عنوان مقاله [English]
Cereal grains are the major source of energy for commercial poultry nutrition and incorporate about 60-70% of the diet volume. Corn is mainly used in the production of poultry feed mixtures, but the amount of corn production in Iran is not sufficient and more than 50% of corn requirement for poultry production is provided via import, therefore, for economic reasons its content in poultry diets might reduce. Barley can be the preferred grain for cultivation in many areas in Iran due to its resistance to drought region. Hull-less barley (HLB) differs from conventional barley in that the hulls firmly attached to the kernel and consequently is detached after thrashing, leading to a higher level of valuable nutrients and increased nutrient density. Reported that the HLB has a higher AME and protein content than hulled barley because of diluting effect of the fibrous hulls. The high protein content in HLB compared to corn grain and its considerable AMEn make it a potentially good ingredient for poultry diet formulation. However, since the high content of non-starch polysaccharides (NSP) probably decrease nutrient digestibility and performance due to the lack of an appropriate enzyme in the digestive tract of chickens, some concern has been expressed in relation to the inclusion levels of HLB in broiler diets. This experiment was carried out to study the influence of enzyme supplementation on the apparent metabolizable energy corrected for nitrogen (AMEn), apparent digestibility of dry matter (DMD), and crude protein (ACD) of two varieties of HLB by using the total excreta collection method in broiler chickens.
Materials and Methods Sixty-four male broiler chicks "Ross-308", 16d of age, assigned to 16 metabolic cages in a completely randomized design (CRD) experiment with a factorial arrangement (2×2), 4 treatments with 4 replicates/treatment and 4 birds/replicate. The factors included two varieties of HLB (HMB-83-7 and native of Tabas, Iran) and two levels of enzyme cocktail (was a blend of 3500 U/g β-glucanase, 1600 U/g xylanase, 25 U/g cellulase and 1000 U/g phytase activity obtained from Phileo-Lesaffre-Animal-Care, Co. "Marcq-en-Baroeul-France") supplementation (0 and 0.5 g/kg of diet). The experimental diets were made so that the HLB barley was the sole source of energy and nitrogen supply. The digestion trial included a 4-day preliminary period in 16–19d of age, followed by 4 days of total excreta collection. The feed was provided ad libitum during the preliminary and the collection period. During the collection period (20-23d of age) total feed intake was measured, and excreta from each cage were collected twice a day, pooled, and kept frozen at -18oC until subsequent analyses. The excreta samples were freeze-dried to determine DM content. The dried excreta and diet samples were ground through 20 mesh screens, and nutrient content was determined according to AOAC (2000). The gross energy of the dried excreta and diet samples was measured. The apparent digestibility of crude protein (CPD) and dry matter (DMD) of HLB was calculated. The apparent metabolizable energy corrected for nitrogen (AMEn), of HLB was calculated.
Results and Discussion The average DMD, CPD and AMEn of HLB were obtained 64.39±2.80%, 59.50±7.66% and 3034±212 kcal/kg as-fed basis, respectively. The DMD, CPD and AMEn of HLB in Tabas native variety were 67.45, 67.41% and 3189 kcal/kg as-fed basis respectively, which were significantly more than HMB-83-7 variety (Vs 64.67, 55.1% and 2961 kcal/kg for DMD, CPD and AMEn). Dietary enzyme supplementation increased the hull-less barley DMD (64.39% Vs 67.73%, 5.18% improvement compared to basal content), as well as increasing the CPD (50.59% Vs 63.03%, 5.93% improvement compared to base value) and AMEn (3034 Vs 3107 kcal/kg, 2.41% improvement compared to base value), so that the differences were significant (P <0.05). The effectiveness of dietary enzyme supplementation on the improvement of nutritional value of different HLB varieties that used in this experiment was varied. The Tabas native HLB variety was more effected than HMB-83-7 variety by dietary enzyme supplementation. Hull-less barley contains considerably higher levels of anti-nutritional factors consisting mainly of soluble non-starch polysaccharides (NSPs), especially ß-glucans compared to corn and wheat. Water-soluble β-glucan with gel-forming characteristics increases the gastrointestinal (GI) tract contains viscosity, decreases digestive enzymes contact with substrates, increases the thickness of the unstirred water layer in the GI tract mucosa and hence depresses nutrient digestibility. Many researchers have studied the beneficial effects of the addition of exogenous enzymes to the rich non-starch polysaccharide diets. The positive nutritional effects achieved by the dietary supplementation of exogenous enzymes are proposed to be caused by several mechanisms. Mainly, it has been shown that the anti-nutritive effects of viscous cereals such as barley, wheat, rye, oats, and triticale are associated with raised intestinal viscosity caused by soluble β-glucans and arabinoxylans present in those cereals. These problems are overcome by dietary supplementation of β-glucanases and xylanases. It is assumed that the ability of β-glucanases and xylanases to degrade plant cell walls leads to release of nutrients from grain endosperm.
Conclusion According to the results of this experiment; the hull-less barley AMEn, DMD and CPD value affected by variety. The dietary exogenous enzyme supplementation improved the hull-less barley DMD, CPD and AMEn value.