Impact of grazing duration on stress biomarkers and heat shock protein (HSP) expression in Kachhi sheep

Abstract

This study examined the impact of varying grazing durations on stress biomarkers and heat shock protein (HSP) expression in Kachhi sheep under heat stress conditions. Fifteen lambs were randomly assigned into three groups (n=5): morning grazing (KMG; 7:00 AM–11:00 AM), hot hours grazing (KHG; 11:00 AM–3:00 PM), and evening grazing (KEG; 3:00 PM–7:00 PM), with all lambs receiving a basal diet of green fodder and concentrate in addition to grazing. The 90-day trial included fortnightly recording of physiological parameters (rectal temperature, pulse rate, and respiration rate), as well as blood sampling on days 0 and 90 for hematological, hormonal, biochemical, oxidative stress, and gene expression analysis. Rectal temperature, pulse rate, and respiration rate were recorded using standard methods; rectal temperature was significantly higher (p<0.05) in KHG lambs, while pulse and respiration rates did not differ significantly (p>0.05). Hematological parameters (RBC, Hb, PCV, WBC, MCV, MCH, MCHC), analyzed using an automatic Nihon Kohden analyzer, showed non-significant differences (p>0.05) among the groups. Hormonal level (T3, T4, cortisol), measured by Electrochemiluminescence Immunoassay (ECLIA) on a Cobas-e analyzer, revealed higher T4 in KMG and KEG lambs. In contrast, T3 and cortisol levels were not significantly different (p>0.05) across groups. Oxidative stress parameters (SOD, GSH-Px, MDA), assessed using assay kits, also showed non-significant variation (p>0.05). Serum biochemical parameters, analyzed using a Roche Hitachi C311 analyzer, indicated significant differences (p<0.05) in glucose, total protein, sodium, and potassium. At the same time calcium, magnesium, AST, ALT, creatinine, and urea nitrogen levels were not significantly affected (p>0.05). Gene expression of HSP-70 and HSP-90, determined by quantitative real-time PCR (qRT-PCR), showed significant upregulation in KHG lambs and downregulation in KMG and KEG lambs. These findings suggest that morning grazing mitigates heat stress in Kachhi lambs by improving physiological responses, stabilizing hormonal levels, and reducing cellular stress, thereby enhancing overall health and performance.