Validation of the cannulated pig model for determining intestinal nutrient disappearance in cattle

Validation of the cannulated pig model for determining intestinal nutrient disappearance in cattle D. M. Loveday 1, P. A. Thacker 1, D. G. Wilson 2, and J. J. McKinnon 1,3 1 Department of Animal and Poultry Science, University of Saskatchewan,51 Campus Drive, Saskatoon, Saskatchewan, Canada S7N 5A8; 2 Large Animal Clinical Sciences, University of Saskatchewan, 52 Campus Drive, Saskatoon, Saskatchewan, Canada S7N 5B4. Received 20 August 2004, accepted 5 January 2005. Loveday, D. M., Thacker, P. A., Wilson, D. G. and McKinnon, J. J. 2005. Validation of the cannulated pig model for determining intestinal nutrient disappearance in cattle. Can. J. Anim. Sci. 85: 85 91. The mobile nylon bag technique was used to determine the potential of cannulated pigs to model intestinal dry matter (DM) and crude protein (CP) digestibility of ruminal undegradable residues (RUDR) of various feed samples in cattle. A total of 11 feeds (six protein supplements and five forages) varying in rumen degradability were utilized: canola meal (regular vs. heated); soybean meal (regular vs. heated); distillers grains (regular vs. heated); alfalfa hay (regular vs. dehydrated alfalfa pellets); barley silage (regular vs. heated); and barley straw. Ruminal undegradable residues of each feedstuff were placed into eight polyester bags and inserted into the duodenum of two cannulated Hereford steers (644 ± 14 kg). Another eight bags for each RUDR sample were randomly allocated to six crossbred gilts (Camborough 15 line female Canabred sire; 50 ± 1.2 kg body weight) and inserted into the pigs duodenum via duodenal cannulas. Bags were recovered in the feces from both the cattle and pigs. Regression analysis was used to relate intestinal DM and CP digestibility obtained in pigs with those obtained in steers. Intercepts not different from zero were forced through the zero intercept to obtain a measure of bias and loss of precision resulting from forcing the zero intercept. The non-zero regression equations relating steer estimates to those obtained from pigs were 3.17 + 0.95 X [r 2 = 0.98, residual standard deviation (RSD) = 3.84] and 0.35 + 0.96 X (r 2 = 0.98, RSD = 6.16) for DM and CP disappearance, respectively. Forcing the non-zero intercept resulted in pigs over predicting intestinal DM disappearance in cattle by 10.6% with a RSD of 4.30. Using the pig model, intestinal CP disappearance of cattle was over predicted by 3.1% with a RSD of 5.85. It was concluded that pigs can be used to model intestinal DM and CP disappearance of ruminal undegraded feed residues in cattle. Key words: Cattle, pigs, mobile nylon bag technique, intestinal nutrient availability Loveday, D. M., Thacker, P. A., Wilson, D. G. et McKinnon, J. J. 2005. Validation du modèle du porc canulé pour l étude de la disparition des éléments nutritifs dans l intestin des bovins. Can. J. Anim. Sci. 85: 85 91. Les auteurs ont recouru à la technique du sac en nylon mobile pour savoir si l on pourrait se servir de porcs canulés pour modéliser la digestibilité de la matière sèche (MS) et des protéines brutes (PB) présentes dans les résidus non dégradables dans le rumen (RNDR) de divers aliments dans l intestin des bovins. En tout, ils ont testé 11 aliments (6 suppléments protéiques et 5 types de fourrage) se dégradant de manière variable dans le rumen : du tourteau de canola (ordinaire et traité thermiquement), du tourteau de soja (ordinaire et traité thermiquement), des céréales de distillerie (ordinaires et traitées thermiquement), du foin de luzerne (ordinaire et déshydraté), de l ensilage d orge (ordinaire et traité thermiquement) et de la paille d orge. Les RNDR de chaque aliment ont été déposés dans 8 sacs en polyester puis glissés dans le duodénum de deux bouvillons Hereford (644 ± 14 kg) canulés. Huit autres sacs par échantillon de RNDR ont été répartis au hasard entre 6 truies hybrides nullipares (femelle Camborough de lignée 15 géniteur Canabred; 50 ± 1,2 kg de poids corporel) puis insérés dans le duodénum de l animal par la canule qu il portait. Les sacs ont été récupérés dans les fèces. Les auteurs ont recouru à l analyse de régression pour relier la digestibilité de la MS et des PB dans l intestin des porcs à celle mesurée chez les bouvillons. Les points d intersection non nuls ont été contraints à passer par le point zéro, ce qui a permis d établir le biais et le degré d imprécision résultants. Les valeurs non nulles des équations de régression reliant les valeurs estimatives des bouvillons aux valeurs observées chez les porcs étaient de 3,17 + 0,95 X [r 2 = 0,98, écart-type résiduel (ETR) = 3,84] et de 0,35 + 0,96 X (r 2 = 0,98; ETR = 6,16) pour la disparition de la MS et des PB, respectivement. Contraindre le passage par le point zéro a pour conséquence de surestimer la disparition prévue de la MS dans l intestin des bovins de 10,6 %, avec un ETR de 4,30. Le modèle porcin surestime la disparition prévue des PB dans l intestin des bovins de 3,1 %, avec un ETR de 5,85. On en conclut qu on peut utiliser les porcs pour modéliser la disparition de la MS et des PB des résidus d aliments non dégradables dans le rumen chez les ruminants. Mots clés: Bovins, porcs, technique du sac en nylon mobile, disponibilité des éléments nutritifs dans l intestin Modern ration formulation programs for beef and dairy cattle distinguish between ruminal degradable and undegradable protein [National Research Council (NRC) 1996, 2001]. Estimates of the intestinal digestibility of ruminal 3 To whom correspondence should be addressed (e-mail mckinnon@sask.usask.ca). 85 undegradable protein for individual feeds are used to improve the accuracy of measuring the contribution that the ruminal undegradable protein fraction makes to metabolis- Abbreviations: CP, crude protein; DM, dry matter; RUDR, rumen undegradable residues; RSD, residual standard deviation

86 CANADIAN JOURNAL OF ANIMAL SCIENCE able protein, and therefore the prediction of animal responses to the addition of a feed into a ration (NRC 2001). Research using surgically prepared steers is expensive and labor intensive, especially when both rumen and duodenal cannulas are used. During the past few years, there has been interest within the research community to use other animals to model intestinal protein digestibility for cattle (Chaudhry and Webster 1993; Titgemeyer et al. 1990; Griffin et al. 1993; Mustafa et al. 2000). Non-ruminant animal models have been developed to decrease labor and cost while still providing the physiological environment of the gastrointestinal tract (Stern et al. 1997). Smaller animals are easier to handle and require less expensive handling systems. At the University of Saskatchewan, pigs have been successfully used to model intestinal protein digestibility of steers (Mustafa et al. 2000). Regression equations indicated that cannulated pigs accounted for 96 and 97% of the variation in steer intestinal and total tract CP digestibility of unheated and heated canola meal samples. However, the work of Mustafa et al. (2000) was limited in the number and types of feedstuffs tested. More research is required to validate the technique using a variety of protein and forage sources typically fed to cattle. Therefore, the objective of this study was to use the in situ ruminal nylon bag technique in combination with the mobile nylon bag technique to determine if pigs could serve as a model for cattle to determine intestinal DM and CP disappearance of RUDR from a variety of feed sources. MATERIALS AND METHODS Animal Models Steers Two Hereford steers, weighing 664 ± 14 kg and previously fitted with flexible rumen cannulas (Bar Diamond Inc., Parma, ID, USA), were surgically inserted with simple-t cannulas (Central Hydraulic Manufacturing Co. Ltd., Edmonton, AB) in their proximal duodenum. The steers were housed and fed individually in 13 m 2 concrete floored pens, equipped with individual water bowls and rubber mats, located in the Livestock Research Barn at the University of Saskatchewan. The steers were fed twice daily with a 50:50 barley silage and barley concentrate diet (DM basis), with equal amounts provided at each feeding (Table 1). The diet was fed at 1.5% of body weight (DM basis) at 0800 and 1600. Lighting was continuous and the barn temperature ranged from 15 to 25 C. Pigs Six crossbred gilts (Camborough 15 line female Canabred sire), initially weighing 50 ± 1.2 kg were fitted with simple T-cannulas (24 mm diameter 65 mm length; Johnston Industrial Plastics, Edmonton, AB) in the proximal duodenum following the surgical procedures described by Sauer et al. (1983). The gilts were housed in individual stainless steel metabolism crates (135 65 cm) with a grated floor. During the trial, the pigs were given 1.5 kg d 1 of standard grower pellets (Table 1). As with the steers, the pigs were fed twice daily at 0900 and 1600 while water was provided ad libitum. Table 1. Ingredient and chemical composition of the rations fed to the pigs and cattle (DM basis) Diet Feed ingredient (% DM) Cattle Pigs Barley silage 50.00 Concentrate mix Barley grain 44.06 78.23 Soybean meal 16.49 Canola meal 3.63 Tallow 0.84 1.83 Limestone 0.79 0.87 Dicalcium phosphate 1.57 Salt z 0.28 0.50 Rumensin y 0.20 Vitamin premix xw 0.20 0.50 Diet chemical composition v Dry matter (%) 51.17 89.00 Crude protein (%) 11.87 18.47 Ash (%) ND 5.62 Ether extract (%) ND 3.99 Acid detergent fiber (%) ND 7.64 Calcium (%) 0.52 0.85 Phosphorus (%) 0.40 0.79 Ca:P 1.30 1.08 z Trace mineralized salt: 120 ppm selenium, 36.5% sodium, 91.5% salt, 12 000 ppm zinc, 10 000 ppm manganese, 4000 ppm copper, 200 ppm iodine, and 60 ppm cobalt. y Rumensin (20% active) mixed with barley grain. x Cattle vitamin premix: 416 650 IU kg 1 vitamin A and 83 333 IU kg 1 vitamin D. w Pig vitamin mineral premix supplied per kilogram of diet: 4125 IU vitamin A, 275 IU vitamin D 3, 13.5 IU vitamin E, 2 mg vitamin K, 0.5 mg thiamin, 4 mg riboflavin, 22 mg niacin, 16.5 mg pantothenic acid, 14 mg vitamin B 12, 250 mg choline chloride, 0.12 mg biotin, 40 mg iron, 21.3 mg manganese, 76.5 mg zinc, and 0.05 mg selenium. v ND = not determined. Lighting for the pigs was continuous and the barn temperature was maintained between 20 and 25 C. All experimental animals were cared for according to the guidelines of the Canadian Council on Animal Care (1993). Feeds Tested Ruminal (cattle) and intestinal (cattle and pigs) disappearance of DM and CP were determined in six protein supplements and five forages. Feed samples were chosen to provide a range of ruminal degradable and undegradable residues. Heating was carried out to increase the range of ruminal degradability of the feeds tested. The feeds tested included canola meal (regular vs. heated); soybean meal (regular vs. heated); distillers grains (regular vs. heated); alfalfa hay (regular vs. dehydrated alfalfa pellets); barley silage (regular vs. heated) and barley straw. The distillers grains were obtained as wet wheat-based distillers grains (ca. 35% DM) from Pound-Maker Agventures Ltd., Lanigan, SK. The alfalfa hay and dehydrated alfalfa pellets were provided by Tisdale Alfalfa Dehy Ltd., Tisdale, SK, and were produced from the same batch of alfalfa. Barley silage and straw were obtained from the University of Saskatchewan farm, while all other feeds were derived from commercial feed sources.

LOVEDAY ET AL. MOBILE NYLON BAG TECHNIQUE FOR CATTLE 87 Heating of Feed Samples Prior to rumen incubation, representative samples of the test feeds (except barley straw due to its low CP and relatively high ruminal undegradable content) were heated at 145 ± 2 C in a drying oven. Samples were spread on trays to a 1 cm depth with the temperature of the sample monitored with a temperature probe. Samples were heated for 1 h from the time it took the sample to initially reach 145 C. High moisture feeds (wet distillers grains and barley silage) were dried at 55 C for 48 h before being heated to 145 C. Unheated feed samples were ground through a 2- mm (protein supplements) or 3-mm (forages) screen prior to the rumen incubations. Unheated high-moisture feeds (i.e. wet distillers grains and barley silage) were dried at 55 C for 48 h prior to grinding. Heated samples were ground using the same protocol as for the unheated samples. Rumen Incubations Seven grams of protein supplement (Mustafa et al. 2000) or 5 g of forage (Mustafa et al. 1996) were weighed into large nylon bags, measuring 8 19 cm with a pore size of 40 µm (Sefar Canada Inc., Mississauga, ON) and tied with nylon string. The sample size to surface area ratio was 23.0 and 16.4 mg cm 2 for the protein and forage samples, respectively. The number of bags incubated for each feed depended on the feed s estimated degradability. A sufficiently large sample was incubated in order to produce at least 150 g of RUDR. The nylon bags were placed inside polyester mesh bags (38.1 45.7 cm) and incubated in the ventral sac of the rumen for 12 h. Following removal from the rumen, the bags were washed, 10 at a time, in 1000 ml of cold tap water for 2 min. The washing procedure was repeated six times and the bags were then dried at 55 C for 48 h (McKinnon et al. 1991). Rumen residues for each feed were pooled and ground in a coffee grinder. The rumen residues of each feedstuff were subsequently used for intestinal incubations in both steers and pigs in order to determine the intestinal disappearance of DM and CP of the RUDR from each feed source. Intestinal Incubations for Steers Small polyester bags (2.5 4.0 cm; 48 µm pore size; Sefar Canada Inc. Mississauga, ON) were filled with either 0.52 g of protein supplement residue or 0.15 g of forage residue and heat-sealed. Eight bags were prepared for each feed. Intestinal bags were grouped into batches of 12 and placed in a 1000-mL beaker containing 500 ml of a pepsin solution made up of deionised water, 0.01 N HCl, and 1 g of purified activated pepsin powder (3000 3500 IU; Fischer-Scientific Ltd., Nepean, ON). The solution had a ph of 2.0. The beaker was placed in a 37 C water bath for 4 h and agitated at a rate of 65 oscillations min 1. After the bags were removed from the beaker, they were rinsed with deionised water and dried at room temperature for 2 h. The bags were then frozen at 5 C until required for insertion into the intestine of the designated experimental animal. Polyester bags containing ruminal-undigested residues were inserted through the cannulas into the proximal duodenum of each steer at a rate of one bag per hour. Four empty bags were also inserted into the duodenum of each steer. These bags were used as blanks to correct for any microbial or feed protein contamination in or on the bag (Moshtaghi Nia and Ingalls 1992). Polyester bags were recovered in the feces and washed for 10 s under a gentle stream of cold tap water five times, and then dried at 55 C for 48 h. One person washed all the bags to eliminate human variation in washing. Bags not recovered within 72 h as well as any broken bags were not used for this trial. Instead, another bag containing the same feed residue was put into the same steer as a replacement. Intestinal Incubations for Pigs As with the intestinal incubation procedure for the steers, 0.52 g of protein supplement or 0.15 g of forage was weighed into the small polyester bags (2.5 4.0 cm; 48 µm pore size; Sefar Canada Inc. Mississauga, ON) and heatsealed. These polyester bags were incubated in a pepsin-hcl solution prepared the same way as for the steer incubations. Eight bags were prepared for each feed type. However, since there were six pigs instead of two steers, the bags were randomly assigned to each pig. This meant that each pig was inserted with at least one bag of each feed type, while two of the pigs had two bags with the same feedstuff. Intestinal bags were put into the duodenum of pigs during the morning and afternoon feedings. Two polyester bags were placed into the duodenal cannulas while the pigs were eating, and then 15 min later, another two bags were inserted (Thacker and Qiao 2001). Bags that were either broken or not recovered within 72 h were not used for the trial and another bag was produced to replace it. Repeat bags were put into the same pig used for the original bag that was either broken or missing. Chemical Analysis All feed samples, ruminal undegradable residues, and intestinal undegradable residues were analyzed for moisture (method No. 930.15) and Kjeldahl N (method No. 984.13) according to the procedures of the Association of Official Analytical Chemists (1990). From the chemical analysis, DM and CP disappearance from the rumen and intestine were determined. For the swine feeds, analyses were conducted for acid detergent fibre (AOAC method 973.18), ash (AOAC method 942.05) and ether extract (AOAC method 920.39). The calcium and phosphorus contents were determined using the nitric-perchloric acid digestion method of Zasoski and Burau (1977) with calcium determined on a Perkin-Elmer Model 4000 Atomic Absorption Spectrophotometer (AOAC method 968.08) and total phosphorus determined colorimetrically (Pharmacia LKB Ultrospec III) using a molybdovanadate reagent (AOAC method 965.17). Statistical Analysis Dry matter and CP disappearance data of cattle were analyzed as a randomized complete block design, whereas the data from the pigs were analyzed as a randomized complete block design with unequal sub-samples using the Mixed Model procedure of SAS Institute Inc. (1999). For rumen disappearance, steer crossed with feed type was specified as

88 CANADIAN JOURNAL OF ANIMAL SCIENCE the random term using the random statement. Individual animals nested within feed type and species was the term specified in the random statement for the models determining the effects of species and feed type on intestinal disappearance. The repeated statement was utilized to indicate that variances were heterogeneous over both feed type and species. Mean comparisons were conducted to compare cattle and pig intestinal DM and CP disappearance and to compare feedstuffs. Where appropriate, treatment means were separated at P < 0.05 using estimate statements by the Mixed Model of SAS software (Steel et al. 1997). Regression analysis followed the method described by Mustafa et al. (2000). Using the Regression Procedure of SAS Institute, Inc. (1999), linear regression was used to relate intestinal CP and DM disappearance of pigs to that of steers. The non-zero intercept equation included an intercept and indicated the variation (adjusted r 2 ) and precision (residual standard deviation) of pig nutrient disappearance on steer nutrient disappearance. If the intercept of the nonzero regression line was not significantly different (P > 0.05) from zero, the regression coefficient was forced through the origin as an indicator of bias and loss of precision that resulted from forcing the zero intercept (Mustafa et al. 2000). The bias calculation followed that described by Thacker and Qiao (2001). The degree to which pigs either under or over estimated nutrient disappearance for cattle was calculated as the percentage deviation of the slope from 1.0 when pigs were regressed on steer nutrient disappearance using a zero intercept model. RESULTS AND DISCUSSION For the protein supplements, DM disappearance from the rumen ranged from 27.8% for heated distillers grains to 64.3% for canola meal (Table 2). Crude protein disappearance ranged from 18.1% for heated soybean meal to 68.7% for canola meal. For both DM and CP, ruminal bypass was significantly enhanced (P < 0.05) due to heating for all three-protein sources tested. For the forages, DM disappearance from the rumen ranged from 18.7% for barley straw to 58.0% for dehydrated alfalfa pellets (Table 3). CP disappearance ranged from 38.8% for barley straw to 79.5% for barley silage. For both alfalfa and barley silage, heating increased (P < 0.05) ruminal bypass of DM and CP. For the protein supplements, significant differences were observed between cattle and pigs in intestinal DM disappearance for both heated (P = 0.004) and unheated (P = 0.031) canola meal (Table 2). For the remaining four protein supplements, there were no significant differences (P > 0.05) in intestinal DM disappearance when determined with cattle or pigs. Across all six-protein supplements, intestinal DM disappearance was 5.5 percentage units higher (47.1 vs. 41.6%) in pigs than in cattle (P = 0.003). Significant differences were also observed between cattle and pigs in intestinal CP disappearance for heated (P = 0.031) and unheated (P = 0.001) canola meal (Table 2). For the remaining four protein supplements, there were no significant differences (P > 0.05) in intestinal CP disappearance when determined with cattle or pigs. Across all six-protein supplements, intestinal CP disappearance was 3.3 percentage units higher (P = 0.008) in pigs than in cattle (74.8 vs. 71.5%). For the forage samples (Table 3), intestinal DM disappearance was significantly different between cattle and pigs for heated barley silage (P = 0.001) while for the four remaining feeds, intestinal DM disappearance did not differ between cattle and pigs (P > 0.05). Across all five forages, intestinal DM disappearance was 3.4 percentage units higher for pigs than for cattle (P = 0.046). There were no significant differences between cattle and pigs in intestinal CP disappearance for any of the forages (Table 3). Across all five forages, intestinal CP disappearance was only 1.1 percentage units higher for cattle than for pigs (14.3 vs. 13.2%; P = 0.753). These results indicate that the intestine of swine tends to digest more of the ruminal undegraded DM and CP than does the intestine of cattle. One possible reason for this species difference is transit time in the post-gastric intestinal tract. We have observed that the mobile nylon bags take approximately 24 h to pass out of the intestinal tract in the pig, while in cattle; the bags take approximately 12 h to pass. Therefore, in pigs, feedstuffs are exposed to the digestive process longer, possibly resulting in the higher intestinal disappearance seen in this study. It is of interest to note that with the forage samples, negative intestinal DM and CP disappearance values were obtained (Table 3). Such a finding was particularly evident with barley straw where the intestinal CP disappearance values were 48.5 and 49.1% in cattle and pigs, respectively. This apparent anomaly can be attributed to two factors. First, one would expect that the intestinal digestibility of most forages, particularly after a 12 h ruminal incubation, would be minimal. This is based on the fact that one would expect that most of the soluble and readily available carbohydrates and proteins would be fermented in the rumen during the 12-h incubation, leaving behind the relatively indigestible complex cell wall carbohydrates that are crosslinked to lignin and their associated proteins. Second, it is been reported that microbial contamination of feed residues occurs in feeds that have been incubated in the rumen (Nocek 1988) as well as during passage through the large intestine. Vanhatalo and Varvikko (1995) reported that with protein-rich feeds, such as rapeseed meal, contamination by non-feed N is small and does not affect intestinal CP disappearance estimates. However, with fibrous feeds low in N content, such as straw, contamination by non-feed N seriously affects intestinal CP disappearance values obtained by the mobile bag technique (Vanhatalo and Varvikko 1995). Intestinal CP disappearance of RUDR high in fiber can be underestimated when bags are collected from the feces because of non-feed N contamination (Vanhatalo and Ketoja 1995). In the current experiment, microbial contamination of feed residues, particularly the barley straw residue, would result in an underestimation of intestinal CP disappearance resulting in negative disappearance results. Regression analysis was used to determine how well pigs serve as a model for determining intestinal nutrient disappearance in cattle. Both linear and non-linear regressions were used to determine the relationship between intestinal

LOVEDAY ET AL. MOBILE NYLON BAG TECHNIQUE FOR CATTLE 89 Table 2. Dry matter and crude protein disappearance (% of DM) of various protein sources in cattle and pigs Dry matter Crude protein Rumen Intestine z Rumen Intestine y Feed Cattle Pigs SED x P value w Cattle Cattle Pigs SED x P value v Unheated canola meal 64.3a 24.3c 35.2c 4.83 0.031 68.7a 51.2e 64.5c 3.19 0.001 Heated canola meal 36.9d 38.4b 50.1b 3.83 0.004 23.9d 62.8d 70.9b 3.61 0.031 Unheated soybean meal 62.0b 70.8a 74.6a 3.99 0.345 47.0b 84.6a 86.7a 2.54 0.402 Heated soybean meal 43.6c 72.5a 76.9a 4.52 0.339 18.1e 86.2a 86.6a 2.59 0.883 Unheated distillers grains 33.6e 20.8c 20.5d 4.21 0.943 41.3c 73.8b 71.1b 2.60 0.294 Heated distillers grains 27.8f 22.9c 25.5d 3.71 0.477 23.3d 70.4c 68.9b 2.56 0.553 SED xu 0.91 4.81 3.45 1.04 2.96 2.64 Average of cattle vs. pigs 41.6 47.1 1.72 0.003 71.5 74.8 1.17 0.008 z Calculated as the percentage of rumen undegradable DM that went into the intestine. y Calculated as the percentage of rumen undegradable CP that went into the intestine. x Standard error of the difference between means. w Comparison of intestinal DM disappearance of feeds in cattle vs. pigs. v Comparison of intestinal CP disappearance of feeds in cattle vs. pigs. u Average of the standard error of the difference between means for all combinations of treatments comparisons. a e Means in each column with different letters are different (P < 0.05). Table 3. Dry matter and crude protein disappearance (% of DM) of various forages in cattle and pigs Dry matter Crude protein Rumen Intestine z Rumen Intestine y Feed Cattle Pigs SED x P value w Cattle Cattle Pigs SED x P value v Alfalfa hay 56.6b 12.4b 15.8b 3.83 0.388 75.7b 44.6b 45.7b 5.05 0.822 Dehydrated alfalfa pellets 58.0a 24.0a 27.8a 4.86 0.441 58.8d 68.2a 66.6a 5.42 0.769 Unheated barley silage 49.9c 3.5c 0.1c 4.28 0.428 79.5a 9.8c 0.1c 10.37 0.359 Heated barley silage 41.8d 1.5c 5.3c 1.86 0.001 63.6c 2.7c 2.7c 3.25 0.107 Barley straw 18.7e 11.0d 11.5d 2.57 0.866 38.8e 48.5d 49.1d 10.29 0.955 SED xu 0.53 2.87 4.16 0.40 7.18 7.10 Average of cattle vs. pigs 4.1 7.5 1.63 0.046 14.3 13.2 3.34 0.753 z Calculated as the percentage of rumen undegradable DM that went into the intestine. y Calculated as the percentage of rumen undegradable CP that went into the intestine. x Standard error of the difference between means. w Comparison of intestinal DM disappearance of feeds in cattle vs. pigs. v Comparison of intestinal CP disappearance of feeds in cattle vs. pigs. u Average of the standard error of the difference between means for all combinations of treatments comparisons. a e Means in each column with different letters are different (P < 0.05). DM and CP disappearance of pigs with those of steers. However, even though nonlinear regression equations were significant, it was concluded that linear regression best represented the relationship between pigs and cattle because nonlinear regressions did not improve the adjusted coefficient of determination by more than 5% (R. J. Baker, personal communication). Regression equations relating intestinal DM and CP disappearance in pigs with those of steers are given in Table 4. Intestinal DM disappearance in pigs explained 95 to 98% (r 2 ) (P < 0.05) of the variation in intestinal DM disappearance in steers. Residual standard deviations for these regression equations ranged from 2.66 to 5.24%. When forced through the zero intercept, it was found that for every 1% increase in pig DM disappearance, there was a 0.83 to 0.90% increase for cattle. Therefore, when using pigs as a model for measuring DM disappearance in cattle, digestibility was over predicted by 10.1 to 17.0% depending on feed type. Intestinal CP disappearance in pigs explained 77 to 98% (r 2 ) (P < 0.05) of the variation in intestinal CP disappearance in steers. Residual standard deviations for these regression equations ranged from 6.16 to 6.36%. When the regression equation was forced through the zero intercept, it was found that when using pigs as a model for measuring CP disappearance of protein supplements and then both protein supplements and forages, cattle digestibility was over predicted by 3.1 and 4.0%, respectively. It was observed that when pigs were used as a model for measuring the CP disappearance of forages, cattle digestibility was under predicted by only 0.14%. The high r 2 values and the low residual standard deviations for intestinal disappearance indicate that duodenally cannulated pigs can be used to predict intestinal DM and CP digestibility of RUDR for a variety of feeds. Overall, cannulated pigs over predicted intestinal DM and CP disappearance in cattle. The pig model predicted the DM and CP

90 CANADIAN JOURNAL OF ANIMAL SCIENCE Table 4. Regression analysis for predicting intestinal disappearance of ruminal undegraded dry matter and crude protein in cattle from the pig model for protein and forage sources Non-zero intercept Zero Intercept Slope Intercept Slope Item r 2z Value SE y Value SE x RSD w Value SE x RSD w Dry matter Protein supplements 0.95 0.97 0.10 4.08 v 5.01 5.24 0.90 u 0.04 5.06 Forages 0.96 0.92 0.09 2.81 v 1.36 2.66 0.83 u 0.10 3.59 Protein and forage sources combined 0.98 0.95 0.04 3.17 v 1.70 3.84 0.90 u 0.03 4.30 Crude protein Protein supplements 0.77 1.26 0.30 22.92 v 22.54 6.36 0.96 u 0.03 6.38 Forages 0.98 0.99 0.07 1.16 v 2.98 6.34 1.00 u 0.06 5.63 Protein and forage sources combined 0.98 0.96 0.04 0.35 v 2.80 6.16 0.97 u 0.03 5.85 z Adjusted coefficient of determination. Standard error of the slope. Standard error of the intercept. Residual standard deviation. v Intercept is not different from zero (P > 0.05). u Slope is different from one (P < 0.05). digestibility of forages better than that of the protein supplements. The P values given in Table 2 show that the intestinal DM and CP disappearance of cattle vs. pigs was statistically different (P < 0.05) only for canola meal and heated canola meal. These differences would have contributed to the lower r 2 values, particularly for intestinal ruminal undegradable CP disappearance of the protein supplements. To date, there have been only two studies using the pig model to estimate intestinal digestibility of ruminal undegradable residues in cattle. Based on the results of the current study and that of Mustafa et al. (2000), it appears that pigs make an excellent model for cattle to measure intestinal DM and CP digestibility for a variety of feedstuffs. Mustafa et al. (2000) tested unheated and heated canola meal. A high correlation of 96% was found between cannulated pigs and steers for intestinal CP disappearance. Mustafa et al. (2000) found that pigs over predicted intestinal CP disappearance by 6%. One of the limitations of the study of Mustafa et al. (2000) was that only canola meal was tested. Thus, in the present study, a variety of protein supplements and forage samples were tested with the pig model. In addition, these feed samples were heated to vary the ruminal undegradable protein content and intestinal protein disappearance from mobile bags. When protein and forage sources were combined in the regression analysis, the pig model accounted for 98% of the variation in steer intestinal CP disappearance. CONCLUSION The results indicate that cannulated pigs can be used as a model to measure intestinal digestibility of ruminal undegradable CP and DM for cattle when using the mobile nylon bag technique. Regression equations used to predict cattle intestinal DM and CP disappearance from those of pigs had high coefficient of determination and low residual standard deviations ranging between 2.66 and 5.24% for intestinal DM disappearance and 6.16 and 6.36% for intestinal CP disappearance. In addition, the results show the value of the pig model using a variety of feedstuffs with a large variation in rumen and intestinal digestibility. Based on the results, it is recommended that the pig can be used as a model for cattle to measure intestinal DM and CP disappearance, producing results that can be used in modern ration formulation programs that predict the contribution of ruminal undegraded feed CP to metabolisable CP. ACKNOWLEDGMENTS This study was funded by Saskatchewan Agriculture, Food and Rural Revitalization s Agriculture Development Fund. The work of Dr. J. V. Bailey in conducting the surgery on the pigs is gratefully acknowledged. 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