Comparative Assessment of Thermotolerance in Dorper and Second-Cross (Poll Dorset/Merino × Border Leicester) Lambs

Abstract

The objective of this study was to compare the thermotolerance of second-cross (SC; Poll Dorset × Merino × Border Leicester) and Dorper lambs. Dorper and SC lambs (4–5 months of age) were subjected to cyclic heat stress (HS) (28–40 °C). The temperature was increased to 38–40 °C between 800 and 1700 h daily and maintained at 28 °C for the remainder of the day (30–60% relative humidity (RH)) in climatic chambers for 2 weeks (n = 12/group), with controls maintained in a thermoneutral (TN) (18–21 °C, 40–50% RH) environment (n = 12/group). Basal respiration rate (RR), rectal temperature (RT) and skin temperature (ST) were higher (p p p p p p p p 2, cHCO3− and cSO2, but higher (p p 2 were recorded under HS in both genotypes. Blood electrolytes and base excess were reduced (p p + and hemoglobin concentrations. Basal plasma prolactin concentrations were lower (p p < 0.01) in both genotypes. Dorper lambs are more resilient to HS than SC lambs. Future research should focus on confirming whether the better heat tolerance of Dorpers is translated to better returns in terms of growth performance and carcass traits over the summer months.

Keywords

• heat stress
• physiology
• prolactin
• sheep
• thermotolerance