The influences of ambient temperature and crude protein levels on performance and serum biochemical parameters in broilers

High-energy and high-amino acid diet enhances production performance and antioxidant capacity in yellow-feathered broilers under heat stress

This study investigated the ameliorating effects of high-energy and high-amino acid (HEHA) diets on heat stress (HS) in yellow-feathered broilers. Broilers aged 35 d were randomly assigned to 3 groups: control and HS groups fed the basic normal diet, and the HEHA group fed the HEHA diet (basal diet + 100 kcal/kg AME + 15 % DAAs). The HS and HEHA groups were exposed to cyclic HS (30 ± 1 to 34 ± 1 ℃) for 2 wk, while the control group was maintained at 26 ± 1 ℃. The results indicated that the HEHA diet significantly alleviated HS-induced feed intake and body weight loss. HEHA feeding mitigated the increase in body temperature during HS. Compared with observations in the HS group, the HEHA diet reduced the levels of ALT, Alb, and corticosterone in the serum and downregulated the gene expression of HSP27 and HSP60 in the liver. Moreover, the HEHA group showed higher GSH-px activity in the serum and SOD and GSH-Px activity in the jejunal mucosa than that of the HS group. HEHA supplementation also reduced MDA levels in the liver. In conclusion, the HEHA diet improved the production performance of broilers under HS by increasing their antioxidant capacities. These findings suggest an effective strategy to combat HS in poultry production.

Early-age thermal manipulation and supplemental antioxidants on physiological, biochemical and productive performance of broiler chickens in hot-tropical environments

Heat stress has been ranked as a critical environmental issue confronting chicken farmers worldwide because of its detrimental effect on the growth, performance and health of the birds. This study evaluated the effects of early-age thermal manipulation (EATC) and supplemental antioxidants on the physiological responses of broilers in a hot tropical environment. A total of 300 day-old Ross broiler chicks were allocated to five thermal and dietary treatments, having 5 replicates of twelve birds each. The treatments were: chicks reared using the conventional method (CC), chicks exposed to early thermal manipulation with a temperature of 38 °C at day 5 with no antioxidant supplementation (TC), TC plus vitamin E at 250 mg/kg of feed (TV), TC plus selenium at 0.5 mg/kg of feed (TS) and the combination of TS and TV(TVS). The experiment was laid out in a Completely Randomized Design and data collected were analyzed using SAS (2008). The results showed that TVS broilers had significantly higher (P < 0.05) body weights at the finisher phase than the other treatment groups. The feed conversion ratio of TVS broilers was comparable to the TV group but lower (P < 0.05) than the other treatments. Reduced levels (P < 0.05) of heterophil, lymphocytes and hetrophil and lymphocyte ratio were recorded in the TVS compared to TV, TS and TC broilers. On day 42, the rectal temperature was significantly higher in CC than those in other treatment groups, which were comparable. TVS birds had higher (P < 0.05) weights of spleen, liver and lower abdominal fat than other treatments. The lowest concentration of plasma malondialdehyde and the highest activity of superoxide dismutase and glutathione peroxidase were recorded in TV and TVS birds. The study concluded that the growth performance and oxidative status in broilers were improved by the combination of EATC with supplemental Se and vitamin E (TVS).

Optimal dietary energy and protein levels for breeding pigeons in the winter "2 + 3" lactation pattern

The nutritional requirements of breeding pigeons depend on their physiological period, breeding pattern, and environmental conditions. Despite works on reduced litter size in winter production to combat high mortality and the poor welfare of squabs, there are few studies on the related nutritional requirements of these pigeons. A total of 432 pairs of European Mimas pigeons were randomly divided into 9 groups in which 3 crude protein (CP) levels (15, 16.5, and 18%) and 3 metabolizable energy (ME) levels (12.2 MJ/kg, 12.4 MJ/kg, and 12.6 MJ/kg) were tested to determine the optimal energy and protein requirements of breeding pigeons in the winter "2 + 3" breeding pattern. The results showed that ME and CP levels had little effect on the body weight, feed intake, and egg quality of breeding pigeons during the lactation period. An 18% CP diet significantly increased the laying rate and hatchability (P < 0.05), but there was no difference in the laying rate with 18% CP and 16.5% CP during the whole reproductive cycle (P > 0.05). There was a significant interaction between ME and CP levels, and the laying interval of breeding pigeons in group 9 (18% CP; 12.6 MJ/kg) was significantly shortened (P < 0.05). For squabs, the ME level had no effect on growth performance, slaughter performance, or meat quality. The body weight of 21-day-old squabs in the 18% CP group increased by 3.16% compared with that of the 15% CP group, but there was no difference between the 18% CP and 16.5% CP groups. Compared with other experimental groups, group 7 (18% CP; 12.2 MJ/kg) had the fastest growth rate in squabs (P < 0.05), and the corresponding slaughter weight was also the heaviest (P < 0.05). We further found that the height of the squab intestinal epithelium was significantly increased in both the 16.5% CP and 18% CP groups of squabs (P < 0.01), but male breeding pigeons showed a certain degree of oxidative stress with an increase in CP level. In conclusion, the effects of 15 to 18% CP levels and 12.2 to 12.6 MJ/kg ME levels on the reproductive metabolism of breeding pigeons and the growth and development of squabs in the "2 + 3" breeding pattern during winter are small. For economic efficiency, we suggest that the CP level can be reduced to 16.5% while the ME level should not be less than 12.2 MJ/kg in practical production.

Impact of bioclimatic factors on physio-biochemical and molecular response of slow-growing poultry reared in tropics

Most of the climatic studies projected on heat stress have considered heat extremes, but not the humidity. Hence, this work was carried out to evaluate thermotolerance, production performance, physio-biochemical and immunological response of slow-growing poultry towards various temperature-humidity levels in coastal climate. A total of 240 straight run CARI-Debendra birds were reared in three groups based on temperature-humidity indices (THI > 80, = 75-80 and < 75). Significant difference (P < 0.01) in rectal and body surface temperatures was observed among treatment groups. Lowest body weight was observed in THI > 80 group as 1.45 kg at 12 weeks. There was no significant difference in feed intake and FCR; however, total water intake had increased in heat-stressed group. Birds under THI > 80 group had significantly low gizzard weight only at the 12th week compared to other groups. Significant differences (P < 0.05) in relative weight and length of intestine were noticed which was comparable between seasonal control and THI > 80 group but lower than THI < 75 group at the 6th week. However, at the 12th week, intestinal weight varied among the groups (P = 0.08), but intestinal size did not differ. Among immune organs, significant difference (P < 0.05) was noted only in weight of thymus. Except Cl^-, other biochemical indices such as cholesterol, lactate dehydrogenase, creatinine kinase, K⁺ and Na⁺ did not differ among treatment groups. Relative expression of HSP70 gene was differed significantly (P < 0.01) in the liver, intestine and breast muscles under different THI. The changes reported in seasonal control group during month of October to December revealed better thermotolerance capacity and adaptability of CARI-Debendra birds to coastal hot-humid climate. However, response of this breed to heat stress (THI > 80) reported decrease in growth, immune response and mineral balance attributable to heat loss efficacy in high humidity.

Effect of individual or combination of dietary betaine and glycine on productive performance, stress response, liver health, and intestinal barrier function in broiler chickens raised under heat stress conditions

The current experiment was conducted to investigate the effect of individual or combination of dietary betaine (Bet) and glycine (Gly) on productive performance, stress response, liver health, and intestinal barrier function in broiler chickens raised under heat stress (HS) conditions. A total of four hundred twenty 21-d-old Ross 308 broiler chickens were randomly allotted to 1 of 5 dietary treatments with 7 replicates. Birds in treatment 1 were raised under the thermoneutral condition (TN; 23 ± 0.6°C). Birds in other 4 treatment groups were subjected to a cyclic HS by exposing them to 32 ± 0.9°C for 8 h/d (from 09:00 to 17:00 h) and 28 ± 1.2°C for the remaining time for 14 d. Birds were fed a basal diet in TN condition (TN-C) and one group in HS conditions (HS-C), whereas other birds raised under HS conditions were fed the basal diet supplemented with 0.20% Bet (HS-Bet), 0.79% Gly (HS-Gly), or their combination (0.20% Bet + 0.79% Gly; HS-Bet+Gly). Results indicated that birds in HS-Bet, HS-Gly, or HS-Bet+Gly treatment had higher (P < 0.05) final BW and BW gain, but lower (P < 0.05) feed conversion ratio (FCR) than those in HS-C treatment. However, values for improved final BW, BW gain, and FCR by dietary treatments were lower (P < 0.05) than those measured in TN-C treatment. Under HS conditions, birds in HS-Bet, HS-Gly, or HS-Bet+Gly treatment had lower (P < 0.05) heterophil to lymphocyte ratio than those in HS-C treatment. Birds in HS-Gly or HS-Bet+Gly treatment had higher (P < 0.05) villus height and goblet cell number than birds in HS-C treatment. Intestinal permeability was higher (P < 0.05) in all HS-treatment groups than in TN-C treatment, but it was not affected by dietary treatment. In conclusion, individual supplementation of 0.20% Bet or 0.79% Gly in diets alleviates the negative effect of HS in broiler chickens. However, the synergistic effect of the combination of 0.20% Bet and 0.79% Gly in broiler diets seems lower than expected.

The Role of Supplementing a Complex Phytobiotic Feed Additive Containing (Castanea sativa mill) Extract in Combination with Calcium Butyrate, Zinc–Methionine and Essential Oils on Growth Indicators, Blood Profile and Carcass Quality of Broiler Chickens

The purpose of this study was to determine the level of application and effectiveness of the use of vegetable feed additives from complex phytobiotic feed additives (CPFA) in the diets of broiler chickens, as well as their effects on growth indicators, carcass characters and blood profile. A total of 258 Ross 308 chicks were divided into six dietary regimens, including: a basal diet without additives as a first control group (CON); the second group received a basal diet supplemented with 200 g/t in the starter phase and 100 g/t in the grower and finisher phase; the third group—400 g/t and 200 g/t; the fourth group—600 g/t and 300 g/t; the fifth group—800 g/t and 400 g/t; and the sixth group—1000 g/t and 500 g/t of a complex phytobiotic supplement based on tannins, respectively. The CPFA contains the following: tannins 36.8–55.2%, eugenol 0.4–0.6%, cinnamon aldehyde 0.8–1.2%, zinc–methionine 1.6–2.4%, calcium butyrate 8–12%, silicon dioxide 1.2–1.8% and dextrose up to 100%. The maximum introduction of phytobiotics (1000 g/t) at 7 days of age leads to a decrease in the live weight of broilers which reduced by 8.27% (p < 0.05) compared to the minimum level of phytobiotics (200 g/t). From 15–21 days, the live weight was significant between the supplemented and control groups and represented 396.21, 384.81 and 384.16 vs. 316.91 g for the CPFA 4, CPFA 5, CPFA 1 and control group, respectively. Furthermore, the same trend was recorded in the average daily gain during the periods between 15–21 and 22–28 days of the experiment. Feeding CPFA had a positive effect on the carcass indicators, except for the feeding of CPFA 3 in the amount of 600 g/t in the starter phase and 300 g/t in the grower and finish phases, which recorded the lowest weight in relation to the CPFA 1 and 2 groups and represented 1309.58 vs. 1460.06 and 1456.52 g, respectively, and the difference was significant. The inclusion of CPFA in poultry diets contributed to an increase in lung mass in the experimental groups relative to the control group, except for the CPFA 5 group which represented the lowest weight of lung mass (6.51 g) and the differences were significant between the CPFA 2 and CPFA 3 and the control groups. The highest concentration of leukocytes was observed during the experiment period in the group of poultry receiving phytobiotics (CPFA 3), which significantly exceeded the control group by 2.37 × 109/L. A significant decrease in the level of cholesterol was recorded in the CPFA groups when compared to the control group and represented 2.83 vs. 3.55 mmol/L, respectively. Consequently, the introduction of vegetable feed additives from complex phytobiotic feed additives (CPFA) in the diets of Ross 308 chicks had a positive effect on the growth production, the carcass yield, the mass of the pectoral muscles and the mass of the lungs. Moreover, it did not cause a harmful effect on the biochemical parameters of the blood.

A review of heat stress in chickens. Part II: Insights into protein and energy utilization and feeding

With the growing global demand for animal protein and rising temperatures caused by climate change, heat stress (HS) is one of the main emerging environmental challenges for the poultry industry. Commercially-reared birds are particularly sensitive to hot temperatures, so adopting production systems that mitigate the adverse effects of HS on bird performance is essential and requires a holistic approach. Feeding and nutrition can play important roles in limiting the heat load on birds; therefore, this review aims to describe the effects of HS on feed intake (FI) and nutrient digestibility and to highlight feeding strategies and nutritional solutions to potentially mitigate some of the deleterious effects of HS on broiler chickens. The reduction of FI is one of the main behavioral changes induced by hot temperatures as birds attempt to limit heat production associated with the digestion, absorption, and metabolism of nutrients. Although the intensity and length of the heat period influences the type and magnitude of responses, reduced FI explains most of the performance degradation observed in HS broilers, while reduced nutrient digestibility appears to only explain a small proportion of impaired feed efficiency following HS. Targeted feeding strategies, including feed restriction and withdrawal, dual feeding, and wet feeding, have showed some promising results under hot temperatures, but these can be difficult to implement in intensive rearing systems. Concerning diet composition, feeding increased nutrient and energy diets can potentially compensate for decreased FI during HS. Indeed, high energy and high crude protein diets have both been shown to improve bird performance under HS conditions. Specifically, positive results may be obtained with increased added fat concentrations since lipids have a lower thermogenic effect compared to proteins and carbohydrates. Moreover, increased supplementation of some essential amino acids can help support increased amino acid requirements for maintenance functions caused by HS. Further research to better characterize and advance these nutritional strategies will help establish economically viable solutions to enhance productivity, health, welfare, and meat quality of broilers facing HS.

Effect of Heat Stress, Dietary Electrolytes, and Vitamins E and C on Growth Performance and Blood Biochemistry of the Broiler Chicken

Environmental heat stress creates a detriment to the welfare and performance in broiler chickens. While there are some dietary mineral and vitamin supplements that mitigate this condition, a rapid, plasma-based detection method would improve management response and broaden the scientific understanding of heat stress. A total of 960 broilers were used to determine the effect of heat stress and dietary electrolyte balance on blood biochemistry. Sex sorted chicks were allocated to 48 pens with 20 chicks per pen creating 6 treatments (3 diets x 2 house environments) with eight replicates and fed one of three dietary treatments: a control containing primarily sodium chloride (NaCl), a heat stress formulation containing bicarbonate (NaHCO3), or heat stress fortified with 200 ppm vitamin C and E (NaHCO3 Fortified). Birds were housed in two different temperature-controlled environments either a thermoneutral (Control) or heat stressed (Heat Stress) environment. At day 28, 35 and 42 venous blood was collected and analyzed using rapid detection methods followed by post-mortem veterinary evaluations. Performance was measured at weekly intervals. Mortality was significantly higher in broilers exposed to heat stress as compared to thermoneutral, while broilers that received dietary sodium chloride also had higher mortality than bicarbonate fed birds. Heat stress significantly impacted potassium, hematocrit, uric acid, total protein, globulin, hematocrit, lymphocytes, sodium, and glucose. This study demonstrates that blood biochemistry of broiler chickens is influenced by dietary intervention and changing environmental conditions. This pattern suggests a blood biomarker footprint of sub-optimal nutrition or poor environmental conditions that may provide valuable information into physiological changes in response to dietary electrolytes, vitamins, and heat stress. Furthermore, this footprint may potentiate the development of diagnostic tools, combining biomarkers to determine nutrition and health status of individual broiler flocks, for nutritionists, veterinarians, and live production managers to manage flocks for environmental, humane, and productive purposes.

Physiological dynamics in broiler chickens under heat stress and possible mitigation strategies

High ambient temperature has emerged as a major constraint for the future development of the poultry industry, especially in the tropics and subtropics. The scarcity of resources coupled with harsh environmental conditions is the most crucial predicaments in the way to rationalize optimum production of broiler. Heat stress disturbs the physiological biochemistry of the broiler which ultimately reduces feed intake and feed efficiency which ultimately results in reduced performance and productivity. Under hot environmental conditions, feed utilization is disturbed by the deposition of fat and oxidative stress. In addition, changes in blood cells, acid-base balance, immune response, liver health, and antioxidant status are some of the major dynamics altered by heat stress. The broilers have a narrow range of temperatures to withstand heat stress. In this review, we have discussed the various physicochemical changes during heat stress, their possible mechanisms, and mitigation strategies to reduce heat stress.

Effects of Glycyrrhiza polysaccharide in diet on growth performance, serum antioxidant capacity, and biochemistry of broilers

In the present study, we analyzed the effects of Glycyrrhiza polysaccharide (GCP) on growth performance, serum antioxidant capacity, and biochemistry of broilers. A total of 600, one-day-old AA broilers randomly divided into 5 treatment groups with 6 replicate pens of 20 birds per cage received dietary supplementation with GCP (0, 200, 500, 1,000, and 1,500 mg/kg) for 42 d. The supplementation of GCP linearly decreased (P < 0.05) feed conversion rate on day 22 to 42. Dietary supplementation with GCP reduced (P < 0.05) serum total cholesterol on day 21 and 42 and linearly improved (P < 0.05) albumin and high-density lipoprotein cholesterol. Dietary supplementation with 1,000 or 1,500 mg/kg GCP significantly increased (P < 0.05) serum total superoxide dismutase (T-SOD) activity on day 21 and 42 and reduced (P < 0.05) serum malondialdehyde content on 21 d. Dietary supplementation with 1,000 or 1,500 mg/kg GCP significantly improved (P < 0.05) interleukin-1β (IL-1β) and interferon-γ (IFN-γ) expressions in liver on day 21 and 42. At the end of the experiment, we randomly selected 20 broilers from 3 treatment groups (0, 1,000, and 1,500 mg/kg), respectively, to perform an lipopolysaccharide (LPS)-induced acute stress experiment. The 60 broilers were divided into 6 treatment groups with 10 birds per cage. The experiment was designed as a 3 × 2 factorial arrangement with GCP (0, 1,000, or 1,500 mg/kg) and LPS (injection of saline or 1 mg/kg body weight) levels as treatments. When the grouping was finished, the broilers were immediately intraperitoneally injected with LPS or normal saline. Six hours after challenged, serum antioxidant and liver immunity were analyzed. The results showed that dietary GCP prevented LPS-induced reductions in T-SOD activity and increases in malonaldehyde content (P < 0.05). Also, dietary GCP supplementation mitigated the LPS-induced increase in IL-1β and IFN-γ in the liver. Supplementation with 1,500 mg/kg GCP showed the most optimal effect in broilers. GCP has the potential to be used as feed additive in broilers.

Effects of Inclusion of Different Doses of Persicaria odorata Leaf Meal (POLM) in Broiler Chicken Feed on Biochemical and Haematological Blood Indicators and Liver Histomorphological Changes

Simple Summary

The frequent use of antimicrobial growth promoters (AGPs) in poultry feed leads to antimicrobial resistance, resulting in a ban on their subtherapeutic use in food-producing animals. In this context, there is a dire need to find safe and potential alternatives. Recently, phytobiotics, especially herbs, have gained attention and have been studied extensively for their possible use as alternative poultry feed additives. Persicaria odorata is a herb (phytobiotic) that is reported to possess antioxidant, antimicrobial, immunomodulatory, and hepatoprotective properties. This study is the first of its kind to assess the effects of different doses of supplementation of Persicaria odorata leaf meal (POLM) on haematological blood indicators, serum biochemistry, organ parameters, and histomorphology of the liver in broiler chickens. The results revealed that the dietary supplementation of POLM enhanced the growth performance, positively improved the haematological indices and serum biochemistry profile with no deleterious effects on internal organs, and ameliorated the histomorphology of the liver, even at dietary supplementation of 8 g/kg. Thus, POLM would be safe at an inclusion rate of 8 g/kg as an alternative phytogenic feed additive in broiler chickens.

Abstract

This research was conducted to estimate the effects of Persicaria odorata leaf meal (POLM) on haematological indices, serum biochemical attributes, and internal organs parameters, including histomorphological features of the liver, in broiler chickens. A total of 120 one-day-old male broiler chicks (Cobb-500) were randomly allocated into four experimental groups. The dietary treatments were basal diet (BD), which served as the control (C), along with BD + 2 g/kg POLM (Po2), BD + 4 g/kg POLM (Po4), BD + 8 g/kg POLM (Po8), which were the supplemented groups. The body weight gain (BWG) showed a linear increase and feed conversion ratio (FCR) showed a linear decrease with increasing POLM dosage at day 42 (p ˂ 0.05) and for the overall growth performance period (p ˂ 0.01). On day 21 and day 42, the values of red blood cells (RBCs), white blood cells (WBCs), haemoglobin (Hb), and packed cell volume (PCV) showed linear increases (p ˂0.05) as the dosage of POLM increased in the diet. On day 21, dietary supplementation of POLM linearly decreased (p ˂ 0.05) the serum activity of alkaline phosphatase (ALP), aspartate aminotransaminase (AST), alanine aminotransaminase (ALT), and serum levels of urea and creatinine. On the other hand, serum levels of total protein (TP), albumin, and globulin showed a linear increase (p ˂ 0.05) as the POLM dosage increased. On day 42, the serum activity of AST and ALT and serum levels of glucose, cholesterol, triglycerides, urea, and creatinine showed linear decreases (p ˂ 0.05) with increased levels of POLM in the diet. However, POLM supplementation linearly increased (p ˂ 0.05) the serum levels of TP and globulin. Dietary inclusion of POLM did not influence the organ parameters and showed no adverse effects on the liver histomorphology. In conclusion, supplementation of POLM increased the growth performance, improving haematological indices and serum biochemistry profiles of broiler chickens without any deleterious effects on the liver histomorphology. The results of the present study provide evidence that POLM can be safely used at a dose rate of 8 g/kg of feed as an alternative to conventional antimicrobial growth promoters (AGPs).

Response of broilers to supplementation of branched-chain amino acids blends with different valine contents in the starter period under summer conditions

Objective

The objectives of this study were to compare the effects of normal and low protein content (PC) of starter diet supplemented or not with blends of branched-chain amino acids (BCAAs) on growth performance of broilers under summer conditions and to investigate whether these effects altered some quality traits and the characteristics of gastrointestinal tract.

Methods

A total of 768 mixed-sex broiler chicks (Ross 308, one-d-old) with an average initial body weight (BW) of 47.6±1.03 g were allocated into six treatments with four replications in 2×3 factorial arrangement. Factors were: PC, normal (N, 22% to d 15); and low (L, 20% to d 15); and added BCAA blends, L-leucine, L-isoleucine, and L-valine at zero (0L:0I:0V); 1.0, 0.25, and 0.25 (4L:1I:1V); or 1.0, 0.25, 0.75 (4L:1I:3V) g/kg of diet. Hence, six dietary treatments were named as N0L:0I:0V, N4L:1I:1V, N4L:1I:3V, L0L:0I:0V, L4L:1I:1V, and L4L:1I:3V. Average indoor temperature and humidity were 32.8°C±1.7°C and 61.1% ±4.12%, respectively.

Results

BW, feed conversion ratio (FCR) and carcass weight were not affected by PC, BCCA and their interaction (p>0.05). The L diets decreased the water holding capacity of the breast (p = 0.002) and thigh (p = 0.050) meats and dressing percentage (p = 0.005) compared to the N diets. The 4L:1I:1V diet decreased breast yield compared to the 0L:0I:0V diets (p = 0.041). The effect of PC on feed intake, mortality and gastrointestinal trait weight were depended on the L:I:V ratios under summer conditions due to interactions between factors (p<0.05). The FI and mortality of L4L:1I:1V broilers were lower than those of N4L:1I:1V birds (p<0.05).

Conclusion

It was concluded that the blends of BCAAs used failed to improve performance and to promote breast yields, because diets with normal or with reduced protein supplemented or not with BCAAs up to d 15 produced a similar BW and FCR in broilers raised in hot-climate conditions.

Effects of dietary energy level on appetite and central adenosine monophosphate-activated protein kinase (AMPK) in broilers

Adenosine monophosphate-activated protein kinase (AMPK) acts as a sensor of cellular energy changes and is involved in the control of food intake. A total of 216 1-d-old broilers were randomly allotted into 3 treatments with 6 replicates per treatment and 12 broilers in each cage. The dietary treatments included 1) high-energy (HE) diet (3,500 kcal/kg), 2) normal-energy (NE) diet (3,200 kcal/kg), and 3) low-energy (LE) diet (2,900 kcal/kg). The present study was conducted to investigate the effects of dietary energy level on appetite and the central AMPK signal pathway. The results showed that a HE diet increased average daily gain (ADG), whereas a LE diet had the opposite effect (P < 0.05, N = 6). The average daily feed intake (ADFI) of the chickens fed the LE diet was significantly higher than that of the control (P < 0.05, N = 6). Overall, the feed conversion rate gradually decreased with increasing dietary energy level (P < 0.05, N = 6). Moreover, the chickens fed the LE and HE diets demonstrated markedly improved urea content compared with the control group (P < 0.0001, N = 8). The triglyceride (TG) content in the LE group was obviously higher than that in the HE group but showed no change compared with the control (P = 0.0678, N = 8). The abdominal fat rate gradually increased with increased dietary energy level (P = 0.0927, N = 8). The HE group showed downregulated gene expression levels of liver kinase B1 (LKB1), neuropeptide Y (NPY), cholecystokinin (CCK), and glucocorticoid receptor (GR) in the hypothalamus compared with the control group (P < 0.05, N = 8). However, LE treatment significantly increased the mRNA level of AMP-activated protein kinase α2 (AMPKα2) compared with other groups (P = 0.0110, N = 8). In conclusion, a HE diet inhibited appetite and central AMPK signaling. In contrast, a LE diet activated central AMPK and appetite. Overall, the central AMPK signal pathway and appetite were modulated in accordance with the energy level in the diet to regulate nutritional status and maintain energy homeostasis in birds.

Physiological alterations of poultry to the high environmental temperature

Heat stress has become a serious problem in poultry industry along with rising of the global temperatures. High environmental temperature causes deleterious impacts on physiology and immunology of poultry and impairs their productivity. Heat stress is linked to compromised productivity through a decline in growth rate, feed utilization, blood biochemistry and immunity. In addition, heat stress induced adverse effects on mineral balance of birds and the extent of such effects depended on the type of mineral and the severity of heat stress. Exposure of broilers to high temperature adversely affects mineral metabolism and their excretion route and reduced the retention of some minerals like P, Na, K, S, Mg, Mn, Zn and Cu. On the other hand, the effect of climate on intestinal microbiota has been described in a number of studies. Where, exposure to heat stress can also increase the colonization of Salmonella in the intestine and increase the susceptibility of birds to E. coli and change ileal contents. It is also characterized by decreased antioxidant enzymes in poultry species, resulting in increased oxidative stress that means presence of reactive oxygen species (ROS) in excess of the available antioxidant capacity of animal cells. However, further studies are still required to increase the information and knowledge of basic mechanisms associated with the consequences of heat stress on poultry. This article focuses on the scientific evidence available on the negative role of heat stress on physiological responses, biochemical blood parameters, immunity, antioxidant, mineral balance, acid-base balance, osmoregulation, body and rectal temperature, intestinal and ileal microbiota as well as the parameters related to thyroid, liver and kidney functions in some poultry species.