Cr. Saha and Gilbreath (1991) also showed significant effects on recovery when varying the concentration of Ca, P or Mg in diets and faeces of pigs. These minerals occur in high concentrations in the digesta or faeces of pigs. This possibility is presently under investigation in our laboratory. In an initial study, three levels of Cr 2 O 3 corresponding to 5, 10, 20 ppm were added to the faeces of pigs which had not received Cr 2 O 3 in the diet. The recoveries were 88.0, 87.7, 83.3%, respectively. This is similar to the mean recovery values reported by Saha and Gilbreath (1991) and the mean ileal recovery of Cr 2 O 3 measured in this study. In addition, although Cr 2 O 3 is insoluble in water, it is slightly soluble in acids and alkalis (Merck Index, 1989) and therefore it might be soluble to a certain extent in the acid or alkaline digestive juices of the gastrointestinal tract of pigs (Moore, 1959) or the acid solution used during Cr analysis. Saha and Gilbreath (1991) suggested that the soluble Cr might be lost due to the formation of volatile Cr compounds at the sample digestion stage. Compared with

139

Cr 2 O 3, TiO 2 is insoluble in water, HCl, HNO 3 or dilute H 2 SO 4 (Merck Index, 1989) and analysis of TiO 2 is a relatively simple and straightforward procedure. High recoveries (95–100%) in samples of feeds and excreta of poultry and pigs have been reported (Njaa, 1961; Leone, 1973; Peddie et al., 1982; Jagger et al., 1992).

4.2. Comparison of methods for measurement of ileal apparent digestibility of nutrients The excellent marker recoveries with TiO 2 for the W, WR and WM with the PVTC method and for the W, WM and WB diets with the IRA method indicate that, under these conditions, digesta collection was fully representative of the material reaching the terminal ileum. This would be expected with the IRA method where a complete 5-d collection was made but it is noteworthy that similar results occurred with the much shorter period of collection (24 h) using the PVTC technique. However, the result for the highfibre diet WB using the PVTC technique demonstrates that quantitative collection of digesta was not achieved. This result therefore supports the reports of ¨ Kohler et al. (1991) and van Leeuwen et al. (1991) of variable recovery with the PVTC technique dependant on diet composition and confirms the necessity of using an appropriate indigestible marker. Although a direct statistical comparison of the PVTC and IRA techniques is not valid due to the separate locations in which the techniques were used and the different sources of pigs, the results given in Table 3 for PVTC (TiO 2 ) and IRA show close numerical agreement. This, taken with the excellent marker recoveries (Table 1), suggests that both methods were giving reliable estimates of ileal digestibility. Furthermore, the good agreement between IRA and PVTC (TiO 2 ) for diet WB, where PVTC collection was not quantitative, suggests that the digesta recovered was similar in composition to that by-passing the cannula. As discussed in the Introduction, the main advantage of the end-to-end IRA technique is that it is a quantitative method for collecting ileal digesta and, therefore, it is not necessary to use any marker for calculating digestibility. However, compared with the PVTC method, the main disadvantages are: (1) relatively complex surgical procedures and post-

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operative animal care. (2) Longer time for recovery from the surgery. (3) Need for greater care to minimise skin irritation and discomfort due to the outpouring of digesta around the hind legs. (4) The need for additional water, minerals and vitamins to offset the loss of the large intestine. Compared with the IRA method, the surgery for the PVTC cannulation is much easier to perform and less severe on the animals than the IRA procedure and the PVTC cannulation technique causes less discomfort to the animal. Furthermore this method permits simultaneous measurement of ileal and overall digestibility in contrast to the IRA method. Taking all of these aspects into account it is concluded that the PVTC method is a better method for measuring ileal digestibility in most situations. It would, however, be of considerable interest to make a direct comparison of the PVTC and SICV techniques.

5. Conclusions The results highlighted problems with poor recovery of Cr 2 O 3 marker resulting in low estimates of ileal digestibility, while the TiO 2 marker appears to be satisfactory as shown by good agreement with the IRA (total collection) method. PVTC total collection proved is satisfactory for measurement of ileal digestibility with low- or medium-fibre diets but not with a high-fibre diet. Considering its simplicity, acceptability on animal welfare grounds and the good agreement with in measurements of digestibility made with the IRA technique, the PVTC technique, in combination with TiO 2 as a marker, is considered to be a good method for determination of ileal digestibility of nutrients for pigs.

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