Browsing by Author "Steyn, Shannong"
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- ItemStudies on the response of lambs and ewes to changes in the ambient climate owing to climate change(Stellenbosch : Stellenbosch University, 2022-12) Steyn, Shannong; Cloete, Schalk W. P.; Brand, T. S.; Van Zyl, Johan Hendrik Combrink ; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Sciences.ENGLISH ABSTRACT: This study investigated the impact of climate instability on neonatal lamb behaviour as a proxy for lamb survival in a winter lambing season in the Western Cape, as well as the impact of increased temperatures on heat stress indicator traits in mature ewes in the Western and Eastern Cape. Historic data were used to establish the relationship of neonatal lamb behaviour with cold stress and to derive genetic parameters for early lamb behaviour. Merino lambs of the Elsenburg flock were phenotyped for behaviour latencies from birth to first standing (LTBS) and from standing to first suckling (LTSS). These data were analysed in relation to a cold stress gradient (CSG) derived from a combination of wind, rain, and temperature. The flock consisted of a line selected for number of lambs weaned per ewe mated (NLW; the High or H-Line) and a line selected against NLW (Low or L-Line). H-line lambs progressed faster from standing to first suckling than L-line lambs. Increased CSG-levels resulted in 18% faster progress in LTBS when mild conditions at 800kJm⁻²h⁻¹ were compared to stressful conditions at 1200kJm⁻²h⁻¹. LTSS was compromised by 76.0% as CSG-values increased from 800kJm⁻²h⁻¹ to 1200kJm⁻²h⁻¹. Heritability estimates were 0.22 for LTBS and 0.06 for LTSS. The maternal heritability for LTBS was 0.06 and the dam permanent environment variance ratio 0.09 for LTSS. The traits were not genetically correlated. Further research is required to understand the responses of lambs to cold stress. Average temperatures are likely to increase, resulting in hotter and dryer conditions in South Africa. The impact of these changes on animal production and welfare is not well-defined. Three trials were conducted on 10 to 20 mature, dry ewes at 2 locations to determine the homeothermic response of nine sheep breeds between 2016 and 2022. These breeds were the Dohne, Dormer, Dorper, Ile de France, Meatmaster, Merino, Namaqua Afrikaner, South African Mutton Merino (SAMM) and White Dorper. They were studied in different combinations across trials. On days forecast to be hot at noon, animals were assessed under cool conditions in the morning and hot conditions at noon/afternoon by monitoring individual rectal temperature, eye temperature (thermal imaging), spot temperature, and respiration rate. The increased heat in the afternoon sessions markedly increased all traits across trials. In general, hair breeds (Dorper, White Dorper, Meatmaster, and particularly Namaqua Afrikaner) were able to maintain lower basal respiration rates compared to the wool breeds originating from temperate regions (Dohne, Dormer, Ile de France, Merino, and SAMM). These results suggest that hair sheep and hardy indigenous breeds such as the Namaqua Afrikaner may cope better with the anticipated higher heat load in the future when compared to the breeds originating from temperate regions. Rectal temperature was low- moderately repeatable across trails, while outcomes for respiration rate and spot temperature were more variable and commonly affected by the reranking of ewes across sessions as well. Eye temperature was not repeatable. There is still marked scope for research on ovine adaptation to heat stress conditions in South Africa.