Nicobari is an indigenous bird reared for meat and eggs. This study evaluated the effect of heat stress on plasma levels of leptin, growth hormone and their receptors, liver AMP kinase, plasma cholesterol and lipid peroxide (MDA). The laying period coincided with the post summer period. The birds were equally divided into three groups, control group was offered ad libitum feed and treatment groups were supplemented with fermented yeast culture at 700 mg (T1) and 1.4 g/kg (T2) of feed/day. The levels of plasma Leptin and GH hormones were higher (p < 0.05) in the control group when compared to the treatment groups. The expression of the hormone receptors was higher in the brain, and MMP3 gene expression in the magnum was lower in the treatment group. Plasma cholesterol, MDA and AMP kinase were significantly higher (p < 0.05) in the control group. Fermented yeast culture supplementation decreased feed intake and increased egg production parameters, which indicates a greater efficiency of supplementation. Supplementation reduced the severity of necrosis of villi in the jejunum when compared to control. In conclusion, higher ambient temperature during summer had negative effect on production parameters through modulation of physiological parameters which could be ameliorated by supplementation of FYC.

Heat stress (HS) affects the production performance in chickens and causes economic loss to the producers. Most of the studies have been conducted on and for the welfare of broilers. We still lack information on the physiological parameters being affected during chronic heat stress in layers. To fill this gap, the present study evaluated the effect of heat stress (induced in the chamber) during the prelaying period (21–23 weeks) on plasma levels of the hormones leptin and ghrelin and GH and expression of the respective receptors and heat stress markers. Three groups were considered, one at room temperature (CR) and the other two groups (SH and CH) subjected to heat stress at 39°C for four hours for three weeks (21–23 weeks of age). The SH group (SH) feed was supplemented with fermented yeast culture (FYC, 700 mg/kg), whereas the CH group was devoid of it. After that, all the groups were shifted to shed under natural ambient conditions till 31 weeks of age. Studies were restricted to production performance only. Feed offered without yeast culture (CH group) had a smaller concentration of plasma hormones ( P < 0.01 ) and increased expression fold of the hormone receptors ( P < 0.01 ). Further, the group also presented higher liver AMP kinase enzyme, plasma MDA (malondialdehyde), and cholesterol concentrations. These changes likely explained the decrease in feed intake and the CH group’s body weight and further reduced the production performance during the laying period. Supplementation with FYC to birds had an opposite effect on the above-mentioned parameters, reducing HS effects. In summary, supplementation with FYC (700 mg/kg) maintained physiological parameters as in the CR group under HS conditions and negated adverse effects on parameters both before and during laying periods.

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