Title Page
Table of Contents
List of Abbreviations

1.1       Background of the Study
1.2       Statement of Research Problem
1.3       Justification
1.4       General Aim of the Study
1.5       Objectives of the Study
1.6       Statement of Research Hypothesis (Ho)

2.1       Poultry Production
2.2       Importance of Broiler Production
2.3       Management Systems in Poultry Industry
2.4       Environmental Factors and Welfare of Broiler Chickens
2.5       Thermo-neutral Zones of Broiler Chickens
2.6       Effects and Responses of Broiler Chickens to Heat Stress
2.7       Biomarkers of Heat Stress in Broiler Chickens
2.8       Reactive Oxygen Species and their Roles in Broiler Chickens During Heat Stress
2.9       Beneficial Roles of Reactive Oxygen Species Signaling in Broiler Chickens
2.10     Antioxidant System of the Body
2.11     Antioxidant Supplementation in Broiler Chickens
2.12     Physiologic Roles of Ascorbic Acid
2.13     Uses of Betaine in Livestock Production
2.14     Physiologic Roles of Methylation in Broiler Chickens

3.1       Experimental Site and Meteorological Conditions
3.2       Experimental Animals, their Management and Antioxidant Administration
3.3       Experimental Measurements
            3.3.1   Ascorbic acid and betaine administration
            3.3.2   Thermal environmental parameters
            3.3.3   Evaluating the cloacal temperature
            3.3.4   Collection of blood samples

3.3.5    Determination of erythrocytic osmotic fragility
3.3.6    Deterrmination of biomarkers of oxidative stress
3.4.      Statistical Analysis

4.1       Thermal Environmental Parameters in Poultry Pen
4.2       Cloacal Temperature Responses of Broiler Chickens During the Study Period
4.3       Changes in Erythrocyte Osmotic Fragility of Broiler Chickens During the Study Period
4.4       Serum Biochemical Analysis in Broiler Chickens During the Study Period
            4.4.1   Variations in malondialdehyde levels
            4.4.2   Variations in antioxidant enzymes

5.1       Thermal Environmental Recordings During the Study Period
5.2       Fluctuations of Cloacal Temperature in Broiler Chickens During the Study Period
5.3       Erythrocyte Osmotic Fragility of Broiler Chickens During the Study Period
5.4       Evaluations of Serum Biochemical Parameters of Broiler Chickens During the Study Period

6.1 Conclusions
6.2 Recommendations

High ambient temperature and high relative humidity adversely affect poultry. They result in heat stress, and, consequently, oxidative stress, especially during the hot-dry season in the Northern Guinea Savannah zone. The experiment was aimed at evaluating the effects of betaine and ascorbic acid (AA) on biomarkers of stress in broiler chickens during the hot-dry season in Zaria, Nigeria. Eighty White Ross breed of broiler chickens at day-old allotted into four groups of 20 birds each, were used. Group I (control) was given only sterile water per os, while Group II, Group III and Group IV were administered betaine (250 mg/kg), AA (50 mg/kg) and betaine+AA (250 mg/kg + 50 mg/kg), respectively, using gavage for forty-two days. The cloacal temperature (CT) of the birds, and dry-bulb temperature (DBT), relative humidity (RH) as well as temperature-humidity index (THI) in the pen, were measured bi-hourly, from 06:00 – 18:00 h, on days 28, 35 and 42. Blood samples were collected from birds in each group on days 21 and 42, through venopuncture, with and without anticoagulant, sodium ethylenediaminetetraacetate. Erythrocyte osmotic fragility (EOF) was determined. Serum obtained from blood samples were assayed for malondialdehyde (MDA) concentration and activities of superoxide dismutase (SOD) and glutathione peroxidase (GPx). The mean DBT, RH and THI recorded (32.52 ± 0.61 oC, 77.81 ± 0.61 % and 31.98 ± 0.58, respectively) were predominantly outside the thermoneutral zone for broiler chickens. The results of this study showed that the mean CT value in group III broiler chickens (41.60 ± 0.02 oC) was significantly lower (P < 0.05) than that in group I (41.79 ± 0.03oC), but mean CT values in group IV birds (41.95 ± 0.03 oC) were significantly higher (P < 0.001) than those in control group. Groups II, III and IV birds recorded significant decreases (P < 0.05) in EOF (6.66 ± 1.51%, 7.17 ± 1.31% and 7.00

± 1.29%, respectively), when compared with that of group I (13.65 ± 2.30%). Betaine (1.37 ± 0.038 nmol/L), AA (1.41 ± 0.039 nmol/L) and betaine+AA (1.41 ± 0.040 nmol/L) significantly (P < 0.05) decreased MDA concentration when compared with that in control (1.54 ± 0.043 nmol/L) broiler chickens. A highly significant (P < 0.01) increase in SOD activity in group IV broiler chickens (1.76 ± 0.06 IU/L) was observed, when compared with those in group I (1.44 ± 0.05 IU/L). GPx activity was significantly higher in birds of groups II (44.30 ± 1.00 IU/L; P < 0.01), III (43.10 ± 0.66 IU/L; P < 0.05) and IV (46.60 ± 1.61 IU/L; P < 0.001), when compared with those in group I (39.60 ± 1.09 IU/L). The results showed that betaine and/or AA exerted antioxidant properties. Administration of betaine and/or AA enhanced ability of broiler chickens to thrive under heat stress conditions occurring during the hot-dry season. It is concluded that, the administration of betaine and/or ascorbic acid is beneficial to broiler chickens in ameliorating the adverse effects of heat stress.

1.1              Background of the Study
Meteorological factors, such as high ambient temperature and high humidity, exert adverse effects on poultry production in many tropical countries, including Nigeria (Chen et al., 2013). They are known to cause heat stress in poultry during the hot-dry season (Minka and Ayo, 2007; Rhoads et al., 2013). Heat stress is a major danger facing poultry production in tropical and sub-tropical countries owing to increasing changes in climate resulting from global warming (Anna et al., 2014). The production of broiler chickens under heat stress condition results in reduction of feed intake (Azad et al., 2010a). The decrease in feed intake is an attempt to reduce heat production in the body (Mujahid, 2011). The decrease in live performance of birds reared under high ambient temperature, exceeding the comfort zone, is due to decreased feed conversion to meat (Lagana et al., 2007). Heat stress damages the intestinal barrier in broilers due to oxidative stress (Gu et al., 2012), and negatively influences the welfare of broilers kept under pre-slaughter conditions (Vieira et al., 2011). It induces a rise in serum corticosterone concentration, mortality, and a reduction in the percentage of phagocytizing macrophages (Quinteiro-Filho et al., 2012). Body temperature measurement is regarded as indicator for the development of both hypothermia and hyperthermia (Knezacek et al., 2010). However, practical and physiological obstacles make it irrelevant as a source of information to determine the thermal status of commercial poultry flocks (Gilohet al., 2012). Christensen et al. (2012), stated that core body temperatures decrease at night, when feeding activity is expected to be reduced. Osmotic fragility has been described as a potential biomarker of oxidative membrane....

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