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A broiler chick bioassay for measuring the feeding value of wheat and barley in complete diets
A Broiler Chick Bioassay for Measuring the Feeding Value of Wheat and Barley in Complete Diets1 T. A. SCOTT,*,2 F. G. SILVERSIDES,† H. L. CLASSEN,‡ M. L. SWIFT,§ M. R. BEDFORD,‚ and J. W. HALL# †426
ABSTRACT Energy is an important component of poultry feed and is derived principally from cereal grains. Unfortunately, all of the chemical energy is not available to the bird, and biological assays must be used to determine the digestible energy value of a cereal grain. The bioassay described uses four pens of six male broiler chicks, complete diets containing 80% of a test cereal grain (with or without an appropriate commercial enzyme), and ad libitum feed intake. Apparent metabolizable energy values (kilocalories per kilogram of cereal grain, DM basis) values are calculated from gross energy and acid insoluble ash measurements of diet and excreta collected for 24 h at 16 d of age. To monitor variation between broiler chick assays, due to bird, environment, etc., common control samples of Hard Red Spring (HRS) and Canadian Prairie Spring
(CPS) wheat were tested in each of 15 separate assays over 2 yr. Similarly, for barley, control samples of hulled and hulless barley were repeatedly tested in five assays. Broiler performance in this study was lower than expected for commercial broilers, in part due to a high dietary cereal grain component and the fine mash texture. However, AME values as determined were comparable to those reported in the literature for wheat and barley. The CV for AME measured among pens, representing the intra-assay CV, was between 1.2 and 3.4% and was lower with enzyme supplementation. The interassay CV was only slightly higher than the intraassay CV. This assay provides precise estimations of ME in cereal grains fed to young broilers that can be used for diet formulation or for verification of laboratory measures of feeding value of cereal grains.
(Key words: metabolizable energy, broiler, wheat, barley, enzymes) 1998 Poultry Science 77:449–455
Approximate ME values for wheat and barley are provided in published summary tables (Leeson and Summers, 1991; NRC, 1994). The actual ME value can vary according to the cereal type and variety (March and Biely, 1973; Sibbald, 1976; Classen et al., 1988) and the environment in which the cereal grain is grown (Willingham et al., 1960; Gohl and Thomke, 1976; Jeroch and Da¨nicke, 1996). Variation in digestible energy of a cereal grain is principally due to differences in the energy content (contributed, respectively, by starch, protein, and fat) and the presence of anti-nutritive factors that can limit the availability of nutrients to the bird. The principal anti-nutritive factors in some cer eal grains (e.g., wheat and barley) are soluble nonstarch polysaccharides (NSP, Annison and Choct, 1991; Smits and Annison, 1996). The
INTRODUCTION Sibbald (1982) estimated that energy in feed represents 40% of the cost of producing poultry meat and eggs, underlining the importance of accurate energy determination of feed ingredients for the formulation of poultry rations. Cereal grains make up the greatest proportion of a poultry diet and they are the major energy source. In Western Canada, the most common feed cereal grain for poultry is wheat, although the evolution of commercial feed enzymes has allowed increased use of barley in diets for broiler chickens. Hulless barley varieties with reduced fiber content have been developed for use in poultry feed (Rossnagel et al., 1983) but varieties selected for reduced anti-nutritive factors are not available.
Received for publication May 29, 1997. Accepted for publication October 20, 1997. 1AAFC Contribution Number 569. 2To whom correspondence should [email protected]
be
Abbreviation Key: CPS = Canadian Prairie Spring wheat; HRS = Hard Red Spring wheat; GE = gross energy; NSP = nonstarch polysaccharide.
addressed:
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*Pacific Agri-Food Research Centre, P.O. Box 1000, Agassiz, British Columbia, Canada, V0M 1A0; St. Andrew’s Street, Nanaimo, British Columbia, Canada, V9S 1S2; ‡Department of Animal and Poultry Science, University of Saskatchewan, Saskatoon, Saskatchewan, Canada, S0N 5B5; §Pro-Form Feeds, P.O. Box 1000, Chilliwack, British Columbia, Canada V2P 6J6; ‚Finnfeeds International, Box 777, Marlborough, Wiltshire, United Kingdom, SN8 1XN; and # Pacific Agri-Food Research Centre, Summerland, British Columbia, Canada, V0H 1Z0
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3Jacobson Machine Works, Inc., Minneapolis, MN 55427. 4Celite Corp., Lompac, CA 93436. 5Finnfeeds International, Marlborough, Wiltshire, UK, SN8 1XN. 6Western Hatchery Ltd., Abbotsford, BC, Canada, V2T 6B6.
MATERIALS AND METHODS The bioassay described typically requires a minimum of 45 kg of unground cereal grain. On reception, whole grain is subsampled, and bushel and 1,000 kernel weights recorded. The cereal grain is then ground using a Jacobson grinder (Model P-241-DTF-Pulverator3) equipped with a 3.6-mm screen. It is then mixed with other feed ingredients (Table 1) to produce 50 kg of a complete ration, of which the test cereal grain makes up 80%. In the assays of wheat samples described here, the basal ingredients were changed between 1994 and 1995, in an attempt to alleviate what was felt to be a palatability problem associated with high levels of corn gluten or crystalline amino acids. The basal ingredients used for wheat in 1995 were used for all of the barley samples. The diet ingredients include 0.80% Celite4 as an acid insoluble ash digestibility marker and 0.3% chromic oxide. The use of Celite has been validated (Scott and Boldaji, 1997) and future assays will use only Celite. Following mixing, the diet is divided into two equal portions, one of which is supplemented with 0.15% of a commercial enzyme5 (Avizyme TX for wheat and Avizyme SX for barley) and one of which is fed as is. In Table 1, for specific cereal grains, there were no differences in determined levels of gross energy, crude protein, acid insoluble ash, or dry matter due to enzyme supplementation. Therefore, the values presented were the average of all measurements for a specific cereal grain with or without an enzyme. However, the addition of enzyme resulted in significant increases in AME values for the control wheat and barley samples (Table 1) and have been reported separately. Typically a bioassay accommodated four pens (2,500 cm2) of six male broilers (Arbor Acres × Peterson6) for each diet studied. Up to 36 diets (e.g., 18 cereal grains, each with or without supplemental enzyme) with four replicate pens per diet can be accommodated in the 144-cage bioassay facility. Whole room brooding was practiced. Initial brooding temperatures at bird level were 34 C and were gradually reduced to 28 C by 17 d of age. Chicks were provided free access to feed and nipple drinkers. Care and management of the broilers was in accordance with the Canadian Council of Animal Care Guidelines (1993). Experimental protocols were approved by the Pacific Agri-Food Research Centre Animal Care Committee. Chicks were fed a standard broiler starter diet (22% CP; 2,900 kcal ME/kg) from 0 to 4 d of age. Beginning at 4 d the test diets were fed and subsequent growth rate and feed intake monitored at 17 d of age, the last day of the assay. Although not all of the data from the following measurements will be presented herein, a complete description of the bioassay procedure follows: On Day 17, all chicks were killed by cervical dislocation and the intestinal tract was excised. Digesta from the upper
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main NSP in wheat and barley are pentosans and bglucans, respectively. Choct and Annison (1990) added purified sources of NSP to wheat-based diets, fed them to young broiler chicks, and observed the classic symptoms of sticky droppings, reduced feed intake, and weight gain, resulting in poor feed conversion. These problems were alleviated with the addition of xylanase to wheat-based diets and b-glucanase to barley-based diets. Enzyme supplementation increases the ME values of wheat and barley containing high levels of NSP, and decreases the variation in ME caused by these antinutritive factors (T. Scott, unpublished data). Adult Leghorn cockerels have been used for ME determinations because of their low cost and maintenance requirements and neutral productive energy balance, and because they can be trained for individual bird measurements and reused in subsequent tests (Sibbald, 1982, 1986). However, differences in AME determination exist between broiler and egg laying strains of chickens (Slinger et al., 1964; March and Biely, 1971; Spratt and Leeson, 1987) as well as between broilers of different ages (Zelenka, 1968, 1997; Coates et al., 1977). These differences are exacerbated in diets requiring enzymes, as adult Leghorn cockerels in particular appear to have a negligible response to enzyme supplementation in comparison to broilers (Jeroch and Da¨nicke, 1996). Therefore, quantifying ME values for wheat- and barley-based diets with enzymes requires the use of a broiler bioassay. The energy content of a feed can also be affected by the method of measurement, for review see Sibbald (1976, 1982), Farrell (1978), Ha¨rtel (1986), McNab and Blair (1988), Askbrant (1990), and Zelenka (1997). The present bioassay is designed to: 1) measure the feeding value of an ingredient; 2) reduce the physiological and animal welfare concerns attached to the use of a starvation period(s) [Yamauchi et al. (1996) reported dramatic changes in gut morphology with 24 h starvation]; 3) assess the palatability of the ingredient; 4) assess the bird’s adaptation to the feed (with time); and 5) assess the bird’s response to enzyme supplementation of the diet. Accurate and precise AME values are needed to predict the feeding value of a cereal grain and the efficiency of treatments to reduce the effects of antinutritive compounds, and they will be needed to validate predictions of AME from laboratory measures. The aim of this report is to describe an AME assay for cereal grains and to compare the values and the intraand interassay variation to those obtained by using ME assays.
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BROILER BIOASSAY FOR WHEAT AND BARLEY TABLE 1. Composition of the diets containing Hard Red Spring (HRS) and Canadian Prairie Spring (CPS) wheat and hulled and hulless barley 1994 wheat HRS wheat
Ingredient
CPS wheat
1995 wheat/1994 and 1995 barley HRS wheat
CPS wheat
Hulled barley
Hulless barley
(%) 80.000 2.000 7.000 7.000 0.400 0.500 2.000 0.800 0.300
11 90.2 4,660 25.1 1.17 3,200 3,060
80.000 2.000 11.512 1.100 0.154 0.044 4.090 0.800 0.300
11 91.5 4,600 22.6 1.19 3,200 3,040
4 88.4 4,570 24.6 1.22 3,140 3,020
4 90.5 4,450 22.4 1.23 3,150 3,020
5 91.3 4,440 24.3 1.64 3,130 2,980
5 90.1 4,460 25.1 1.24 3,230 2,910
1Supplied per kilogram of diet: vitamin A, 9,000 IU; cholecalciferol, 1,500 IU; vitamin E, 10 IU, vitamin K, 0.5 mg; vitamin B12, 0.007 mg; thiamin, 0.4 mg; riboflavin, 6 mg; folic acid, 1 mg; biotin, 0.15 mg; niacin, 35 mg; pyridoxine, 4 mg; choline chloride, 1,000 mg; DL-methionine, 1,184 mg; ethoxyquine, 0.125 mg. 2Supplies per kilogram of diet: salt (NaCl), 2 g; manganese SO , 60 mg; copper SO , 5 mg; selenium 4 4 (sodium selenate), 0.1 mg; iodine (EEI), 0.35 mg; zinc SO4, 50 mg. 30.15% enzyme was added to the mixed diet, therefore actual levels of ingredients in this diet portion should be factored by 0.9985.
small intestine (duodenum and jejunum) was collected from four birds in each of the first two replicate pens for each diet. The digesta of two birds were pooled to provide a total of four samples per diet for viscosity measurement with a Brookfields Viscometer (Model LVDVII+CP7). Ileal digesta from two replicate pens (total of 12 broilers) per diet was combined to provide two ileal samples per diet for chemical analysis. Diet, excreta, and ileal digesta were dried, ground, and analyzed for DM, insoluble ash marker (Vogtmann et al., 1975), GE (measured with a Leco Automatic Calorimeter, AC-300, Model 789-4008), and nitrogen (measured with a Leco nitrogen analyzer, FP-4288) using standard procedures (Association of Official Analytical Chemists, 1990). The diet (Table 1) AME based on excreta collected at 16 d (DM basis) was calculated as: AME = GEdiet –
(GEexcreta or digesta
× Markerdiet/Markerexcreta
).
or digesta
The NRC (1994) values for basal components of the diet were calculated and used to correct the AME of the
7Brookfield Engineering 8Leco Corp., St. Joseph,
Labs, Stoughton, MA 00207. MI 49085-2396.
diet to reflect the AME of the dietary cereal grain component alone (Tables 2, 3, 4): AME of the cereal grain = (AME of total diet – 599.8) × 100/80 Over a 2-yr period, 108 samples of wheat were tested in 15 assays, and 79 samples of barley were tested in five assays. To monitor variability (e.g., due to variation between sources of broilers or environment) between assays, we employed a common sample of Hard Red Spring wheat (HRS) and Canadian Prairie Spring wheat (CPS) in each wheat assay. Two single-pen replications of these control wheat samples were included in the first 11 assays, and four pens were included in the last 4 assays. In a similar manner, four replicate pens of a single source of hulled and hulless barley were included in each of the five barley assays. Although the assay records three AME values (based on excreta collected for 24 h at 8 and 16 d and ileal digesta collected at 17 d), the variation of that obtained from the excreta at 16 d only was described here. All data was subjected to analysis of variance using the General Linear Models (GLM) procedure of SAS (Littell et al., 1991). Data on the diet composition [DM, gross energy (GE), percentage nitrogen × 6.25, and insoluble ash] were analyzed separately for wheat and
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Cereal Tallow Isolated soy protein Corn gluten meal L-Lysine DL-Methionine Vitamins1 and minerals2 Celite Chromic oxide Enzyme3 Analyzed composition n DM Gross energy (kcal/kg) Crude protein (N × 6.25) Acid insoluble ash, % AME (kcal/kg) + enzyme AME (kcal/kg) no enzyme
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TABLE 2. Performance and AME values of broilers fed diets containing Hard Red Spring (HRS) and Canadian Prairie Spring (CPS) wheat with (+) and without (–) enzyme supplementation in 11 assays performed in 1994 Cultivar
Enzyme n
Excreta DM
Feed intake
BW (17 d)
Feed:gain
AME (16 d)1
HRS HRS CPS CPS SE Source of variation Assay Cultivar Enzyme Assay × Cultivar Assay × Enzyme Cultivar × Enzyme Assay × Cultivar ×
+ – + –
(%) 41.5 43.3 40.9 39.1 1.0
(g/bird/d) 29.6 27.3 28.8 26.7 0.4
(g) 317 282 301 268 4
(g:g) 1.60 1.74 1.69 1.81 0.03
(kcal/kg) 3,650 3,440 3,560 3,340 15
** * NS * ** NS NS
** NS ** NS NS NS NS
** ** ** NS NS NS NS
NS * ** * NS NS NS
NS ** ** ** ** NS NS
22 22 22 22
Probability
matter basis for cereal grain component of the diet. *P ≤ 0.05. **P ≤ 0.01.
barley, and within year for wheat, using a model including the cultivar type, enzyme addition, and the interaction between the two. Broiler performance and AME values for cereal grains were analyzed using a model that included the effects of the assay, cultivar type (HRS and CPS for wheat; hulled and hulless for barley), enzyme addition, and all of the interactions. Data for wheat assays in 1994 and 1995 were analyzed separately because the basal diet changed between the years. The AME and BW at 17 d were also analyzed within the year (for wheat), cultivar type, and enzyme supplementation to determine the variance components among assays and among pens within assays. In these analyses, the series was the only source of variation. The among pens CV is given as the error CV of the model and the assay MS was used to calculate the between assay CV.
RESULTS In the 1994 assays, the diets using HRS wheat had slightly lower (P ≤ 0.01) DM, higher (P ≤ 0.01) GE, and higher (P ≤ 0.01) CP levels than the diets using CPS wheat (Table 1). The same results were found in the 1995 assays except that the difference in GE was not significant (P ≤ 0.06). The diets using hulled barley had a higher DM (P ≤ 0.05) and insoluble ash (P ≤ 0.01) content than those using hulless barley. Neither enzyme addition nor the interaction between cultivar and enzyme addition were significant for any of these measures. In 1995, the performance of the chicks on the wheat diets was improved over that in 1994 (Tables 2 and 3), probably as a result of the change in the basal diet. Body weights were higher and feed to gain ratios were lower for chicks fed the HRS wheat than for chicks fed the CPS
TABLE 3. Performance and AME values of broilers fed diets containing Hard Red Spring (HRS) and Canadian Prairie Spring (CPS) wheat with (+) and without (–) enzyme supplementation in 4 assays performed in 1995 Cultivar
Enzyme n
Excreta DM
Feed intake
BW (17 d)
Feed:gain
AME (16 d)1
HRS HRS CPS CPS SE Source of variation Assay Cultivar Enzyme Assay × Cultivar Assay × Enzyme Cultivar × Enzyme Assay × Cultivar ×
+ – + –
(%) 60.5 45.8 58.6 46.7 1.2
(g/bird/d) 44.5 41.4 43.4 40.8 0.5
(g:g) 1.43 1.46 1.44 1.49 0.01
(kcal/kg) 3,650 3,480 3,580 3,400 18
NS NS ** NS NS NS NS
** NS ** NS NS NS NS
(g) 488 450 471 438 6 Probability ** * ** NS NS NS NS
** ** ** * NS NS NS
NS ** ** ** NS NS NS
1Dry
Enzyme
16 16 16 16
matter basis for cereal grain component of the diet. *P ≤ 0.05. **P ≤ 0.01.
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Enzyme
1Dry
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BROILER BIOASSAY FOR WHEAT AND BARLEY TABLE 4. Performance and AME values of broilers fed diets containing hulled and hulless barley with (+) and without (–) enzyme supplementation in five assays Cultivar
Enzyme n 20 20 20 20
Feed intake
BW (17 d)
Feed:gain
AME (16 d)1
(%) 47.2 34.9 39.5 30.0 1.0
(g/bird/d) 42.7 36.8 42.2 32.7 0.4
(g:g) 1.46 1.58 1.42 1.71 0.01
(kcal/kg) 3,160 2,980 3,290 2,890 14
** ** ** NS NS NS NS
** ** ** NS NS ** NS
(g) 460 382 468 330 5 Probability ** ** ** NS NS ** NS
** ** ** NS NS ** NS
** NS ** * * ** **
1Dry
matter basis for cereal grain component of the diet. *P ≤ 0.05. **P ≤ 0.01.
wheat in both years, but feed intake was not different between cultivars. Enzyme supplementation increased feed intake and 17-d BW, and reduced the feed to gain ratio consistently for both wheat types in both years. In 1994, the excreta DM was higher for HRS wheat but the effect of the enzyme supplementation was not significant. In 1995, excreta DM of the cultivars were not different, and enzyme addition had a major, and nearly equal effect on both wheat types. The hulled and hulless barley cultivars were significantly different for the excreta DM, feed intake, 17-d BW, and the feed to gain ratio (Table 4). Enzyme supplementation had a significant effect on all performance measures and the interaction between the cultivar and enzyme supplementation was significant for feed intake, BW, and feed to gain ratio, with the enzyme having a greater effect on the hulless variety. Although no statistical comparison was made between chicks fed the wheat and the barley samples, feed intake, BW, and the feed to gain ratios were comparable between wheat tested in 1995 and barley with the enzyme supplementation. Apparent metabolizable energy values (as determined for the respective cereal grains) are presented in Tables 2, 3, and 4. The HRS wheat had higher AME values than the CPS wheat in both years. Enzyme supplementation increased the AME values and did so equally for the two wheat cultivars. Enzyme supplementation increased the AME of both barley types, but that of the hulless barley by a greater amount. There were significant effects for assay on feed intake and BW for the control wheat samples tested in both years, for excreta DM in 1994, and for the feed to gain ratio in 1995. Assay did not significantly effect the AME measurements in either year, although the assay by cultivar interaction was significant in both years and the assay by enzyme interaction was significant in 1994. There were significant differences between assays for all
measures taken for control hulled and hulless barley samples. The among-pens CV (the error CV) for AME within each combination of year, cereal type, and enzyme addition (Table 5) were all less than 3.4%, and the between-assays CV were only slightly higher. Enzyme addition reduced the among pens CV in all cases, but had little effect on the between-assays CV. The CV for BW were higher than those for AME, as were the between-assay CV for wheat.
DISCUSSION The aim of a bioassay is to determine the feeding value of a feedstuff as accurately and precisely as possible. Accuracy is important for ration formulation and for the eventual validation of laboratory measures designed to predict ME values that could potentially replace bioassays in the prediction of feeding value. The NRC (1994) suggests that young broilers need a feed containing 3,200 kcal/kg ME and 23% CP. Although chickens will vary intake of diet with energy level, intake is also influenced by levels of other nutrients in the diet. The diets used here all supported broiler chick growth, although the energy, and presumably other nutrient, levels varied between cereal grains with or without enzyme. Performance data (e.g., feed intake and growth rate) from the 1994 wheat assays suggest that these diets resulted in limited feed intake, possibly due to the high inclusion levels of corn gluten meal or crystalline amino acids (lysine and methionine), however, even on these diets, the chicks were in a positive energy balance and there was no indication that they were physiologically abnormal. For wheat-based diets, there was a large difference in excreta DM between years, and the enzyme had a significant effect only in 1995. Feed intake was much lower in 1994, which may have resulted in increased water intake and
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Hulled + Hulled – Hulless + Hulless – SE Source of variation Assay Cultivar Enzyme Assay × cultivar Assay × enzyme Cultivar × enzyme Assay × cultivar × enzyme
Excreta DM
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SCOTT ET AL. TABLE 5. Among-pen and between-assay CV based on variance components for AME measured at 16 d and BW at 17 d for Hard Red Spring (HRS) and Canadian Prairie Spring (CPS) wheat samples and Hulled and Hulless barley samples with (+) and without (–) enzyme supplementation CV among pens Grain
Cultivar
Enzyme
AME
BW (17 d)
CV between assays n
AME
BW (17 d)
n
(%) Wheat 1994
+ – + – + – + –
1.3 2.1 1.7 2.9 2.3 2.3 1.2 2.3
6.3 6.4 5.1 7.5 3.2 5.4 4.4 6.8
2 2 2 2 4 4 4 4
1.8 3.0 4.3 4.0 2.6 2.0 3.6 2.2
6.9 9.4 12.4 7.2 7.8 4.9 6.1 7.4
11 11 11 11 4 4 4 4
Hulled Hulled Hulless Hulless
+ – + –
1.3 1.5 1.5 3.4
5.1 4.6 5.8 6.9
4 4 4 4
4.3 3.6 3.6 5.6
6.4 7.8 9.9 5.5
5 5 5 5
Barley
therefore lower excreta DM independently of either NSP or enzyme level. The AME values for wheat in 1994 and 1995 were very similar, suggesting that maximum feed intake or growth was not necessary to obtain consistent AME values for a cereal grain. The AME values obtained using the bioassay varied from 3,340 to 3,650 kcal/kg for wheat and from 2,890 to 3,290 kcal/kg for barley (DM basis). Farrell (1981) reported ME values between 3,050 kcal/kg and 3,770 kcal/kg for 33 samples of Australian wheat and between 2,810 and 3,480 kcal/kg for 33 samples of barley. March and Biely (1973) reported ME values for 33 Canadian wheat samples that varied from 3,005 to 3,795 kcal/kg. The AME values obtained using the bioassay described here fall within these ranges. The AME values obtained were higher than the values reported by NRC (1994) for HRS wheat, about equal to the NRC (1994) values for CPS wheat with enzyme supplementation but lower without, and much higher than NRC values for barley, especially with enzyme supplementation. The feed industry in British Columbia has questioned the NRC (1994) values (Swift, unpublished data) because they do not appear to be accurate when used in commercial broiler diets. Few authors report CV that allow comparisons of precision between methods. McNab and Blair (1988) reported that the average CV of TME values from several feedstuffs was 5.5%, and that the CV of TME with a nitrogen correction was 4.7%. Using their modifications to the TME assay (longer starvation, administration of glucose and water) they reduced these CV to 1.5 and 1.8% respectively. Farrell (1978) reported SD values for two diets obtained using trained roosters that would suggest CV of 1.2%. The low among-pen CV in the present study indicate that this assay is at least as precise as other assays, and the lower CV when diets were supplemented by enzyme suggests that the precision is improved by enzyme addition. The between-assay CV for wheat samples were also low,
suggesting that values for wheat samples included in different series can be compared. The effect of the assay was significant for AME of the barley samples. The same genetic strain of chicks was used for each assay and the management conditions have been standardized in an effort to minimize between-assay variation. The present AME bioassay was developed primarily as a tool to accurately predict the feeding value of western Canadian cereal grains (i.e., barley and wheat) for broiler chickens. The merits of the procedure are: 1) it provides a relatively accurate and repeatable estimate of feeding value (e.g., AME) of wheat or barley; 2) it utilizes ad libitum feeding, thereby reducing physiological change and animal welfare concerns from feed deprivation periods; 3) measurements of feed intake supply information on palatability, which is not the case when samples are intubated; 4) a 13-d feeding period allows the broiler chick time to adjust to the diet, as would be observed in a commercial situation (e.g., adjust gut capacity or gut microflora); and 5) allows the assessment of both bird performance to, and digestibility of, dietary ingredients with or without an appropriate enzyme. The latter, enzyme response, must be measured with broiler chicks as adult cockerels are not affected, or as affected, by levels of NSP in the diet.
ACKNOWLEDGMENTS We would like to gratefully acknowledge the financial support of the Alberta Barley Commission, Canadian Wheat Board, Finnfeeds, Int., IRAP/NSERC, BC Broiler Chicken Marketing Board, and Agriculture and Agri-Food Canada. We would also like to thank J. Helm, B. Rossnagel, and P. Hucl for growing and shipping the wheat and barley samples. The poultry staff of Pacific Agri-Food Research Centre, are also thanked for their dedication and hard work in maintaining the birds and collecting and analyzing samples.
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1995
HRS HRS CPS CPS HRS HRS CPS CPS
BROILER BIOASSAY FOR WHEAT AND BARLEY
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McNab, J. M., and J. C. Blair, 1988. Modified assay for true and apparent metabolizable energy based on tube feeding. Br. Poult. Sci. 29:697–707. National Research Council, 1994. Nutrient Requirements of Poultry. 8th rev. ed. National Academy Press, Washington, DC. Rossnagel, B. G., B. L. Harvey, and R. S. Bhatty, 1983. Scout hulless barley. Can. J. Plant Sci. 63:751–752. Scott, T. A., and F. Boldaji, 1997. Comparison of inert markers (chromic oxide or insoluble ash (Celite)) for determining apparent metabolizable energy of wheat- or barley-based broiler diets with or without enzymes. Poultry Sci. 76: 594–598. Sibbald, I. R., 1976. A bioassay for true metabolizable energy in feeding stuffs. Poultry Sci. 55:303–308. Sibbald, I. R., 1982. Measurement of bioavailable energy in poultry feeding stuffs: a review. Can. J. Anim. Sci. 62: 983–1048. Sibbald, I. R., 1986. The TME system of feed evaluation: methodology, feed composition data and bibliography. Technical Bulletin 1986-4E. Agriculture Canada, Research Branch, Ottawa, ON, Canada. Slinger, S. J., I. R. Sibbald, and W. F. Pepper, 1964. The relative abilities of two breeds of chickens and two varieties of turkeys to metabolize dietary energy and dietary nitrogen. Poultry Sci. 43:330–333. Smits, C. H., and G. Annison, 1996. Non-starch plant polysaccharides in broiler nutrition—towards a physiologically valid approach to their determination. World’s Poult Sci. J. 52:203–221. Spratt, R. S., and S. Leeson, 1987. Determination of metabolizable energy of various diets using Leghorn, dwarf, and regular broiler breeder hens. Poultry Sci. 66:314–317. Vogtmann, H., P. Frirter, and A. L. Prabuck, 1975. A new method of determining metabolizability of energy and digestibility of fatty acids in broiler diets. Br. Poult. Sci. 67: 641–646. Willingham, H. E., K. C. Leong, L. S. Jensen, and J. McGinnis, 1960. Influence of geographical area of production on response of different barley samples to enzyme supplements or water treatment. Poultry Sci. 39:103–108. Yamauchi, K., H. Kamisoyama, and Y. Isshike, 1996. Effects of fasting and refeeding on structures of the intestinal villi and epithelial cells in White Leghorn hens. Br. Poult. Sci. 37:909–921. Zelenka, J., 1968. Influence of the age of the chicken on the metabolizable energy values of poultry diets. Br. Poult. Sci. 9:135–142. Zelenka, J., 1997. Effects of sex, age and foot intake upon metabolisable energy values in broiler chickens. Br. Poult. Sci. 38:281–284.
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Annison, G., and M. Choct, 1991. Anti-nutritive activities of cereal non-starch polysaccharides in broiler diets and strategies minimizing their effects. World’s Poult. Sci. J. 47: 232–242. Association of Official Analytical Chemists, 1990. Official Methods of Analysis. Association of Official Analytical Chemists. Washington, DC. Askbrant, S., 1990. The concept of metabolizable energy for poultry. Swedish University of Agricultural Sciences, Department of Animal Nutrition and Management, Report 194, Uppsala, Sweden. Canadian Council on Animal Care, 1993. Guide to the Care and Use of Experimental Animals. Vol. 1. 2nd ed. Canadian Council on Animal Care, Ottawa, ON, Canada. Choct, M., and G. Annison, 1990. Anti-nutritive activity of wheat pentosans in poultry diets. Br. Poult. Sci. 31: 809–819. Classen, H. L., G. L. Campbell, and J.W.D. Grootwassink, 1988. Improved feeding value of Saskatchewan-grown barley for chickens with dietary enzyme supplementation. Can. J. Anim. Sci. 68:1253–1259. Coates, B. J., S. J. Slinger, J. D. Summers, and H. S. Bayley, 1977. Metabolizable energy values and chemical and physical characteristics of wheat and barley. Can. J. Anim. Sci. 57:195–207. Farrell, D. J., 1978. Rapid determination of metabolizable energy of foods using cockerels. Br. Poult. Sci. 19:303–308. Farrell, D. J., 1981. An assessment of quick bioassays for determining the true metabolizable energy and apparent metabolizable energy of poultry feedstuffs. World’s Poult. Sci. J. 37:72–83. Gohl, B., and S. Thomke, 1976. Digestibility coefficients and metabolizable energy of barley diets for layers as influenced by geographical area of production. Poultry Sci. 55:2369–2374. Ha¨rtel, H., 1986. Influence of food input and procedure of determination on metabolizable energy and digestibility of a diet measured with young and adult birds. Br. Poult. Sci. 27:11–39. Jeroch, H., and S. Da¨nicke, 1996. Barley in poultry feeding: a review. World’s Poult Sci. J. 51:271–291. Leeson, S., and J. D. Summers, 1991. Commercial Poultry Nutrition. University Books, Guelph, ON, Canada. Littell, R. C., R. J. Freund, and P. C. Spector, 1991. SAS System for Linear Models. 3rd ed. SAS Series in Statistical Applications. SAS Institute Inc., Cary, NC. March, B. E., and J. Biely, 1971. Factors affecting the response of chicks to diets of different protein value: breed and age. Poultry Sci. 50:1036–1040. March, B. E., and J. Biely, 1973. Chemical, physical and nutritional characteristics of different samples of wheat. Can. J. Anim. Sci. 53:569–577.
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ABSTRACT Energy is an important component of poultry feed and is derived principally from cereal grains. Unfortunately, all of the chemical energy is not available to the bird, and biological assays must be used to determine the digestible energy value of a cereal grain. The bioassay described uses four pens of six male broiler chicks, complete diets containing 80% of a test cereal grain (with or without an appropriate commercial enzyme), and ad libitum feed intake. Apparent metabolizable energy values (kilocalories per kilogram of cereal grain, DM basis) values are calculated from gross energy and acid insoluble ash measurements of diet and excreta collected for 24 h at 16 d of age. To monitor variation between broiler chick assays, due to bird, environment, etc., common control samples of Hard Red Spring (HRS) and Canadian Prairie Spring
(CPS) wheat were tested in each of 15 separate assays over 2 yr. Similarly, for barley, control samples of hulled and hulless barley were repeatedly tested in five assays. Broiler performance in this study was lower than expected for commercial broilers, in part due to a high dietary cereal grain component and the fine mash texture. However, AME values as determined were comparable to those reported in the literature for wheat and barley. The CV for AME measured among pens, representing the intra-assay CV, was between 1.2 and 3.4% and was lower with enzyme supplementation. The interassay CV was only slightly higher than the intraassay CV. This assay provides precise estimations of ME in cereal grains fed to young broilers that can be used for diet formulation or for verification of laboratory measures of feeding value of cereal grains.
(Key words: metabolizable energy, broiler, wheat, barley, enzymes) 1998 Poultry Science 77:449–455
Approximate ME values for wheat and barley are provided in published summary tables (Leeson and Summers, 1991; NRC, 1994). The actual ME value can vary according to the cereal type and variety (March and Biely, 1973; Sibbald, 1976; Classen et al., 1988) and the environment in which the cereal grain is grown (Willingham et al., 1960; Gohl and Thomke, 1976; Jeroch and Da¨nicke, 1996). Variation in digestible energy of a cereal grain is principally due to differences in the energy content (contributed, respectively, by starch, protein, and fat) and the presence of anti-nutritive factors that can limit the availability of nutrients to the bird. The principal anti-nutritive factors in some cer eal grains (e.g., wheat and barley) are soluble nonstarch polysaccharides (NSP, Annison and Choct, 1991; Smits and Annison, 1996). The
INTRODUCTION Sibbald (1982) estimated that energy in feed represents 40% of the cost of producing poultry meat and eggs, underlining the importance of accurate energy determination of feed ingredients for the formulation of poultry rations. Cereal grains make up the greatest proportion of a poultry diet and they are the major energy source. In Western Canada, the most common feed cereal grain for poultry is wheat, although the evolution of commercial feed enzymes has allowed increased use of barley in diets for broiler chickens. Hulless barley varieties with reduced fiber content have been developed for use in poultry feed (Rossnagel et al., 1983) but varieties selected for reduced anti-nutritive factors are not available.
Received for publication May 29, 1997. Accepted for publication October 20, 1997. 1AAFC Contribution Number 569. 2To whom correspondence should [email protected]
be
Abbreviation Key: CPS = Canadian Prairie Spring wheat; HRS = Hard Red Spring wheat; GE = gross energy; NSP = nonstarch polysaccharide.
addressed:
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*Pacific Agri-Food Research Centre, P.O. Box 1000, Agassiz, British Columbia, Canada, V0M 1A0; St. Andrew’s Street, Nanaimo, British Columbia, Canada, V9S 1S2; ‡Department of Animal and Poultry Science, University of Saskatchewan, Saskatoon, Saskatchewan, Canada, S0N 5B5; §Pro-Form Feeds, P.O. Box 1000, Chilliwack, British Columbia, Canada V2P 6J6; ‚Finnfeeds International, Box 777, Marlborough, Wiltshire, United Kingdom, SN8 1XN; and # Pacific Agri-Food Research Centre, Summerland, British Columbia, Canada, V0H 1Z0
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3Jacobson Machine Works, Inc., Minneapolis, MN 55427. 4Celite Corp., Lompac, CA 93436. 5Finnfeeds International, Marlborough, Wiltshire, UK, SN8 1XN. 6Western Hatchery Ltd., Abbotsford, BC, Canada, V2T 6B6.
MATERIALS AND METHODS The bioassay described typically requires a minimum of 45 kg of unground cereal grain. On reception, whole grain is subsampled, and bushel and 1,000 kernel weights recorded. The cereal grain is then ground using a Jacobson grinder (Model P-241-DTF-Pulverator3) equipped with a 3.6-mm screen. It is then mixed with other feed ingredients (Table 1) to produce 50 kg of a complete ration, of which the test cereal grain makes up 80%. In the assays of wheat samples described here, the basal ingredients were changed between 1994 and 1995, in an attempt to alleviate what was felt to be a palatability problem associated with high levels of corn gluten or crystalline amino acids. The basal ingredients used for wheat in 1995 were used for all of the barley samples. The diet ingredients include 0.80% Celite4 as an acid insoluble ash digestibility marker and 0.3% chromic oxide. The use of Celite has been validated (Scott and Boldaji, 1997) and future assays will use only Celite. Following mixing, the diet is divided into two equal portions, one of which is supplemented with 0.15% of a commercial enzyme5 (Avizyme TX for wheat and Avizyme SX for barley) and one of which is fed as is. In Table 1, for specific cereal grains, there were no differences in determined levels of gross energy, crude protein, acid insoluble ash, or dry matter due to enzyme supplementation. Therefore, the values presented were the average of all measurements for a specific cereal grain with or without an enzyme. However, the addition of enzyme resulted in significant increases in AME values for the control wheat and barley samples (Table 1) and have been reported separately. Typically a bioassay accommodated four pens (2,500 cm2) of six male broilers (Arbor Acres × Peterson6) for each diet studied. Up to 36 diets (e.g., 18 cereal grains, each with or without supplemental enzyme) with four replicate pens per diet can be accommodated in the 144-cage bioassay facility. Whole room brooding was practiced. Initial brooding temperatures at bird level were 34 C and were gradually reduced to 28 C by 17 d of age. Chicks were provided free access to feed and nipple drinkers. Care and management of the broilers was in accordance with the Canadian Council of Animal Care Guidelines (1993). Experimental protocols were approved by the Pacific Agri-Food Research Centre Animal Care Committee. Chicks were fed a standard broiler starter diet (22% CP; 2,900 kcal ME/kg) from 0 to 4 d of age. Beginning at 4 d the test diets were fed and subsequent growth rate and feed intake monitored at 17 d of age, the last day of the assay. Although not all of the data from the following measurements will be presented herein, a complete description of the bioassay procedure follows: On Day 17, all chicks were killed by cervical dislocation and the intestinal tract was excised. Digesta from the upper
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main NSP in wheat and barley are pentosans and bglucans, respectively. Choct and Annison (1990) added purified sources of NSP to wheat-based diets, fed them to young broiler chicks, and observed the classic symptoms of sticky droppings, reduced feed intake, and weight gain, resulting in poor feed conversion. These problems were alleviated with the addition of xylanase to wheat-based diets and b-glucanase to barley-based diets. Enzyme supplementation increases the ME values of wheat and barley containing high levels of NSP, and decreases the variation in ME caused by these antinutritive factors (T. Scott, unpublished data). Adult Leghorn cockerels have been used for ME determinations because of their low cost and maintenance requirements and neutral productive energy balance, and because they can be trained for individual bird measurements and reused in subsequent tests (Sibbald, 1982, 1986). However, differences in AME determination exist between broiler and egg laying strains of chickens (Slinger et al., 1964; March and Biely, 1971; Spratt and Leeson, 1987) as well as between broilers of different ages (Zelenka, 1968, 1997; Coates et al., 1977). These differences are exacerbated in diets requiring enzymes, as adult Leghorn cockerels in particular appear to have a negligible response to enzyme supplementation in comparison to broilers (Jeroch and Da¨nicke, 1996). Therefore, quantifying ME values for wheat- and barley-based diets with enzymes requires the use of a broiler bioassay. The energy content of a feed can also be affected by the method of measurement, for review see Sibbald (1976, 1982), Farrell (1978), Ha¨rtel (1986), McNab and Blair (1988), Askbrant (1990), and Zelenka (1997). The present bioassay is designed to: 1) measure the feeding value of an ingredient; 2) reduce the physiological and animal welfare concerns attached to the use of a starvation period(s) [Yamauchi et al. (1996) reported dramatic changes in gut morphology with 24 h starvation]; 3) assess the palatability of the ingredient; 4) assess the bird’s adaptation to the feed (with time); and 5) assess the bird’s response to enzyme supplementation of the diet. Accurate and precise AME values are needed to predict the feeding value of a cereal grain and the efficiency of treatments to reduce the effects of antinutritive compounds, and they will be needed to validate predictions of AME from laboratory measures. The aim of this report is to describe an AME assay for cereal grains and to compare the values and the intraand interassay variation to those obtained by using ME assays.
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BROILER BIOASSAY FOR WHEAT AND BARLEY TABLE 1. Composition of the diets containing Hard Red Spring (HRS) and Canadian Prairie Spring (CPS) wheat and hulled and hulless barley 1994 wheat HRS wheat
Ingredient
CPS wheat
1995 wheat/1994 and 1995 barley HRS wheat
CPS wheat
Hulled barley
Hulless barley
(%) 80.000 2.000 7.000 7.000 0.400 0.500 2.000 0.800 0.300
11 90.2 4,660 25.1 1.17 3,200 3,060
80.000 2.000 11.512 1.100 0.154 0.044 4.090 0.800 0.300
11 91.5 4,600 22.6 1.19 3,200 3,040
4 88.4 4,570 24.6 1.22 3,140 3,020
4 90.5 4,450 22.4 1.23 3,150 3,020
5 91.3 4,440 24.3 1.64 3,130 2,980
5 90.1 4,460 25.1 1.24 3,230 2,910
1Supplied per kilogram of diet: vitamin A, 9,000 IU; cholecalciferol, 1,500 IU; vitamin E, 10 IU, vitamin K, 0.5 mg; vitamin B12, 0.007 mg; thiamin, 0.4 mg; riboflavin, 6 mg; folic acid, 1 mg; biotin, 0.15 mg; niacin, 35 mg; pyridoxine, 4 mg; choline chloride, 1,000 mg; DL-methionine, 1,184 mg; ethoxyquine, 0.125 mg. 2Supplies per kilogram of diet: salt (NaCl), 2 g; manganese SO , 60 mg; copper SO , 5 mg; selenium 4 4 (sodium selenate), 0.1 mg; iodine (EEI), 0.35 mg; zinc SO4, 50 mg. 30.15% enzyme was added to the mixed diet, therefore actual levels of ingredients in this diet portion should be factored by 0.9985.
small intestine (duodenum and jejunum) was collected from four birds in each of the first two replicate pens for each diet. The digesta of two birds were pooled to provide a total of four samples per diet for viscosity measurement with a Brookfields Viscometer (Model LVDVII+CP7). Ileal digesta from two replicate pens (total of 12 broilers) per diet was combined to provide two ileal samples per diet for chemical analysis. Diet, excreta, and ileal digesta were dried, ground, and analyzed for DM, insoluble ash marker (Vogtmann et al., 1975), GE (measured with a Leco Automatic Calorimeter, AC-300, Model 789-4008), and nitrogen (measured with a Leco nitrogen analyzer, FP-4288) using standard procedures (Association of Official Analytical Chemists, 1990). The diet (Table 1) AME based on excreta collected at 16 d (DM basis) was calculated as: AME = GEdiet –
(GEexcreta or digesta
× Markerdiet/Markerexcreta
).
or digesta
The NRC (1994) values for basal components of the diet were calculated and used to correct the AME of the
7Brookfield Engineering 8Leco Corp., St. Joseph,
Labs, Stoughton, MA 00207. MI 49085-2396.
diet to reflect the AME of the dietary cereal grain component alone (Tables 2, 3, 4): AME of the cereal grain = (AME of total diet – 599.8) × 100/80 Over a 2-yr period, 108 samples of wheat were tested in 15 assays, and 79 samples of barley were tested in five assays. To monitor variability (e.g., due to variation between sources of broilers or environment) between assays, we employed a common sample of Hard Red Spring wheat (HRS) and Canadian Prairie Spring wheat (CPS) in each wheat assay. Two single-pen replications of these control wheat samples were included in the first 11 assays, and four pens were included in the last 4 assays. In a similar manner, four replicate pens of a single source of hulled and hulless barley were included in each of the five barley assays. Although the assay records three AME values (based on excreta collected for 24 h at 8 and 16 d and ileal digesta collected at 17 d), the variation of that obtained from the excreta at 16 d only was described here. All data was subjected to analysis of variance using the General Linear Models (GLM) procedure of SAS (Littell et al., 1991). Data on the diet composition [DM, gross energy (GE), percentage nitrogen × 6.25, and insoluble ash] were analyzed separately for wheat and
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Cereal Tallow Isolated soy protein Corn gluten meal L-Lysine DL-Methionine Vitamins1 and minerals2 Celite Chromic oxide Enzyme3 Analyzed composition n DM Gross energy (kcal/kg) Crude protein (N × 6.25) Acid insoluble ash, % AME (kcal/kg) + enzyme AME (kcal/kg) no enzyme
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TABLE 2. Performance and AME values of broilers fed diets containing Hard Red Spring (HRS) and Canadian Prairie Spring (CPS) wheat with (+) and without (–) enzyme supplementation in 11 assays performed in 1994 Cultivar
Enzyme n
Excreta DM
Feed intake
BW (17 d)
Feed:gain
AME (16 d)1
HRS HRS CPS CPS SE Source of variation Assay Cultivar Enzyme Assay × Cultivar Assay × Enzyme Cultivar × Enzyme Assay × Cultivar ×
+ – + –
(%) 41.5 43.3 40.9 39.1 1.0
(g/bird/d) 29.6 27.3 28.8 26.7 0.4
(g) 317 282 301 268 4
(g:g) 1.60 1.74 1.69 1.81 0.03
(kcal/kg) 3,650 3,440 3,560 3,340 15
** * NS * ** NS NS
** NS ** NS NS NS NS
** ** ** NS NS NS NS
NS * ** * NS NS NS
NS ** ** ** ** NS NS
22 22 22 22
Probability
matter basis for cereal grain component of the diet. *P ≤ 0.05. **P ≤ 0.01.
barley, and within year for wheat, using a model including the cultivar type, enzyme addition, and the interaction between the two. Broiler performance and AME values for cereal grains were analyzed using a model that included the effects of the assay, cultivar type (HRS and CPS for wheat; hulled and hulless for barley), enzyme addition, and all of the interactions. Data for wheat assays in 1994 and 1995 were analyzed separately because the basal diet changed between the years. The AME and BW at 17 d were also analyzed within the year (for wheat), cultivar type, and enzyme supplementation to determine the variance components among assays and among pens within assays. In these analyses, the series was the only source of variation. The among pens CV is given as the error CV of the model and the assay MS was used to calculate the between assay CV.
RESULTS In the 1994 assays, the diets using HRS wheat had slightly lower (P ≤ 0.01) DM, higher (P ≤ 0.01) GE, and higher (P ≤ 0.01) CP levels than the diets using CPS wheat (Table 1). The same results were found in the 1995 assays except that the difference in GE was not significant (P ≤ 0.06). The diets using hulled barley had a higher DM (P ≤ 0.05) and insoluble ash (P ≤ 0.01) content than those using hulless barley. Neither enzyme addition nor the interaction between cultivar and enzyme addition were significant for any of these measures. In 1995, the performance of the chicks on the wheat diets was improved over that in 1994 (Tables 2 and 3), probably as a result of the change in the basal diet. Body weights were higher and feed to gain ratios were lower for chicks fed the HRS wheat than for chicks fed the CPS
TABLE 3. Performance and AME values of broilers fed diets containing Hard Red Spring (HRS) and Canadian Prairie Spring (CPS) wheat with (+) and without (–) enzyme supplementation in 4 assays performed in 1995 Cultivar
Enzyme n
Excreta DM
Feed intake
BW (17 d)
Feed:gain
AME (16 d)1
HRS HRS CPS CPS SE Source of variation Assay Cultivar Enzyme Assay × Cultivar Assay × Enzyme Cultivar × Enzyme Assay × Cultivar ×
+ – + –
(%) 60.5 45.8 58.6 46.7 1.2
(g/bird/d) 44.5 41.4 43.4 40.8 0.5
(g:g) 1.43 1.46 1.44 1.49 0.01
(kcal/kg) 3,650 3,480 3,580 3,400 18
NS NS ** NS NS NS NS
** NS ** NS NS NS NS
(g) 488 450 471 438 6 Probability ** * ** NS NS NS NS
** ** ** * NS NS NS
NS ** ** ** NS NS NS
1Dry
Enzyme
16 16 16 16
matter basis for cereal grain component of the diet. *P ≤ 0.05. **P ≤ 0.01.
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Enzyme
1Dry
453
BROILER BIOASSAY FOR WHEAT AND BARLEY TABLE 4. Performance and AME values of broilers fed diets containing hulled and hulless barley with (+) and without (–) enzyme supplementation in five assays Cultivar
Enzyme n 20 20 20 20
Feed intake
BW (17 d)
Feed:gain
AME (16 d)1
(%) 47.2 34.9 39.5 30.0 1.0
(g/bird/d) 42.7 36.8 42.2 32.7 0.4
(g:g) 1.46 1.58 1.42 1.71 0.01
(kcal/kg) 3,160 2,980 3,290 2,890 14
** ** ** NS NS NS NS
** ** ** NS NS ** NS
(g) 460 382 468 330 5 Probability ** ** ** NS NS ** NS
** ** ** NS NS ** NS
** NS ** * * ** **
1Dry
matter basis for cereal grain component of the diet. *P ≤ 0.05. **P ≤ 0.01.
wheat in both years, but feed intake was not different between cultivars. Enzyme supplementation increased feed intake and 17-d BW, and reduced the feed to gain ratio consistently for both wheat types in both years. In 1994, the excreta DM was higher for HRS wheat but the effect of the enzyme supplementation was not significant. In 1995, excreta DM of the cultivars were not different, and enzyme addition had a major, and nearly equal effect on both wheat types. The hulled and hulless barley cultivars were significantly different for the excreta DM, feed intake, 17-d BW, and the feed to gain ratio (Table 4). Enzyme supplementation had a significant effect on all performance measures and the interaction between the cultivar and enzyme supplementation was significant for feed intake, BW, and feed to gain ratio, with the enzyme having a greater effect on the hulless variety. Although no statistical comparison was made between chicks fed the wheat and the barley samples, feed intake, BW, and the feed to gain ratios were comparable between wheat tested in 1995 and barley with the enzyme supplementation. Apparent metabolizable energy values (as determined for the respective cereal grains) are presented in Tables 2, 3, and 4. The HRS wheat had higher AME values than the CPS wheat in both years. Enzyme supplementation increased the AME values and did so equally for the two wheat cultivars. Enzyme supplementation increased the AME of both barley types, but that of the hulless barley by a greater amount. There were significant effects for assay on feed intake and BW for the control wheat samples tested in both years, for excreta DM in 1994, and for the feed to gain ratio in 1995. Assay did not significantly effect the AME measurements in either year, although the assay by cultivar interaction was significant in both years and the assay by enzyme interaction was significant in 1994. There were significant differences between assays for all
measures taken for control hulled and hulless barley samples. The among-pens CV (the error CV) for AME within each combination of year, cereal type, and enzyme addition (Table 5) were all less than 3.4%, and the between-assays CV were only slightly higher. Enzyme addition reduced the among pens CV in all cases, but had little effect on the between-assays CV. The CV for BW were higher than those for AME, as were the between-assay CV for wheat.
DISCUSSION The aim of a bioassay is to determine the feeding value of a feedstuff as accurately and precisely as possible. Accuracy is important for ration formulation and for the eventual validation of laboratory measures designed to predict ME values that could potentially replace bioassays in the prediction of feeding value. The NRC (1994) suggests that young broilers need a feed containing 3,200 kcal/kg ME and 23% CP. Although chickens will vary intake of diet with energy level, intake is also influenced by levels of other nutrients in the diet. The diets used here all supported broiler chick growth, although the energy, and presumably other nutrient, levels varied between cereal grains with or without enzyme. Performance data (e.g., feed intake and growth rate) from the 1994 wheat assays suggest that these diets resulted in limited feed intake, possibly due to the high inclusion levels of corn gluten meal or crystalline amino acids (lysine and methionine), however, even on these diets, the chicks were in a positive energy balance and there was no indication that they were physiologically abnormal. For wheat-based diets, there was a large difference in excreta DM between years, and the enzyme had a significant effect only in 1995. Feed intake was much lower in 1994, which may have resulted in increased water intake and
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Hulled + Hulled – Hulless + Hulless – SE Source of variation Assay Cultivar Enzyme Assay × cultivar Assay × enzyme Cultivar × enzyme Assay × cultivar × enzyme
Excreta DM
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SCOTT ET AL. TABLE 5. Among-pen and between-assay CV based on variance components for AME measured at 16 d and BW at 17 d for Hard Red Spring (HRS) and Canadian Prairie Spring (CPS) wheat samples and Hulled and Hulless barley samples with (+) and without (–) enzyme supplementation CV among pens Grain
Cultivar
Enzyme
AME
BW (17 d)
CV between assays n
AME
BW (17 d)
n
(%) Wheat 1994
+ – + – + – + –
1.3 2.1 1.7 2.9 2.3 2.3 1.2 2.3
6.3 6.4 5.1 7.5 3.2 5.4 4.4 6.8
2 2 2 2 4 4 4 4
1.8 3.0 4.3 4.0 2.6 2.0 3.6 2.2
6.9 9.4 12.4 7.2 7.8 4.9 6.1 7.4
11 11 11 11 4 4 4 4
Hulled Hulled Hulless Hulless
+ – + –
1.3 1.5 1.5 3.4
5.1 4.6 5.8 6.9
4 4 4 4
4.3 3.6 3.6 5.6
6.4 7.8 9.9 5.5
5 5 5 5
Barley
therefore lower excreta DM independently of either NSP or enzyme level. The AME values for wheat in 1994 and 1995 were very similar, suggesting that maximum feed intake or growth was not necessary to obtain consistent AME values for a cereal grain. The AME values obtained using the bioassay varied from 3,340 to 3,650 kcal/kg for wheat and from 2,890 to 3,290 kcal/kg for barley (DM basis). Farrell (1981) reported ME values between 3,050 kcal/kg and 3,770 kcal/kg for 33 samples of Australian wheat and between 2,810 and 3,480 kcal/kg for 33 samples of barley. March and Biely (1973) reported ME values for 33 Canadian wheat samples that varied from 3,005 to 3,795 kcal/kg. The AME values obtained using the bioassay described here fall within these ranges. The AME values obtained were higher than the values reported by NRC (1994) for HRS wheat, about equal to the NRC (1994) values for CPS wheat with enzyme supplementation but lower without, and much higher than NRC values for barley, especially with enzyme supplementation. The feed industry in British Columbia has questioned the NRC (1994) values (Swift, unpublished data) because they do not appear to be accurate when used in commercial broiler diets. Few authors report CV that allow comparisons of precision between methods. McNab and Blair (1988) reported that the average CV of TME values from several feedstuffs was 5.5%, and that the CV of TME with a nitrogen correction was 4.7%. Using their modifications to the TME assay (longer starvation, administration of glucose and water) they reduced these CV to 1.5 and 1.8% respectively. Farrell (1978) reported SD values for two diets obtained using trained roosters that would suggest CV of 1.2%. The low among-pen CV in the present study indicate that this assay is at least as precise as other assays, and the lower CV when diets were supplemented by enzyme suggests that the precision is improved by enzyme addition. The between-assay CV for wheat samples were also low,
suggesting that values for wheat samples included in different series can be compared. The effect of the assay was significant for AME of the barley samples. The same genetic strain of chicks was used for each assay and the management conditions have been standardized in an effort to minimize between-assay variation. The present AME bioassay was developed primarily as a tool to accurately predict the feeding value of western Canadian cereal grains (i.e., barley and wheat) for broiler chickens. The merits of the procedure are: 1) it provides a relatively accurate and repeatable estimate of feeding value (e.g., AME) of wheat or barley; 2) it utilizes ad libitum feeding, thereby reducing physiological change and animal welfare concerns from feed deprivation periods; 3) measurements of feed intake supply information on palatability, which is not the case when samples are intubated; 4) a 13-d feeding period allows the broiler chick time to adjust to the diet, as would be observed in a commercial situation (e.g., adjust gut capacity or gut microflora); and 5) allows the assessment of both bird performance to, and digestibility of, dietary ingredients with or without an appropriate enzyme. The latter, enzyme response, must be measured with broiler chicks as adult cockerels are not affected, or as affected, by levels of NSP in the diet.
ACKNOWLEDGMENTS We would like to gratefully acknowledge the financial support of the Alberta Barley Commission, Canadian Wheat Board, Finnfeeds, Int., IRAP/NSERC, BC Broiler Chicken Marketing Board, and Agriculture and Agri-Food Canada. We would also like to thank J. Helm, B. Rossnagel, and P. Hucl for growing and shipping the wheat and barley samples. The poultry staff of Pacific Agri-Food Research Centre, are also thanked for their dedication and hard work in maintaining the birds and collecting and analyzing samples.
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1995
HRS HRS CPS CPS HRS HRS CPS CPS
BROILER BIOASSAY FOR WHEAT AND BARLEY
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