Effect of ambient temperature and light intensity on physiological

Effect of ambient temperature and light intensity on physiological reactions of heavy broiler chickens1 H. A. Olanrewaju,2 J. L. Purswell, S. D. Collier, and S. L. Branton USDA, Agricultural Research Service, Poultry Research Unit, PO Box 5367, Mississippi State, MS 39762-5367 ABSTRACT The effects of ambient temperature, light intensity, and their interaction on blood acid-base balance, metabolites, and electrolytes in broiler chickens under environmentally controlled conditions were examined in 2 trials. The experiment consisted of a factorial arrangement of treatments in a randomized complete block design. The 9 treatments consisted of 3 levels of temperatures (low = 15.6°C; moderate = 21.1°C; high = 26.7°C) from 21 to 56 d of age and 3 levels of light intensities (0.5, 3.0, 20 lx) from 8 to 56 d of age at 50% RH. A total of 540 Ross 708 chicks were randomly distributed into 9 environmentally controlled chambers (30 male and 30 female chicks/chamber) at 1 d of age. Feed and water were provided ad libitum. Venous blood samples were collected on d 21 (baseline), 28, 42, and 56. High ambient temperature significantly (P ≤ 0.05) reduced BW, partial pressure of CO2, bicar-

bonate, hematocrit, hemoglobin, K+, and Na+ along with significantly (P ≤ 0.05) elevated pH level, Cl−, glucose, osmolality, and anion gap concentrations. Partial pressure of O2 was slightly increased in response to increased ambient temperature. There was no effect of light intensity on most of the blood variables examined. Acid-base regulation during high ambient temperature and light intensity exposure did not deteriorate despite a lower partial pressure of CO2, which consequently increased blood pH because of a compensatory decrease in HCO3− concentration. Plasma corticosterone was not affected by temperature, light intensity, or their interaction. These results indicate that continuous exposure of broiler chickens to varying light intensities had a minor effect on physiological blood variables, whereas high ambient temperature markedly affected various blood variables without inducing stress in broilers.

Key words: temperature, light intensity, acid-base balance, broiler, well-being 2010 Poultry Science 89:2668–2677 doi:10.3382/ps.2010-00806

INTRODUCTION International animal welfare concerns have included the effects of temperature and lighting programs on broilers (Food Marketing Institute and National Council of Chain Restaurants, 2003; National Chicken Council, 2005). Research development in poultry production has been displayed through the genetic selection of breeds for high productivity. However, this genetic potential will not be fully realized until microenvironmental constraints (temperature, humidity, light intensity, air velocity, etc.) have been fully addressed. It has been reported that during heat stress, behavioral, physiological, hormonal, and molecular adjustments can occur (Etches et al., 1995; Nalini et al., 2008). Exposure of poultry to ambient temperatures outside the thermoneutral zone during the course of production may adversely ©2010 Poultry Science Association Inc. Received March 26, 2010. Accepted September 19, 2010. 1 Mention of trade names or commercial products in this publication is solely for providing specific information and does not imply recommendation or endorsement by the USDA. 2 Corresponding author: [email protected]

affect production [BW, BW gain (BWG), and feed conversion ratio (FCR)] efficiency, meat yield, immune response, and mortality (Washburn, 1985; Howlinder and Rose, 1989). Heavy broilers (>2.5 kg) may need to be grown under lower ambient temperature than previously reported because of their higher BW and metabolic rates. The body temperature of an adult chicken is 40.6 to 41.7°C, and the thermoneutral zone that allows chickens to maintain their body temperature is 18 to 24°C. However, under high ambient temperature, fast-growing broilers of heavy BW are particularly susceptible to heat stress because of their high level of production. The highest and lowest temperatures that are critical for optimal performance are dependent on bird age, BW, housing system, feeding level, RH, air velocity, and overall health. In the southern United States and in many countries of the world, especially those in tropical regions that are characteristically hot and humid, broiler chickens are often maintained at ambient temperatures above the thermoneutral zone. In these areas where high ambient temperatures are prevalent for most of the year, further studies are required to elucidate the responses of modern broilers to temperatures that vary from the thermoneutral zone to determine

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temperature levels and light intensities that may limit production. Chickens raised where ambient temperature is high have higher energy needs than those that are in thermoneutral environments. Major losses result from a less efficient conversion of feed to meat, which detrimentally affects poultry health and productivity. It is estimated that a 1% improvement in feed conversion would save US poultry producers more than $50 million/yr. Light management is also an important factor affecting broiler production. Most modern lighting programs begin with a high light intensity (approximately 20 lx) that is decreased to approximately 5 lx by 14 to 21 d, and is then maintained at 5 lx or less for the remainder of the grow-out period. However, a wide variety of lighting programs currently exist that take into account light wavelength, intensity, duration, and the various devices for their regulation that are available to poultry producers. Each program possesses its own characteristics and applicability to rearing poultry. Although we have a good understanding of how photoperiod affects poultry production, our knowledge of how light intensity affects poultry production is shallow by comparison. These deficiencies, as well as the associated financial losses, have led to an increased interest in developing management techniques that will maximize broiler productivity while minimizing other associated problems. As such, poultry house ambient conditions along with adequate management strategies affect productivity and livability of poultry. The potential for changing temperature and light intensity to influence broiler productivity and health is under considerable investigation. Therefore, it is important to determine the levels of the various ambient factors in poultry houses that can influence the genetic growth potential in poultry (Xin et al., 1994; Gates et al., 1998). An evaluation of blood pH, electrolytes, blood gases, and metabolites could elucidate acid-base disturbances and differentiate between metabolic and respiratory disorders in broilers exposed to fluctuations in factors controlling ambient environmental conditions (Lin et al., 2000). Although many studies have been conducted to evaluate the effect of the thermal environment in birds (Borges et al., 2004, Rahimi, 2005), still more studies are necessary to examine the interrelationship of temperature and light intensity in affecting the mechanisms that control the physiology of the bird (acid-base balance, electrolytes, metabolites, endocrine system). Determination of these factors is essential so that therapeutic or nutritional strategies can be applied to reduce these negative effects and thereby optimize the environment in broiler houses to maximize the genetic potential of birds while reducing production costs. The objective of the present study was to evaluate the specific effects of ambient temperature, light intensity, and their interaction on various key physiological parameters in heavy broiler chickens.

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MATERIALS AND METHODS Bird Husbandry In each of 2 trials, with each lasting 8 wk, a total of 540 one-day-old Ross 708 (Aviagen Inc., Huntsville, AL) chicks were purchased from a commercial hatchery, and on arrival, the chicks were sexed and then group weighed. Chicks were randomly distributed into 9 environmentally controlled chambers (30 males and 30 females chicks/chamber). Each environmentally controlled chamber had a floor area of 6 m2 (2.3 m width × 2.6 m depth) with a chamber volume of 15.3 m3 (2.5 m height). Chicks were vaccinated for Marek’s, Newcastle, and infectious bronchitis diseases at the hatchery. At 12 d of age, birds received a Gumboro vaccination via water administration. Each chamber contained fresh pine shavings at a depth of 7.62, tube feeders, and a 7-nipple watering system. Birds were provided a 4-phase feeding program (starter: 1 to 14 d; grower: 15 to 28 d; finisher: 29 to 42 d; withdrawal: 43 to 56). Diets were formulated to meet or exceed NRC (1994) nutrient recommendations. Starter feed was provided as crumbles, and subsequent feeds were provided as whole pellets. Feed and water were offered ad libitum. Ambient temperature was maintained at 33°C at the beginning of experimentation and was reduced as the birds progressed in age until d 22, when temperature treatments started.

Experimental Treatments The experiment consisted of a factorial arrangement of treatments in a randomized complete block design. The treatments consisted of 3 levels of temperature (low = 15.6°C; moderate = 21.1°C; high = 26.7°C) from d 21 to 56 d of age and 3 levels of light intensity (0.5, 3.0, 20 lx) from 8 to 56 d of age at 50% RH. There were 3 different chambers for each temperature treatment along with 3 different chambers for each light intensity treatment, for a total of 9 chambers. Each of the 3 temperature level treatments was paired with 1 of the 3 light intensity treatments so that each chamber represented a particular temperature:light intensity level combination. The ambient temperatures in each temperature treatment were stepped down so that they decreased linearly every day from 33°C at 1 d of age to reach their targeted temperatures of 26.7, 21.1, and 15.6°C, respectively, by d 21, and were continued through 56 d of age (Figure 1). The light intensity from d 1 to 7 was 20 lx in each chamber. Each chamber was equipped with incandescent lighting, typical of that used in commercial housing. Light intensity settings were verified at the bird level (30 cm) by using a photometric sensor with National Institute of Standards and Technology-traceable calibration (403125, Extech Instruments, Waltham, MA) for each intensity adjustment. The light fittings and tubes were dusted weekly to minimize dust buildup, which would otherwise reduce the intensity.

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Blood Collections and Chemical Analyses On d 21 (day before initiation of the treatments), 28, 42, and 56, blood samples were collected between 0800 and 0900 h on sampling day from a brachial vein of 6 (3 male and 3 female chicks/chamber) randomly selected birds from each chamber, and the birds were then returned to the appropriate chambers by using our standard handling procedure (Olanrewaju et al., 2008). In addition, unnecessary discomfort to the birds was avoided by using proper housing and handling techniques, as described by the NRC (1996). Blood samples (3 mL) were collected directly into heparinized (50 IU/ mL) monovette syringes. All bleedings were completed within 45 s after birds were caught. Blood samples were drawn directly from the syringes into a blood gas electrolyte analyzer (ABL-80 Flex, Radiometer America, Westlake, OH) for immediate analysis of partial pressure of CO2 (pCO2), partial pressure of O2 (pO2), pH, hematocrit (Hct), hemoglobin (Hb), and electrolytes (Na+, K+, Ca2+, HCO3−, and Cl−). In addition, immediate glucose (GLU), osmolality (mOsm), and anion gap were analyzed. The pH, pCO2, pO2, and HCO3− values were corrected to reflect a body temperature of 41.5°C (Burnett and Noonan, 1974). The mean corpuscular Hb concentration was calculated using the standard formula [(Hb × 100)/Hct]. The needle mounted on each monovette syringe was then removed, a cap was placed over the needle port, and the syringes containing the blood samples were plunged into ice. After

all birds were bled, the iced samples were transferred to the laboratory and centrifuged at 4,000 × g for 20 min at 4°C, and the packed blood cells were expelled from the syringes. The plunger on each monovette was broken off and the syringe served as a storage vial for the remaining plasma. This procedure ensured that the plasma samples were never exposed to ambient air. Plasma samples were stored at −20°C for later chemical analysis. Plasma samples were removed from the freezer, thawed, and analyzed for corticosterone (CS) using a universal microplate spectrophotometer (BioTek Instruments Inc., Winooski, VT) with ELISA reagent assay test kits from Assay Designs (EIA-CS Kit, Assay Designs Inc., Ann Arbor, MI), according to the manufacturer’s instructions. We have previously used this methodology of the kit as it relates to the manufacturer’s instructions in broilers (Olanrewaju et al., 2006, 2008).

Heart and Blood Collections for Analysis On d 56 at the end of each trial, 10 (5 males and 5 females) birds were randomly selected from each chamber. The birds were weighed individually, and rectal temperatures (RT) were measured using a thermocouple digital thermometer (accuracy of ±0.1°C; VWRTraceable, Friendswood, TX). After inserting the thermometer, the temperature was allowed to stabilize for 30 s before the reading was obtained. Immediately after temperature measurement, blood samples (3 mL) were

Figure 1. Ambient temperature treatments stepped down to decrease linearly every day from 33°C at 1 d of age to reach the targeted temperatures of 26.7, 21.1, and 15.6°C, respectively, on d 21 through 56 d of age.

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Table 1. Influence of temperature and light intensity on plasma pH and HCO3 of heavy broiler chickens HCO3− (mm of Hg)

pH Item

21 d

28 d

42 d

56 d

Temperature treatment (°C) Low (15.6) Moderate (21.1) High (26.7) Intensity treatment 0.5 lx 3.0 lx 20 lx SEM1 Temperature-light intensity treatment Low-0.5 lx Low-3.0 lx Low-20 lx Moderate-0.5 lx Moderate-3.0 lx Moderate-20 lx High-0.5 lx High-3.0 lx High-20 lx SEM2

7.35 7.37 7.37 7.36 7.38 7.36 0.016 7.33 7.38 7.34 7.35 7.39 7.37 7.39 7.35 7.37 0.022

7.37 7.39 7.38 7.38 7.39 7.38 0.015 7.36 7.41 7.35 7.38 7.40 7.38 7.38 7.36 7.40 0.020

7.35 7.37 7.37 7.36 7.37 7.37 0.015 7.34 7.37 7.35 7.37 7.38 7.36 7.35 7.35 7.40 0.026

7.36b 7.38ab 7.40a 7.38 7.39 7.37 0.008 7.35 7.37 7.37 7.38 7.38 7.37 7.41 7.41 7.38 0.038

Source of variation Temperature Light intensity Temperature × light intensity

0.412 0.608 0.276

0.712 0.566 0.231

0.729 0.845 0.587

0.047 0.915 0.967

P-value

21 d

28 d

42 d

56 d

25.86 26.17 26.47 25.98 26.67 25.85 0.424 24.96 26.94 25.68 25.70 26.63 26.18 27.28 26.44 25.40 0.734

26.30 26.01 25.84 26.05 26.62 25.47 0.382 25.32 27.30 26.27 26.63 26.59 24.82 26.21 25.97 25.33 0.662

26.18a 25.80a 24.04b 25.44 25.65 24.93 0.401 25.99 26.92 25.62 26.32 25.71 25.37 24.00 24.33 23.79 0.695

26.42a 26.08ab 23.85b 25.64 25.43 25.28 0.709 26.36 26.74 26.15 26.63 26.31 25.31 23.93 29.23 24.39 1.227

0.609 0.381 0.384

0.701 0.161 0.295

0.010 0.453 0.838

0.051 0.938 0.891

a,bMeans

within a column and effect that lack common superscripts differ significantly (P ≤ 0.05). SEM for main effects (n = 6). 2Pooled SEM for interaction effect (n = 2). 1Pooled

collected directly into heparinized (50 IU/mL) monovette syringes, as stated above for plasma analysis of cholesterol (CHOL), triglycerides (TRIG), total protein (TP), and high-density lipoprotein (HDL) using an autoanalyzer (Vitro DT 6011, Ortho-Clinical Diagnostic, Rochester, NY). This analyzer uses the enzymatic procedures described by Elliott (1984). Subsequently, birds were euthanatized by cervical dislocation according to the Animal Care and Ethics Committeeapproved blood sampling and organ collection procedures. The chest was opened and the heart was removed and the atria, great vessels, and epicardial fat were trimmed off. The weight of the total heart was determined and calculation of the BW:total heart ratio was determined.

Statistical Analysis A 3 × 3 factorial data analysis arranged in a randomized complete block design was used in this study. Data were replicated over time, with trial being the blocking factor. Chamber was considered the experimental unit. The 9 treatments consisted of 3 levels of temperature × 3 levels of light intensity. The main effects of temperature and light intensity and the interaction of these 2 factors on physiological variables were tested using the MIXED procedure of SAS software (SAS Institute, 2004). Means comparisons on d 21, 28, 42, and 56 were

assessed by least significant differences, and statements of significance were based on P ≤ 0.05.

RESULTS Table 1 shows the effect of ambient temperature exposure, light intensity, and their interaction on plasma pH and HCO3−. In comparison with low ambient temperature, high ambient temperature significantly increased pH on d 56 (P ≤ 0.0465). The main effect of light intensity on pH was not observed on any of the sampling days. Furthermore, high ambient temperature significantly reduced HCO3− on d 42 (P ≤ 0.0097) and d 56 (P ≤ 0.0510). However, there was no main effect of light intensity on HCO3− on any of the sampling days. No significant temperature × light intensity interaction for pH or HCO3− was found on any of the sampling days. High ambient temperature caused a significant decrease in pCO2 on d 28 (P ≤ 0.0030), d 42 (P ≤ 0.0526), and d 56 (P ≤ 0.0021) in comparison with low and moderate ambient temperatures (Table 2). No effects of temperature or light intensity on pO2 were found on any of the sampling days. No significant temperature × light intensity interaction for either pCO2 or pO2 was found on any of the sampling days. As shown in Table 3, high ambient temperature significantly decreased Hb (P ≤ 0.0098, P ≤ 0.0541) and Hct (P ≤ 0.0086, P ≤ 0.0408) on d 42 and 56, respec-

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tively. No effect of light intensity on Hb and Hct was found on any of the sampling days. Table 4 shows the influence of temperature and light intensity on plasma Na+ and Cl−. High ambient temperature significantly reduced plasma Na+ levels from d 21 (P ≤ 0.0002) through d 56 (P ≤ 0.0001). In addition, high ambient temperature significantly increased Cl− on d 56 (P ≤ 0.0146). No effect of light intensity on plasma Na+ and Cl− was found on any of the sampling days. No temperature × light intensity interaction for either plasma Na+ or Cl− was found on any of the sampling days. No main effects on Ca2+ or interactions were due to temperature or light intensity on any of the sampling days (data not shown). Table 5 shows the influence of temperature and light intensity on plasma K+ and mOsm. High ambient temperature caused a significant decrease in plasma K+ on d 42 (P ≤ 0.0024) and d 56 (P ≤ 0.0015) compared with low and moderate ambient temperatures. High ambient temperature also significantly increased plasma mOsm levels from d 21 (P ≤ 0.0005) through d 56 (P ≤ 0.0027). No significant temperature × light intensity interaction for plasma K+ or plasma mOsm was found on any of the sampling days. The effects of temperature and light intensity on plasma GLU and CS are presented in Table 6. High ambient temperature caused a significant increase in plasma GLU concentration on d 42 (P ≤ 0.0002) and on d 56 (P ≤ 0.0009) compared with low and moderate

ambient temperatures. The high (20 lx) light intensity significantly increased plasma GLU concentration on d 56 (P ≤ 0.0369). Corticosterone concentrations were not significantly affected by the temperature and light treatments or their interaction on any of the sampling days in the present study. As shown in Table 7, there was a main effect of temperature on BW, RT, CHOL, TRIG, HDL, and plasma TP on d 56 of age. At d 56, high ambient temperature significantly reduced BW (P ≤ 0.0001), HDL (P ≤ 0.0001), and TP (P ≤ 0.0002), whereas it increased RT (P ≤ 0.0001), CHOL (P ≤ 0.0001), and TRIG (P ≤ 0.0004) compared with low and medium ambient temperatures. Furthermore, on d 56, there was a significant main effect of light intensity on TRIG (P ≤ 0.0010) and HDL (P ≤ 0.0078). Temperature and light intensity also had an interaction effect on BW (P ≤ 0.0158), RT (P ≤ 0.0497), TRIG (P ≤ 0.0216), HDL (P ≤ 0.0001), and TRIG:HDL (P ≤ 0.0001) on d 56.

DISCUSSION The principal organ systems used in acid-base homeostasis in birds are the lungs and kidneys, and these are supported by the gastrointestinal tract (Long, 1982). The cardiovascular system also participates in thermoregulatory processes through modulation of heat dissipation on the one hand, and by oxygen transport

Table 2. Influence of temperature and light intensity on plasma partial pressure of CO2 (pCO2) and partial pressure of O2 (pO2) of heavy broiler chickens pCO2 (mm of Hg) Item Temperature treatment (°C) Low (15.6) Moderate (21.1) High (26.7) Intensity treatment 0.5 lx 3.0 lx 20 lx SEM1 Temperature-light intensity treatment Low-0.5 lx Low-3.0 lx Low-20 lx Moderate-0.5 lx Moderate-3.0 lx Moderate-20 lx High-0.5 lx High-3.0 lx High-20 lx SEM2 Source of variation Temperature Light intensity Temperature × light intensity a,bMeans

pO2 (mm of Hg)

21 d

28 d

42 d

56 d

42.90 40.32 38.25 42.08 40.07 39.32 1.458 42.25 41.45 45.00 43.15 40.10 37.70 40.85 38.65 35.25 4.515

46.07a 44.33a 36.93b 42.32 42.05 42.97 1.408 45.65 43.80 48.75 46.30 43.60 43.10 35.00 38.75 37.05 2.439

44.63a 42.25a 37.62b 44.23 40.08 40.18 1.823 46.40 43.60 43.90 45.45 39.50 41.80 40.85 37.15 34.85 3.158

43.72a 42.25a 31.67b 39.45 38.35 39.83 1.804 44.85 43.00 43.30 42.10 39.40 45.25 31.40 32.65 30.95 3.125

0.479 0.747 0.863

0.003 0.895 0.449

0.053 0.239 0.940

0.002 0.837 0.779

P-value


21 d

28 d

42 d

56 d

38.97 42.73 43.82 40.78 42.50 42.23 5.197 42.05 43.00 35.85 39.50 44.45 44.25 44.80 40.05 46.60 9.002

35.87 37.32 39.43 37.30 37.83 37.48 4.012 37.65 37.65 32.30 32.85 41.05 38.05 41.40 34.80 42.10 6.956

44.92 45.38 38.22 43.00 43.40 42.12 2.531 46.10 45.15 43.50 41.85 48.15 46.15 41.05 36.90 36.70 4.384

42.18 38.82 35.43 38.50 39.92 38.02 2.959 42.35 42.95 41.25 39.10 43.35 34.00 34.05 33.45 38.80 5.125

0.792 0.969 0.940

0.823 0.996 0.776

0.136 0.935 0.779

0.319 0.896 0.711

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Table 3. Influence of temperature and light intensity on plasma hemoglobin (Hb) and hematocrit (Hct) of heavy broiler chickens Hb (g/dL)

Hct (%)

Item

21 d

28 d

42 d

56 d

21 d


7.46 7.15 7.36 7.46 7.13 7.37 0.173 7.57 7.42 7.39 7.30 6.93 7.21 7.51 7.06 7.50 0.299

7.30 7.21 7.17 7.20 7.24 7.24 0.156 6.93 7.38 7.61 7.27 7.29 7.07 7.41 7.05 7.06 0.270

8.25a 7.95ab 7.69b 8.00 8.05 7.84 0.099 8.49 8.23 8.02 7.68 8.01 8.17 7.82 7.92 7.33 0.171

8.32a 7.94ab 7.66b 7.96 7.98 7.97 0.165 8.10 8.36 8.51 7.99 7.99 7.83 7.80 7.60 7.58 0.285


0.460 0.426 0.953

0.834 0.975 0.378

0.010 0.329 0.072

0.054 0.996 0.800

23.28 22.32 22.95 23.25 22.32 22.98 0.520 23.6 23.15 23.10 22.75 21.70 22.50 23.40 22.10 23.35 0.8998 P-value 0.443 0.457 0.963

28 d

42 d

56 d

22.82 22.53 22.38 22.50 22.60 22.63 0.468 21.70 23.00 23.75 22.70 22.80 22.10 23.10 22.00 22.05 0.811

25.63a 24.75ab 23.95b 24.88 25.05 24.40 0.290 26.35 25.60 24.95 23.95 24.90 25.40 24.35 24.65 22.85 0.502

25.92a 24.73ab 23.88b 24.80 24.93 24.80 0.473 25.20 26.15 26.40 24.90 24.95 24.35 24.30 23.70 23.65 0.819

0.806 0.978 0.372

0.009 0.305 0.067

0.041 0.974 0.760

a,bMeans


Table 4. Influence of temperature and light intensity on plasma Na+ and Cl− of heavy broiler chickens Na+ (mEq/L) Item Temperature treatment (°C) Low (15.6) Moderate (21.1) High (26.7) Intensity treatment 0.5 lx 3.0 lx 20 lx SEM1 Temperature-light intensity treatment Low-0.5 lx Low-3.0 lx Low-20 lx Moderate-0.5 lx Moderate-3.0 lx Moderate-20 lx High-0.5 lx High-3.0 lx High-20 lx SEM2 Source of variation Temperature Light intensity Temperature × light intensity a,bMeans

21 d

28 d

42 d

146.3a 146.1a 131.6b 141.2 141.3 141.5 1.691 146.7 145.7 146.4 146.0 145.9 146.4 130.8 132.2 131.9 2.929

146.3a 146.7a 131.5b 142.0 141.5 141.1 1.472 141.9 146.0 146.1 147.5 146.7 146.1 131.7 131.7 131.1 2.550

149.3a 150.3a 125.7b 141.6 141.4 142.4 1.874 144.1 149.3 154.6 151.8 150.4 148.8 129.0 124.5 123.8 3.245

0.000 0.987 0.996

0.000 0.901 0.999

0.000 0.928 0.225

Cl− (mEq/L) 56 d 153.3a 151.1a 120.9b 143.0 141.5 140.8 1.724 153.1 153.5 153.4 151.8 150.9 150.6 124.3 120.1 118.3 2.9853 P-value 0.000 0.652 0.857


21 d

28 d

42 d

56 d

103.6 103.9 103.9 103.4 103.6 104.4 0.512 104.1 103.2 103.7 103.1 104.2 104.5 103.2 103.6 105.0 0.887

104.1 105.3 104.8 105.2 104.5 104.6 0.405 105.5 103.5 103.4 105.4 105.5 105.1 104.9 104.4 105.2 0.702

110.7 108.4 107.7 110.1 107.8 108.9 1.266 113.3 106.7 112.0 109.7 109.3 106.4 107.4 107.4 108.4 2.193

111.1ab 109.1b 113.6a 111.5 111.4 110.8 0.861 110.8 111.4 111.1 109.8 108.8 108.7 114.1 114.2 112.7 1.492

0.919 0.445 0.696

0.177 0.371 0.450

0.281 0.454 0.364

0.015 0.815 0.959

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Table 5. Influence of temperature and light intensity on plasma Ca2+ and osmolality (mOsm) of heavy broiler chickens K+ (mEq/L)

mOsm (mmol/kg)

Item

21 d

28 d

42 d

56 d

21 d


4.23 4.30 3.14 3.78 4.17 3.73 0.430 4.34 4.18 4.18 4.06 4.57 4.28 2.95 3.75 2.73 0.745

4.13 4.25 2.98 3.73 3.88 3.75 0.455 4.23 4.14 4.01 4.05 4.46 4.23 2.90 3.04 3.01 0.788

4.24a 4.38a 2.50b 3.30 4.02 3.80 0.2948 3.36 4.75 4.62 4.39 4.43 4.33 2.16 2.89 2.44 0.511

4.85a 4.85a 2.37b 4.01 4.17 3.89 0.373 4.92 5.05 4.58 4.64 5.13 4.77 2.47 2.34 2.31 0.646


0.158 0.743 0.947

0.151 0.968 0.998

0.002 0.262 0.662

0.002 0.863 0.986

28 d

42 d

56 d

306.2b 305.5b 326.5a 312.8 312.6 312.8 2.660 307.7 305.2 305.8 305.6 305.0 306.0 325.1 327.7 326.7 4.608 P-value

305.8b 306.0b 329.0a 313.8 314.0 313.1 2.123 308.2 304.9 304.2 306.9 306.1 305.1 326.3 330.9 329.9 3.676

318.4b 313.8b 325.5a 321.6 314.6 319.4 2.198 321.6 311.7 321.8 316.6 314.7 310.1 324.6 317.6 326.2 3.807

320.8b 316.4b 329.3a 322.0 312.3 323.2 1.862 320.1 320.8 321.4 317.4 315.9 316.0 328.5 327.1 332.2 3.225

0.001 0.999 0.985

0.000 0.953 0.807

0.037 0.126 0.398

0.003 0.770 0.904

a,bMeans


Table 6. Influence of temperature and light intensity on plasma glucose (GLU) and corticosterone (CS) of heavy broiler chickens GLU (mg/dL) Item Temperature treatment (°C) Low (15.6) Moderate (21.1) High (26.7) Intensity treatment 0.5 lx 3.0 lx 20 lx SEM1 Temperature-light intensity treatment Low-0.5 lx Low-3.0 lx Low-20 lx Moderate-0.5 lx Moderate-3.0 lx Moderate-20 lx High-0.5 lx High-3.0 lx High-20 lx SEM2 Source of variation Temperature Light intensity Temperature × light intensity a,bMeans

CS (pg/mL)

21 d

28 d

42 d

56 d

246.8 240.6 246.6 250.3 245.0 238.6 8.134 258.9 248.9 232.6 244.9 237.6 239.5 247.3 248.7 243.8 14.088

234.0 226.0 251.3 238.0 241.1 232.2 7.577 251.7 232.2 218.2 214.2 230.2 233.7 248.1 261.1 244.9 13.124

236.5b 236.1b 270.9a 246.5 255.0 242.0 4.028 238.2 241.6 229.7 233.3 250.1 224.9 268.0 273.3 271.6 6.977

255.3b 257.5b 285.3a 260.8b 260.8b 276.4a 4.086 251.7 249.7 264.5 249.5 253.3 269.7 281.2 279.5 295.1 7.077

0.835 0.611 0.911

0.105 0.711 0.386

0.000 0.122 0.544

21 d

28 d

42 d

56 d

2,054 1,424 1,626 2,051 1,539 1,515 439 3,200 1,607 1,355 1,830 1,541 902 1,123 1,469 2,287 760.3 P-value

1,239 1,074 1,208 1,168 1,242 1,111 194.9 1,376 1,047 1,296 774 1,645 804 1,355 1,033 1,234 337.5

1,763 1,585 1,770 1,830 1,498 1,790 308.4 2,129 1,351 1,808 1,463 1,254 2,038 1,899 1,888 1,524 535.1

1,655 1,838 2,917 2,207 2,066 1,938 421.6 1,462 1,725 1,477 1,778 1,888 1,848 3,148 2,586 2,489 731.2

0.001 0.037 0.983


0.602 0.636 0.401

0.820 0.895 0.353

0.894 0.717 0.763

0.087 0.905 0.780

2675


on the other. In the present study, exposure of broilers to high ambient temperature significantly affected the acid-base balance, especially at 56 d of age. Exposure of modern heavy broilers to high ambient temperature with and without increased light intensity significantly increased pH, Cl−, mOsmo, GLU, CHOL, TRIG, Cl−, and RT, but significantly reduced pCO2, HCO3−, Hb, Hct, Na+, K+, TP, HDL, and BW at 56 d of age. However, exposure of modern heavy broilers to high ambient temperature with and without increased light intensity produced no significant effect on pO2, Ca2+, HW, HW:BW, TRIG:HDL, and CS. Disturbances in venous blood acid-base status (pCO2 and pH) reflecting thermal panting-induced hypocapnic alkalosis were observed frequently in the older birds, which may be attributed to relative differences in the body sizes of birds. This would suggest that thermoregulatory efforts (panting, CO2 elimination) might be greater in the older birds. The older broilers exhibited greater resting venous blood pCO2 tensions and were relatively more acidotic (hypercapnic acidosis). This may be due to age-dependent differences in ventilation rate or may reflect the consequences of an increased metabolic demand in the larger birds (Korte et al., 1999). Results suggest an increased respiratory rate in broilers exposed to the higher ambient temperature with or without increased light intensity. Birds exposed to high ambient temperature exhibited higher respira-

tory rates in an effort to dissipate heat by evaporation. Evaporative heat loss through panting is the most important mechanism used to control body temperature under heat stress (Robertshaw, 2006). The increased respiratory rate disrupted their acid-base balance because of excessive CO2 losses (Toyomizu et al., 2005). Decreases in circulating pCO2 cause a decrease in the concentrations of H2CO3 and H+. In response to this, the kidneys increase HCO3− excretion and reduce H+ excretion in an attempt to control the acid-base balance of the bird homeostatically. This change in acidbase balance is known as respiratory alkalosis (Bottje and Harrison 1985). Physiologically, the changes in systemic pH in response to heat stress are complex in that they involve an initial respiratory response phase, which may produce a systemic alkaloidosis and then a compensatory phenomenon involving homeostatic mechanisms that can produce systemic acidosis. This condition can be accentuated in big birds, as observed in this study. Exposure of broiler chickens to the 26.7°C ambient temperature treatment like this rather than the 15.6°C or 21.1°C temperatures resulted in a significant (P < 0.0001) depression in BW. Increased electrolyte excretions through urine and feces along with continuous loss of water through panting have been shown to further disrupt the acid-base balance (Belay et al., 1992). The degree of water loss in intracellular fluids has been associated with losses

Table 7. Influence of temperature and light intensity on BW, heart weight (HW), and hematological variables1 of heavy broiler chickens at 56 d of age Item

BW (kg)

HW (kg)

HW:BW (%)

RT (°C)

CHOL (mg/dL)

TRIG (mg/dL)

HDL (mg/dL)

TRIG: HDL

TP (g/dL)

Temperature treatment (°C) Low (15.6) Moderate (21.1) High (26.7) Light intensity treatment 0.5 lx 3.0 lx 20 lx SEM2 Temperature-light intensity treatment Low-0.5 lx Low-3.0 lx Low-20 lx Moderate-0.5 lx Moderate-3.0 lx Moderate-20 lx High-0.5 lx High-3.0 lx High-20 lx SEM3

4.08a 3.92b 3.35c 3.81 3.78 3.76 0.065 4.07ab 3.95ab 4.24a 3.92ab 4.00ab 3.84b 3.44c 3.40c 3.20c 0.113

0.017 0.017 0.016 0.018 0.015 0.016 0.003 0.017 0.016 0.019 0.017 0.017 0.016 0.024 0.012 0.013 0.0004

0.415 0.427 0.491 0.522 0.388 0.423 0.087 0.410 0.389 0.445 0.443 0.420 0.417 0.713 0.354 0.408 0.151

40.9b 41.1b 41.6a 41.1 41.3 41.2 0.092 40.8c 41.1bc 40.9c 41.1bc 41.2abc 41.1abc 41.5ab 41.6a 41.6a 0.159

129.1b 126.4b 166.4a 137.0 149.7 135.1 5.508 131.9 131.9 123.4 114.4 141.2 123.5 164.7 176.1 158.4 9.540 P-value

71.0b 97.9a 100.3a 102.8a 72.9b 93.5ab 7.812 80.2bcd 81.8bcd 56.8d 118.2ab 64.9cd 102.6abc 125.3a 86.5abcd 91.4abcd 13.531

137.8a 120.0a 78.7b 114.8ab 99.1b 122.6a 7.453 151.3ab 149.0ab 117.2bc 164.6a 97.6cd 151.0ab 86.1cd 82.4cd 67.6d 12.91

0.515 0.816 1.274 0.895 0.736 0.763 0.099 0.530b 0.549b 0.485b 0.718b 0.665b 0.679b 1.455a 1.050a 1.352a 0.171

3.59a 3.57a 3.34b 3.50 3.55 3.45 0.062 3.55 3.69 3.56 3.36 3.43 3.53 3.53 3.28 3.32 0.107


0.000 0.718 0.016

0.969 0.251 0.315

0.643 0.289 0.391

0.000 0.114 0.050

0.000 0.219 0.362

0.124 0.072 0.000

0.000 0.298 0.519

a–dMeans

0.000 0.001 0.022

0.000 0.008 0.000

within a column and effect that lack common superscripts differ significantly (P ≤ 0.05). = rectal temperature; CHOL = cholesterol; TRIG = triglycerides; HDL = high-density lipoprotein; TP = total protein. 2Pooled SEM for main effects (n = 6). 3Pooled SEM for interaction effect (n = 2). 1RT

2676

Olanrewaju et al.

K+.

of intracellular This loss of extracellular fluid has been linked to a loss in plasma Na+. Plasma Na+, K+, and Cl− levels were affected by heat stress in this study. Plasma K+ and Na+ concentrations are known to decrease as temperature rises (Belay and Teeter, 1993, Borges et al., 2003), whereas Cl− increases (Belay and Teeter, 1993). The increase in Cl− decreases H+ excretion and HCO3− reabsorption by the kidneys. This might contribute to blood acidification, which, in turn, seems to be an appropriate response to alkalosis. The plasma K+ and Na+ concentration results in the current study are consistent with these earlier reports. High ambient temperature also significantly affected plasma mineral balance and mineral concentrations of broilers in this study. It has been reported that Hct values can decrease with increasing rearing temperature (Kubena et al., 1972; Yahav and Hurwitz 1996). Hematological examinations in these studies have also proved that the total amount of Hb in blood can decrease with increased rearing temperature, which can result in lower metabolic rate, as shown by others (Donkoh, 1989; Jamadar and Jalnapurkar 1995). Concentrations of certain plasma hormones, enzymes, and metabolites such as CS have been suggested to be sensitive indicators of stress levels in broiler chickens (Puvadolpirod and Thaxton, 2000; Olanrewaju et al., 2006). Nonsignificant increases in plasma CS observed in the present study indicated that birds were not stressed. This nonsignificant increase in plasma CS was accompanied by increased concentrations of energy nutrients in sera, such as GLU, CHOL, and TRIG. The increase in plasma GLU concentration indicated stimulation of gluconeogenetic processes as a direct response to increased epinephrine, norepinephrine, and glucocorticoid secretion (Borges et al., 2003, 2004). Hyperthermia has been reported to induce hyperglycemia, whereas hypothermia can cause hypoglycemia in domestic fowl (Hazelwood 1976). Increases in GLU and HDL in response to increased light intensity may have stimulated increased physical activity in birds exposed to bright light (20 lx), with a subsequent increase in energy expenditure for activity rather than growth. Decreased levels of total plasma proteins in birds subjected to hot ambient temperature confirmed the role of CS as a proteolytic hormone (Khan et al., 2002; Kataria et al., 2008). Thus, it is suggested that at high ambient temperatures, a high degree of water loss caused by increased panting together with reduced drinking may lead to dehydration and increases in plasma mOsm (Yahav et al., 1995). Vo et al. (1978) have reported reductions in total plasma protein with increasing ambient temperature similar to those observed in this study. Evidence suggests that decreases in total plasma protein may also be indicative of increased heat stress in chickens (Kutlu and Forbes, 1993; Berrong and Washburn, 1998). Elevated body temperature may also occur in response to heat stress. In this study, RT increased similarly with increased ambient temperature. Ambient temperatures have a considerable influence on

the body temperatures of chickens, as shown by others (Huston 1965; Boone and Hughes 1971). Based on our finding, broilers raised under low and medium ambient temperatures performed better, as indicated by increased BW, and were healthier, as reflected in higher plasma HDL and TP and lower CHOL and TRIG, when compared with those raised under high ambient temperatures. In agreement with our findings, there is evidence that serum TRIG may be an independent risk factor for cardiovascular diseases (Hokanson and Austin, 1996; Jia et al., 2006). Elevated TRIG and low HDL are basic characteristics of a metabolic syndrome that is strongly associated with coronary heart disease (McLaughlin et al., 2003). Calculation of the TRIG:HDL ratio has been shown to be a good predictor of coronary heart disease (Barzi et al., 2005; Hadaegh et al., 2009). A low TRIG:HDL ratio is indicative of primarily large, nonatherogenic low-density lipoprotein particles, whereas a high TRIG:HDL ratio indicates a larger population of small, dense proatherogenic lowdensity lipoprotein particles (Dobiášová and Frohlich, 2001; Maruyama et al., 2003). It has been reported that the log concentration of TRIG:HDL can be used as an atherogenic index to indicate a balance between the actual concentrations of plasma TRIG and HDL, which may predetermine the direction of CHOL transport in the intravascular volume pool (Dobiášová and Frohlich, 2001). Studies have been conducted to examine the effect of high temperature on the thermal levels within birds (Borges et al., 2004; Rahimi, 2005). However, the modulations of the physiological mechanisms involved are poorly understood. The results of this study supplement current knowledge of the hematology and biochemistry of plasma in modern chickens with heavy BW during the growth period and provide warning that even relatively small changes in the ambient temperature from the thermoneutral zone (18 to 24°C) can have a negative effect on their metabolism and performance. In addition, the high ambient temperatures and light intensities used in this study apparently did not act together or separately to affect plasma CS, suggesting that these factors may not be stressors to modern heavy broiler chickens.

ACKNOWLEDGMENTS The authors thank Larry N. Halford and M. Robinson (both of the USDA Poultry Research Unit) for their contributions to this study.

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