A Review of Studies on Improvement of Sheep Resilience to Climate Change Stresses

Abstract

Sheep are economically, nutritionally and culturally very important in the world, particularly in developing countries. However, there are many climate change stresses constraining sheep production. Climate change directly and adversely impacts on sheep production in terms of reduced quantity and quality of water and feeds, and increased animal health and husbandry challenges. Sheep with high water and feed use efficiencies can survive on less water and feed during drought periods. These efficiencies can be improved at the animal level (breeding animals with high water and feed use efficiencies, etc.), feed level (breeding drought resistant feed crops, etc.) and or at the water or feed resource management levels (increasing sheep product produced per unit of water or feed through cutting of water or feed wastage). This chapter reviews studies on the efficiency with which sheep products are produced from feed and water resources. It is concluded that selection of sheep that have high water and feed use efficiencies per unit of sheep product can be a mitigating option against limited water and feeds due to climate change.

1. Introduction

Sheep are domesticated small ruminants that have been a vital part of human civilization for more than 10,000 years ago [1]. Sheep were firstly introduced to Europe, Africa and Asia and eventually made their way to other continents, including Australia and the America [2]. Currently, there are approximately 1.266 billion sheep in the world with China as the biggest contributor (14%) followed by Australia and India contributing 5%, UK at 3%, South Africa 2%, Mongolia 2%, Argentina 1%, Uruguay 0.5%, USA 0.4% and other countries contributing 62% [3]. Sheep are important for meat, milk, wool and hides [3]. Sheep meat (mutton and lamb) are vital sources of protein in various cultures. World annual sheep meat consumption is 2.5 kg per person, which is about 6% of the annual world total meat consumption per person. Sheep’s milk is normally for production of dairy products such as yogurt, cheese, and butter, whereas mutton and lamb are vital sources of protein in various cultures, then wool is used for clothing and textiles [4, 5]. Sheep farming contributes to rural economies by producing income for farm workers, farmers, wool processing, meat processing, and textile production [6]. Sheep also play a vital role through grazing in maintaining and managing the landscapes and contributing to soil health by promoting nutrient cycling through their grazing behaviors [5]. Mutton, lamb and wool are produced from sheep raised mainly on extensive production systems, while milk is mainly produced by sheep raised on intensive production systems. The traditional pastoral production systems produce meat, milk, wool and hides. The different production systems are efficient provided there are adequate resources and husbandry practices available when required. Generally, production risks are higher in the traditional pastoral production systems [7, 8]. However, climate change adversely affects all the production systems, and hence there is need for these systems to be resilient against climate change stresses [9].

There are many climate change stresses constraining sheep production in the world. Climate change stresses are directly and adversely impacting on sheep production in terms of reduced quantity and quality of feeds, changes to the dynamics of pests and diseases, higher animal husbandry and health risks, and limited water and feed supplies [10, 11]. Seventy percent of world freshwater is used by the agriculture sector [10]. There is, therefore, need to reduce the amount of water required for agriculture through better water use efficiencies without compromising productivity of crops and livestock. Limited amount of freshwater and increasing demand for food from growing populations of humans and animals [11] dictate that there must be ways of improving water and feed use efficiencies for livestock. Expected future shortage of water due to climate change requires that water use has to be much more efficient. Thus, research emphasis has been on improving water and feed use efficiencies for livestock products. Sheep with high water and feed use efficiencies can survive on less water and feed during drought periods. These efficiencies can be improved at the animal level (breeding animals with high water and feed use efficiencies, etc.), feed level (breeding drought resistant feed crops, etc.) and or at the water or feed resource management levels (increasing sheep product produced per unit of water or feed through cutting of water or feed wastage) [11]. The following sections review studies aimed at water and feed use efficiencies for sheep products.

2. Methodology

The studies focusing on water and feed use efficiencies for sheep products were reviewed as studies of the improvement of sheep resilience to climate change stresses. Both researchers independently conducted a publication search using “water use efficiencies for sheep products” and “feed use efficiencies for sheep products” as key terms. Studies were considered for inclusion in this review provided: they included key terms used for searching. Articles that were talking about a different specie other than sheep were excluded. Duplicate studies were also excluded [12].

3. Discussion

3.1 Water use efficiencies for sheep products

Water is a very important nutrient in the body of an animal. An animal can live for a maximum of 3 days if deprived of water [12]. An animal body contains 50–80% of water. Water functions as an important solvent for body temperature regulation, digestion, metabolic processes, production of milk and many other biological processes [13]. The main sources of water for animals are drinking water, feed water and metabolic water. Body water is lost through urine, feces, perspiration and respiration. Water requirements for sheep will vary with type of production (for example growing, lactating or pregnant sheep will require more water), climatic factors (for example, high ambient temperatures increase water requirements) and feed factors (for example, sheep on dry feed will have higher water requirements than those on wet feed) [12]. Depriving an animal of water will adversely affect its productivity [12, 13].

Water use efficiency in sheep is a measure of how much water is needed per unit of meat, milk, lamb, wool, etc. produced. Factors such as sheep breed, diet, climate and quality of water determine the amount of water to be consumed. Ninety eight percent of the total sheep water footprint is accounted for growing feed. More than 92% of the total water footprint in farming comes from rainfall [14].

Good quality water supply is important sheep welfare and business profitability [15]. Barros de Freitas et al. [16] observed a difference of 35% in water intake between the most and least efficient lambs (2.6 and 4.0 L/day, respectively). The authors [16] observed that 95 and 5% were from drinking water and feed intake, respectively. However, water consumption will depend on climate, diet, physiological state of the animal, and other factors [15].

Sheep with better water use efficiencies eat less food and drink less water per metabolic body weight [16]. The authors [16] observed a 7.1% reduction in feed intake for lambs having better water use efficiencies compared to less efficient lambs. This was attributed to less nutrient requirements for basal metabolic processes [17]. The water use efficiency ratios for gain in live weight range from 10.4 to 20.6 [16, 18], while those for milk production range from 4.0 to 5.0 (Table 1) [13, 14], depending on factors that include climate, diet and physiological state of the sheep [15]. In production systems with limited water, sheep with higher water use efficiencies are more desirable for resilience against climate change stresses like limited water and feed availability [13]. Water efficient sheep ingest less water per kg of dry matter feed (Table 1). Thus, efficiency in water use can be considered as a trait in sheep selection as it does not adversely affect performance and carcass characteristics of sheep [13, 22]. Estimates for lambs are 4–6 liters of water/kg dry matter intake (DMI) for ambient temperatures above 16°C or 2 liters of water/kg DMI for ambient temperatures below 15°C [18]. Sheep breeds in areas experiencing seasonal water shortages have better water use efficiencies through adaptations than those in areas where no seasonal water shortages occur. Such breeds tend to reduce water intakes and water losses [13]. Head et al. [23] found that Mutton Merino and Dorper sheep consumed more water than Blackhead Persian sheep. Selection of sheep that have high water use efficiencies per unit of product can, thus, be a mitigating option against climate change stresses.

Sheep product	FCR ratio (kg feed/kg product gain)	Water intake to weight gain ratio (L/kg gain)	Water intake to DMI ratio (L/kg DMI)	Water intake to milk production ratio (L/kg milk)	References
Meat	1.814–3.629	—	—	—	[19]
Meat	4.0–6.0	—	—	—	[20]
Milk	4.0–6.0	—	—	—	[21]
Meat	—	10.4–20.6	—	—	[18]
Meat	—	13.3–17.3	—	—	[16]
Meat	—	—	4.0–6.0	—	[13, 22, 23]
Meat	—	—	2.5–3.0	—	[18]
Milk		—	—	4.0–5.0	[13, 14]

Table 1.

Feed and water use efficiencies for sheep products.

3.2 Feed use efficiencies for sheep products

Feed use efficiency is a critical concept in livestock production and agriculture. It measures how effectively animals convert the feed they consume into a desired output, such as meat, milk, or other agricultural products. The efficiency of feed use is essential for economic and environmental reasons, as it impacts on production costs, resource utilization, and sustainability [24]. Efficiency of feed use in sheep production is vital for increasing productivity, reducing production costs, and minimizing environmental impacts. Efficient feed use is not only important for profitability in agriculture but also for reducing the environmental footprint of livestock production [20]. By optimizing feed use efficiency, farmers can produce more with fewer resources, contributing to sustainability in the agricultural industry. Efficiency of feed use in sheep production not only benefits producers by reducing costs, but also contributes to more sustainable and environmentally friendly farming practices [25]. Optimizing feed use efficiency helps ensure that sheep are productive and healthy while minimizing the resources required for their upkeep [26].

Feed conversion ratio (FCR) is a common metric that quantifies feed use efficiency in sheep. It’s calculated by dividing the amount of feed consumed by an animal by the weight gain or product yield. For example, in meat production, FCR is calculated as the amount of feed required to produce 1 kg of meat. A lower FCR indicates higher feed efficiency [27]. There are different FCR values for different sheep products as shown in Table 1. The amount of feed needed to produce a unit of meat in sheep can vary depending on several factors including the breed of sheep, age, diet, management practices, and environmental conditions. Generally, FCR values for sheep meat production range from 1.814 to 3.629 kg of feed per kg of live weight gain [19].

In dairy production, milk FCR measures the amount of milk produced per unit of feed consumed. It’s calculated by dividing the milk yield in liters or kilograms by the total feed intake in kilograms [28]. The amount of feed needed to produce a unit of milk in sheep can vary based on several factors, including the breed of sheep, their nutritional requirements, management practices, and environmental conditions [29]. On average, FCR values for milk production in dairy sheep can range from 4 to 6 kg of dry matter feed intake per kg of milk produced [21].

In sheep farming, wool FCR assesses the weight and quality of wool produced per unit of feed consumed by sheep. It considers factors such as fleece weight, fiber quality, and feed intake [30]. The amount of feed needed to produce a unit of wool in sheep is not typically measured in the same way as for meat or milk production. Wool production in sheep is influenced by various factors, including genetics, management practices, and environmental conditions [31]. Wool growth is influenced by the sheep’s overall health, age, genetics, and the quality of their diet. To maximize wool production efficiently, sheep should receive a balanced diet that meets their nutritional requirements, including adequate protein and energy [32]. High-quality forage and supplementary feeds may be necessary, especially during periods of increased wool growth, such as the late winter and early spring. Improving wool production efficiency involves optimizing the nutritional management of the flock, ensuring that sheep receive the necessary nutrients for healthy wool growth [33]. This includes monitoring the quality and quantity of forage, providing proper supplements when needed, and maintaining the overall health and well-being of the sheep. There is not a straightforward FCR equivalent for wool production because wool growth is not a direct product of feed conversion like meat or milk [34]. Instead, wool production is a result of the sheep’s overall health and nutrition, and it’s influenced by factors beyond just feed intake. Therefore, the focus in wool production is on optimizing the quality and quantity of wool produced per sheep, rather than calculating a feed conversion ratio [35].

4. Conclusion

There are many climate change stresses constraining sheep production. Climate change directly and adversely impacts on sheep production in terms of reduced quantity and quality of water and feeds, and increased animal health and husbandry challenges. Sheep with high water and feed use efficiencies can survive on less water and feed during drought periods. It is concluded that selection of sheep that have high water and feed use efficiencies per unit of sheep product can be a mitigating option against limited water and feeds due to climate change.

Acknowledgments

The authors acknowledge financial support from the University of Limpopo and the University of South Africa.

Conflict of interest

There are no conflicts of interest.