A Review on the Influence of Climate Change on Sheep Reproduction

Abstract

Increasing food and natural fibre production ensure food security for nearly 10 billion people, the projected global population in 2050, without causing further environmental damage can be achieved by transforming systems and adopting sustainable agriculture practices within a changing climate. Globally, climate change effects are having both direct and indirect effects on agricultural productivity including changing rainfall patterns, drought, flooding and the geographical redistribution of pests and diseases. Climate change induced heat stress is thus one of the complex factors making sheep management and husbandry challenging in many geographical locations in the world. Within the sheep industry, reproductive wastage (RW) is a major challenge throughout the varying breeding landscapes. Reproductive wastage is defined as the early losses of embryos undergoing natural and/or artificial breeding programs. Our previous research showed that heat stress (THI > 75) and elevated glucocorticoid levels (indexed using faecal glucocorticoid metabolites) are linked to embryo loss in Merino ewes. This mini review discusses how extreme variation in climate such as heat stress affects the maternal reproductive performance in the Merino sheep and the impacts on the wool industry. We provide recommendations to sheep producers for monitoring and managing the effects of heat stress on-farm.

Pre- and post-partum variation in wool cortisol and wool micron in Australian Merino ewe sheep (Ovis aries)

“…The wool cortisol assay method is exactly as per our earlier research trial on Merino sheep ( Sawyer, Webster & Narayan, 2019 ). Wool samples analysis for cortisol is detailed in our earlier paper ( Sawyer, Webster & Narayan, 2019 ; Sawyer & Narayan, 2019 ; Sawyer, 2019 ). Specifically, wool was washed in 90% isopropanol and air dried for 3 days using a dessicator prior to steroid extraction using 90% ethanol (all solvents were analytical grade).…”

“…These factors (nutrition, disease and pregnancy) influence wool quality (fibre diameter, staple length, staple strength, yield, vegetable matter content position of break) ( Cottle et al, 2013 ; Naidoo et al, 2016 ; Sawyer, Webster & Narayan, 2019 ; Ikusika et al, 2020 ) and wool production (kilograms produced) between shearing(s) ( Narayan et al, 2020 ). Secondary influences include the age and sex of a sheep that affect the quality and quantity of the volume of wool being produced between shearing cycles ( Cottle et al, 2013 ; Naidoo et al, 2016 ; Ikusika et al, 2020 ; Sawyer & Narayan, 2019 ). As the sheep ages, its early adult wool characteristics (micron, style, visual crimp) and wool quantity in grams diminishes.…”

“…Several previous studies that have highlighted the influence of stress on wool follicle development and growth, and wool quality indices using controlled experiments (see latest research in this field; ( Weaver et al, 2020 )). Raw wool fibres have also been identified as a reliable indicator of stress hormone (cortisol) levels at a point of time within the wool growth period ( Sawyer & Narayan, 2019 ; Davenport et al, 2006 ; Nejad et al, 2014 ). There is an interconnection between quality of the wool fibre on the sheep’s body and the processing ability of the wool fibre that are determined by the animal’s reaction to its environment, not just its genetics.…”

“…There is an interconnection between quality of the wool fibre on the sheep’s body and the processing ability of the wool fibre that are determined by the animal’s reaction to its environment, not just its genetics. Research into how the pregnancy status of the ewe influences wool staple characteristics has been conducted for over two centuries from Darwin in 1859 ( Darwin’s, 1859 ) (inheritance) through to recent research ( Narayan et al, 2020 ; Sawyer & Narayan, 2019 ). Earlier research into pregnant ewes’ interaction and commodity output (wool growth - kilograms produced) decreases throughout gestation and even more reduced during the first month of lactation ( Oddy, 1985 ).…”

“…Earlier research into pregnant ewes’ interaction and commodity output (wool growth - kilograms produced) decreases throughout gestation and even more reduced during the first month of lactation ( Oddy, 1985 ). When the animal is stressed by its environment, the presence of high plasma cortisol levels can cause wool follicle shutdown ( Sawyer & Narayan, 2019 ; Chapman & Bassett, 1970 ; Hansford & Kennedy, 1988 ) demonstrated within a housed sheep operation that pregnancy itself is a moderate stressor which caused fibre micron reduction in individually pen housed ewes. To our knowledge, this relationship has not been evaluated by testing the same wool sample for wool morphometrics and cortisol levels.…”