جستجوی مقالات مرتبط با کلیدواژه « heat stress » در نشریات گروه « دامپزشکی »

Reducing the protein and amino acid content of diet or altering the dietary electrolyte balance were suggested as the effective strategies to prevent the harmful effects of the heat stress in poultry.

This study surveyed the effects of various levels of threonine and dietary cation-anion balance on the broiler chickens under the heat stress conditions.

700 one-day-old male broilers (Ross 308) were used for 6 weeks under high- temperature conditions. This experiment was conducted using a 2 × 3 + 1 factorial experiment based on a completely randomized design, with 7 treatments (5 replicates per treatment and 20 birds per replicate). Experimental factors included two threonine concentrations (recommended level and 10 % above recommended level) and three dietary electrolyte balances (175, 250, and 325 mEq/kg). The control group considered the treatment with a normal threonine concentration (recommended level) and a dietary electrolyte balance of 250 mEq/kg under optimal temperature conditions.

Although there was no interaction between threonine level and electrolyte balance, the electrolyte balance of 175 meq/kg increased the performance index compared to the electrolyte balance of 250 or 325 mEq/kg (P<0.05). The villus height to crypt depth ratio and villus surface area in the jejunum improved with an electrolyte balance of 175 or 250 mEq/kg (P<0.05). A decrease in the dietary electrolyte balance increased in the nitrogen-corrected apparent metabolizable energy (P<0.05). Besides, an increase in the population of lactobacilli and bifidobacteria in the cecum, as well as an increase in protein digestibility, were observed by increasing levels of threonine in the diet (P<0.05).

Based on these results, a high level of threonine or a low electrolyte balance in diet (175 mEq/kg) may improve the performance, metabolizable energy, and intestinal microbial flora of broilers reared under heat stress.

Optimal levels of minerals in the diet are crucial for improving performance and immune response against the environmental stresses.

This study was conducted to evaluate the effects of water supplementation of chelated trace mineral (CTM) on growth performance, hematology, blood biochemistry, antioxidant status, and antibody response in broilers reared under heat stress condition.

A total of 240 male Ross 308 broiler chickens were randomly allocated into one of the following five treatments (each consisting of four replicates): (1) positive control (PC; thermoneutral condition), (2) negative control (NC; heat stress condition), (3) low-CTM (NC + low CTM level in tap water), (4) medium-CTM (NC + medium CTM level in tap water),  and (4) high-CTM (NC + high CTM level in tap water). The CTM levels in the tap water for the low-CTM treatment were 0.1, 0.15, 0.3, 0.4, and 0.45 mg/bird/day on days 1-10, 11-20, 21-30, 31-40, and 41-50, respectively. The respective values were 1.0, 1.5, 3.0, 4.0, and 4.5 for the medium-CTM, and 10, 15, 30, 40, and 45 mg/bird/day for the high-CTM water.

The average weight gain during the whole experimental period in the medium-CTM treatment was higher compared to that in the negative control treatment, but lower than that in the positive control treatment (P<0.05). The heterophil/lymphocyte ratio and total antibody titers against Newcastle disease in the medium-CTM and high-CTM groups were similar to those of the broilers in the PC group, yet better (P<0.05) those of the NC group. The serum superoxide dismutase activity was also higher (P<0.05) in the high-CTM group compared to that of the NC group.

The results suggested that the water supplementation of CTM at a moderate level (1.0, 1.5, 3.0, 4.0, and 4.5 mg/bird/day during different rearing periods) could be a strategy to ameliorate the detrimental effects of heat stress in broilers.

This study was conducted to assess the gene expression of antioxidant enzymes (superoxide dismutase and catalase) in broiler chickens under heat stress. For this purpose, 200 Ross 308 broiler chicks in a completely randomized design with 5 treatments, 4 replicates and 10 chicks were used in each replicate. The treatments included: 1- control diet (base diet without any additives), 2- basal diet plus 200 mg / kg vitamin E, 3- basal diet plus 100 mg / kg of wild pistachio extract, 4- basal diet with 100 mg / kg of Common Purslane extract, 5- basal diet plus 100 mg / kg of wild pistachio extract and 100 mg / kg of Common Purslane extract. After 42 days, at the end of testing two chickens each replicate were slaughtered and their livers were excised quickly and transported with liquid nitrogen to the laboratory. The expression of the enzymes catalase and superoxide dismutase were evaluated by Real-time qPCR. In this way as beta-actin gene as housekeeping gene is used to normalize the data. The results indicate that the expression of antioxidant enzymes superoxide dismutase and catalase, included the highest level in the 5 treatments. Moreover, the expression of these genes showed a significant increase compared to the control in other treatments (treatments 2, 3 and 4). Therefore, the results indicated that the combination of extracts of wild pistachio and purslane can be together to be great impact on gene expression of antioxidant enzyme than the other groups under heat stress condition.

Thyme extract has the antimicrobial and antioxidant components that can be useful for the broilers under heat stress condition.

This experiment was conducted to investigate the effects of Thymus vulgaris extract in comparison with some common feed additives on performance, blood biochemical parameters and antibody response in broiler chickens under heat stress conditions.

This study was conducted using 192 one-day-old male broiler chicks (Ross 308) in a completely randomized design with 8 treatments in 4 replicates and 6 chicks per replicate. Treatments were as follows: 1) basal diet + standard temperature conditions (positive control); 2) basal diet + heat stress conditions (negative control); 3) negative control + 200 mg virginiamycin; 4) negative control + 150 mg Protoxin probiotic, 5) negative control + 250 mg vitamin C, 6) negative control + 250 mg vitamin E, 7) negative control + 250 mg thyme extract, and 8) negative control +500 mg thyme extract per kg diet.

Dietary thyme extract at the rate of 500 mg/kg as well as probiotic and vitamin E increased (P<0.05) body weight gain (2202, 2183 and 2199, respectively) and improved feed conversion (1.65, 1.74 and 1.66, respectively) compared with negative control group (body weight gain 1960 g and feed conversion ratio 1.96). Moreover, 500 mg/kg dietary thyme extract, probiotic and vitamin C reduced triglycerides, total cholesterol and low density lipoprotein during heat stress conditions (P<0.05). All dietary supplements groups significantly increased antibody titers against red blood cells as compared with negative control.

In general, the results of the present study suggest that thyme extract at the level of 500 mg/kg of diet can be recommended as an alternative to the common feed additives to improve growth performance and health benefits of the heat-stressed broilers.

To investigate the effects of dietary zinc and betaine (Bet) substitution to methionine on performance, egg quality and blood parameters in laying hens under heat stress, an experiment with 288 Hy-line W-36 leghorn (at 50 to 62 weeks old) in complete randomized design (CRD) with a 3×2×2 factorial arrangement of treatments with twelve treatments, 3 replicates and 8 hens in each replicate was performed. There were 6 dietary treatments: three doses of Bet (0, 13 and 26%) substitute to methionine combined with three levels of zinc (50 and 100 mg/kg) supplemented to the basal diets that were combined with two environmental conditions (thermoneutral (23°C constant) and heat stress ( 23.9 to 35°C cycling) conditions). The results indicated that performance parameters of laying hens and egg quality were all significantly reduced by heat stress (HS) (P<0.05). Substitution of methionine with Bet led to significantly increase of egg production (P<0.05); whereas it had no effect on egg weight and egg quality. Supplementation of the basal diets with zinc significantly increased laying performance of hens and egg quality (P<0.05). Moreover, the results of this experiment indicated that, there were significant effect of Betaine on blood cholesterol and triglyceride, (p<0.05), but no significant effect on glucose in broiler chickens. Moreover, results demonstrated that Zinc supplementation decreased cholesterol, triglyceride and glucose. The present study showed that dietary supplemental Bet and zinc at the level of 13% and 100 mg/kg resulted in an improving egg quality and performance of laying hens under heat stress.

Production of high quality eggs is an important subject in the egg industry and egg shell characters have roles on the egg quality. There are many factors that affect the egg shell quality such as: layers breed, age and diet, producing period, molting, infectious diseases and stresses, specially heat stress. In this study the effect of induced heat stress on some of eggs quality indices in white leghorn layers (Hyline W-36) were studied. Atotal 80 white leghorn hens were divided in two groups including control and heat stress groups in the same condition of egg and diet. Heat stress condition induced via increasing in bird's environment. Produced eggs from two groups were collected and 20 eggs were then chosen randomly for each group weekly. Then samples examined for eggs quality parameters. Results of this study showed a significance decrease (P 0.05) in the egg's weight, egg's size, egg's shell weight, egg's shell thickness in heat stress group compared to the control group. Also eggs shell's ash percent and eggs shell's calcium percent in heat stress group decreased significantly compared to the control group. In addition, comparison of eggs quality indices showed that negative effect of heat stress increased due to heat stress continuation. This study shows the effect of heat stress on eggs quality as a routine stress condition in commercial layer flocks.