The feed intake recorded in this study was slightly lower compared to Petek (1999) who recorded 115g/bird/day in laying birds. Attia (2018) reported non-significant impact of feed intake which ranged from 115.00 to 115.70g/bird/day and 111.61 to 118.28g/bird/day for ISA Brown layers and White Lohmann LSL respectively. Contrariwise, Elwardany et al. (1998) reported a mean value of 102g while Moeini et al. (2011) reported 89.91; 93.63g/bird/day and 80.37; 86.84g/bird/day in 1 and 3% ginger and turmeric powder diets, respectively for single comb White Leghorns Hyline. The disparity obtained in feed intake from these previous works could be due to different strains and management of birds used in the various studies (Farooq et al. (2002). Feed intake is a variable phenomenon affected by diverse factors which include strain of the birds (Farooq et al. (2002), stocking density (Carey et al. (1995) and environment (Zahir-ud-Din et al. (2001).
Generally, the action of phytobiotics is caused by primary and secondary compounds/ingredients (Wald, 2003). Primary compounds are major nutrients which include protein content and fats, while secondary compounds comprise volatile oils: curcuminoids (Toennesen, 1992), turmerone (Baik et al., 1993) and arturmerone (Ferreira et al., 1992); colorants such as demethoxycurcumin, bisdemethoxycurcumin (Huang et al., 1995) and phenolic compounds such as flavonoids and chicoric acid (Grashorn, 2010). The crucial indispensable bioactive compound responsible for the biological action of turmeric is curcumin (Nouzarian et al., 2011).
In laying birds, FCR is determined by the amount of feed consumed per kilogram of egg production (Gumus et al., 2018). According to Ascard et al. (1995), a hen requires 2.5kg feed to produce 1kg eggs. Thus, feed consumption and efficient feed utilization is one of the main concerns for commercial egg enterprise because feed contributes 60 to 70% to the total cost of production in egg-type chickens (Mian, 1994 and Qunaibet et al., 1992). The least (p<0.05) value of FCR (2.64) obtained for birds on 1.5% ginger powder suggests that this inclusion percentage enhanced feed utilization and stimulated endogenous digestive enzymes for absorption of ingested nutrients resulting in optimum egg production (Incharoen and Yamauchi, 2009). This could probably be traced to the biological activities of gingerol, gingerdiol and gingerone contents of ginger powder for enhanced reproductive performance (Mansoub et al., 2011).
The studies of Abdollah et al. (2011) and Moeini et al. (2011) agrees with the current work which demonstrated that laying birds consuming diet containing 1.5% of ginger powder had the highest value of egg mass (46.14g/bird/day); indicating that ginger enhanced egg production of laying hens at this level of inclusion. The effect of ginger powder on egg production (hen-day/hen-housed) coupled with the individual egg weights seemed to be responsible for the increase observed in egg mass. Zhao et al. (2011) partially attributed the increased egg mass to the enhanced antioxidant status by the addition of ginger powder. However, the authors reported that the mechanisms by which ginger powder elevated egg mass without impacting feed intake (as also obtained in this experiment) were not clear (Zhao et al., 2011).
Lower mortality observed among the phytobiotic groups compared to the control groups (11.71 and 9.82%) was probably due to greater capacity of the supplied ginger and turmeric powder rations to reduce morbidity among the birds as a result of their medicinal functions (Chattopadhyay et al., 2004), culminating in improved livability. Previous studies conducted using phytobiotics as feed additives have shown encouraging results with respect to lowered mortality and increased livability in poultry birds (Issa, 2012 and Oleforuh-Okoleh et al., 2014). Hertog et al. (1993) and Knekt et al. 1996) reported that the phenolic flavonoids constituents of phytobiotics have been shown to have an inverse association with morbidity and mortality.
Besides this, turmeric has been noted to ameliorate the effects of afflatoxin, common in maize-based feed, causing hepatotoxic and hepatocarcinogenic effects, which poses serious challenge to poultry production (da Rocha et al., 2014). According to Kumari et al. (2007), Faghani et al. (2014) and Qasem et al. (2015), turmeric powder inclusion could raise the immune response and antibody titer values of poultry after vaccination by its supplementation in feed. Such effect would be very useful when vaccinating against a highly contagious viral disease like Newcastle disease which causes high mortality and huge economic losses. Although, it is clear that vaccination could not prevent disease occurrence on the farm (Moomivand et al., 2013), yet phytobiotics like ginger and turmeric have been proven to contain immuno-modulatory properties which play a very important role at the post-vaccination periods for avian infectious viruses, such as the infectious bronchitis virus (IBV) and Gumboro disease (IBD), thereby controlling mortality rate in the birds (Akhtar et al., 2008; Ali et al., 2008).
Conversely, high mortality rate experienced among the control groups (11.71 and 9.82%) in the present study could partly be due to the hot environmental conditions at some period (between January and March, 2018) of the experiment leading to heat stress in the laying birds. High ambient temperature or heat stress has been a major environmental stressor and thus a concern for the poultry industry, mostly in the hot regions of the world. Growth, feed intake and egg production are usually negatively influenced (Haruhiko et al., 2015) during heat stress. Good management which includes good control of feeding timetable, lighting programme (ISA, 2009) as well as nutritional strategies aimed at eradicating the negative influence of heat stress through the use of medicinal herbs (such as ginger and turmeric), and micronutrients like vitamins and minerals to meet the requirements of birds during heat stress have proven to be of immense advantage (Lin et al., 2006). According to Devegowda (1996), curcumin present in turmeric are included in feed for the enhancement of animal performance by improving livability and lowering mortality in poultry birds.
The attainment of lay at an earlier age among birds fed ginger powder rations (as opposed to a later age obtained for the turmeric groups) could possibly be connected to higher body weight at first lay among these groups. The earliest age at first lay observed among the birds placed on 1.5% ginger powder group is higher than those obtained by Islam et al. (2015) and Kabir and Haque (2010) who both recorded 141days in Isa Brown pullets. Age at sexual maturity is a very vital trait from economic standpoint. The age at first oviposition is crucial, not only because it determines its first year production but also because the earlier a pullet comes to lay, the sooner revenue is generated (Jull, 1970). However, the least age at first lay obtained in this research was older than the recommended (126days) for ISA Brown by Hendrix Genetic Company Limited (www.HendrixGenetics.com), and this variation may be due to environmental factors. In most domestic animals, reproductive functions are known to be considerably affected by nutrition (Armstrong and Benoit, 1996; Williams, 1998). Feed consumption, lighting schedule, length of daylight and environmental factors are major factors that determine age and weight at sexual maturity (Morris and Fox, 1960). The commercial layer usually comes to lay between 18 and 19 weeks (126-133 days) of age, egg production then rises sharply to a peak of 94-96% (www.HendrixGenetics.com) at 26-27 weeks of age and finally declines gradually (Rahman, 2003). Age at sexual maturity is also influenced by pronounced sexual effect (Eaton, 1961) which is characterized by egg lay. Therefore, the probable explanation for this delay may be due to the fact that a threshold of ovary and oviduct weights must be achieved before sexual maturity is attained; since these organs are responsive to feed allocation and influenced by body weight profile (Robbinson et al., 2007). The impact of the bioactive compounds of turmeric powder on the reduction of adipocyte number which resulted in decreased fat accretion influencing body weight and in turn the age at first lay (Attia, 2018) may as well be responsible for this delayed sexual maturity.
Egg production is the most important index of performance of commercial layer and it accounts for 90% of the income from the enterprise (Oluyemi and Robert, 1979). The results obtained in this study depicted that hens maintained on 1.5% ginger powder diets had superior laying performance in terms of hen-day egg production, hen-housed egg production, egg mass and feed conversion ratio. Gingerol compounds contained in ginger powder may be responsible for the improvement in the digestive tract of laying hens which in turn boost egg production. This observation is comparable to those reported by Moeini et al. (2011) who discovered that the incorporation of 1% ginger rhizome powder increased the egg production and egg mass in white leghorn laying birds. Similar values obtained for hen-day and hen-housed production birds on 1.5% ginger powder diets indicated low mortality rate among these birds during the laying period. Abdollah et al. (2011) documented an increase in egg production with 0.5% dietary inclusion of ginger root with no negative effect on egg weight and feed conversion ratio of laying birds. The authors also found that egg production and egg mass in the groups fed diets containing turmeric powder were higher than those of control groups. Samarasinghe et al. (2003) reported that 0.1, 0.2 and 0.3% turmeric treatments did not affect feed intake, egg production, egg weight and egg mass.
The incorporation of phytobiotics at varied inclusion levels did not impact egg weight among the dietary treatment groups. This could be due to the low levels or concentrations of the primary (protein content and fats) compounds and the volatility of the secondary compounds (volatile oils) in ginger and turmeric powder which may be required to enhance egg weight. The finding is similar to Samarasinghe et al. (2003) and Emadi and Kermanshahi (2007) but contrary to Pandian et al. (2013) and Kanagaraju et al. (2016). Malekizadeh et al. (2012) reported that turmeric powder at 1 or 3% inclusion level had no beneficial effect on egg weight and reduced egg production compared to the control groups. The ability to make significant changes to egg weight enables the egg producer to adapt to market demands (ISA, 2009), since most consumers tend to appreciate larger egg size. According to ISA (2009), it is possible to change egg size by 1 to 3g by changing the age at sexual maturity, or the body weight at start of lay.
The mean values obtained for egg width and egg shape index (ESI) in the current study differed from the findings of Attia (2018) who reported that the incorporation of 1.5 and 3% of turmeric powder in the layer diet did not show improvement on ESI among the groups. Nasiroleslami and Torki (2010) reported that addition of essential oil of ginger had no significant impact on ESI. The significantly higher values of albumen height, albumen weight, % albumen weight noted in hens maintained on 3% turmeric powder suggests that eggs produced by this group are of superior quality compared to the other treatment groups. Increase in albumen showed that the bioactive compounds in turmeric powder stimulated the growth of the epithelial cells and tubular gland cells in the magnum of the reproductive tract to synthesize and secrete substantial amount of albumen compared to the rest of the groups (Saraswati et al., 2013).
Regarding yolk parameters, birds on 3% turmeric powder produced eggs with the best values of yolk weight and yolk colour which implies that turmeric had a major role to play in improving the yolk quality of eggs. Park et al. (2012) observed that the value of yolk colour in Lohmann Brown laying hens fed 0.50% turmeric powder was higher than those in control. Yolk colour is very vital feature which determines the acceptability of the egg and depends on the presence and profile of carotenoids in feed (Puvača et al., 2018). Jacqueline et al. (1998) reported that the body system of laying hens cannot synthesize egg yolk pigments (Karaskova et al., 2015) by their own biochemical processes. This suggests that the yellow orange pigment present in turmeric was deposited in the yolk. This may also have contributed to the higher yolk weight recorded for this group of birds. Thus, the natural yellow-orange substances in turmeric could be used to improve yolk colour in light-coloured feeds (Park et al., 2012). According to Riasi et al. (2012), enhancement of yolk color could be as a result of curcumin, curcuminoids and its related compounds which are the yellowish pigment of turmeric.
Consumers give preference to deep yolk colour (Englmaierova et al., 2014) as they are associated to healthier and more natural eggs. Therefore, some phytobiotic additives are commonly added to laying hen diets to enrich the yolk. Xanthophyll is attached to fat-soluble pigments in the feed (Yıldırım et al., 2013). Carotenoids modify egg yolk colour and are a source of red and yellow (xanthophylls) pigments (Englmaierova et al., 2014).
The higher Haugh unit of birds placed on 1.5% turmeric powder in the present study could mean that turmeric enhanced the internal quality of the eggs produced by this treatment group and thus may prolong the keeping quality during storage. Our result was higher than those obtained by Nasiroleslami and Torki (2010) who reported a value of 70.64. The Haugh unit is the most widely accepted measure of internal egg quality and tends to decrease with the time of storage (Williams, 1992). The quality of eggs and their stability during storage are largely determined by their physical structure and chemical composition (Seidler, 2003).
The results of shell weight (7.00g), % shell weight (11.06%) and shell thickness (0.48mm) obtained in 3% dietary ginger groups revealed that eggs produced were of superior external quality. These values are in agreement with those of Zomrawi et al. (2014) who observed higher values of shell weight and thickness in laying hens fed varying levels of ginger root powder. The use of ginger in layer diets might have caused an improved environment in the shell gland (uterus), which is a calcium deposition site, and thus enhanced shell weight and thickness (Radwan et al., 2008). The observation in the present study is similar to the findings of Nasiroleslami and Torki (2010) who concluded that addition of the essential oil of ginger increased egg shell weight and thickness in laying hens. In contrast, Incharoen and Yamauchi (2009) reported there was no difference in shell thickness and shell ratio with 1 and 5% dietary dried fermented ginger. The relationship observed between egg shell thickness and ESI in the current study is in conformity with the findings of Altuntaş and Şekeroğlu (2008), who reported that the mean shell thickness increased as ESI increased.
Although, all haematological parameters measured in this current study were not significantly influenced by dietary ginger or turmeric, yet, the slight increase in PCV and Hb levels in birds placed on turmeric diets may indicate an enhanced oxygen carrying capacity of the blood (Larsson et al. 1985), and could be linked to the elevation observed in the red blood cells. Increased RBC depicts a better transportation of red blood components in response to erythropoietic system stimulation which may be associated with the effects of bioactive compounds in turmeric to improve the antioxidant status of the birds (Rababah et al., 2004). Afolabi (2010) posited that haematological parameters of farm animals are affected by a number of factors: breed, climate, geographical location, season, day length, time of day, nutritional status, life habit of species, present status of individual among other factors. MCV, MCH and MCHC levels obtained in this study were in line with the normal range (90-140fL, 33-47pg and 26-35g/dl respectively) as reported by Patra et al. (2010). A low level of MCH and MCHC is an indication of anaemia (Aster, 2004) in farm animals and humans. It is noteworthy that the normal levels of these parameters among birds placed on turmeric powder diets could mean that turmeric inclusion in the diet did not negatively impair the transport of oxygen in the body tissues via the blood throughout their laying period. According to Oyawoye and Ogunkunle (2004), haematological components such as MCV, MCH and MCHC are valuable in monitoring feed toxicity especially with feed constituents that affect the blood as well as the health status of farm animals.