In the present study, Incubation temperature manipulation during embryogenesis had negative long-lasting effects on quail development and physiology, including weight and production performance traits. The results revealed incubation period and TEPH were significantly decreased by thermal stress similar to previous findings in quails (Piestun et al., 2008; Alkan et al., 2013; Sgavioli et al., 2015). The chicks cloacal temperature in the CIT group was significantly (p≤0.05) increased compared with control as indicated by (Abuoghaba, 2017) suggesting that heat stress caused internal temperature dysregulation. The achieved results showed no impact of thermal manipulation during quail’s embryogenesis in embryonic mortality and hatchability percentages similar results were obtained in previous studies in quails (Alkan et al., 2013; Vitorino Carvalho et al., 2020).
Previous studies in broilers revealed heat stress impact on weights of newly hatched chicks as well as weights before and after slaughtering (Abuoghaba, 2017). Similarly in quails, the results showed a negative impact of thermal stress on newly hatched quail weights. The heart weight was significantly lower in CIT group than in the control group. Also, in broilers the heart weight was decreased in the heat-stressed group may be related to the increased susceptibility of cardiovascular disorders such as ascites (Leksrisompong et al., 2007, Abuoghaba, 2017). The liver weight was significantly higher (p≤0.05) in CIT group than in the control group. These findings agree with (Sgavioli et al., 2015) who found that incubation heat stress led to an increase in liver weight as well as a decrease in heart weight in broilers. At slaughter age (D42) in female quails, the quail's weight and weight of the first egg were significantly decreased by incubation thermal manipulation this may be due to decrees in the initial body weight of the chick that affected the final body weight. These results agreed with the findings of (Hulet et al., 2007).
The slaughter weights of TV (g), and spleen (%) were significantly decreased, while RV and RV/TV ratio were significantly increased by incubation thermal manipulation. These results are in agreement with findings in broilers (Molenaar et al., 2011). The increase in RV/TV ratio was an indicator for ascites (Wideman, 2001). No impacts of thermal stress were observed in the female reproductive traits.
The obtained findings showed adverse impacts of thermal stress on quail blood parameters. The CIT quails displayed a higher number of red blood cells and H/L ratio than the control group similar results were obtained in quails (Mehaisen et al., 2019) and in broilers (Abuoghaba, 2017). The increase of the H/L ratio is an indicator of stress in quails (Nazar and Marin, 2011). Furthermore, the total leucocyte count reduction in CIT quails may be due to increased corticosterone levels which increased in response to heat stress (Mehaisen et al., 2017; Mehaisen et al., 2019).
The total protein, albumin, and globulin levels in the CIT groups were significantly decreased compared with the control group as previously seen in quails (Mehaisen et al., 2019). These results could be explained by heat stress-induced increase levels of CORT which included denaturation and breakdown of protein (Sahin et al., 2006; Mehaisen et al., 2019).
The thermal stress resulted in a decrease T3 level which was observed in CIT females compared with NIT females as previously seen in quails (Badran et al., 2012) and broiler (Yalçın et al., 2009; Abuoghaba, 2017). The increase in ALT and AST enzymes is an indicator of the harmful effects of heat stress in liver tissues (Vahdatpour et al., 2011). These results are consistent with the obtained findings that ALT and AST enzymes were significantly increased in CIT quails compared to NIT quails. Furthermore, lipase enzyme activity becomes low at heat stress with low digestion of nutrients (Al-Zghoul et al., 2019). Therefore, CIT quails were displayed higher concentrations of triglyceride and cholesterol compared to NIT quails. This is in agreement with a previous study in quails (Sahin et al., 2006).
Positive impacts of nutrients in ovo administration including support egg nutrients (Foye et al., 2006) increase chick weight at hatch day (Saki et al., 2014) and improve the immune system (Sławinska et al., 2014). The embryonic mortality in the betaine-treated eggs decreased compared with those of the control group. Spraying of betaine improved hatchability percent compared with a control group. Furthermore, increasing betaine level caused a numerical increase in hatchability percent. These results agree with the report of (Gholami et al., 2015) that increasing in ovo injected betaine level improved hatchability percent. Hatch weight was significantly affected by betaine treatments. These results agree with those of (Saki et al., 2014; Gholami et al., 2015) that the betaine administration improved hatching weight. Interestingly, the interaction between incubation temperature and betaine treatment significantly decreases the relative water loss may be due to betaine is an osmoregulatory agent that increases water retention (Attia et al., 2005), and reduce water evaporation from the eggs or may be due to the ability of betaine to substitute methyl group donor such as Met (Metzler-Zebeli et al., 2009).
Newly hatched chick weights before and after slaughter were significantly increased with betaine spraying (T4 and T5). No impacts of betaine spraying in internal organ weights were observed.
At slaughter age, BW and TWG were significantly affected by experimental treatments, spraying of betaine improved BW and TWG than control groups. The obtained results agree with (Gholami et al., 2015) that betaine administration improved the final weight of chickens. These positive effects of betaine could be attributed to betaine can replace methyl group donors such as Met (Metzler-Zebeli et al., 2009) therefore decreased Met needed (McDevitt et al., 2000). In ovo administration of Met would increase utilization of amino acids, deposition of protein, and improve BW in geese (Li et al., 2015).
Positive impacts were obtained by spraying different betaine levels in incubated eggs. Total feed consumption and feed conversion ratio were significantly decreased by betaine spraying. Due to its osmotic properties, betaine may have the potential to improve the digestibility of nutrients, improved protein utilization, and reduced protein breakdown (Eklund et al., 2006). In laying hens, the betaine supplementation in the diets increased FC (Ezzat et al., 2011). Previous reports have revealed that betaine supplementation improves nutrient digestibility because of its osmoprotective properties and supporting intestinal microbes growth (Ratriyanto et al., 2009; Ratriyanto et al., 2010). Furthermore, betaine significantly decreased the total feed consumption and feed conversion ratio in quails under heat stress. Similar findings in the broiler, that dietary betaine supplementation increased the feed intake and reduced the FCR of broilers subjected to heat stress (Attia et al., 2009; Sakomura et al., 2013; Chand et al., 2017).
The betaine spraying in the eggs would improve the feed intake, feed conversion, and body weight gain in post-hatch life this was confirmed by starting egg-laying at earlier ages and improve the weight of the first egg (Table 4).
This in agreement with previous observations in laying hens indicated that betaine supplementation in the diets increased egg weight (Ezzat et al., 2018), who found that the feed conversion ratio, egg production and egg mass in Mamourah chickens fed the diet containing 1600 mg betaine + 600 mg/Kg GAA under summer conditions in Egyptian significantly (P<0.01) improved in hens as compared to the control group.
The observed increase in the egg weight may due to higher egg components with betaine supplementation. These results may be attributed to the methyl donor function of betaine, which is involved in protein and energy metabolism (Ratriyanto et al., 2009). Supplementation of betaine improved and increased egg albumen weight (Joseph et al., 2000). Also, the oviduct % was increased due to spraying betaine in incubated eggs these findings agree with the effects of dietary supplementation of betaine in laying hen (Attia et al., 2011).
In this study, when spraying betaine in heat-stressed eggs, the carcass traits were subsequently improved. Interaction between betaine and incubation heat stress significantly increases the EC weight and normalizes the spleen weight. Moreover, betaine treatments and the interaction between betaine and incubation temperature significantly decrease the RV/TV ratio. Consistent with the obtained results in broiler, dietary betaine supplementation enhances and improves the carcass traits of heat-stressed chicks (Attia et al., 2009; Rao et al., 2011; Nofal et al., 2015).
No impact of betaine in blood parameters except total leukocyte count significantly increased this in line with that betaine improve the immune status of the birds through protecting leukocytes (Klasing et al., 2002).
Serum ALT and AST are important indexes of liver status. ALT and AST were decreased by spraying betaine to incubated eggs this may be due to betaine protects the liver (Klasing et al., 2002). Betaine increases the choline availability for the synthesis of very low-density lipoprotein, which avoids deposition of fat in the liver and increases the removal of fat from the liver (Attia et al., 2005; Ratriyanto and Mosenthin 2018).
Betaine treatment decreased serum lipids, triglyceride, and cholesterol. This was in agreement with the findings in quails (El-Bahr et al., 2021) and in laying hens (He et al., 2015), that betaine supplementation increased lipase activity and reduced the concentration of triglyceride and cholesterol (Ratriyanto et al., 2009).
Betaine treatment elevated serum levels of T3 hormone. The activity of T3 hormone is positively impacted with betaine compared to the control group. Accordingly, it’s reported that betaine supplementation elevated the thyroid activity in broilers as indicated by increases in the levels of T3 hormone (Nofal et al., 2015; Attia et al., 2011). Besides, the obtained results revealed that betaine supplementation increased levels of total protein and globulin as previously reported in laying hens (Rao et al., 2011).
In conclusion, the spraying betaine in eggs during incubation phase would likely reduce the mortality rate, feed intake and feed conversion as well as improve hatchability rate, chick weight at hatch, chick weight at slaughter age, so that quail birds start the egg-laying at earlier ages. This could be reflected positively on the egg weight and egg quality traits. Moreover, betaine positively improves the WBC, blood proteins, liver enzymes, blood lipids, and thyroid activity. Under heat stress conditions the results showed increase cloacal temperature, RV/TV ratio, H/L ratio, ALT, AST, cholesterol, triglyceride levels in quail. While, the hatching time, chick weight at hatch, chick weight at slaughter age, the weight of the first egg, TWBC’s and blood proteins were significantly decreased compared to the control group.
The present data showed that spraying of betaine could reduce the adverse effects of heat stress on RWL, TFC, FCR, carcass weight and RV/TV ratio indicating that betaine has an anti-heat stress role. The beneficial impacts of betaine on quail’s performance may be due to its osmoregulatory action, methyl group donors and anti-oxidative effect.