The effect of tree shade on ambient conditions and heat stress indicator traits of new-born South African Mutton Merino and Dormer lambs: Preliminary results

• Published in: Journal of thermal biology Vol. 99; p. 103024
• Main Authors: Cloete, Schalk W.P., Muller, Anieka, Steyn, Shannon, van der Merwe, Daniël A., Nel, Cornelius L., Cloete, Schalk, Kruger, Anna C.M., Brand, Tertius S.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01-07-2021; Elsevier BV
• Subjects: Animal welfare; Animals; Autumn; Birth; Body Weight; Breed; Heat; Heat stress; Heat-Shock Response; Humidity; Maximum daily temperature; Mutton; Rectal temperature; Respiration rate; Seasons; Shade; Sheep, Domestic - physiology; South Africa; Survival; Temperature; Trees; Weaning; South Africa; Respiration rate; Breed; Maximum daily temperature; Rectal temperature
• ISSN: 0306-4565; 1879-0992
• DOI: 10.1016/j.jtherbio.2021.103024

This preliminary study investigated the provision of shade on heat stress indicators of South African Mutton Merino (SAMM) and Dormer lambs shortly after birth, during the autumn 2017 and 2018 lambing seasons. Newborn lambs were assessed to determine whether welfare, as assessed by respiratory response and rectal temperature as heat stress indicators, survival and early growth benefitted from the provision of shade. Groups consisting of 4–17 pregnant SAMM and Dormer ewes were randomly allocated to 5–10 paddocks with natural shade from trees and 5–9 paddocks that were directly in the sun with no shade available. The lambs were recorded within 24 h of birth at noon. Climate data were obtained from a nearby weather station. The lambs were also weighed at 12 (SD = 2) days of age at tail-docking. Tree shade had a moderating effect on temperature, resulting in lower maximum daytime and higher minimum night-time temperatures. There was an interaction between a temperature-humidity index (THI) and the treatments (access to shade or no access to shade) for respiration and rectal temperature (P < 0.01). Both traits were relatively unaffected by the THI at values below 77. Unshaded lambs exhibited a pronounced upwards trend following a THI-threshold of 77–78. Tailing weight tended to be higher while lamb survival of live-born lambs to tail-docking was lower in lambs born in shaded paddocks but these trends did not persist to weaning. Shade is needed to enhance animal welfare by alleviating the effect of high THI-values on hot days in an autumn lambing season.
•Shade and a temperature-humidity index (THI) were studied on lambs.•Tree shade tempered the ambient climate experienced by lambs.•Respiration rate (RR) was at first independent of THI in both treatments.•RR of unshaded lambs rose faster than shaded lambs above a THI of 77-78.•Shade benefitted recently born lambs in ethical and welfare terms.