In the present study, feed intake did not differ between the control and treatment groups of birds under heat stress conditions; however, weight gain and FCR were significantly improved in the treatment groups. Similar to our study, Aengwanich et al. (2009) reported no significant change in the feed intake and feed efficiency in broiler fed different levels of Tamarind extract during 36–42 days of age, however, weight gain was significantly higher in response to 100 mg/kg at 38°C. In the study of Saleh et al. (2012) feed intake was decreased linearly in broiler fed with DTSP in drinking water at the increasing rate of 20, 30 and 40 g/l under thermoneutral temperature, which was attributed to the presence of anti-nutritional factors in this plant. In another study, Shinde et al. (2015) reported significant improvement in weight gain and FCR in broilers supplemented with DTSP at the rate of 250 g/100 kg with depression in these traits at higher doses (500, 1000 and 1500 g/kg) under normal temperature. It has been suggested that the pulp of Tamarind contains antioxidant (Razali et al. 2015) and antibacterial activities against the microorganisms (Daniyan and Muhammad 2008), which may result in higher growth performance in broilers. Unlike the previous studies, we did not find reduction in feed intake with the increasing level of DTSP, probably the higher doses in the current study were not enough to produce anti-nutritional factor effect. The flavonoides in Tamarind have been reported for the presence of hepatoprotective, nutrient digestibility, balancing mirobiota, antioxidative and anti-inflammatory effects (Adeniyi et al. 2021) and might have contributed to the enhanced growth in birds.
In the current study, no significant change was observed in the serum MDA concentration in the control and treatment groups, however, PON1 concentration was increased significantly in DTSP-10 and DTSP-12.5 compared to the control. In some recent studies, improved serum PON1 was observed in broilers supplemented with different natural compounds such as taurine, ginger and milkthistle under heat stress conditions (Safiullah et al. 2019; Ahmad et al. 2020; Hafeez et al. 2021). PON1 is an important HDL-related antioxidant enzyme and its concentration has been reported to be augmented by the supplementation of antioxidants. Oxidative stress occurs due to perturbance in the balance between the oxidative stress and antioxidant capacity. Tamarind has been reported to suppress lipid peroxidaiton due to the anti-free radical activities of the phenolic compounds, two b-diketone and (-) epicatechin (Tsuda et al. 1994; Martinello et al. 2006). Limited studies have been conducted on the antioxidant activity of TDSP. In the present study, antibody titre against ND decreased in the control group and improved in DTSP-7.5, DTSP-10.0 and DTSP-12.5. The lymphocyte count is decreased during heat stress (Ahmad et al. 2020) as seen in this study and hence there is a lower antibody titre against an infection. The higher antibody titre against ND in this study seems to be due to the production of greater levels of lymphocytes in response to Tamarind supplementation.
The search for novel agents regulating blood cholesterol has gained momentum over the last few decades, resulting in a significant number of reports on natural agents with anticholesteremic activities. In view of the previous experiments, we evaluated the effect of DTSP on serum lipid profile. The seed coat of Tamarind is a low-cost source of antioxidant and exhibits antioxidant activity against thiocyanate and thiobarbituric (Pazhanivelan et al. 2008). Lipids are easily susceptible to the injury of free radicals. Compounds in Tamarid have been reported to improve the lipid profile (Martinello et al. 2006). In the current study, Tamarind pulp exhibited a significant reduction in lipid profile in serum of broilers. Decreased serum cholesterol and triglycerides have been attributed to epicatechins contents in Tamarind (Chan et al 1999). Biradar et al. (2017) reported reduced serum cholesterol by 25 and 28% in layers fed DTSP at the level of 0.25, 0.5 and 1% at thermoneutral temperature. Similarly, Chowdhury et al. (2005) also found reduced serum cholesterol in laying hens at the level of 2% level. Shinde et al. (2015) also reported reduced serum cholesterol in broilers fed DTSP extract. Similar observations were reported by Iftekhar et al. (2006) in human and Khairunnuur et al. (2011) in rats. It is speculated that the extra cholesterol is converted into bile acid in the hepatocytes or conjugated with taurine and glycine. Remarkably, serum HDL-cholesterol increased in the Tamarind treated birds. Biradar et al. (2017) reported increased serum HDL by 45% in Tamarind supplemented laying hens. Martinello et al. (2006) recorded increased serum HDL by 61% in hamsters in response to TDSP extract. Similar findings were also reported by Jindal et al. (2011) and Khairunnuur et al. (2011) with a significant increase in serum HDL in rats supplemented with 100 and 50 mg/kg Tamarind extract respectively. The level of serum LDL decreased significantly in DTSP-7.5, DTSP-10 and DTSP-12.5 as compared to the control during heat stress. Similar observations were also reported by Khairunnuur et al. (2011), Chor Yin lin et al. (2013) and Biradar et al. (2017) in response to Tamarind pulp in commercial layers, rats and hamsters respectively. The reduced serum LDL in Tamarind supplemented animals has been attributed to epicatechins contents (Luengthanaphol et al., 2004), which are known for the suppression of hypercholesterolemia by modulating lipid metabolism.
Environmental temperature is one of the most important factors affecting the immune system of broiler chickens. Exposure of the chickens to high ambient temperature causes significant physiological changes including immunosuppression and high mortality rate (Khan et al. 2012). Leucocyte count has been used as an indicator of heat stress in poultry. In the current study, TLC increased significantly in birds fed with DTSP at the rate of 12.5 g/kg. Moreover, heterophil and monocytes count increased in the control and DTSP-5 and the same were restored at the higher doses. Lymophocytes count was also lower in the control and DTSP-5, however, it was restored at higher doses. Rise in TLC is considered to enhance the immune system with increased resistance against infectious diseases and improvement in production performance. Almost similar findings were reported by Shinde et al. (2018) in broiler fed with different levels of DTSP. Aengwanich et al. (2009) reported restoration of heterophils and monocytes count in broiler under heat stress (38°C) for 8 h at a dose rate of 400 mg/kg. The resultant increase of leucocytes under heat stress has been attributed to the increased secretion of glucocorticoides. In addition, lymphocyte count was decreased in the control group and improved in broilers in Tamarind supplemented birds. Lymphopenia occurs in heat stress conditions due to increased secretion of glucocroticoides, DNA damage, lymopholysis and shift of lymphocytes from blood to the other body compartments (Compton et al. 19990; Heckert et al. 2002).
In conclusion, weight gain and FCR were improved in broilers supplemented with DTSP. PON1 was improved in DTSP-10 and DTSP-12.5 while antibody titre was greater in DTSP-7.5, DTSP-10 and DTSP-12.5 in broilers during heat stress. Except DTSP-5, total cholesterol and LDL increased in the rest of the treatment groups. Furthermore, TLC increased significantly in DTSP-12.5 while lymphocytes count was greater in all the treatments except DTSP-5. Similarly, heterophils and moncytes count decreased significantly in all the treatment groups except DTSP-5.