ABSTRACT
The study investigated the effects of a potent antioxidant, quercetin, on some physiological parameters, performance, and carcass and meat pH in broiler chickens, raised at different stocking densities. A total of 60 one-day-old Ross 308 broiler chicks were randomly assigned to four treatment groups based on stocking density (12 birds/m2 or 18 birds/m2) and 50 mg/kg body weight quercetin treatment (quercetin-treated or untreated). Quercetin was administered per os once daily for 28 consecutive days at 18:00 h. The stocking density of 12 birds/m2 was categorised as low stocking density (LSD) condition while 18 birds/m2 represented high stocking density (HSD) condition. The circadian cloacal temperature was recorded at 2 h interval, three times, one-week apart on days 22, 29 and 36 while the haematological profile and erythrocyte osmotic fragility (EOF) were recorded on days 28, 35 and 42. Broiler performance was recorded daily. The carcass characteristics and meat pH was determined at the end of the study period. Fluctuations in diurnal cloacal temperature (CT) showed that increasing stocking density induced an elevation (P < 0.05) in the overall mean CT of untreated HSD group (40.96 ± 0.02 ºC) while the CT was lower (P < 0.05) in the treated HSD group (40.72 ± 0.02 ºC). The CT of the untreated LSD group (40.88 ± 0.02 ºC) was lower (P < 0.05) when compared with the untreated HSD group (40.96 ± 0.02 °C). On day 28, the total white blood cell count (TWBC), heterophils and H:L ratio (8.50 ± 0.67 x 109/L, 1.35 ± 0.30 x 109/L and 0.19 ± 0.03 respectively) were significantly lower (P < 0.05) in the quercetin-treated HSD group when these parameters were compared with those of the untreated HSD group (12.36 ± 1.22 x 109/L, 3.91 ± 0.79 x 109/L and 0.53 ± 0.13 x109/L respectively). The overall mean variation in percentage erythrocyte osmotic fragility (EOF) was significantly higher (P < 0.05) at 0.5 %, 0.3 % and 0.1 % NaCl concentrations in the quercetin-treated LSD group with corresponding values of 10.29 ± 6.09 %, 67.41 ± 3.30 % and 88.93 ± 3.47 % respectively, while the EOF was 0.24 ± 0.16 %, 62.21 ± 4.22 % and 85.50 ± 3.56 % in the untreated LSD group. HSD condition caused a higher (P < 0.05) erythrocyte osmotic fragility at 0.5 %, 0.3 % and 0.1
.NaCl concentration. The final live body weight (1,344.0 ± 54.22 g) and weight gain (1,120.0 ± 52.48 g/chick) of quercetin-treated HSD was significantly higher (P < 0.05) when compared with the final live body weight (1,071.0 ± 60.76 g) and weight gain (842.50 ± 57.07 g/chick) of the quercetin-treated LSD group. The feed conversion ratio was significantly lower in the quercetin-treated HSD group (1.43 ± 0.07) when compared with untreated HSD (1.79 ± 0.10), LSD (2.20 ± 0.10) and quercetin-treated LSD (2.10 ± 0.12) groups. A higher viability ratio was recorded in the quercetin-treated groups. Quercetin administration had a weight-enhancing effect, correlated directly with the increasing age of broiler chicks in quercetin-treated HSD (r = 0.950; P < 0.01) and quercetin-treated LSD (r = 0.968; P < 0.01) groups. Low stocking density condition and quercetin administration enhanced meat quality by preventing early rise in pH. This is beneficial to consumers that may wish to refrigerate meat for future consumption. The results suggest that quercetin was most beneficial in conditions of discomfort and, may, be useful as a supplement in broiler chicken production, especially in stress due to HSD. It was concluded that the administration of quercetin at 50 mg/kg body weight enhanced performance through efficient feed utilisation, alleviated stocking density-induced social and physiological stress and prolonged the shelf-life of stored broiler breast meats.
CHAPTER ONE
1.0 INTRODUCTION
1.1 Background of the Study
The influence of stocking density (the number of birds calculated on a weight basis per metre square of different poultry species on growth and productive performance) has generated considerable interest (Skrbic et al., 2009a; Tayeb et al., 2011). High stocking density (HSD) reduces growth rate (Sekeroglu et al., 2011), feed efficiency, livability, carcass quality and body weight in chickens (Puron et al., 1995; Feddes et al., 2002; Bessei, 2006; Rambau et al., 2016). The causes of adverse effects of HSD are: poor air quality as a result of inadequate air exchange, increased microbial activity (Adebiyi et al., 2011), leading to increased build-up of ammonia production and reduced access to feed and water in commercial broilers (Feddes et al., 2002; Uzum and Toplu, 2013). Despite the clear welfare problems associated with HSD, producers of broiler chickens have derived some economic benefits from it. In the tropics, the total kilogramme produced per unit of space increases with stocking density, profit margins also increase to a point, as birds are raised in increasingly crowded environments (Puron, et al., 1995; Utnik-Banas, 2014). However, Kow et al. (2015) reported a progressive reduction in feed intake as stocking density increased, but neither season nor stocking density influence feed conversion ratio. Under stressful situations, the behavioural patterns of birds change and, consequently, their energy consumption increases (ZulKifli and Azah, 2004). El-Gogary and Azzam (2014) reported that increased stocking density does not affect plasma total protein. Studies have shown that some antioxidants (Boots et al., 2008; Tan et al., 2014), including polyphenols accumulate in tissues to provide antioxidant protection, similar to that offered by vitamin E (Eraslan et al., 2007; Sinkalu et al., 2008; Durak et al., 2010; Eroglu et al., 2013; Surai, 2013) and may, thus, prolong shelf-life as well as preserve keeping quality and taste of meat (Zhang et al., 2015). Quercetin (3, 31, 41, 5, 7–Pentahydroxyflavone) is one of the ubiquitous flavanol–type flavonoids, predominantly found in edible fruits and vegetables (Anjaneyulu and Chopra, 2004; Zhang, 2005). Quercetin prevents oxidative injury and cell death by scavenging reactive oxygen species (Cox et al., 2000), inhibiting xanthine oxidase (Chang et al., 1993), lipid peroxidation, and chelating metal ions (Chen et al., 1990). Guardia et al. (2011) reported non-linear effects of increased stocking density on mortality rate in broiler chickens when raised under experimental conditions. However, under commercial conditions the situation may be very different (Berg and Yngvesson, 2012). Reactive oxygen species (ROS) are increasingly being generated in the body under the influence of stressful conditions and these results in lipid peroxidation (Puttachary et al., 2015). Lipid peroxidation is the oxidative degradation of polyunsaturated fatty acids. It occurs in biological membranes, inactivates several membrane-bound enzymes, and impairs membrane fluidity (Goel et al., 2005) and integrity. Malondialdehyde (MDA) is one of the major oxidation products of peroxidised polyunsaturated fatty acids; therefore, increased MDA content is an important indicator of lipid peroxidation (Kalender et al., 2012). The health status of broiler chickens is linked to their haematological parameters (Kwari et al., 2011), which are influenced by diurnal fluctuations (Azeez et al., 2009). Leucocytic responses have been used as an indicator of heat or cold stress in poultry (Ben Nathan et al., 1976). An increased core body temperature that is due to ambient temperature can influence the changes that are observed in circulating leucocyte components of broiler chickens. In addition, an exposure to heat stress and increased stocking density in broilers causes an increase in both cloacal temperature and heterophil/lymphocyte (H:L) ratio (Altan et al., 2000; Altan et al., 2003; Sepp et al., 2010; Uzum and Toplu, 2013). Erythrocyte osmotic fragility (EOF) describes the sensitivity to changes in osmotic pressure that an erythrocyte has been exposed to (Oyewale and Durotoye, 1988). It is used as an indicator of oxidative stress in animals (Adenkola and Ayo, 2009; Abdul Wahab et al., 2010). Oyewale et al. (2011) reported that pH, temperature and storage are among factors influencing EOF.
1.2 Statement of Research Problems
Due to increase in awareness of poultry welfare and concomitant legislation, it has become necessary to determine response of poultry to stress (Wein et al., 2017). The stocking densities used in previous studies have been highly variable (Lee et al., 2017) but it is universally acknowledged that stocking density affects broiler performance, with poorer performance at high stocking densities (Feddes et al., 2002; Velo and Ceular, 2017). It has been reported that lower stocking densities also contributes to farmer‟s loss (Lee et al., 2017). Subjective husbandry systems that are associated with high stocking density may indicate a greater degree of stress, thus, increasing the risk of poor life performance in commercial broilers. This contributes significantly to the loss incurred by producers (EL-Gogary and Azzam, 2014; Ibrahim, 2017). Determination of the optimum stocking density in broiler chickens is still subject of discussion (Tayeb et al., 2011). Many farmers around the world increase stocking density to maximise profitability in production of broiler chickens (Heckert et al., 2002; Thaxton et al., 2006; Estevez, 2007) and this adversely affects welfare the welfare of broiler chickens (Beloor et al., 2010). The intensive management system associated with HSD results in stress and negatively impacts production in broiler chickens; thus, increasing the risk of poor life or welfare and performance in the birds (El-Gogary and Azzam, 2014; Kang et al., 2016). Consequently, HSD contributes significantly to the production loss, incurred by farmers (Velo and Ceular, 2017). Some detrimental consequences of increasing the stocking density of broilers include; foot pad lesions (Skrbic et al., 2015), poor air circulation (Etim et al., 2013) and poor litter quality (Taira et al., 2014; Bergmann and Schwarzer, 2017; Swiatkiewicz et al., 2017). For many decades, great concerns have been expressed over the continued use of antibiotics as a growth enhancer in animal husbandry and the associated emergence of antibiotic-resistant bacteria strains (Broom et al., 2006; Goliomytis et al., 2014; Meek et al., 2015). The indiscriminate use of antibiotics in broiler production has enhanced the proliferation of resistant strains of disease-causing microbial organisms. Similarly, farmers are criticised for irrational use of medications, especially antibiotics (WHO, 2014; O‟Neill, 2015), and so faced with the problem of how to rear more animals, more efficiently and with higher standards of food safety but without using antibiotics. There is dearth of information on the potential of quercetin to alleviate stressful conditions and preserve the shelf-life of meat in commercial broiler production. Great interest in the development of novel plants and their bioactive metabolites to be used as feed additives in animal nutrition has attracted great research attention. However, scientists are yet to establish a „balanced antioxidant‟ that is ubiquitous, effective, affordable, readily available and can be derived from natural source.
1.3 Justification of the Study
There is paucity of information on ameliorative effects of quercetin on physiological responses of broiler chickens to management stressors, including HSD, and meat quality parameters. The objective of this research was, therefore, to evaluate the effect of quercetin administration on some physiologic parameters, including; CT, haematology, erythrocyte osmotic fragility and performance and meat quality characteristics of broiler chickens, raised at different stocking density conditions. Stocking density is of great significance in broiler chicken production as it influences not only production performance, vitality and health status (Skrbic et al., 2009b), but it is also associated with environmental impact on broiler chickens (Dawkins et al., 2004). It eventually reflects on all aspects of broiler production: economic efficiency, quality of products and welfare aspects of broiler chickens (Skrbic et al., 2009b). Scientific research in the area of dietary manipulation of poultry feed is on-going (Bhattacharyya et al., 2017) and researchers have reported increased benefits in the use of natural and synthetic antioxidants to promote broiler health and productivity (Makri et al., 2017), internal physiological changes and product quality (Lee et al., 2017). The health benefits of herbs and botanicals have been demonstrated (Surai, 2002; Wenk, 2003; Surai, 2013) and this has resulted in a growing body of research that has been devoted to natural antioxidants that are currently receiving considerable attention in animal nutrition fields (Lee et al., 2017). The study of quercetin has been focused mainly on its therapeutic and antioxidant effects in man (Boots et al., 2008). Quercetin has the potential as functional feed additive in poultry production. It improves performance in laying hens (Liu et al., 2014). Quercetin administration may compensate for any compromise that is encountered during physiologic stress, especially if due to stocking density in chickens. The study of antioxidant effects and the underlying mechanism of dietary phytochemicals is currently of great research interest (Lee et al., 2017). There is, therefore, an urgent need to improve animal welfare and demonstrate the resultant financial benefits to both individual farmers and the society (Dawkins, 2017) using a potent antioxidant. It is, therefore, important to establish the effects of different stocking densities on physiological parameters, performance and meat quality characteristics and to study the modulatory role of quercetin in broiler chickens.
1.4 Research Hypotheses
The following hypotheses were put forward for this research:
Ho:
- Stocking densities do not have any effect on the cloacal temperature (CT), haematology, meat quality characteristics and performance of broiler chickens.
- Quercetin administration does not have any significant effect on CT, haematology, performance and meat quality characteristics of broiler chickens, raised at different stocking densities.
1.5 Aim of the Study
The aim of the study was to investigate the effects of quercetin on some physiological parameters and performance of broiler chickens, raised at different stocking-densities.
1.6 Specific Objectives
The specific objectives of the study were:
- to investigate the effects of different stocking densities on CT, haematology, performance, and meat quality of broiler chickens.
- to investigate the effects of quercetin on CT, haematology, performance, and meat quality of broiler chickens raised at different stocking densities.
