Prediction of the energy value of rabbit feeds varying widely in fibre content

Transcription

1 ANIMAL FEED SCIENCE AND TECHNOLOGY ELSEVIER Animal Feed Science Technology 64(19%) Prediction of the energy value of rabbit feeds varying widely in fibre content J. Fernfindez-Carmona *, C. Cervera, E. Blas Departamento Ciencia Animal, Universidad Polithica, Apartado Valencia, Spain Accepted 12 March 19% Abstract Digestibility trials of 23 pelleted diets, with one or two ingredients and having % acid detergent fibre (ADF) on a dry matter (DM) basis, were carried out in adult rabbits fed ad libitum. Using a step-wise linear regression approach, the relationship between the digestible energy content (DE) or the coefficient of digestibility of gross energy (dge) and the chemical composition of diets was established. Excluding beet pulp, with a very high crude fibre digestibility (54.8%), the prediction equations obtained were: DE (MJ kg- DM) = ADF EE CP (R* = 0.965, RSD = 0.494) and dge (%) ADF (R* = 0.951, RSD = 3.15) where ADF, ether extract (EE) and crude protein (CP) are expressed as a percentage on a DM basis. When diets with level of EE or CP higher than 6% or 18% respectively (grape mart, olive oil cake, brewer s grains, sunflower meal) were also removed, the prediction equations became: DE = ADF (R* , RSD = 0.391) and dge = ADF (R* = 0.977, RSD = 2.02). The contents in DE, digestible crude protein and undigestible crude fibre of 21 ingredients are presented and discussed in comparison with other studies. Keywords: Digestibility; Energy; Fibre; Rabbit 1. Introduction Digestibility values and particularly digestible energy content of diets and ingredients are of basic interest for the rabbit feed industry and research. To avoid in vivo digestibility trials, some linear regression equations which predict digestible energy * Corresponding author. Tel: ; fax: , jfernand@dca.upv.es /%/$15.00 Copyright Elsevier Science B.V. All rights reserved. PII SO (96)

2 62 J. Fertukdez-Camwna et al./animal Feed Science Technology 64 (1996) content (DE> or the coefficient of digestibility of gross energy (dge) from the chemical composition of the feed have been published. Most works report that fibre content shows the highest correlation with DE and dge, giving rise to equations in which acid detergent fibre (ADF) or crude fibre (CF) are the main independent variables. In these works, the DE and dge values were obtained directly for diets, with fibre values on a dry matter (DM) basis between 12-27% ADF (Battaglini and Grandi, 19841, 8-34% ADF (Corino, 19871, 15-39% ADF (Maertens et al., 19881, 9-33% ADF (De Blas et al., 1992) or 7-34% CF (Liu et al., 1992b). When ingredients were studied, DE and dge values were calculated by the substitution method, i.e. substituting a part of a basal diet previously evaluated by the testing ingredient, with values from 2-33% CF (Fekete and Gippert, 1986) or l-x% CF (Wiseman et al., 19921, with the exception of Raharjo et al. (19861, who deduced the values for different tropical forages having 20-49% ADF through the substitution method in the case of grasses, but directly for legumes. Finally, Ortfz and De Blas (1989) considered diets and ingredients all together, with a range of 4-53% ADF. In the present work, digestibility of several diets containing one or two ingredients, with a wide variation of fibre content, was determined and the relationship between DE or dge and their chemical components was established. The methodology used also allowed determination of the energy value of the ingredients, some of them scarcely referenced in the literature. 2. Material and methods 2.1. Diets 23 diets were pelleted from one ingredient or from two, when the utilization of one ingredient alone produced an inadequate pellet, which was rejected by the rabbits, or was very low in fibre or protein content (corn, barley, paprika residue, olive tree leaves, corn stover, sunflower hulls). The ingredients and chemical composition of the diets are shown in Table Digestibility trial Apparent digestibilities of DM, organic matter (OM), CF, crude protein (CP) and gross energy (GE) were determined for each diet on 10 three-way crossbreed rabbits, 4-5 months old and of 3-4 kg live weight, housed in metabolism cages and fed ad libitum. The adaptation period was 7 days and the faeces collection period was 4 days Analytical methodr Chemical analyses followed the methods of the AC (1984) for DM, ash, CP, ether extract (EE) after acid hidrolysis and CF. Neutral detergent fibre (NDF) and ADF were analysed sequentially following Van Soest et al. (1991), with a thermo-stable amylase pre-treatment. GE content was measured using an adiabatic bomb.

3 J. Fernhdez-Camwna er al. / Animal Feed Science Technology 64 (1996) Table 1 Ingredients and chemical composition of diets (% on DM basis) a Diet no. Ingredients ADF NDF CF EE CP Ash GE (MJ kg- ) II Grape. mart Olive oil cake Sunflower hulls. 90%; Soybean meal-44, 10% Sainfoin hay Grass hay Alfalfa hay C Vetch-oats hay Alfalfa hay B, 66.7%; Paprika residue, 33.3% Alfalfa hay B Olive tree leaves, 66.7%; Barley, 33.3% Sunflower meal Beet pulp Alfalfa hay C, 66.7%; Corn, 33.3% Orange tree leaves Alfalfa hay B, 66.7%; Barley, 33.3% Brewer s grains Barley, 66.7%; Corn stover, 33.3% Barley, 66.7%; Alfalfa hay B, 33.3% Barley, 80%; Straw, 20% Corn, 66.7%; Alfalfa hay C, 33.3% Oats Barley, 90%; Rice hulls, 10% Wheat shorts a All diets were corrected by mineral-vitamin mixes ( %) Statistical analysis and calculations The relationship between DE or dge and the chemical composition of diets was established, using a step-wise linear regression approach. Independent variables affected by a coefficient related to a probability value P > 0.05 or highly correlated to some of the variables previously introduced (R > 0.90) were not allowed to enter the model. Two different analyses were performed: (A) excluding those diets with some particular non-fibrous organic component clearly out of the standard range, namely Diets 1 and 2 (high EE), Diet 11 (high CP> and Diet 16 (high both EE and CP), and also a diet with fibre highly digestible (Diet 12); and (B) excluding only the latter.

4 64 J. Ferniindez-Carmona et al./animal Feed Science Technology 64 (1996) The contents of DE, digestible crude protein (DCP) and undigestible crude fibre (UCF) of the ingredients were calculated: directly for 13 of them, used as the only ingredient of the diet; (2) by simple linear regression and extrapolation from the results for Diets 6, 13 and 20 for corn or Diets 9, 15 and 18 for barley; and (3) by difference for the rest of the ingredients. In all cases, the values corresponding to diets were corrected for the mineral-vitamin supplement. 3. Results 3.1. Digestibility of diets Table 2 shows feed intake, apparent digestibility coefficients of DM, OM, CF and CP (ddm, dom, dcf and dcp, respectively), and dge and DE of the diets. As a consequence of the differences in composition of the diets, a great range of variation for all those values was observed, especially noticeable for dcf (from - 1.5% and 0.9% in Diets 22 and 5 up to 54.8% in Diet 12) and dcp (from 6.5% and 9.7% in Diets 1 and 2 up to 81.6% in Diet 11). High standard errors of the means were detected for feed intake and dcf in most cases, and for all values in Diets 1 and Prediction of DE and dge The simple correlation matrices and equations obtained from the step-wise linear regression analyses are presented in Table 3. When the effects of components independent of fibre content were limited through the exclusion of diets out of range in EE, CP and dcf (Analysis A), ADF was the best single predictor for both DE and dge (Eqs. and (2); Fig. l), and no significant improvement was obtained when some more independent variables were introduced into the model. Including diets high in EE and CP (Analysis B) decreased the accuracy of prediction of DE from ADF (Eq. (3)), but successive inclusion of EE and CP as independent variables led to a partial recovery of accuracy (Eqs. (4) and (5)). The inclusion of GE as a second variable in the prediction of DE (Eq. (6)) provided precision similar to that provided by the inclusion of both EE and CP, for which reason introducing EE and CP did not improve prediction of dge from ADF (Eq. (7)) Nutritive value of ingredients The chemical composition and the nutritive value, expressed as DE, DCP and UCF, of the ingredients used in the present work are summarized in Table 4. Expressing the UCF value instead of the digestible CF value involved a lower error in calculation and adds to the understanding of the discussion as the role of fibre is essentially related to its indigestible nature. Considering the methods used to calculate the values, the standard errors of the means were lower in the direct method, where the only source of error is the individual variability observed in digestibility results. However, the estimation of DCP for grape

5 J. Ferruhiez-Carmona et al./animal Feed Science Technology 64 (1996) Table 2 Digestibility of diets (%, mean and SE) Diet no. Intake ddm (g DM kg-0.75 day- ) dom dcf dcp dge DE I I I I (MJ kg- DM)

6 Table 3 Prediction of DE and dge from chemical composition of diets Analysis A: excluding diets high in EE or/and CP or dcf ( n = 18) Correlation matrix NDF CF EE CP Ash GE dge DE ADF 0.% NDF CF EE CP Ash GE dge Linear regression equations Eq. no. Intercept a, ADF R2 RSD y=de(mjkg- DM) P < y = dge (%I P < Analysis B: excluding diet high in dcf (n = 22) Correlation matri2 ADF NDF CF EE CP Ash GE dge (3.7%) P < (3.6%) P < NDF CF EE CP Ash GE dge DE 0.8%

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9 J. Ferruindez-Carmona et al./animal Feed Science Technology 64 (1996) Table 4 Chemical composition and nutritive value (%, mean and SE) of ingredients (on DM basis) Ingredient ADF NDF CF EE CP DE a (MJ kg- 1 DCP a (a) UCF 1 X%0> Corn Barley 6.7 Oats 12.8 Wheat shorts 8.8 Brewer s grains 20.4 Beet pulp 24.0 Sunflower meal 28.7 Paprika residue Alfalfa hay B 31.8 Alfalfa hay C 32.8 Vetch-oats hay 32.5 Sainfoin hay 36.9 Grass hay 36.5 Orange tree leaves 22.8 Olive tree leaves 39.9 Corn stover 40.5 StraW 51.5 Olive oil cake 53.1 Grape mart 54.3 Sunflower hulls 55.6 Rice hulls ~ (2) (2) (3) (3) (3) (3) (3) b (3) a DE, DCP and UCF: directly, (2) by simple linear regression; SE is SE of intercept or (3) by difference, SE=[SEZ,+(100-L)2SE;r]-0~5100L- where SE, is SE of diet, SE,, is SE of joined ingredient and L is level of inclusion of tested ingredient (%I. Values of diets were corrected for the added mineral-vitamin mix. b Considering for soybean meat-44 values of 15.5 MJ DE kg-, 36.9% DCP and 5.1% UCF.

10 70 J. Fernrindez-Carmom et al./animal Feed Science Technology 64 (1996) mart and olive oil cake was very poor, resulting in a very low value, which was affected by a considerable error, as mentioned before. The error associated with other methods tends to be higher with a low level of substitution; in the case of straw (20%) and rice hulls (10%) the variance, which includes that from the corresponding diet and the proportional part of that from barley, is multiplied by five and ten respectively, causing very unreliable estimates of DE and DCP. 4. Discussion 4.1. Prediction of DE and dge It is well established that the energy value of feedstuffs is related to the fibre content because of the low digestibility of this component. In the present work, ADF was the best single predictor of DE and dge, better than other fibrous fractions (NDF, CF). The same conclusion has been reached in most other works which compare these fractions (Battaglini and Grandi, 1984; Maertens et al., 1988; Ortfz and De Blas, 1989; De Blas et al., 1992). Only the data of Villamide (19891, recalculated by Wiseman et al. (19921, show crude fibre resulted to be a better single predictor than ADF, perhaps because they considered 14 ingredients from which ten may be defined as concentrates (CF < 13.5% on a DM basis, DE > 11 MJ kg- DM), where the gap between the meaning of these fractions could be reduced. Certainly, predictions of DE and dge based on ADF lose precision for diets in which the level of other fibre-independent fractions affecting DE, such as EE and CP, are significant. In this respect, several works have pointed out that the diets with added fat and the protein concentrates move away from the equations based on fibre content (Ortiz and De Blas, 1989; De Blas et al., 1992; De Blas, 19941, but in our case those deviations could be partly corrected by including EE and CP (or, alternatively, GE) in the model. The exclusion of Diet 12 (beet pulp) in the step-wise linear regression analyses avoided a large decrease of accuracy in the prediction of DE and dge. Several works have shown that prediction equations based on chemical analysis underestimate DE value for diets with high levels of beet or citrus pulps, rich in digestible fibre (Maertens et al., 1988; Ortfz and De Blas, 1989; De Blas et al., 1992; De Blas, 1994). Table 5 lists different prediction equations for DE and dge. Comparisons between our equations and others previously published are hindered by the variety of feeds used in deducing them, giving big differences in the range of any chemical component, which affect its predictive value. In spite of that, it is remarkable that the coefficient affecting ADF is about 0.21 in predicting DE and in predicting dge: DE and dge fall 0.21 MJ kg- DM and 1.2% respectively for each percentage-unit of increment in dietary ADF content. This fibre effect on the energy value seems reliable for a range of fibre far wider than is usual in commercial diets and, to a high degree, is independent of the effect of variations in EE, CP or GE. The equations could not be applied to high digestible-fibre feeds (pulps) as commented above, nor to those rich in UFC having a large particle size (straw), probably related to a faster digestive passage, which in turn

11 Reference Battaglini and Grandi, 1984 Corino, 1987 Maertens et al., 1988 Ortiz and De Bias, 1989 De Blas et al., 1992 (dge) De Blas, 1994 (DE) De Bias et al., 1992 (dgej De Blas, 1994 (DE) Current work, Analysis A Current work, Analysis B a ADF, EE and CP in % on DM basis, GE in MJ kg- DM. b From ddm = ADF and DE = ddm. Assuming DM content of 89%. Table 5 Linear regression equations of DE and dge on chemical composition a of diets for rabbits DE (MJ kg- DM) RSD dge (%) RSD ADF range ADF b ADF ADF GE ADF ADF EE ADF GE ADF ADF+O.lOOCP ADF EE range CPrange n IO ADF EE ADF ADF EE ADF ADF ADF ADF ADF EE ADF+0.77 GE ADF EE CP

12 72 J. Fermhdez-Carnwna et al./animal Feed Science Technology 64 (1996) further lowers DE value (De Blas et al., 1989; De Blas and Villamide, 1990; Villamide et al., 1991; De Blas, 1994) Nutn tive value of ingredients The nutritive value of any ingredient is essentially affected by its chemical composition, which vary greatly from one batch to another, but the methodology used must be also considered. A complete discussion of these effects on each ingredient is beyond the objectives of this work, and we will limit ourselves to consideration of the data summarized in Table 6, especially of the restrictions imposed and of the most significant deviations. We have chosen to limit the variations in fibre level of some well documented ingredients (barley, wheat shorts, beet pulp, sunflower meal, alfalfa hay and grass hay), in order that our results could be compared with others. Furthermore, some values having a great experimental error (SE > 20% of the mean) and some ingredients lacking any suitable reference (paprika residue, vetch-oats hay, olive tree leaves) have not been considered for discussion. The differences in DE for brewer s grains can be partially explained by composition differences: as compared with ours, those used by Fonolll et al. (1984) had higher ADF (29% vs. 20%) and those used by Maertens et al. (1990) lower EE (2% vs. lo%), and consequently the DE values were lower. Another cause of the observed differences may be the very low feed intake in our experiment (34 g DM kg-o.75 day- ), resulting in abnormal increments in both digestive retention time and digestibility. Fonolll et al. (1984) recommended a substitution method with a 50% inclusion of brewer s grains in the basal diet, because of the low palatibility of this ingredient. The effect of feed intake on the rate of digestive passage and the digestibility (unfortunately not cited in many papers on digestibility) could be related to some confusing data. The low feed intake for beet pulp (43 g DM kg-o.75 day- ) could explain the rather high values of DE and dcf found in the current work. Even so, Martinez and Femtidez (1980) reported higher values for DE and dcf (14.2 vs MJ kg- DM, 70% vs. 55%), recording a feed intake of only 28 g DM kg-o.75 day- when using also beet pulp alone. Garcia et al. (1993) reported an increment in the DE value of this ingredient with the level of inclusion in the diet. Reciprocally, De Blas and Villamide (1990) related a decrease in the digestibility of beet pulp to an increase in the proportion of large particles of indigestible fibre in the basal diet, that are likely to shorten cecal retention; and a similar effect has been described for soybean meal (Villamide et al., 1991). Along the same lines, DE value of olive oil cake was far higher than the recalculated value from the data of Martinez and FemSndez (1980), who used a level of inclusion of 90% and observed a feed intake more than twice as high (113 vs. 48 g DM kg-. day- ). Conversely, the digestibility of orange tree leaves was lower than that reported by Cervera (1976), using natural non-pelleted dry leaves, their ingestion being only 30 g DM kg-o.75 day- compared with 47 g DM kg-o.75 day- in the present work. Raharjo et al. (1986) observed important increments in feed intake and lower digestibilities of different tropical forages as a consequence of pelleting.

13 J. Ferna ndez-carmona ef al./animal Feed Science Technology 64 (1996) Table 6 Nutritive value for rabbits of several ingredients from different authors (on DM basis) DE(MJ kg- ) dcp (%I dcf (%) Reference a Corn Barley (4-5% Oats CF) b c l5.4( ) ( ) ( ) (60-85) :: (55-75) (73-90) (27-100) :: (33-86) % 88 (74-100) 94 1,2,3,4,5,6,7, ,?,, 7 ~2.3S6.8 Wheat shorts (5-8% CF) Brewer s gram Beet pulp (18-22 CF) Sunflower meal (2429% CF) Alfalfa hay (25-29% CF) Sainfoin hay Grass hay (28-33% CFJ Orange tree leaves Corn stover Olive oil cake Grape mart Sunflower hulls 13.8 ( ) ( ) ( ) ( ) ( ) ( ) ( ) (75-77) (71-76) (45-87) ( (55-66) (56-87) (56-81) (82-88) (28-50) (85-95) (75-88) (64-75) (63-88) (88-97) I, > IO, > 598? 14,15,16, a 1: Fekete and Gippert, 1986; 2: Maertens et al., 1988; 3: De. Blas and Villamide, 1989; 4: INRA, 1989; 5: Maertens et al., 1990; 6: Villamide and De Blas, 1991; 7: Hullar et al., 1992; 8: Liu et al., 1992a; 9: Fonolll et al., 1984, 10: Gippert et al., 1988; 11: De Blas and Villamide, 1990; 12: Maertcns and De Groote, 1984, 13: Villamide et al., 1991; 14: Maertens and De Groote, 1981; 15: Cavani et al., 1993; 16: Perez, 1994; 17: Garcia et al., 1995; 18: Cervera, 1976; 19: Martinez and Femandez, b Other authors, mean and, between brackets, range. Current study. A basic assumption in the methods of determining in vivo nutritive value of ingredients (direct, multiple substitution level-simple linear regression-extrapolation and single substitution level-difference) implies the additivity of the values, that must be independent of both the composition of the basal diet and the inclusion level of the ingredient. As has been said above, the main transgression of that principle appears to result from changes in the rate of digestive passage, linked to an altered feed intake and to high levels either of digestible fibre or of undigestible fibre in large particle form.

14 74 J. Fermkdez-Carmona et al./animal Feed Science Technology 64 (1996) When no such transgression occurs, the direct method should be applied, especially if the fraction to be studied is present at a low level in the ingredient. Although the values for alfalfa hay were not much different between the current and other works, the importance of this ingredient in rabbit diets deserves some attention. Most works have determined its nutritive value in growing animals, where De Blas et al. (1995) have shown that NDF digestibility is low compared with adult animals and that this difference increases with the level of NDF in the diet, leading to an underestimation of the energy value of fibrous feeds for adult animals, that could explain the not much higher values for our alfalfa hay. Cavani et al. (1993) verified an increase for dcf and DE of alfalfa between the 8th and the 1 lth weeks of life (12% vs. 25%, 8.8 vs. 9.0 MI kg- DM). Grape mark had a DE very different from that reported by Martinez and Femtidez (1980), with a similar product in terms of EE and CP and even similar feed intake, but the second referenced value (INRA, 1989) is very near. Some other evident deviations, such as those in the indigestibility of CF (loo-dcf) for corn and barley or in dcp for grass hay and sunflower hulls, are not discussed because of the limited practical significance of the corresponding fractions, moreover affected by large standard errors. Acknowledgements The present work was supported by a grant from CICYT (AFG CO2-02). References AC, Official Methods of Analysis of the Association of Official Analytical Chemists, 14th edn. AC, Washington, DC. Battaglini, M. and Grandi A., Stima del valore nutritivo dei mangimi composti per conigli. In: Proc. 3th Congress of World Rabbit Science Association, Roma. WRSA Pub]., Vol 1, pp Cavani, C., Minelli, G. and Urrai, G.F., Digeribilita in vivo e valore nutritivo dell erba medica disidratata nell coniglio in accrescimento. In: Proc. 10 Congresso Nazionale dell Associazione Scientifica di Produzione Animale, Bologna. ASPA Publ., pp Cervera, C., Digestibilidad de la hoja de naranjo en el conejo. Tesina de Licenciatura, Universidad de Valencia, 25 pp. Corino, C., Alcune considerazioni sulla stima del valore nutritivo dei mangimi composti integrati utilizzati nell alimentazione del coniglio. Coniglicoltura, 24 (9): De Bias, C., Avarices en alimentackk energetica de conejos. In: 12 Conferencia Colbom-Dawes para la Industria de Producci6n Animal, Madrid, 22 pp. De Bias, C., Taboada, E., Mateos, G.G., Nicodemus, N. and Mkndez, J., Effect of substitution of starch for fibre and fat in isoenergetic diets on nutrient digestibility and reproductive performance of rabbits. J. Anim. Sci., 73: De Bias, C. and Villamide, M.J., Valor nutritive de 10s alimentos. In: C. De Bias (Editor), Alimentaci6n del Conejo. Mundi-Prensa, Madrid, pp De Bias, C. and Villamide, M.J., Nutritive value of beet and citrus pulp for rabbits. Anim. Feed Sci. Technol., 31: De Bias, C., Villamide, M.J. and Carabatio, R., Nutritive value of cereal by-products for rabbits. 1. Wheat straw. J. Appl. Rabbit Res., 12: De Blas, C., Wiseman, J., Fraga, M.J. and Villamide, M.J., Prediction of the digestible energy and digestibility of gross energy of feeds for rabbits. 2. Mixed diets. Anim. Feed Sci. Technol., 39:

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