It was observed from the study that the extracts contained water soluble vitamins (C and B-complex) and fat-soluble vitamins (A, E, and D) in different proportions. Vitamin A, which was above its minimum dietary requirements in poultry (54µg/100g) (Ogunmodede, 1981) is important for the development of feathers, strong and improved egg production, increase in hatchability and decrease in embryonic mortality (Leeson, 2015). Also, vitamin A is implicated in the improvement of the local immune defences within the gut-associated lymphoid tissue (GALT) of chickens (Dalloul et al., 2002).
Again, the findings of this study show that the vitamin E content of the plants are below the daily requirements of 5–10 mg/kg by National Research Council (1994) in poultry production. Nevertheless, the nutritional requirements of broilers, from 1994 till date, are likely to have changed in response to intense genetic selection that has been observed in poultry over the years (Pompeu et al., 2018). Thus, this study suggests that the extracts can contribute in increasing the level of vitamin E available for broiler intake. An increase in vitamin E intake may lead to the enhancement of the immune responses, regulate platelet aggregation by inhibiting prostaglandin (thromboxane) production as well as play a key role in the regulation of protein metabolism and hormonal production (Pompeu et al., 2018).
Vitamin D which was above its requirement in poultry (5 µg/kg) (National Research Council, 1994) is important for the prevention of bone malformation, as its deficiency can result in rickets, osteoporosis, or poor egg shell quality in laying hens not minding the quantity of the available calcium and phosphorus (Leeson, 2015; Sakkas et al., 2019).
The results revealed that thiamine, riboflavin, niacin, and pyridoxine contents of the plants were lower than 1.0 mg, 1.8 mg, 11 mg and 3.0 mg respectively, required for these vitamins, whereas, cobalamin was higher than the 0.009 mg daily requirement for this vitamin (National Research Council, 1994). Though, some of these vitamins were not as high as cited in National Research Council recommendation, many factors might have contributed to the observed low values such as geographical location of the plants and methods of extraction used. Again, the ingredients utilized in poultry feed production also contain all the necessary nutrients required by the birds. In this light, the presence of these vitamins in the extracts is an indication that this plant adds to the quantity of B-vitamins available for broiler consumption.
The presence of thiamine and niacin implies that broilers treated with this plant will have improved appetite, a healthier nervous system and a higher release of energy from the diets (Leeson, 2015; Attaugwu and Uvere, 2017). Similarly, researchers have pointed out that the presence of cobalamin, riboflavin and pyridoxine in broiler diet is important to maintain and promote growth and good feathering through their activities as co-enzymes in many enzymes systems (Keles, 2010; Leeson, 2015; Pal, 2017; Uraku, 2015).
Again, the findings of this study revealed that the calcium content of the plants where between 7.288 mg/g to 8.180 mg/g. This is consistent with the findings of Mako et al. (2013) who reported 7.8 mg/g of calcium for A. brasiliana. Calcium has been reported to be involved in the activation of a large number of enzymes adenosine triphosphate, succinic dehydrogenase and lipase (Talpur et al., 2012). Leeson (2015) added that a deficiency of extracellular blood calcium in young growing broilers results in abnormal bone development, increased irritability of the nerve tissues and subsequent osteoporosis in laying hens.
In the same vein, the sodium values of the extracts where 0.663 mg/g and 0.734 mg/g for for ethanol and aqueous extracts respectively. These values were in the lines of earlier literature (Mako et al., 2013) that reported 0.855 mg/g for A. brasiliana. Reports have shown that sodium and potassium are very essential in poultry production as they are the major determinants of acid-base balance in the cells (National Research Council, 1994). These elements are involved in the transmission of nerve impulses and absorptive processes of monosaccharide, amino acids, pyrimidines and the bile salts (Soetan et al., 2010). Low level of sodium in poultry diet can result in poor growth, poor feed conversion efficiency, soft bones, and increase in oxygen utilization and heat production (Leeson, 2015). Similarly, a deficiency of potassium in poultry diet results in muscle weakness and growth retardation (Balos et al., 2016)
Again, the results revealed that the extracts contain phosphorus which were in line with the 0.022 mg/g for A. brasiliana reported by Mako et al. (2013) for the plant. Just like calcium, a deficiency of phosphorus in poultry diet can result in lack of normal skeletal calcification, which may induce rickets in broilers (Leeson, 2015). Research has also shown that the presence of phosphorus in poultry diet is responsible for normal muscle growth, egg formation and functioning of nucleic acids and genetic codes (Soetan et al., 2010; Li et al., 2016).
The trace elements present in the extracts were grossly below the requirements for these elements by the National Research Council (1994). Nevertheless, this result is consistent with the findings Delaporte et al. (2005) and Mako et al. (2013) who reported that the trace elements present in A. brasiliana were below the National Research Council (1994) daily requirements for broilers. Nevertheless, the low levels of trace elements in the extracts might not constitute any problem because the main ingredients utilized in the production of poultry diets might have contained all the minimum trace elements sufficient for the poultry needs. Therefore, it could be deduced from the findings of this study, that the presence of these trace elements in the extracts increases the minimum available elements for broiler consumption.
Manganese is an essential trace element necessary for proper functioning of many enzyme systems involved in lipid and carbohydrate metabolism. Soetan et al. (2010) concluded that manganese is required for the synthesis of mucopolysaccharides, such as chondroitin sulphate, to form the matrices of bones and egg shells. Leeson (2015) added that a deficiency of manganese in broiler diet can lead to perosis, poor growth and impaired blood clotting.
Iron is another important trace element for all living cells as it plays important role in oxygen and electron transport, as well as an integral component of myoglobin for the delivery, storage and use of oxygen in the muscle (Lin et al., 2020). Craig et al. (2017) added that Iron is important for the maintenance of meat quality. A deficiency of iron in broiler diets can result in loss of pigmentation of the feathers, severe anemia followed by a reduced packed cell volume (Leeson, 2015).
Copper is essential for the incorporation of iron in hemoglobin, assists in the absorption of iron from the gastrointestinal tract, and helps in the transfer of iron from tissues to the plasma (Soetan et al., 2010). In addition, copper is required for bone formation by promoting the structural integrity of the bone collagen and for normal elastin formation in the cardiovascular system (Samanta et al., 2011). A deficiency of copper in poultry diet can lead to poor feathering, rupture of the aorta and bone disorder (fragile and broken) and causes anemia (Leeson, 2015; Mustafa et al., 2018; Yang et al., 2018).
Zinc was reported by Park et al. (2004) to have a catalytic function in zinc dependent enzymes such as dehydrogenases, oxidoreductases, carbonic anhydrase, DNA and RNA polymerases and also involved in macronutrient metabolisms and cell replication. Also, zinc is essential for growth, bone development and immune functions in chickens (Park et al., 2004; Naz et al., 2016; Zhang et al., 2018). Leeson (2015) reported that a deficiency of zinc in poultry diet can result in stunted growth, poor hatchability, decreased egg production, poor feathering, shortening and thickening of the bones, and in some cases, loss of appetite and death.
Table 3 confirmed that the plants contain alkaloids and polyphenols such as flavonoids, tannins, phenols, saponins, and anthocyanins in different proportions, which is consistent with the reports of Mpiana et al. (2010), Mea et al. (2017) who concluded that these plants contain these phytochemicals. These phytochemicals have important antioxidant, anti-inflammatory, anti-microbial, anti-fungal, anti-viral, immunomodulatory, and other pharmacological properties (Umerie and Ekuma, 2016; Osioma and Hamilton-Amachree, 2017; Ubaoji et al., 2018; Attaugwu and Uvere, 2017)
The water holding capacity (WHC) of broiler meat is measured as the fraction of bound water retained in the muscle (Oko et al., 2012; Oko, 2013; Oko et al., 2013). The groups fed aqueous extracts with lower values of drip losses and cooking losses, are considered to have higher water holding capacities compared to the groups fed ethanol extracts. Thus, the meats of the groups fed aqueous extracts are considered to be of better qualities, because, the lower the drip and cooking losses of meat, the higher the water holding capacity, and the better the meat quality (Oko et al., 2013). In addition, the low cooking loss of the breast meat of broilers fed the extracts suggests that their meats are of high quality because there are limited nutrients losses (especially proteins) into the water during cooking.
Thus, it could be deduced from the results that the plant extracts, especially the aqueous extracts, improve the meat quality of the chicken used in this study. Among the plausible explanations for these findings could be due to the phytochemicals, minerals and vitamins contained in the extracts. Similarly, Yang et al. (2020) reported that broiler drinking water with the inclusion of plant extracts can be used to enhance the oxidative stability, shelf life and meats quality of broilers, which is in good agreement with the reports presented in this study.
Again, it was observed from the results that the extracts improved the weight gain and the specific growth rate of the broilers better than the negative control group, although, the aqueous extracts performed this function better than the ethanol extract. Also, the extracts produced weight gain and specific growth rate values that were not significantly different from the positive control groups. Again, these findings could be attributed to the pharmacological properties of the phytochemicals, minerals and vitamins contain in the extracts. Reports have shown that feeding broiler chickens with diet containing phytogenic blend leads to improvement in body weight gain and specific growth rate (Hernandez et al., 2004; Mohammadi-Gheisar et al., 2015; Jayanti et al., 2017)
It was observed from this study that the concentrations of blood proteins (total protein and globulin) in the serum of the broilers were significantly increased (p < 0.05) by the extracts better than the negative control group. These findings are consistent with the report of Ghazalah and Ali (2008), who suggested that supplementing broiler diets with phytogenic growth promoters (such as rosemary leaves) increases the total protein and globulin levels compared to the control. The findings of this study could be attributed to the crude proteins present in the plants as earlier reported (Mako et al., 2013; Preetha et al., 2018; Arogbodo, 2020).
In addition, the increase in the globulin fraction observed in this study indicates the effective roles of A. brasiliana in increasing immunity due to their roles in developing and protecting cells and inhibiting non-enzymatic oxidation (Mpiana et al., 2010; Kumar et al., 2011; Barua et al., 2012; Onoja et al., 2017; Anyasor et al., 2019).
The values recorded by the groups fed aqueous extracts for and packed cell volume were within the normal ranges of 7.5 g/dl to 13.1 g/dl (hemoglobin) and 26.0–45.2% (packed cell volume) reported by Mitruka and Rawnsley (1977) for healthy birds. Again, these observed comparable values recorded for hemoglobin and packed cell volume in the birds fed aqueous extracts and commercial growth promoters indicate nutritional adequacy and improvement / stability of their hematological profile (Oloruntola, 2019).
Finally, the extracts were able to lower the levels of total white cell count and differential white blood cell counts in the chickens compared to the negative control. Olugbemi et al. (2010) opined those increased concentrations of differential white blood cells in the body connotes a threat to normal health, therefore the body builds up its defence against such threat. Thus, the findings of this study suggest that the extracts improved the health status of the chicken through increasing their ability to fight infections and defend their bodies against foreign invasion.
Phytobiotics are potent alternatives to synthetic / chemical growth promoters. The current practice in feeding phytobiotic compounds to poultry seems to justify the assumption that phytogenic growth promoters may have the potential to promote production performance and health, and thus add to the set of non-synthetic growth promoters for poultry production. So, this study was designed to assess the efficacy of A. brasiliana as a phytogenic growth promoter in poultry. The study has found that generally, the ethanol and aqueous extracts of A. brasiliana are potent alternatives to chemical growth promoters in chicken farming. Nevertheless, the aqueous extract, which is easier to prepare and cost effective, produced better effect than the ethanol extract. Considerably, more work will need to be done for a better understanding of the exact mechanisms of action of these extracts.