PHYSIOLOGY, ENDOCRINOLOGY, AND REPRODUCTION Interactive effects of photoperiod and light intensity on blood physiological and biochemical reactions of broilers grown to heavy weights1 H. A. Olanrewaju,2 J. L. Purswell, S. D. Collier, and S. L. Branton USDA, Agricultural Research Service (ARS), Poultry Research Unit, PO Box 5367, Mississippi State, MS 39762-5367 ABSTRACT The effects of photoperiod, 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. A 3 × 3 factorial experiment in a randomized complete block design was used in this study. In each trial, all treatment groups were provided 23L:1D with 20 lx of intensity from placement to 7 d, and then subjected to the treatments. The 9 treatments consisted of 3 photoperiods [long/continuous (23L:1D) from d 8 to 56, regular/intermittent (2L:2D), and short/nonintermittent (8L:16D) from d 8 to 48 and 23L:1D from d 49 to 56, respectively] and exposure to 3 light intensities (10, 5.0, and 0.5 lx) from d 8 through d 56 at 50% RH. Feed and water were provided ad libitum. Venous blood samples were collected on d 7, 14, 28, 42, and 56. Main effects indicated that short/nonintermittent photoperiod significantly (P < 0.05) reduced BW, pH, partial
pressure of O2, saturated O2, Na+, K+, Ca2+, Cl−, osmolality, triiodothyronine (T3), and total protein along with significantly (P < 0.05) elevated partial pressure of CO2, hematocrit, hemoglobin, and lactate concentrations. In addition, there were no effects of photoperiod on HCO3−, glucose, anion gap, and thyroxine (T4). Plasma corticosterone was not affected by photoperiod, light intensity, or their interaction. There was no effect of light intensity on most of the blood variables examined. Acid-base regulation during photoperiod and light intensity exposure did not deteriorate despite a lower pH and higher partial pressure of CO2 with normal HCO3−. These results indicate that continuous exposure of broiler chickens to varying light intensities had a minor effect on blood physiological variables, whereas the short photoperiod markedly affected most blood physiological variables without inducing physiological stress in broilers.
Key words: photoperiod, light intensity, acid-base balance, broiler, well-being 2013 Poultry Science 92:1029–1039 http://dx.doi.org/10.3382/ps.2012-02792
INTRODUCTION The poultry industry has made rapid progress in improving the efficiency of broiler growth and production. Advances include improved genetics and nutrition along with changes in environmental management, resulting in more rapid broiler growth. To maximize the genetic potential of modern heavy weight broilers while ensuring bird health, environmental factors (light, air, temperature, humidity) are important. Exposure of broilers to suboptimal environmental factors including temperature, diets, and gases among others during the course of poultry production has an impact on blood physiological variables such as blood acid-base balance, electrolytes, and metabolites (Olanrewaju et al., 2007, ©2013 Poultry Science Association Inc. Received September 21, 2012. Accepted January 10, 2013. 1 Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the USDA. 2 Corresponding author:
[email protected]
2008, 2009). Rapid growth rate of modern broiler chickens is associated with a series of physiological disorders leading to higher mortality during grow-out (Julian, 2005). Therefore, it is important to determine the optimal poultry housing environment for broilers grown to heavy weights, which maximizes their genetic potential to maintain profitability while ensuring bird health. Several studies have indicated that lighting regimen has significant effects on growth performance, and skeletal and other body and physiological abnormalities in broilers. Increasing light intensity in early life stimulates activities that are related to bone and muscle growth over the final weeks of grow-out, when the lighting intensity is usually reduced (Alvino et al., 2009). Although broilers have been reared under continuous (24L:0D) or near continuous (23L:1D) photoperiods, mainly with the thought that they could provide constant visual access to feed and water, which in turn would maximize feed consumption and growth rate. Photoperiodic regimens of light/dark reduce early growth, but have welfare and performance advantages in broiler production compared with con-
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ventional continuous lighting (Blockhuis, 1983; Özkan et al., 2000). However, studies that have investigated the relationship between lighting schedule and physiological responses in broilers are limited in comparison with production responses and most of the available data are contradictory (Blair et al., 1993; Zulkifli et al., 1998). Researchers have reported that an increasing light schedule resulted in both lower mortality and leg deformities (Hulan and Proudfoot, 1987; Classen and Riddell, 1989). Recent research has focused on restricting light regimens not only to improve productivity of broiler chickens because the physical activity is very low during darkness and energy expenditure of activity is considerably lower, but also as an indirect feed restriction management practice (Rahimi et al., 2005). It has been reported that controlled amounts of light/ darkness can reduce much of the hypoglycemia, mortality, and runting-stunting associated with spiking mortality syndrome of chickens (Davis et al., 1996). Changes in acid-base balance may be early symptoms of many diseases and they have an influence on the early manifestation of clinical signs and therapeutic effectiveness in both domestic animals and human beings (Brobst, 1975; Gunnerson, 2005). In addition, it has been reported that stress responses are integrally involved with acid-base balance in several species (Sandercock et al., 2001; Parker et al., 2003; Olanrewaju et al., 2007). The most important buffer for maintaining acid-base balance in the blood is the carbonic-acid-bicarbonate buffer. A decrease in pH or an increase in partial pressure of CO2 (pCO2) in the systemic capillaries reduces the affinity of hemoglobin (Hb) for O2 (Bohr effect) and enhances the delivery of O2 to tissue, whereas a decrease in pH or an increase in partial pressure of O2 (pO2) in the pulmonary capillaries reduces the affinity of Hb for CO2 and enhances the removal of CO2 from blood into alveoli (Haldane effect), and the concentrations of the other factors (HCO3−, H2CO3, and CO2) in the reaction are also important. Furthermore, blood fluid homeostasis depends on the correct relationship between lung and kidney activities because both regulate most of the CO2 and H+ concentrations in the extracellular volume, whose total solutes consist almost entirely of Na+, Cl−, and bicarbonate ions (HCO3−). Body electrolytes such as Na+, K+, and Cl− concentrations and acid-base balance are interconnected, and one or more of the electrolytes is usually increased or decreased in acid-base disturbances (Terzano et al., 2012). In addition, other parameters such as lactate (Lac) concentration and osmolality (mOsm) are also associated with acidosis or alkalosis. Although we now have a good understanding of how light intensity affects the blood physiological variables in 2-kg broilers, our knowledge of the effect of the interactive effects of photoperiod and light intensity on the physiological responses of heavy broilers (>3 kg) and the involvement of blood acid-base balance, electrolytes, and metabolites is lacking by comparison. Determination of these factors is essential so that therapeutic or
nutritional strategies can be applied to maximize the genetic potential of birds while reducing production costs and improving health of broiler chickens. Based on the above information, the objective of the present study was to evaluate the effects of photoperiod, light intensity, and their interaction on blood acid-base balance, electrolytes, and metabolites in broiler chickens grown to heavy weights.
MATERIALS AND METHODS Bird Husbandry All procedures relating to the use of live birds in this study were approved by a USDA-ARS Animal Care and Use Committee at the Mississippi State location. In each of 2 trials, each lasting 8 wk, a total of five hundred forty 1-d-old Ross 708 (Aviagen Inc., Huntsville, AL) chicks were purchased from a commercial hatchery. On arrival, the chicks were sexed and then group weighed. Chicks were randomly distributed into 9 environmentally controlled rooms (30 males and 30 females chicks/room). Each environmentally controlled room had a floor area of 6 m2 (2.3 m width × 2.6 m depth) with a room 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 room contained fresh pine shavings at a depth of 10 cm, tube feeders, and a 7-nipple drinker 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 for ad libitum consumption. Ambient temperature was maintained at 33°C at the beginning of experimentation and was reduced as the birds progressed in age until d 42, when temperature reached 15.6°C.
Experimental Treatments Photoperiod consisted of continuous lighting (24L:0D) with 20 lx of intensity from placement to 7 d of age, and then subjected to the following treatments. The treatments consisted of 3 photoperiods [long/continuous (23L:1D) from d 8 to 56; regular/intermittent (2L:2D), and short/nonintermittent (8L:16D) from d 8 to 48 and (23L:1D) from d 49 to 56, respectively) and exposure to 3 light intensities (10, 5.0, and 0.5 lx) from d 8 through d 56. There were 3 different rooms for each photoperiod treatment along with 3 different rooms for each light intensity treatment, for a total of 9 rooms. Each of the 3 photoperiod treatments was paired with 1 of the 3 light intensity treatments so that each room represented a particular photoperiod:light intensity level combination. Each room was equipped with in-
PHOTOPERIOD, LIGHT INTENSITY, AND ACID-BASE BALANCE
candescent lighting typical of that used in commercial housing. Light intensity settings were verified from the center and 4 corners of each room at bird height (30 cm) 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 bulbs were dusted weekly to minimize dust buildup, which would otherwise reduce the intensity.
Blood Collections and Chemical Analyses On d 7 (day before initiation of the treatments), 14, 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/room) randomly selected chickens from each room, and the birds were then returned to the appropriate rooms by using a standard handling procedure (Olanrewaju et al., 2008, 2010). 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 pCO2, pO2, pH, hematocrit (Hct), Hb, and electrolytes (Na+, K+, Ca2+, HCO3−, and Cl−). In addition, immediate glucose, 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). In addition, pH was converted to H+ concentration to determine significance levels between treatments. The mean corpuscular hemoglobin 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. Two milliliters of each of the plasma samples from the syringes was stored in 2.5-mL graduated tubes at −20°C for later chemical analyses. Plasma samples were removed from the freezer, thawed, and analyzed for corticosterone using a universal microplate spectrophotometer (Bio-Tek Instruments Inc., Winooski, VT) with ELISA reagent assay test kits from Enzo life Sciences (EIA-CS Kit, Enzo Life Sciences, Farmingdale, NY), according to the manufacturer’s instructions and previously used with broilers (Olanrewaju et al., 2008, 2010). Levels of plasma triiodothyronine (T3) and thyroxine (T4) concentrations were measured using a universal microplate spectrophotometer (Bio-Tek Instruments Inc.) with ELISA reagent assay test kits from ALPCO Diagnostics (Salem, NH) according to the manufacturer’s instructions and
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previously used with broilers (Olanrewaju et al., 2012). In addition, plasma samples were also analyzed for total protein (TP), Lac, and amylase using an autoanalyzer (Vitro DT 60, Ortho-Clinical Diagnostic, Rochester, NY). This analyzer uses the enzymatic procedures described by Elliott (1984), and this methodology has been previously used with broilers (Olanrewaju et al., 2006, 2007).
Statistical Analysis A 3 × 3 factorial arranged in a randomized complete block design was used in this study. Data were replicated over time, with trial being the blocking factor, and the room was considered the experimental unit. The 9 treatments consisted of 3 levels of photoperiod × 3 levels of light intensity. The main effects of photoperiod and light intensity and the interaction of these 2 factors on physiological variables were tested by using the MIXED procedure of SAS (SAS Institute Inc., 2008). Means comparisons on d 7, 14, 28, 42, and 56 were assessed by least significant differences, and statements of significance were based on P < 0.05. Analyses of variance combined across days were performed to obtain treatment comparisons averaged across days and to test for treatment interactions with equal variances between days. The repeated measures were modeled using a compound symmetry error structure.
RESULTS Table 1 shows the main effects of photoperiod and light intensity on major blood physiological parameters. In comparison with the long/continuous and regular/ intermittent photoperiods, the short/nonintermittent photoperiod significantly reduced BW (P < 0.050), pH (P < 0.013), pO2 (P < 0.039), saturated O2 (sO2; P < 0.001), Na+ (P < 0.048), K+ (P < 0.036), Ca2+ (P < 0.024), Cl− (P < 0.049), osmolality (P < 0.049), T3 (P < 0.001), and TP (P < 0.010), along with significantly elevated pCO2 (P < 0.024), Hct (P < 0.048), Hb (P < 0.052), and Lac (P < 0.002) concentrations. The main effect of light intensity at 10 lx increased K+ significantly (P < 0.001) in comparison with 5 and 0.5 lx. In addition, there were no effects of treatments on HCO3−, glucose, anion gap, T4, and amylase. There was a significant photoperiod × light intensity interaction for pH (P < 0.004), sO2 (P < 0.001), K+ (P < 0.001), Lac (P < 0.005), and TP (P < 0.023). The short/nonintermittent photoperiod significantly (P < 0.028) reduced blood pH on d 42 compared with the long/continuous and regular/intermittent photoperiods (Table 2). There was no main effect of light intensity or photoperiod × light intensity interaction on pH on any of the sampling days. In addition, the short/nonintermittent photoperiod caused a significantly (P < 0.010) increased pCO2 on d 42 in comparison with long/continuous and regular/intermittent. As shown in Table 3, the short/nonintermittent photoperiod significantly increased Hb (P
