Climate change and global warming is placing a responsibility on the wool industry to find ways to select for traits in Merino sheep that will reduce the possible stress caused by high ambient temperatures.
a) To assess breed differences in heat indicator traits in Dormer and SA Mutton Merino lambs born in autumn
Dormer and SA Mutton Merino lambs born at Elsenburg were monitored and measured for traits indicative of heat stress in the first 24 hours after birth. It appeared as if SAMM lambs showed more signs of stress. Lamb survival rate was not breed influenced.
b) To assess the influence of natural tree shade on heat stress in Dormer and SA Mutton Merino lambs born in autumn
Lambs were able to regulate their own body temperature within the thermo-neutral range without negatively affecting lamb growth or production. Therefore, with the data collected so far, the provision of shade did not affect production traits of economic importance. However, it is clear that the provision of shade enhanced animal welfare by alleviating heat stress resulting from high ambient temperatures prevailing at hot days. The dataset collected so far is still too small for the project team to be able to derive accurate heritability estimates for heat stress indicator traits in the resource flocks. Such parameters will be updated as more results become available.
c) To study the breed differences in heat stress indicator traits in a wide range of breeds from the South African ovine genetic resource and to determine if these traits are repeatable and heritable
The homeothermic response of seven sheep breeds, namely the Dohne, Dormer, Dorper, Meatmaster, Merino, South African Mutton Merino (SAMM) and White Dorper, were studied The observed variation in heat stress indicators between breeds can be regarded as an indication of heritable genetic variation for the traits that are associated with heat stress.
Further research is required to determine how temperature and the adaptive responses of animals influence the welfare and productivity of sheep. An easily recorded indicator trait such as respiration rate should be assessed as a tool to improve within-breed heat tolerance by selection.