COMPARISON OF TWO DIETARY MARKERS IN THE DETERMINATION OF AMINO ACID DIGESTIBILITY IN SOME FOODSTUFFS FOR GROWING BROILER CHICKENS

Genaro Monforte-Braga, Luis Sarmiento-Franco, Concepción Capetillo-Leal, Ronald Santos-Ricalde and José Segura-Correa

Genaro Monforte-Braga. M.Sc. in Tropical Animal Production, Universidad Autónoma de Yucatán (UADY), Mexico. Consultant in animal production, Yucatán, México.

Luis Sarmiento-Franco. M.Sc. in Tropical Animal Production, UADY, Mexico. Ph.D. in Animal Nutrition, University of Edimburg, UK. Professor Researcher, UADY, Mexico. Address: Faculty of Veterinary Medicine and Animal Science, UADY. Apartado Postal 4-116 Itzimná, Merida, Yucatan, Mexico. E-mail: fsarmien@tunku.uady.mx

Concepción Capetillo-Leal. Biologist-Chemist and Diploma in Analytical Chemistry, UADY, Mexico. Technician, UADY, Mexico.

Ronald Santos-Ricalde. M.Sc. in Tropical Animal Production, UADY, Mexico. Ph.D. in Animal Nutrition, University of London, UK. Professor, UADY, Mexico.

José Segura-Correa. M.Sc. in Animal Production, Universidad Autónoma de Chapingo, Mexico. Ph.D. in Genetics, McGill University, Canada. Professor Researcher, UADY, Mexico.

SUMMARY

The apparent ileal amino acid digestibility in maize, sorghum, soybean meal, maize gluten, fishmeal, meat and bone meal and wheat bran for growing broiler chickens were determined, using titanium dioxide (TiO₂) and chromium oxide (Cr₂O₃) as dietary markers. Twelve chickens were tube-fed 30g of each ingredient, containing one of the two dietary markers, in two occasions, using the forced feeding technique. Analyses of variance were performed on the data obtained to examine the effects of ingredients and markers. As expected, there were significant differences in amino acid digestibility between ingredients, ranging from 0.53 for cysteine in meat and bone meal to 0.97 for tyrosine in soybean meal. For all ingredients, the aminoacid digestibility coefficients calculated on the basis of the titanium marker were higher (P<0.05) than those determined using the chromium marker. The only exception was wheat bran, in which the marker was without effect (P>0.05). The aminoacid digestibility coefficients showed less variation when TiO₂ was used as the dietary marker. It is concluded that TiO₂ is a more suitable dietary marker than Cr₂O₃, being less variable and obtaining higher digestibility, which indicates a greater recovery.

COMPARACIÓN DE DOS MARCADORES DIETÉTICOS EN LA DETERMINACIÓN DE LA DIGESTIBILIDAD DE AMINOÁCIDOS EN ALGUNOS INGREDIENTES PARA POLLOS DE ENGORDA

RESUMEN

Se determinó la digestibilidad ileal aparente de aminoácidos en maíz, sorgo, pasta de soya, gluten de maíz, harina de pescado, harina de carne y hueso, y salvado de trigo en pollos de engorda, utilizando dióxido de titanio y óxido de cromo como marcadores inertes de la dieta. Doce pollos fueron alimentados en dos ocasiones con 30g de cada ingrediente, con uno de los dos marcadores dietéticos, mediante la técnica de alimentación forzada. Se llevaron a cabo análisis de varianza con los resultados para determinar efectos de ingredientes y de marcadores. Se encontraron diferencias significativas en la digestibilidad de aminoácidos entre ingredientes, cuyo rango fue de 0,53 para cisteína en la harina de carne y hueso, hasta 0,97 para tirosina en pasta de soya. En todos los ingredientes los coeficientes de digestibilidad de aminoácidos calculados con base en titanio fueron mayores (P<0,05) que aquellos determinados con base en cromo. La excepción fue para salvado de trigo donde no se encontró efecto significativo del marcador utilizado (P>0,05). Los coeficientes de digestibilidad de aminoácidos mostraron una menor variación cuando el dióxido de titanio fue usado como marcador dietético. Se concluye que el dióxido de titanio es más confiable que el cromo como marcador dietético, siendo menos variable y obteniéndose mayor digestibilidad, lo cual indica una mayor recuperación.

COMPARAÇÃO DE DOIS MARCADORES DIETÉTICOS NA DETERMINAÇÃO DA DIGESTIBILIADADE DE AMINOÁCIDOS EM ALGUNS INGREDIENTES PARA FRANGOS DE ENGORDA

RESUMO

Determinou-se a digestibilidade ileal aparente de aminoácidos em milho, sorgo, pasta de soja, glúten de milho, farinha de peixe, farinha de carne e osso, e salvado de trigo em frangos de engorda, utilizando dióxido de titânio e óxido de cromo como marcadores inertes da dieta. Doze frangos foram alimentados em duas ocasiões com 30g de cada ingrediente, com um dos dois marcadores dietéticos, mediante a técnica de alimentação forçada. Levaram-se a cabo análises de variância com os resultados para determinar efeitos de ingredientes e de marcadores. Encontraram-se diferenças significativas na digestibilidade de aminoácidos entre ingredientes, cuja faixa foi de 0,53 para cisteína na farinha de carne e osso, até 0,97 para tirosina em pasta de soja. Em todos os ingredientes, os coeficientes de digestibilidade de aminoácidos calculados com base em titânio foram maiores (P<0,05) que aqueles determinados com base em cromo. A exceção foi para salvado de trigo onde não se encontrou efeito significativo do marcador utilizado (P>0,05). Os coeficientes de digestibilidade de aminoácidos mostraram uma menor variação quando o dióxido de titânio foi usado como marcador dietético. Conclui-se que o dióxido de titânio é mais confiável que o cromo como marcador dietético, sendo menos variável e obtendo-se maior digestibilidade, o qual indica uma maior recuperação.

KEYWORDS / Aminoacid / Chickens / Chromium / Digestibity / Titanium /

Received: 05/22/2006. Modified: 11/11/2006. Accepted: 11/13/2006.

Introduction

Food represents ~70% of the production costs in the poultry industry. The formulation of low-cost diets reaching specific production goals is therefore an important aim in poultry nutrition. The supply of aminoacids contribute to ~25% of the cost of the diet; however, not all the aminoacids provided in the diet are available to the animal during the digestive process. The formulation of diets based on available aminoacids constitutes the ideal objective, as this will avoid both the overdose of these expensive nutrients and the risk of under-supplying the nutrient requirements. Because the available aminoacids provide a measure that is closer to the animal requirements, the environmental pollution by excessive N₂ excretion is minimized. A number of factors affect the digestibility of aminoacids in the ingredients, including those inherent to the animal such as genotype, age or live weight (Ten Doescate et al., 1993). Other factors are attributable to the food, such as its chemical composition (Green et al., 1987a, b; Sarmiento et al., 2000), the aminoacid concentration (Villamide and San Juan, 1998) or the presence of toxic or antinutritional factors for the animal (Belmar et al., 1999). Kirby et al. (1993) found that the crude protein content in the corn and in the meat and bone meal samples showed an important variation, which may cause errors in the formulation of diets, besides being able to affect the nutrient digestibility of these ingredients.

The determination of ileal aminoacid digestibility requires the use of dietary markers. However, the variation in the recovery rate of the different markers may lead to inaccuracies in the estimation of the coefficients of digestibility. The most commonly used dietary markers are chromium oxide, titanium dioxide and acid-insoluble ash. Jagger et al. (1992) reported in pigs that an ample variability in the recovery rate of the dietary markers was associated with a great difference between digestibility coefficients of nutrients determined by different markers. The objective of the present study was to determine the apparent ileal amino acid digestibility in some ingredients for broiler chickens using titanium dioxide or chromium oxide as dietary markers.

Materials and Methods

One hundred and sixty eight 4-weeks old Ross male chickens (1.0 ±0.1kg live weight) were housed in wire cages (40×50cm). The cages were placed in a poultry house with an asbestos roof, wired walls and a cement floor, and then the cages were exposed to a natural environment. The climate of the region is tropical sub-humid with maximum and minimum temperatures of 35.7 and 22.5°C respectively, and a relative humidity average of 80%.

The apparent ileal amino acids digestibility of seven ingredients was evaluated: maize, sorghum, soybean meal, maize gluten, fishmeal, meat and bone meal and wheat bran. Either titanium dioxide (TiO₂; 4g·kg^-1) or chromium oxide (Cr₂O₃; 2.5g kg^-1) ^®J.T. BAKER, was added to the ingredients as indigestible dietary markers (Short et al., 1996; Sarmiento-Franco et al., 2003).

Birds were fasted for 24h after which they received 50ml of glucose solution (50% w/v). Twelve chickens at random were then tube-fed 30g of each ingredient, containing one of the dietary markers, at two occasions (16:00 and 8:00 the day after) using the forced feeding technique according to Sibbalad (1979).

Four hours after the tube feeding birds were killed, in the same order as they were fed, by an intravenous injection of sodium pentobarbitone. The small intestines were removed and digesta were collected between Meckel's diverticulum and ileocecal junction (Kadim and Moughan, 1997). The ileal content from every three birds for each ingredient were pooled and the resultant four samples were freeze-dried and passed through a mill (sieve Nº 40).

Determinations of aminoacids were made using high performance liquid chromatography according to Krishnamurti et al. (1984). Methionine and cystine were acid hydrolyzed by performic acid (Williams, 1994). Crude protein was analyzed by the AOAC (1980) procedure. Titanium analyses were made by a colorimetric method (Short et al., 1996) and chromium was determined using the method described by Fenton and Fenton (1979).

Analyses of variance were performed on the data between titanium and chromium determinations in the samples (Minitab, 2000). To determine differences in the digestibility coefficients of amino acids among ingredients analyses of variance were performed on data, according to a completely randomized design. Tukey´s multiple comparison was used when significant effects were identified.

Results

The aminoacid and crude protein (N×6.25) contents of the seven ingredients evaluated are shown in Table I. The ileal digestibility coefficients of aminoacids determined using titanium markers are presented in Table II. There were differences (P<0.05) in aminoacid digestibility between ingredients ranging from 0.53 for cisteine in meat and bone meal to 0.97 for tyrosine in soybean meal. Wheat bran and meat and bone meal showed in general lower coefficients of digestibility than the remainder of ingredients.

The apparent ileal digestibility of aminoacids determined using titanium and chromium are shown in Tables III and IV. In general, the aminoacid digestibility coefficients based on titanium concentration were higher (P<0.05) than those determined by chromium concentration, with the exception of wheat bran, which did not reach statistical significance (P>0.05). In Table V the coefficients of variation of determined digestibility estimates using chromium or titanium markers are shown. It was found that, in general, the aminoacid digestibility showed less variation when the TiO₂ marker was used. Moreover, the differences between these coefficients were dependent on the chemical composition of the ingredient, being 1.86 units for maize gluten meal and 9.7 units for maize.

Discussion

In general, the amino acid concentrations in the ingredients were found to be within the ranges reported in the literature (Bourdon et al., 1987; Green et al., 1987a, b; NRC, 1994, 1998; Ravindran et al., 1999; Kadim et al., 2002). The exceptions were the concentrations of threonine that were lower and those of lysine and histidine, which were higher.

The apparent ileal digestibility of aminoacids determined by titanium in this study are comparable to those reported in previous studies, while those determined by chromium were lower (NRC, 1994; Angkanaporn et al., 1996; Ravindran et al., 1999; Kadim et al., 2002). It must be noted, however, that these values were determined using markers other than titanium or chromium, or determined by total excreta collection. Higher digestibility coefficients for soybean meal, fishmeal, maize, sorghum and maize gluten were determined in this study when using titanium than chromium, yet lower digestibility values for wheat bran and meat and bone meal were determined by both markers. The low digestibility of amino acids in meat and bone meal and wheat bran could be explained on the basis of their chemical composition. In the case of meat and bone meal, it has been observed that there is a negative correlation (r²= -0.80) between protein digestibility and the ash content (Parsons et al., 1997). The ash content in the meat and bone meal in the present study were higher (39.4 vs 22.8%) than that reported by Parsons et al. (1997). Another factor that may have negative effects on the aminoacids digestibility is the high pressure and temperature used in the manufacturing process of the meat and bone meal (Johns et al., 1986; Shirley and Parsons, 2000; Wang and Parsons, 1998a), particularly in the case of cystine and methionine, which was observed in this experiment. Wang and Parsons (1998b) also found low bioavailability of cystine content in meat and bone meal. More recently, Ravindran et al. (2005) reported a notable low coefficient of digestibility for cystine in meat and bone meal, attributable to the processing damage related to increasing processing temperatures in that ingredient.

It is known that the high fibre content (NDF= 352g·kg^-1) in wheat bran could negatively affect nutrient digestibility. Additionally, the presence of soluble fibre mainly in the form of arabinoxylans, which have the property of producing a viscous solution when dissolved in water, has been reported to decrease nutrient digestion and/or absorption. The negative effect is attributed to an increment in the passage rate, impaired protein digestion and increased the endogenous aminoacid losses (Angkanaporn et al., 1994; Yin et al., 2000b).

The trends in ileal aminoacid digestibility coefficients determined by titanium and chromium in this study agreed with those found by Yin et al. (2000a, b), and these differences could be attributed to problems with chromium recovery. Yin et al. (2000c) reported that titanium recovery in pigs’ ileum varied from 95.5 to 99.9% contrasting with a chromium recovery variation ranging from 82.8 to 87.4%. Nevertheless, the same authors also reported that when the diet or evaluated ingredient is high in fibre (eg. wheat bran) the recovery of both markers is even lower (67.8 and 60.6% for titanium and chromium, respectively), which is related to a segregation effect of the markers, caused by the faster passage rate of the digesta of the high-fibre food (Yin et al., 2000c). In the present experiment, the ileal aminoacid digestibility values for wheat bran had a high coefficient of variation, with both chromium (21.65%) and titanium (18.13%), compared to other ingredients, which explains the lack of effect of the markers on the aminoacid ileal digestibility for wheat bran. Van Leeuwen et al. (1996) also found high variation (78 to 109%) in chromium recovery in ileal samples from pigs. Jagger et al. (1992) reported that the average chromium recovery is 10 units less than that for the titanium and concluded that titanium is more appropriate as a dietary marker than chromium, even though the latter is more commonly utilized. Although the exact reasons of these differences are unclear, they may be associated to analytic problems in the chromium determination, due to interference with other minerals (Yin et al., 2000b). Saha and Gilbreath (1993) reported that chromium recovery from diets and excreta determined by colorimetry or spectrophotometry diminishes significantly by the presence of Ca and P, which are found in relatively high concentrations in excreta and digesta. Another analytic difficulty for chromium determination is due to its volatilization caused by either high temperature during the ashing procedure, or through the synthesis of chromic chlorine, a volatile compound produced during acid digestion (Mir et al., 1989; Yiakoulaki et al., 1997). On the other hand, titanium determination has the advantage that the analytic procedure does not affect its determination in spite of burning and filtering the sample, and also does not run the risk of contamination or interference with other substances (Short et al., 1996).

It is concluded that titanium is a more suitable dietary marker than chromium to determine the apparent ileal aminoacid digestibility in food ingredients for poultry. The values obtained based on titanium are less variable and result in higher digestibility coefficients, which indicates a greater recovery. However, apparent digestibility values should be determined under ad libitum feeding conditions; in that context, results showed in the present work have to be taken in terms of relative values between ingredients rather than absolute ones.

Acknowledgements

The authors thank PROMEP-SEP-Mexico for the financial support of this study.

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