Changes in hematological and hematochemical parameters in lactating dairy sheep according to different pasture management and heat stress risk: A longitudinal study

Sheep in Italy are exposed to heat stress (HS) for several months, increasing the risk of HS-related problems such as the decrease in growth, reproductive performance, milk quantity and quality and natural immunity. This study aimed to assess changes in hematological and biochemical parameters in dairy sheep from three different farms with varying pasture management: A (no water or shade), B (water but no shade), and C (both water and shade). From March to June, when HS risk is high, monthly blood samples (T1-T4) were collected from 20 sheep per farm (total n = 60). Blood parameters included red blood cells (RBC), hematocrit (HCT), hemoglobin (HGB), urea, creatinine, and total protein (TP). The impact of HS and management on these parameters was analyzed using a mixed linear model. Heat stress was classified using temperature-humidity index (THI) evaluated in the sampling day in “no HS”, “moderate HS”, “severe HS” or “extreme HS”. Severe HS was observed at T3 and extreme HS at T4. At T4, RBC levels were significantly higher in A compared to C. Both HCT and HGB levels at T3 and T4 were significantly higher in A and B compared to C. Urea levels were higher in A and B compared to C at T1 and T3, in A compared to B and C at T2, and in DSF B compared to C at T4. TP concentrations varied between farms and over time, with significant differences at T1 (B vs C), T2 (A vs B; C), T3 (A vs B vs C), and T4 (A vs B; C). These findings suggest that pasture management may influence blood and biochemical parameters under HS condition, and they could potentially be used as a tool for implementing health and welfare monitoring of grazing dairy sheep. Providing shade and water may improve sheep health in hot climates.