On-line version ISSN 2221-4062
S. Afr. j. anim. sci. vol.39 n.2 Pretoria Feb. 2009
F. AghakhanianI; A. ZareiI, #; H. LotfollahianII; N. EilaI
IAgriculture Research Centre, College of Agriculture and Natural Resources, Islamic Azad University- Karaj Branch, Mehrshahr, Karaj, Iran
IIIranian Animal Science Research Institute, Karaj, Iran
In order to determine the amino acid digestibility of artemia meal, five-week old male broiler chicks were given a semi-purified diet in which artemia meal was the sole source of protein. Apparent amino acid digestibility values of the assay diet, using ileal and excreta contents, were calculated using chromic oxide as indigestible marker. True digestibility values were calculated using endogenous output determined by feeding a nitrogen-free diet. The results showed that in determination of apparent amino acid digestibility of excreta, serine had the lowest (0.80) and methionine the highest (0.92) digestibility, while glycine had the lowest (0.88) and arginine and leucine the highest (0.95) apparent ileal digestibility. In measuring true excreta and ileal amino acid digestibility, alanine and glycine had the lowest (0.90 and 0.93) and methionine the highest (0.96 and 0.99) digestibility, respectively. In general, the site of measurement had no effect on apparent or true amino acid digestibility of artemia meal.
Keywords: Artemia meal, amino acid digestibility, excreta, ileum, broiler
Artemia or brine shrimp is a crustacean that lives in salty habitats in about 500 zones around the world (Van Stappen, 1996). All stages of artemia from cysts and newly hatched nauplii to adult artemia are used as food sources in aquaculture, but there is little research about the use of artemia in poultry nutrition. Ras et al. (2002) and Zarei et al. (2006) used artemia meal (biomass) as a replacement for fish meal in broiler chick diets. These researchers confirmed that artemia meal could be used as a feed ingredient in poultry nutrition.
The amino acid content of artemia in different zones has been determined (Seidel et al., 1980; Ahmadi et al., 1990; Aragao et al., 2004) and this has shown that artemia protein is rich in several amino acids. However, it is recognized that in the diet formulation for chickens the digestibility of amino acids is required rather than the gross amino acid content of the dietary ingredients. The purpose of this study was to determine the digestibility of the amino acids in artemia meal when using the amino acid content of ileal digesta vs. that of excreta in the calculations.
The experiment was approved by Islamic Azad University Committee of Animal Ethics and complied with Iranian guidelines for animal welfare. A total of 100 day-old male broiler chicks (Ross 308 strain) were obtained from a local hatchery and raised in battery brooders. The birds received commercial broiler starter and grower diets from days l to 30. On day 30, forty birds of uniform body weight (1.11 ± 0.15 kg) were allocated to eight groups of five birds each, and assigned to eight cages. The study consisted of two dietary treatments, a diet containing artemia meal and a nitrogen-free diet. Therefore, each treatment was replicated four times.
The test diet was formulated to contain artemia meal as the sole source of dietary protein (Table1). Cellulose (Merck, Darmstadt, Germany) was added as a source of fibre. A nitrogen-free diet was formulated to allow for the determination of the endogenous flow of amino acids. Chromic oxide was included in all diets as an indigestible marker.
On day 30 the birds were given the diets ad libitum for four days and were then fasted for 24 h. The birds were then allowed to consume their diets for a one hour period (Kadim & Moughan, 1997). Excreta were collected for 13 h on a tray placed underneath each cage, transferred to a plastic container and frozen (-20 °C). The birds were offered the same diet ad libitum for a further two days. They were again fasted for 24 h and then allowed to consume their diets for one hour. Four hours after the start of the meal (Kadim & Moughan, 1997) the birds were killed by CO2. The body cavity was opened, the ileum removed and digesta collected from the ileum. Ileal digesta of birds within a cage were pooled to provide adequate material for chemical analysis. The digesta were frozen immediately after collection at -20 °C. The excreta and digesta samples were subsequently freeze dried, finely ground and stored at -20 °C pending chemical analysis.
The amino acid concentration of the diets, the ileal digesta and excreta samples were determined using the cation-exchange HPLC system utilizing post-column OPA (orthophthaldehyde) derivitisation after 24 h hydrolysis with 6 M hydrochloric acid at 110 °C. Tryptophan was determined using alkaline hydrolysis by barium hydroxide according to the procedure of Fontaine et al. (1998). Dry matter (DM) (934.01) and crude protein (CP (N x 6.25)) (976.05) content were determined according to AOAC (1990) procedures and chromic oxide (Cr2O3) determination was done using atomic absorption spectrophotometry, following the method of Fenton & Fenton (1979).
Apparent and true amino acid digestibility were calculated using the following equations (Kadim et al, 2002):
AA output = AA concentration in digesta or excreta x (Diet Cr2O3 concentration / Cr2O3 concentration in digesta or excreta);
Apparent AA digestibility (AID) = (AA concentration in feed - AA output (in ileum or excreta)) / AA concentration in feed;
True amino acid digestibility = (AID + Endogenous amino acid output) / Amino acid concentration in feed.
A paired t-test was used to compare ileal and excreta digestibility values. The Minitab version 13 programme was used for statistical analysis.
When calculating apparent amino acid digestibility using excreta, serine had the lowest (0.80) and methionine the highest (0.92) digestibility, whereas glycine had the lowest (0.88) and arginine and leucine the highest (0.95) apparent digestibility when based on ileal samples. In measuring true excreta and ileal amino acid digestibility, alanine and glycine had the lowest (0.90 and 0.93) and methionine the highest (0.96 and 0.99) digestibility, respectively. Differences between excreta and ileal amino acid digestibility were not significant (P >0.05).
Although the amino acid digestibility values of artemia meal based on ileal collections were higher than values calculated from excreta collections, differences were not significant. This suggests that microbial activity in the hindgut of broilers did not affect the amino acid digestibility. A likely explanation is that because of the high digestibility of amino acids in artemia meal, there was little amino acid reaching the hindgut to be affected by the microflora (Ravindran et al., 1999). Wallis & Balnave (1983) reported that in high quality proteins, digestion and absorption of amino acids were completed in the upper parts of the small intestine, leaving little available for microorganism fermentation. Kadim et al. (2002) showed that, when comparing excreta and ileal digestibility in highly digestible ingredients, there were no significant differences between the two methods of determination.
Among indispensable amino acids, threonine had the lowest apparent digestibility. The same result has been reported with other animal ingredients (Raharjo & Farrell, 1984; Ravindran et al., 1999; Kadim et al., 2002; Huang et al., 2006) and is likely the result of high concentrations of threonine in endogenous protein. Endogenous secretions consist of digestive enzymes and mucin that are rich in threonine, serine, aspartic acid and glutamic acid (Salter & Fulford, 1974; Ravindran et al., 2004) and can affect the apparent threonine digestibility. As shown in this study, using true amino acid digestibility can eliminate the underestimation of threonine digestibility.
Parsons (1984) found that hindgut fermentable carbohydrates caused an increase in amino acid secretion in intact rather than in caecectomised birds. As suggested by Sauer & Ozimek (1986), the amount of energy-yielding carbohydrates reaching the hindgut appears to determine whether net degradation and net synthesis of amino acids will take place. The lower digestibilities based on excreta in the present study suggested that some fermentable carbohydrates reached the large intestines, though that the quantities were too low to cause significant differences between calculations based on excreta vs. ileal collections. On the other hand, the higher ileal value could be due also to contamination of excreta with scurf and feathers.
In this study, crude protein digestibility was lower than total amino acid digestibility. It is probably due to the high content of chitin in artemia meal. Chitin is the crustacean exoskeleton polysaccharide and consists of N-acetyl glucosamine residues that forms part of the protein complex, and is considered to be poorly digested in the gastrointestinal tract of chickens (Austin et al., 1981; Khempaka et al., 2006). As a result it would be voided in excreta, thereby decreasing crude protein digestibility. It seems that N-acetyl glucosamine had little effect on the amino acid digestibility in artemia meal. The protein digestibility values in the present study are in agreement with values reported by Zarei et al. (2005).
Results of the present study showed that site of measurement do not have a significant effect on the apparent or true amino acid digestibility of artemia meal. It demonstrated that the amino acids in artemia meal have relatively high digestibilities, suggesting that artemia meal can be considered as a protein source in poultry nutrition.
We offer our thanks to the chairman, vice president and personnel of the Iranian Animal Science Research Institute, Karaj Islamic Azad University, for making this research possible.
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