Short duration heatwaves increase body temperature and alter blood gas balance but may not cause oxidative stress and intestinal structure variations in lambs

This study investigated the impact of short duration heatwaves (HW) on the body temperature, blood gas, intestinal histology, and oxidative stress parameters of second cross lambs. Seventy-two second cross lambs [Poll Dorset × (Border Leicester × Merino)] were selected and exposed to either one, three or five days HW (28–38°C and 40–60 % relative humidity (RH)) or thermoneutral (TN; 18–21°C, 40–55 % RH) conditions in climate-controlled chambers. Lambs exposed to one to five days HW exhibited higher face, eye and ear temperature compared to animals exposed to equal duration under TN conditions. HW also had a significant impact on blood gas parameters which include higher blood pH, and lower CO 2 , Ca 2+ , Na + , CHCO 3 - and Cl - . However, HW lambs’ histology structure of the ileum and the GSSG: GSH of the ileum and Longissimus thoracis (LT) muscle were not influenced ( P > 0.05) by HW. LT muscle showed higher total antioxidant capacity (TAC) in HW conditions, but the TAC of intestine and blood had no difference between HW and TN groups. These results suggest that short-duration HW (one to five days) had a significant impact on lambs’ body temperature and blood parameters, but neither caused oxidative stress nor any changes in their intestinal structure. • This study assessed the potential impact of extended heatwaves in countries with warm climates such as Australia, China, and the United States on animal body conditions by examining the effects of increased extreme temperatures and humidity. • The study was a meticulously controlled experiment that involves a substantial sample of large animals, consisting of 12 lambs in each group. To maintain a stable ambient temperature and humidity, a climatic chamber was utilized, providing a more controlled environment compared to outdoor experiments. • The study employed 2nd cross lambs, a commonly chosen high-production sheep breed in Australia, created by crossing Poll Dorset with a combination of Border Leicester and Merino genetics. • To determine the impact of short-term heatwaves on the body condition of 2nd cross lambs, the study considered various factors, including body temperature response and physiological parameters such as blood gas levels, intestinal histology, and oxidative stress parameters. • This study serves as the concluding component of our broader investigation into the effects of short-term heat stress. Our earlier research has already substantiated the influence of heat stress lasting from one week to one month on the physiology, growth performance, and meat quality of sheep and lambs (as illustrated in the attached figure and detailed in Chauhan et al., 2023).