Effects of environmental temperature and heat production due to food intake on abdominal temperature, shank skin temperature and respiration rate of broilers

Single nucleotide polymorphism in avian uncoupling protein gene is associated with thermoregulation in chicks

Avian uncoupling protein (av-UCP) is a key protein for thermoregulation in poultry. A single nucleotide polymorphism (SNP) in the av-UCP gene has been reported in chickens. The purpose of the current study was to clarify the association between this av-UCP gene mutation and thermoregulation in chickens. Wild and mutant type chicks for the av-UCP gene SNP (g. 1270 of the av-UCP gene exon 3 with C to T substitution and amino acid substitution) were exposed to high ambient temperature. Rectal temperature, radiation temperature on the body surface, and the expression of heat dissipation behavior (wing drooping and panting) during heat exposure were measured. In addition, oxygen consumption rate in the thermoneutral zone in wild and mutant type chicks was measured. Changes in wing temperature during heat exposure in wild-type chicks were lower than those in mutants. The latency of continuous wing drooping during heat exposure in wild-type chicks was shorter than in mutant chicks. It was also found that the SNP in the av-UCP gene caused reduced oxygen consumption. These results suggest that the av-UCP gene mutation affects thermoregulation, especially heat production, in chickens.

Providing colored photoperiodic light stimulation during incubation: 2. Effects on early posthatch growth, immune response, and production performance in broiler chickens

Previous findings have reported that providing light during incubation can affect hatchability and chick quality. This study was conducted to investigate the effects of providing light during incubation on posthatch broiler production parameters, thermoregulation and immune response. Lights with different wavelengths were used over the course of four separate hatches. Ross 308 broiler hatching eggs were randomly distributed into 4 lighting treatments for each hatch. The incubation lighting treatments included: dark as control, white, red, or blue lights for 12 h d^-1 (200 lux at egg level). Broilers hatched from each incubator with the same gender were placed into one of 8 sets of pens (3 pens/set) and raised under 18 h d^-1 photoperiod. Six birds per pen were immunized intraocularly with AviPro ND-IB Polybanco vaccine on d 10 and 21 posthatch. Chicks hatched under white and blue lights had heavier (P < 0.05) body weight and higher (P < 0.05) feed consumption than the control group during the first 6 h postplacement. No differences in vent temperature were found among treatments at 24 h posthatch (P > 0.05). Chicks hatched with light stimulation however had more stable (P < 0.05) cloaca temperature at 36 h posthatch. No differences in average body weight gain, feed consumption or feed conversion ratio were found among lighting treatments between d 7 and d 35. On d 14 of age, birds hatched from red light had higher (P < 0.05) total IgG concentration than those hatched under dark, blue or white light. These results indicated that in ovo light stimulation with different wavelengths did not affect growth parameters of broilers at market age. Providing photoperiodic blue and white light during incubation improved the production parameters of broilers during the first week posthatch.

Modeling net energy requirements of 2 to 3-week-old Cherry Valley ducks

OBJECTIVE

A total of three hundred unsexed ducks were utilized to estimate net energy requirements of maintenance (NEm) and weight gain (NEg) for 2 to 3-week-old Cherry Valley ducks and to establish a model equation to predict NE requirements using the factorial method.

METHODS

To determine the apparent metabolizable energy (AME) of the diet, fifty 7-day-old ducks at approximately equal body weights (BWs) were randomly assigned into five groups that were fed at different levels (ad libitum, 85%, 75%, 65%, and 55% of ad libitum intake), and the endogenous acid-insoluble ash as indigestible marker. The two hundred and fifty 7-day-old ducks were used for a comparative slaughter experiment. At the beginning of the experiment, ten ducks were sacrificed to determine the initial body composition and energy content. The remaining ducks were randomly assigned into five groups (same as metabolic experiment). Ducks of the ad libitum group were slaughtered at 14 and 21-dayold. At the end of the experiment, two ducks were selected from each replicate and slaughtered to determine the body composition and energy content.

RESULTS

The results of the metabolizable experiment showed AME values of 13.43 to 13.77 MJ/kg for ducks at different feed intakes. The results of the comparative slaughter experiment showed the NEm value for 2 to 3-week-old Cherry Valley ducks was 549.54 kJ/kg of BW0.75/d, and the NEg value was 10.41 kJ/g. The deposition efficiency values of fat (Kf) and crude protein (Kp) were 0.96 and 0.60, respectively, and the values of efficiency of energy utilization (Kg) and maintenance efficiency (Km) were 0.75 and 0.88, respectively.

CONCLUSION

The equation for the prediction of NE requirements for 2 to 3-week-old Cherry Valley ducks was the following: NE = 549.54 BW0.75+10.41 ΔW, where ΔW is the weight gain (g).

Body surface temperature responses to food restriction in wild and captive great tits

During winter at temperate and high latitudes, the low ambient temperatures, limited food supplies and short foraging periods mean small passerines show behavioural, morphological and physiological adaptations to reduce the risk of facing energy shortages. Peripheral tissues vasoconstrict in low ambient temperatures to reduce heat loss and cold injury. Peripheral vasoconstriction has been observed with food restriction in captivity but has yet to be explored in free-ranging animals. We experimentally food restricted both wild and captive great tits (Parus major) during winter months and measured surface temperatures of the bill and eye region using thermal imaging, to investigate whether birds show rapid local heterothermic responses, which may reduce their thermoregulatory costs when facing a perceived imminent food shortage. Our results of a continuously filmed wild population showed that bill temperature was immediately reduced in response to food restriction compared with when food was available ad libitum, an apparent autonomic response. Such immediacy implies a 'pre-emptive' response before the bird experiences any shortfalls in energy reserves. We also demonstrate temporal variation in vasoconstriction of the bill, with bill temperature gradually rising throughout the food restriction after the initial drop. Eye-region temperature in the wild birds remained at similar levels throughout food restriction compared with unrestricted birds, possibly reflecting the need to maintain steady circulation to the central nervous and visual systems. Our findings provide evidence that birds selectively allow the bill to cool when a predictable food supply is suddenly disrupted, probably as a means of minimising depletion of body reserves for a perceived future shortage in energy.

Implementation of net energy evaluating system in laying hens: Validation by performance and egg quality

Three experiments were conducted to determine the effect of different dietary net energy (NE) and AMEn ratios (NE:AMEn) on performance, egg quality, and heat production (HP) in laying hens. In experiment 1, 62 Hy-Line Brown hens were fed 2 treatments with 31 replicates from 44 to 54 wk of age. In experiment 2, 600 hens of the same strain were fed 3 treatments from 22 to 42 wk of age with 10 replicates. Both used a completely randomized design. Diets were based on corn, wheat, wheat bran, barley, soybean meal, canola meal, meat and bone meal, and canola oil. In both experiments, the NE:AMEn ratio of diets was increased with higher oil inclusion compared with T1 controls. The AMEn (kcal/kg), NE (kcal/kg), ether extract (g/kg), and CP (g/kg), respectively, on a DM basis in experiment 1 was T1: 3,011, 2,288, 42, 202 and T2: 3,023, 2,374, 81, 203; and in experiment 2, T1: 3,026, 2,324, 25, 187; T2: 2,949, 2,315, 61, 185; and T3: 3,026, 2,397, 73, 181. Increasing the ratio of NE:AMEn decreased feed intake (P < 0.001) and increased egg mass (P < 0.05) in experiment 2 and increased egg weight (P < 0.01), decreased feed conversion ratio (P < 0.01), increased egg albumen % (P < 0.001), and decreased yolk % (P < 0.05) and shell % (P < 0.05) compared with T1 controls in both experiments. Haugh units and yolk color scores were increased with high NE:AMEn in both experiments (P < 0.001; P < 0.01). Experiment 3 was conducted in calorimetry chambers to measure HP in birds fed experiment 2 diets. Increasing the NE:AMEn increased total retained energy (RE), RE as fat, and RE in the body (kcal/kg BW^0.75/D) and NE:AME. The results indicate that using oil to increase the NE:AMEn results in improved performance and egg quality and more efficient energy utilization.

Comparison of mathematical and comparative slaughter methodologies for determination of heat production and energy retention in broilers

Understanding factors affecting ME availability for productive processes is an important step in optimal feed formulation. This study compared a modelling methodology with the comparative slaughter technique (CST) to estimate energy partitioning to heat production and energy retention (RE) and to investigate differences in heat dissipation. At hatch, 50 broilers were randomly allocated in one of 4 pens equipped with a precision feeding station. From day 14 to day 45, they were either fed with a low-ME (3,111 kcal/kg ME) or a high-ME (3,383 kcal/kg ME) diet. At day 19, birds were assigned to pair-feeding in groups of 6 with lead birds eating ad libitum (100%) and follow birds eating at either 50, 60, 70, 80, or 90% of the paired lead's cumulative feed intake. Heat production and RE were estimated by CST and with a nonlinear mixed model explaining daily ME intake (MEI) as a function of metabolic BW and average daily gain (ADG). The energy partitioning model predicted MEI = (145.10 + u) BW^0.83 + 1.09 × BW^−0.18 × ADG^1.19 + ε. The model underestimated heat production by 13.4% and overestimated RE by 22.8% compared with the CST. The model was not able to distinguish between net energy for gain values of the diets (1,448 ± 18.5 kcal/kg vs. 1,493 ± 18.0 kcal/kg for the low-ME and high-ME diet, respectively), whereas the CST found a 148 kcal/kg difference between the low-ME and high-ME diets (1,101 ± 22.5 kcal/kg vs. 1,249 ± 22.0 kcal/kg, respectively). The estimates of the net energy for gain values of the 2 diets decreased with increasing feed restriction. The heat increment of feeding did not differ between birds fed with the low- or high-ME diet (26% of MEI). Additional measurements on heat dissipation, physical activity, and immune status indicated that the energetic content of the diet and feed restriction affect some parameters (shank temperature, feeding station visits) but not others (leukocyte counts, heterophil to lymphocyte ratio, and immune cell function).

Evidence that stress-induced changes in surface temperature serve a thermoregulatory function

The fact that body temperature can rise or fall following exposure to stressors has been known for nearly two millennia; however, the functional value of this phenomenon remains poorly understood. We tested two competing hypotheses to explain stress-induced changes in temperature, with respect to surface tissues. Under the first hypothesis, changes in surface temperature are a consequence of vasoconstriction that occur to attenuate blood loss in the event of injury and serve no functional purpose per se; defined as the 'haemoprotective hypothesis'. Under the second hypothesis, changes in surface temperature reduce thermoregulatory burdens experienced during activation of a stress response, and thus hold a direct functional value: the 'thermoprotective hypothesis'. To understand whether stress-induced changes in surface temperature have functional consequences, we tested predictions of these two hypotheses by exposing black-capped chickadees (n=20) to rotating stressors across an ecologically relevant ambient temperature gradient, while non-invasively monitoring surface temperature (eye region temperature) using infrared thermography. Our results show that individuals exposed to rotating stressors reduce surface temperature and dry heat loss at low ambient temperature and increase surface temperature and dry heat loss at high ambient temperature, when compared with controls. These results support the thermoprotective hypothesis and suggest that changes in surface temperature following stress exposure have functional consequences and are consistent with an adaptation. Such findings emphasize the importance of the thermal environment in shaping physiological responses to stressors in vertebrates, and in doing so, raise questions about their suitability within the context of a changing climate.

In ovo injection of ascorbic acid and higher incubation temperature modulate blood parameters in response to heat exposure in broilers

1. This study analysed whether in ovo injection of ascorbic acid before incubation and at high incubation temperature influenced blood characteristics and performance in broilers reared in different temperature conditions. 2. A total of 3,000 fertile eggs from broiler breeders (Cobb®) were randomly divided into three incubation treatments: no ascorbic acid injection and egg incubation at 37.5°C (control); no ascorbic acid injection and egg incubation at 39°C; in ovo ascorbic acid injection prior to incubation (6 µg AA/100 µl water) and egg incubation at 39°C. 3. Male chicks hatched from the three incubation treatments were submitted to three distinct rearing temperatures (control, cold and hot) from the third week of age onwards (540 chicks were divided into 6 treatments with 5 replicates per treatment). 4. Measurements at 42 d showed that, after egg incubation at 39°C, the haematocrit, haemoglobin values, ionised calcium and glucose concentrations were increased and base excess values were reduced. However, in ovo injection of ascorbic acid normalised all these parameters. 5. Partial CO₂ and O₂ pressure were higher with increased rearing temperature. Blood pH was lower when eggs were incubated at 39°C and injected with ascorbic acid. In ovo injection of ascorbic acid induced leucocytosis due to lymphocytosis and heterophilia, restored basophils rate and led to monocytopoenia. Leucocytosis was triggered by hot rearing temperature due to lymphocytosis, eosinophilia and heterophilia. 6. The results obtained in this study showed that in ovo injection of ascorbic acid before incubation may serve as a long-term stimulator and modulator of the broiler immune system, and that high incubation temperatures induce adaptations in the electrolytic balance, minimising or avoiding the occurrence of respiratory alkalosis under hot rearing temperature.

Net energy prediction and energy efficiency of feed for broiler chickens

Global consumption of chicken meat has increased at a faster rate than any other animal protein source, and thus refinements in energy formulation techniques for feed have continued to gain importance. Formulation of animal feed based on net energy (NE) has been implemented in ruminants and pigs but not in poultry. A closed-circuit respiratory calorimetry system was employed on 25- to 28-day-old broilers fed 19 diets formulated with varying nutrient composition to produce equations to predict NE and apparent metabolizable energy (AME) efficiency of feed for broiler chickens. Performance, energy and N balance, respiratory quotient, and energy utilization were measured in the birds. Linear regression analysis was performed to generate prediction equations for dietary energy content and AME efficiency. The NE content was positively related to AME and ether extract, but negatively to crude protein. The study generated equations that can accurately predict NE, and NE/AME using AME value and chemical composition of feeds. The NE prediction equations were further validated on a separate set of diets with high correlation (r = 0.99) and accuracy. The outcomes are an important step for the broiler industry to adapt to an NE system in place of AME systems for the formulation of broiler chicken feeds following robust validation experiments.

Unique genetic responses revealed in RNA-seq of the spleen of chickens stimulated with lipopolysaccharide and short-term heat

Climate change and disease have large negative impacts on poultry production, but little is known about the interactions of responses to these stressors in chickens. Fayoumi (heat and disease resistant) and broiler (heat and disease susceptible) chicken lines were stimulated at 22 days of age, using a 2x2x2 factorial design including: breed (Fayoumi or broiler), inflammatory stimulus (lipopolysaccharide (LPS) or saline), and temperature (35°C or 25°C). Transcriptional changes in spleens were analyzed using RNA-sequencing on the Illumina HiSeq 2500. Thirty-two individual cDNA libraries were sequenced (four per treatment) and an average of 22 million reads were generated per library. Stimulation with LPS induced more differentially expressed genes (DEG, log₂ fold change ≥ 2 and FDR ≤ 0.05) in the broiler (N = 283) than the Fayoumi (N = 85), whereas heat treatment resulted in fewer DEG in broiler (N = 22) compared to Fayoumi (N = 107). The double stimulus of LPS+heat induced the largest numbers of changes in gene expression, for which broiler had 567 DEG and Fayoumi had 1471 DEG of which 399 were shared between breeds. Further analysis of DEG revealed pathways impacted by these stressors such as Remodelling of Epithelial Adherens Junctions due to heat stress, Granulocyte Adhesion and Diapedesis due to LPS, and Hepatic Fibrosis/Hepatic Stellate Cell Activation due to LPS+heat. The genes and pathways identified provide deeper understanding of the response to the applied stressors and may serve as biomarkers for genetic selection for heat and disease tolerant chickens.

Visualization of the role of host heme on the virulence of the heme auxotroph Streptococcus agalactiae

Heme is essential for several cellular key functions but is also toxic. Whereas most bacterial pathogens utilize heme as a metabolic cofactor and iron source, the impact of host heme during bacterial infection remains elusive. The opportunist pathogen Streptococcus agalactiae does not synthesize heme but still uses it to activate a respiration metabolism. Concomitantly, heme toxicity is mainly controlled by the HrtBA efflux transporter. Here we investigate how S. agalactiae manages heme toxicity versus benefits in the living host. Using bioluminescent bacteria and heme-responsive reporters for in vivo imaging, we show that the capacity of S. agalactiae to overcome heme toxicity is required for successful infection, particularly in blood-rich organs. Host heme is simultaneously required, as visualized by a generalized infection defect of a respiration-negative mutant. In S. agalactiae, HrtBA expression responds to an intracellular heme signal via activation of the two-component system HssRS. A hssRS promoter-driven intracellular luminescent heme sensor was designed to identify host compartments that supply S. agalactiae with heme. S. agalactiae acquires heme in heart, kidneys, and liver, but not in the brain. We conclude that S. agalactiae response to heme is organ-dependent, and its efflux may be particularly relevant in late stages of infection.

Apparent metabolizable and net energy values of corn and soybean meal for broiler breeding cocks

The AME and net energy (NE) values of 4 corn varieties, including 2 normal corn varieties (Zheng Dan 958 and Xian Yu 335), and one each of waxy corn and sweet corn, and 2 soybean meal samples including regular (RSBM) and dehulled soybean meal (DSBM), were determined in 2 experiments for broiler breeding cocks using the indirect calorimetry method. The 4 test diets in Experiment 1 consisted of each test corn, which replaced 40% of the corn-soybean meal basal diet, and the test diets in Experiment 2 contained 25% RSBM or DSBM, which was used to replace the corn basal diet. Thirty (Experiment 1) or 18 (Experiment 2) 50-week-old Arbor Acre (AA) broiler breeding cocks were used in a completely randomized design. After a 7 d dietary adaptation period, 6 birds as replicates from each treatment were assigned to individual respiration chambers for energy measurement via gaseous exchange and total excreta collection for 10 d. In Experiment 1, the AME, ME intake (MEI), retained energy (RE), NE, and NE:AME ratio values were higher (P < 0.001) in the test diets as compared with the corn-soybean meal basal diet. The AME and NE values in the sweet corn diet were higher (P < 0.05) than those values in the other 3 test diets. The heat production (HP), fasting heat production (FHP), and respiration quotient (RQ) were not influenced by the various experimental diets. The respective AME and NE values were 3,785, 3,775, 3,738, and 3,997 kcal/kg (DM basis), and 2,982, 3,006, 2,959, and 3,146 kcal/kg (DM basis) for Zheng Dan 958, Xian Yu 335, waxy corn, and sweet corn. Birds fed a corn basal diet in Experiment 2 had higher AME, MEI, RE, NE, and NE:AME ratio values (P < 0.001). Soybean meal substitution had no effect on HP, FHP, or RQ. The average AME and NE content was 2,492 and 1,581 kcal/kg (DM basis) for RSBM, and 2,580 and 1,654 kcal/kg (DM basis) for DSBM, respectively.

Environmental heme utilization by heme-auxotrophic bacteria

Heme, an iron-containing porphyrin, is the prosthetic group for numerous key cellular enzymatic and regulatory processes. Many bacteria encode the biosynthetic enzymes needed for autonomous heme production. Remarkably, however, numerous other bacteria lack a complete heme biosynthesis pathway, yet encode heme-requiring functions. For such heme-auxotrophic bacteria (HAB), heme or porphyrins must be captured from the environment. Functional studies, aided by genomic analyses, provide insight into the HAB lifestyle, how they acquire and manage heme, and the uses of heme that make it worthwhile, and sometimes necessary, to capture this bioactive molecule.

Implications and development of a net energy system for broilers

A study was conducted to determine the predictability of energy balance and energy efficiency by using dietary chemical composition. Closed-circuit indirect calorimetry was used to determine the apparent metabolisable energy (AME), respiratory quotient, heat increment (HI), net energy (NE) and ratio of NE to AME (NE : AME) of a series of diets with varying levels of chemical constituents. Diets were analysed for DM, gross energy, protein, fat, ash, crude fibre, acid detergent fibre, neutral detergent fibre, starch, sugars (mono- and disaccharides), and soluble, insoluble and total non-starch polysaccharides. Ross 308 male broilers were acclimatised to chambers and diets for 3 days and 12 days, respectively, before O2 consumption and CO2 expiration were measured gravimetrically. Gross energy of feed consumed and excreta voided were measured and AME was calculated. Heat production was calculated using the Brouwer equation based on O2 and CO2. After taking fasting heat production into account by using a value of 450 kJ/BW0.70, HI was determined. NE was calculated as AME minus HI. The results showed high predictability of AME (R2 = 0.89) and NE (R2 = 0.85) by using chemical components. HI was less predictable (R2 = 0.25). Efficiency of energy utilisation (NE : AME) was predicted (R2 = 0.40). Closed-circuit calorimetry was found to be useful for evaluating the contribution of the chemical components of feed ingredients to the efficiency of energy utilisation in broilers. These results may be used to reduce energy costs in broiler feed formulation.

Thermoregulation responses of broiler chickens to humidity at different ambient temperatures. I. One week of age

Three trials were conducted to investigate the effect of RH (35, 60, and 85%) on thermoregulation of 1-wk-old broiler chickens at different temperatures (35, 30, and 25 degrees C). The response to humidity in rectal temperature and plumage temperature at the back and breast within 24 h after exposure were recorded at 5 time points (1,4,8,16, and 24 h). Humidity affected the thermoregulation of 1-wk-old broiler chickens by redistributing heat within the body at high, low, and thermoneutral temperatures. The redistribution of heat resulted in decreased rectal temperature and increased peripheral temperature, which were, respectively, beneficial and unfavorable at high and low temperatures. These results suggested that feedback effects of surface temperature on core temperature also exist in poultry, as already observed in mammals, and could be induced not only by changed ambient temperature but also by the changes in humidity at high temperature. The disturbance of thermal equilibrium could not be established solely by changes in RT, but rather core and surface temperatures had to be considered. The daily rhythms in rectal and surface temperatures were affected by humidity.

Thermoregulation responses of broiler chickens to humidity at different ambient temperatures. II. Four weeks of age

Two experiments were conducted to investigate the effect of RH (35, 60, and 85%) on thermoregulation of broiler chickens at high (35 degrees C) and mild (30 degrees C) temperatures at the age of 4 wk. The effects of humidity on rectal temperature (RT) and plumage temperature at back (PBAT) and skin temperature at breast (SBRT) were determined at 1, 4, 8, 16, and 24 h after exposure. The RT, PBAT, and SBRT were all significantly increased by high temperature (35 degrees C). Humidity had a significant influence on RT at 35 degrees C but not at 30 degrees C. The peripheral temperatures (PBAT and SBRT) were significantly affected by humidity but responded differently at high (35 degrees C) compared with mild temperature (30 degrees C). In conclusion, high humidity above 60% impaired the heat transmission from body core to the periphery at 35 degrees C but facilitated it at 30 degrees C in 4-wk-old broiler chickens. The effect of humidity on nonevaporative heat loss was depended on air temperature, as nonevaporative heat loss was suppressed by high humidity (>60% RH) at high temperature but enhanced at the mild temperature. The effect of humidity on the relationship between peripheral and core temperature depends on ambient temperature as well as on the age of the broiler chicken. The disturbance of thermal balance could not be determined only by changes in RT or peripheral temperature at a single time point but could be determined by mean body temperature within a certain time frame.

Early age thermal conditioning and a dual feeding program for male broilers challenged by heat stress

The effects of early age thermal conditioning (TC) and dual feeding on responses of male broilers to a thermal challenge at 34 d of age are reported. Three hundred chicks were randomly divided into two equal groups. One group was exposed to thermal conditioning (38 C, 42% relative humidity for 24 h) at the age of 5 d, and the other group was not exposed. From 11 to 41 d of age, temperature was diurnally cyclic: 26 C (1600 to 0900 h) and 30 C (0900 to 1600 h). From Day 19, a factorial (2 x 2, TC x diet) experiment was conducted using eight pens of six broilers per treatment. Diets were control diet and dual feeding of a high protein fraction (1600 to 0900 h) and an energy-rich fraction (0900 to 1600 h). Growth and feed efficiency were slightly enhanced (+4%) by thermal conditioning and slightly reduced (-4%) by dual feeding. Mortality during thermal challenge was reduced by both factors. [In not conditioned chicks (N), 31 fed a control grower diet (NG) and 12 on a dual feeding program (NDF) died; in thermal conditioned chicks (T), 18 fed a control grower diet (TG) and 11 on a dual feeding program (TDF) died.] Before the thermal challenge period, body temperature (Tb) was consistently reduced in T. During the thermal challenge period, Tb was reduced by thermal conditioning and dual feeding. Measured at the age of 32 d, Tb gave an estimation of the ability of the chickens to cope with heat stress 2 d later. Pectoral mass was increased in TG, whereas the liver and the gizzard were significantly heavier in TDF and NDF. These results suggest that thermal conditioning at 5 d of age induces a consistent metabolic change in broiler males. The dual feeding program might have induced transitory effects on heat production during the heat stress.

True metabolisable energy, heat increment and net energy values of two high fibre foodstuffs in cockerels

1. The yields of true metabolisable energy (TME) and net energy (NE) from chaya leaf meal and wheatfeed were mcasured in tube-fed cockerels. 2. TME, 5.76 MJ/kg, from chava leaf meal was lower than from wheatfeed, 8.39 MJ/kg. The total heat increment attributable to the feeding of chaya leaf meal was 1-7 times greater than that of wheatfeed. 3. The net efficiency of utilisation of ME (k) from chaya leaf meal was 0.64, while that from wheatfeed was 0.86. The role of different chemical composition, especially the high fibre content of the materials, is discussed. 4. The metabolisable energy and net energy values derived from chava leaf meal represented 0.34 and 0.23 respectively of its gross energy content. The combination of lower TME and lower net efficiency of utilisation led to chaya having a NE value, 3.86 MJ/kg, which was only 0.53 that of wheatfeed.

Effects of ambient temperature on heat increment of feeding and energy retention in growing broilers maintained at different food intakes

Zero-activity heat production (HP), body temperature (Tb) and energy retention were measured in growing broilers maintained at 5 ambient temperatures (Ta) (14 degrees , 17 degrees , 22 degrees , 27 degrees and 32 degrees C) and at 5 feeding rates (ad libitum intake and 75%, 50%, 25% and 0% (fasting) of ad libitum). Zero-activity HP increased with decreasing Ta and increasing food intake. However, at 14 degrees C, zero-activity HP in birds fed ad libitum and 75% did not show further increase, but those in birds fed less than 75% of ad libitum increased rapidly. Results of the regression of zero-activity HP on Ta ranging from 32 degrees to 17 degrees C indicated that the slope was affected little by food intake, but the intercept decreased with decreasing food intake. Tb increased significantly with increasing food intake. There was little variation with Ta but, at and above 27 degrees C, a slightly increased Tb was observed only in birds fed ad libitum. Overall effects of Ta and food intake on HIF (% TME intake) were not found, but HIF tended to increase with decreasing food intake at 14 degrees C. Total energy retention and energy retention as fat decreased with decreasing Ta and food intake, although energy retention as protein decreased only with decreasing food intake. Results obtained here suggest that availability of TME is affected little by Ta ranging from 32 degrees to 17 degrees C and that HIF is utilised, in part, to maintain Tb at any Ta.

Effects of early heat exposure on thermoregulatory responses and blood viscosity of broilers prior to marketing

1. This study was to determine the effects of heat load early in life on thermoregulatory responses and whole blood viscosity of broilers during a subsequent exposure to high environmental temperature later in life. 2. The birds, which had been subjected to exposure to 38 degrees C for 24 h at 5-d-old, served as prior exposure group (group A). Both group A and control group B were exposed to 33 degrees C for 3 h when near marketable weight. 3. On exposure to 33 degrees C, although there were no significant differences in the increases in heat production (HP) between the two groups, abdominal temperature (Ta), temperature of external ear tract (Tee), shank skin temperature (Tss), standing-lying frequency and lying time were lower in group A than in group B. Heart rate (HR) and comb surface temperature (Tcs) did not differ but increased in both groups during exposure to 33 degrees C. Respiration rate (RR) was greater in group A. 4. Blood viscosity decreased markedly in both groups after exposure to 33 degrees C; the decrease was greater in group A. 5. These results suggest that early exposure may promote broilers' ability to cope with the subsequent heat load by altering thermoregulatory physiological responses and behavioural patterns, resulting in an alleviation of heat stress.