Reproductive characteristics of ethiopian indigenous sheep breeds in different production and management settings as inputs for selective breeding schemes: a review

Abstract

Reproductive traits are economically important and therefore need to be considered during designing sheep breeding and improvement programs, as it determines the efficiency of sheep production. Reproductive performance can be assessed using key performance indicators, including age at puberty, age at first lambing, lambing interval, prolificacy, productive life of ewes, and lifetime lamb crop among others. This review summarizes the findings of previous studies on the reproductive characteristics of Ethiopian indigenous sheep breeds. As evidenced by the literature, the reproductive performances in Ethiopian indigenous sheep breeds ranged from 6.35 to 17.97 months, 11.34 to 24.8 months, 6.1 to 10.46 months, 1.01 to 2.4 lambs, 5.32 to 10.53 years, and 8.18 to 17.0 lambs for female age at puberty, age at first lambing, lambing interval, litter size at birth, ewes’ productive life, and lifetime lamb crop, respectively. Notably, substantial variations exist among genotypes and management conditions. This implies that reproductive performances of Ethiopian indigenous sheep breeds can be enhanced using improved management, and between and within breed selection. However, due to the low heritability, and sex-limited nature of most reproductive traits, identifying and including the genetic bases controlling the traits in the selection programs for enhancing reproductive traits of Ethiopian indigenous sheep breeds is worthwhile.

IMPACT STATEMENT

Ethiopia has a huge and diverse indigenous sheep population to which the majority are managed by smallholder farmers in the extensive production system for multiple economic and social functions. However, production and reproduction performances are constrained by several production challenges including poor availability and quality of feed, high disease prevalence, poor infrastructure settings, absence of planned breeding programs, and low technical capacities. Reproduction traits are economically important traits that are greatly influenced by the genetics of the animal, management practices and by their interaction effects. This review summarizes the major reproductive characteristics including the age at puberty, age at first lambing, lambing interval, prolificacy, productive life of ewes, and lifetime lamb crop among others of Ethiopian indigenous sheep breeds previously reported. As a result, notable variations for the reproductive characteristics were found between genotypes and management systems implying the possibility of improving the traits through between and within breed selection and management interventions. The information presented in this paper can be utilized in the design of sheep breeding programs aimed at enhancing the reproductive performances of Ethiopian indigenous sheep breeds.

Keywords:

• Breeding schemes
• fertility traits
• indigenous sheep
• selective breeding
• reproductive performance

Reviewing Editor:

• Pedro Gonzalez-Redondo, Universidad de Sevilla, Spain

Subjects:

• Agriculture & Environmental Sciences
• Plant & Animal Ecology
• Biodiversity & Conservation

1. Introduction

Domestic sheep (Ovis aries) were among the first ruminant animals domesticated by humans in the Fertile Crescent around 12,000–10,000 years ago (Kijas et al., 2012; Stiner et al., 2022). Following domestication, sheep have been distributed worldwide, where they are reared under different environmental, management, and selection conditions that result in different sheep breeds with unique physiognomies (Deniskova et al., 2018; Dong et al., 2020). As of 2020, there are about 1,173 million sheep worldwide, with the majority found in Asia (512 million) and Africa (352 million), which together account for 73.6% of the world’s sheep population (Mazinani & Rude, 2020). According to a report by Kijas et al. (2009), there are approximately 1,400 recorded sheep breeds in the world, of which 140 variable sheep breeds are found in Africa (Ahbara et al., 2022). Broadly, African sheep populations are classified as fat-tailed and thin-tailed sheep (Deribe, Beyene, et al., 2021), with the former mainly distributed in northern, eastern, and southern Africa, while the latter are dispersed in West Africa, Morocco, and Sudan (Muigai & Hanotte, 2013). As of 2021, Ethiopia has 42.9 million sheep, mainly composed of indigenous breeds (99.52%) (Central Statistical Agency, 2021). Ethiopian indigenous sheep are categorized into 14 phenotypic breeds, which can be further classified into four groups (short fat-tailed, long fat-tailed, thin-tailed, and fat-rumped) based on their tail type (Gizaw et al., 2008), and into nine genetically distinct breeds (Gizaw et al., 2007).

In Ethiopia, almost all sheep are managed in a low-input-low-output extensive production system, with 75% of the sheep population produced in a mixed crop-livestock system, while the remaining 25% is managed in pastoral and agro-pastoral production systems (Ayele & Urge, 2019). This exposes the animals to various production challenges, such as feed shortages, diseases, poor infrastructure, low technical capacity, and the absence of planned breeding, which, in turn, lowers animal performance (Adimasu et al., 2019). Reproductive traits are economically important in sheep production and require great attention when designing breeding programs (Asmare et al., 2021). These traits determine the efficiency of sheep production, which depends on the age at first lambing, lambing interval, litter size, ewes’ productive life, and lifetime lamb crop among others (Ibrahim, 1998). Hence, understanding reproductive phenomena in sheep is crucial for effective breeding management (Assan, 2020c). In this regard, several scholars have reported on the reproductive potential of indigenous Ethiopian sheep. Compiling these reports can provide comparative and exhaustive information to users. Therefore, this review aimed to examine and document the reproductive performance of Ethiopian indigenous sheep breeds under various production and management settings to assist sheep selective breeding schemes in Ethiopia.

2. Methodology

This review is based on a comprehensive literature search conducted with the electronic databases including Google Scholar, ScienceDirect, and PubMed (last search update in April 2024) using key search terms. The search key terms used include reproductive performance of sheep, fertility traits of sheep, sheep reproduction, Ethiopian indigenous sheep breeds, factors affecting sheep reproductive performance, management conditions of sheep, production systems of sheep, and domestication of sheep. To compile this review, various sources, including research articles, review articles, book chapters, conference proceedings, and doctoral and master theses were considerd. The selection of literature for inclusion or exclusion was based on the criteria of relevance and relatedness to the topic (Snyder, 2019).

3. General description of Ethiopian indigenous sheep breeds

Since the domestication of sheep, humans have actively engaged in safeguarding, feeding, and managing their reproductive processes. This influences the behavior, morphology, physiology, and genetics of the sheep (Kijas et al., 2012; Teletchea, 2017). For instance, prior to humans selectively breeding sheep for specialized purposes such as milk and wool production, sheep were primarily raised for their meat (Teletchea, 2019). Recent genetic studies have provided evidence of artificial selection on the sheep genome, including genomic regions that harbor genes regulating horn morphology, pigmentation, reproduction, and body size (Kijas et al., 2012). Furthermore, sheep’s ability to adapt to low-quality diets, extreme environmental conditions, and their manageable size facilitates their dispersal into diverse environments (Kijas et al., 2009). These artificial and natural selections, along with other evolutionary forces, have led to the formation of diverse sheep breeds with unique genetic compositions and distinct phenotypic features (Deniskova et al., 2018).

Similarly, in Ethiopia, the significant sheep population is managed by smallholder farmers across diverse agro-ecologies, production systems, and ethnic communities. These farmers keep sheep for various economic and social purposes (Kenfo, 2021). The diversity of agro-ecologies, production systems, and sheep breeding objectives within Ethiopian societies, combined with the country’s role as a gateway for sheep migration from Asia to Africa, has resulted in the presence of diverse sheep breeds in the country, each with distinct physio-anatomical traits (Deribe, Beyene, et al., 2021). These distinct physio-anatomical traits of each sheep breed are closely linked to and attract the sociocultural and societal beliefs of the producers (Mengesha & Tsega, 2012). Gizaw et al. (2008) classified the Ethiopian indigenous sheep populations into 14 breeds, which can further be clustered into four groups: sub-alpine short-fat-tailed (Menz, Farta, Sekota, Wollo, Tikur, Semien, and Washera), highland long-fat-tailed (Adilo, Arsi-Bale, Horro, and Bonga), lowland fat-rumped (Afar and BHS), and lowland thin-tailed (Gumuz), based on their agro-ecology, geographic vicinity, tail types, and forms (Table 1). However, a molecular study using microsatellite markers by Gizaw et al. (2007), classified them into nine distinct sheep breeds. Recently, phenotypically distinct sheep breeds, including Begait, Elle (Ille), Abergelle, Doyogena, and Abera sheep breeds have also been reported (Bekele et al., 2019; Gebretsadik & Anal, 2014; Marufa et al., 2017). The description of unique phenotypic characteristics, favorable agro-ecologies, and geographic distribution of Ethiopian indigenous sheep breeds are presented in Table 1.

Table 1. Major Ethiopian indigenous sheep breeds, their favorable agro-ecology, geographical distribution, and their unique physical characteristics.

Sheep breed	Local name/s	Agro-ecologies	Geographical distribution	Unique physical characteristics of the breed	Reference/s
Sub-alpine short-fat-tailed group
Washera	Agew, Dangilla	Wet, warmer mid-highlands elevated 1 600–2000 m.a.s.l	West Gojam, East Gojam, and Awi zones, and Alefa Takusa districts of Amhara region, and Dangur and Madura districts of BGUR	Short fat-tailed sheep with large body size, short-hair, mostly brown color, and both sexes are polled. Reared by the Amhara and Agew communities.	Awgichew and Abegaz (2008), Gizaw et al. (2008), and Amane et al. (2020)
Menz	Legegora, Shoa Highland sheep Abyssinian	Sub-moist/dry, sub-alpine highlands elevating 2500–3200 m.a.s.l	Distributed in North shoa zone of the Amhara regional state	Short fat-tailed sheep with small body size; short-legs; long fleece with coarse wool; commonly Mixed colors; straight-faced; horned males; short semi-pendulous ears. Kept by Amhara community.	Awgichew and Abegaz (2008), Gizaw et al. (2008), Edea et al. (2017), and Amane et al. (2020)
Farta	Not available	Sub-moist highland elevated from 2000–2500 m.a.s.l	Spread in South Gondar zone; Gondar Zuria, Belesa, & Dembia districts of the Amhara region	Short fat-tailed with medium size; wooly undercoat; mostly white and brown colored. Males are horned. Reared by the Amhara communities.	Gizaw et al. (2008) and Amane et al. (2020)
Sekota	Tigray-highland, Abergelle Sheep	Cool, dry/sub-moist highlands 2000 m.a.s.l; semi-arid river valley	Mainly found in Wag Himra zone of Amhara national regional State and Tigray regional state	Short fat-tailed sheep with medium-size, mainly brown or white coat colors, or black with brown belly, and have semi-pendulous or rudimentary ears. Found in Wag Himra, and Tigray regional state.	Gizaw et al. (2008)
Wollo	Not available	Cold Highland with altitude range 2000–3200 m.a.s.l.	Distributed in South Wollo zone of Amhara region	Short-fat-tailed sheep with Small size, well developed wooly undercoat, mainly black, white, and brown colored, long hair. Males are horned. Reared by Amhara people.	Gizaw et al. (2008) and Amane et al. (2020)
Tikur	Not available	Sub-alpine highlands	Distributed in North Wollo zone of the Amhara national regional state	Short fat-tailed sheep with wooly undercoat, black color, small body size, short semi-pendulous or rudimentary ears. Reared by Amhara people.	Gizaw et al. (2008)
Semien	Not available	Alpine mountains areas (3000–4000 m.a.s.l.) & Semien Wildlife Park	Spread in North Gondar zone (Debark, Dabat, Janamora, Wegera) of the Amhara regional state	Short fat-tailed sheep with well-developed wooly undercoat, plain brown, plain white or plain black, and patchy (white/brown visversa) tinted. Long laterally spiral horns in males and short horns in most females, largest of the highland wool sheep. Reared by the Amhara people.	Gizaw et al. (2008) and Melaku et al. (2019)
Abergelle	Not available	Dry lowland <1500 m.a.s.l. of semi-arid agro-ecologies	Spread in Central zone of Tigray (Tanqua-Abergelle) in Tigray region	Short fat-tailed sheep. Have dark red coat color with plain pattern, striate face profile, rudimentary ears, curved horns, and medium size. Reared by Tigray and Amhara peoples.	W. G. Berhe (2020)
Highland long-fat-tailed group
Bonga	Gesha, Menit, Kaffa sheep	Humid mid-highland zone elevated from 1200–2500 m.a.s.l.	Distributed in Keffa, Sheka, and Bench-Maji Zones of the SNNPR state	Long fat-tailed sheep with straight pointing end. Have hair, large in size, mainly plain brown coat color. Both sexes are polled. This sheep breed is reared by Keffa, Sheka, and Bench Communities.	Gizaw et al. (2008) and Dolebo (2020)
Horro	Not available	Cool, wet highlands elevated 2991 m.a.s.l. to Humid mid-highlands elevated 1600 m.a.s.l.	Found in East Wellega, West Wellega, Illubabor, Jimma and West Shoa zones of Oromia region, and bordering Gambella and Benishangul districts	Long fat-tailed sheep with extending below the hocks straight or coiled/twisted end. Meat-type sheep, large leggy breed with prolific characteristics. Brown and fawn are the dominant color of the breed. Both sexes are pooled. Are reared by Oromo, Benishangule, and Gambella peoples/communities.	Awgichew and Abegaz (2008), Gizaw et al. (2008), Edea et al. (2017) and Amane et al. (2020)
Arsi-Bale	Not available	West, cool and warmer Highlands elevated 2000–3300 m.a.s.l., and in sub-moist lowlands	Arsi, Bale, East Shoa, West Hararghe, and Borena zones of Oromia, Hadiya, Gurage, Kembata and Sidama zones	Long fat-tailed sheep with twisted end. Medium size meat breed having hairy fiber, all sexes, except some females, have horns, mainly have brown, and mixed coat-color. Reared by Oromo people.	Awgichew and Abegaz (2008), Gizaw et al. (2008) and Edea et al. (2017)
Adilo	Wolaita	Wet, warmer mid-highland elevated from 1800–2000 m.a.s.l.	Distributed in North Omo, Derashie, Gedio and Amaro zones of SNNPR, and in northern Borena districts	Long fat-tailed sheep with large size; meat type, short-hair, shorthorns in males, and some females, and are mainly brown, white, grey and mixed coat-color. Reared by Wolaita/Hadiya peoples.	Gizaw et al. (2008), Edea et al. (2017) and Amane et al. (2020)
Elle (Ille)	Not available	Dry highland (1500– 3200 m.a.s.l.) cool-warm semi arid	Distributed in Southern zone of Tigray regional state (Raya-Alamata)	Long fat-tailed sheep. Have creamy coat color with plain pattern, smooth hair, concave facial profile, rudimentary ears, and are polled. The breed is dwarf in size, and are reared by Tigray peoples.	W. G. Berhe (2020)
Doyogena	Not available	Mid-heighlands 1900 to 2300 m.a.s.l. with a mean annual rainfall 1200 to 1600, and T^o 10 to 16 °C.	Distributed in Sothern Ethiopia such as Kembata Tembaro zone	Long fat-tailed sheep. Have concave facial profile, light red and red and white coat color with plain pattern, short hair, curved horns pointing backward, and horizontal and erected ears. Reared by Kembata communities in the SNNPRS, Ethiopia.	Taye et al. (2016)
Lowland fat-rumped group
Afar	Adal, Danakil	Inhabited in the arid Lowland <1000 m.a.s.l., and in mid-highland 1200–1900 m.a.s.l.	Distributed in Afar region, bordering, Tigray, Amhara; East and West Hararghe and East Shoa zones of Oromia regional state	Fat-rumped sheep with wide fat tail, hair fiber, medium size, creamy white colored, rudimentary ears, polled, dewlap. Reared by Afar, Amhara, and Tigray communities.	Awgichew and Abegaz (2008) and Gizaw et al. (2008)
Black Head Somali (BHS)	Wanke, Ogaden, Berbera black head	Arid lowlands elevated 215–900 m.a.s.l, highlands up to 2000 m.a.s.l.	Somali regional state; lowlands of Bale, Borena and South Omo zones, and part of East Hararghe	Fat-rumped sheep with a stumpy appendage, meat type, have uniform white body and black head and neck; polled, short drooping ears, dewlap. Reared by Somali, Oromo, Konso, and South Omo people.	Awgichew and Abegaz (2008), Gizaw et al. (2008) and Edea et al. (2017)
Lowland thin-tailed group
Gumuz	Not available	Inhabited moist lowlands with an elevation <1000 m.a.s.l.	Distributed in Benishangule Gumuz regional state, and lowlands of North Gondar zone of the Amhara region	Long thin-tailed sheep. Are dwarf with convex facial profile; long-pendulous ear, plain brown or patch mixed color, rear horns and wattles, and ruff on males. Reared by Gumuz and Amhara peoples.	Gizaw et al. (2008) and Abegaz et al. (2011)
Begait	Not available	Dry lowland (1500 m.a.s.l.), warm arid to semiarid area with extreme climatic condition ranging from 29 to 42 °C	Distributed in Western and North-Western zones of Tigray regional state	Long thin-tailed sheep with straight pointed end, have concave facial profile, long and laterally dropping ears, dominantly white coat color, white and black mouth, short and smooth hair, and both sexes are polled with presence of scur. Are meat and milk type sheep breed reared by Tigray peoples.	B. Amare et al. (2012), Gebretsadik and Anal (2014) and W. G. Berhe (2020)

Note: BGUR = Benishangule Gumuz Region, SNNPR = Southern Nation, Nationalities, and Peoples Region.

4. Reproductive performance of Ethiopian indigenous sheep breeds

4.1. Age at puberty/sexual maturity

By definition, puberty is the age of sexual development where animals have the capacity to reproduce and the onset of sexual activities, which are associated with the secretion of sexual hormones from the pituitary gland, resulting in increased size and activity of the gonads (Assan, 2020c). The onset of puberty in sheep can be indicated by follicular activities and ovulation in females, and the increased testicular size simultaneously with the first presence of spermatozoa in the seminiferous tubules, epididymis, and ejaculate of males (Moulla et al., 2018). During sexual maturity in sheep, noticeable anatomical and physiological changes occur, which are initiated and regulated by sexual hormones, such as estrogen in females and testosterone in males (Assan, 2020c). The influence of both genetics and environmental factors, including sheep breeds, rearing location, production system, agro-ecology, and feeding management of sheep, on the age at puberty of sheep breeds has been reported by several researchers in Ethiopia and elsewhere (Adjibode et al., 2017; T. Amare et al., 2017; Asmare et al., 2021; Hussein, 2018; Kerga, 2021; Moulla et al., 2018). Aside from their age, the attainment of puberty in sheep depends on the growth and body weight (Moulla et al., 2018).

The age at puberty of some Ethiopian indigenous sheep breeds under extensive management are presented in Table 2. Under extensive management condition, the attainment of sexual maturity for Ethiopian indigenous sheep breeds ranges from 5.12 ± 1.00 months (A. Berhe et al., 2019) to 13.65 ± 4.75 months (Ferew, 2008) for males, and from 6.35 ± 1.03 months (A. Berhe et al., 2019) to 17.97 ± 3.97 months (Ferew, 2008) for females. This indicates that BHS sheep reared in the warm arid agro-ecology of the Shinile zone in Somali exhibited a longer age of puberty in both sexes, while the shortest ages were recorded for Begait sheep managed in a mixed crop-livestock production system in Setit and Kafta Humera districts. Conversely, in a review presented by W. G. Berhe (2020), the longest ages at puberty were observed for ram lambs of Menz sheep (10.7 months) and ewe lambs of Begait sheep (9.7 months), while the shortest ages at puberty were recorded for ram lambs of BHS sheep (6.3 months) and ewe lambs of Washera sheep (6.3 months). But, all of the recorded values were fell within the range of 212 and 615 days reported for tropical and subtropical sheep (Gatenby, 1986). Variations in genetics, agro-ecologies, production systems, plane of nutrition, and birth season may contribute to the variations in the average age at puberty among sheep breeds. Dýrmundsson (1981) noted the effect of genetics, environmental factors, and their interaction on the onset of puberty in sheep.

Table 2. The age at puberty of some Ethiopian indigenous sheep breeds under extensive management condition in different production systems.

Sheep breed	Age at puberty (month)		Production system	Reference
	Males	Females
Local sheep in Bensa area	7.07 ± 0.16	7.74 ± 0.175	Crop-livestock	Kenfo et al. (2018)
Bonga	7.5 ± 2.1	9.3 ± 2.2	Crop-livestock	Edea et al. (2012)
Horro	7.1 ± 3.0	7.8 ± 2.4	Crop-livestock	Edea et al. (2012)
Menz	10.4 ± 7 3.4	Absent	Crop-livestock	Mengistu (2008)
Afar	7.10 ± 2.49	Absent	Pastoral	Mengistu (2008)
Washera	12.2 ± 0.2	6.5 ± 1.3	Crop-livestock	Asmare et al. (2021)
Gumuz	9.8 ± 0.5	7.6 ± 1.6	Crop-livestock	Asmare et al. (2021)
Local sheep in Southern Ethiopia	Absent	8.3 ± 0.10	Crop-livestock	Hussein (2018)
Begait	5.12 ± 1.00	6.35 ± 1.03	Crop-livestock	A. Berhe et al. (2019)
Local sheep in Arba Minch Zuria	7.24 ± 0.13	7.81 ± 0.14	Crop-livestock	Bekele et al. (2019)
Bonga	7.24 ± 0.13	7.81 ± 0.14	Crop-livestock	Bekele et al. (2019)
Doyogena	7.24 ± 0.13	7.81 ± 0.14	Crop-livestock	Bekele et al. (2019)
Local sheep in West Shoa Zone	8.91 ± 0.04	Absent	Crop-livestock	Neme et al. (2016)
Local sheep in Meket area	9.04 ± 0.13	10.14 ± 0.13	Crop-livestock	Demeke et al. (2020)
Local sheep in Gidan area	8.51 ± 0.13	9.83 ± 0.13	Crop-livestock	Demeke et al. (2020)
Local Wollo highland sheep	Absent	7.0 ± 0.8	Crop-livestock	T. Amare et al. (2017)
Abera sheep	7.9 ± 0.2	Absent	Crop-livestock	Marufa et al. (2017)
Black Head Somalie	13.65 ± 4.75	17.97 ± 3.97	Pastoral	Ferew (2008)
Local sheep in Gurage Zone	7.86 ± 0.15	8.11 ± 0.84	Crop-livestock	Kerga (2021)
Begait	6.90 ± 2.24	7.31 ± 2.42	Crop-livestock	Tsigab (2018)

4.2. Age at first lambing

The age at first lambing can be defined as the age at which a breeding ewe lamb can give her first birth, and it is a function of puberty, age at first mating, conception, and successful completeness of pregnancy (Kenfo, 2021). The age at first lambing is a crucial reproductive indicator in sheep, as it determines the productive life and lifetime productive yields of sheep (Hernandez et al., 2011). Age at first lambing and lambing interval are the two most important economic traits directly related to the reproductive efficiency and profitability of any sheep production business (Abdoli et al., 2019; Kasap et al., 2021). Timely breeding of ewe lambs enhances farm profitability by reducing the unproductive phase of females; however, breeding at a young age may hinder the ewe’s body development and soundness (Kasap et al., 2021). In addition to genetics, the age at first lambing of sheep is influenced by environmental factors and genotype and environment interaction, including agro-ecologies, dam parity, and season of birth (Asmare et al., 2021; Edea et al., 2012; Getachew et al., 2013).

The average age at first lambing for Ethiopian indigenous sheep breeds under extensive management condition ranges from 11.34 ± 1.30 to 23.56 ± 3.63 months for Begait sheep raised in the mixed crop-livestock production system (A. Berhe et al., 2019), and BHS sheep raised in the warm-arid agro-ecology of Shinile zone of Somalia region (Ferew, 2008), respectively. In the semi-intensive management condition, longer age at first lambing was reported for Menz sheep (24.8 ± 0.52 months) (Lemma et al., 2014) than Tumelie (15.63 ± 0.28 months) (Lakew et al., 2014), and Washera (15.66 ± 0.28 months) sheep (Mekuriaw et al., 2013). Surprisingly, yet, all the recorded values were longer than those recorded under extensive management conditions for most Ethiopian sheep breeds, including similar breeds (Table 3).

Table 3. The age at first lambing (AFL) for some Ethiopian indigenous sheep breeds in different management conditions and production systems.

Sheep breed	AFL (month)	Management condition	Production system	Reference
Tumelie	15.63 ± 0.28	Semi-intensive	Absent	Lakew et al. (2014)
Local sheep in Bensa area	12.84 ± 0.24	Extensive	Crop-livestock	Kenfo et al. (2018)
Bonga	14.9 ± 3.1	Extensive	Crop-livestock	Edea et al. (2012)
Horro	13.3 ± 1.7	Extensive	Crop-livestock	Edea et al. (2012)
Chacha local sheep	15.43 ± 0.58	Extensive	Crop-livestock	Getachew et al. (2013)
Menz	17.41 ± 0.58	Extensive	Crop-livestock	Getachew et al. (2013)
Wollo local sheep	14.47 ± 0.71	Extensive	Crop-livestock	Getachew et al. (2013)
Menz	15.67 ± 3.55	Extensive	Crop-livestock	Mengistu (2008)
Menz	21.83 ± 6.32	On-station	Absent	Getachew et al. (2015)
Afar	13.52 ± 3.05	Extensive	Pastoral	Mengistu (2008)
Washera	15.66 ± 0.28	Semi-intensive	Absent	Mekuriaw et al. (2013)
Washera	15.23 ± 0.16	Extensive	Crop-livestock	Mekuriaw et al. (2013)
Local sheep in South Western Ethiopia	13.47 ± 2.18	Extensive	Crop-livestock	Berhanu and Aynalem (2009)
Washera	11.6 ± 1.9	Extensive	Crop-livestock	Asmare et al. (2021)
Gumuz	12.5 ± 1.9	Extensive	Crop-livestock	Asmare et al. (2021)
Local sheep in Southern Ethiopia	13.6 ± 0.11	Extensive	Crop-livestock	Hussein (2018)
Begait	11.34 ± 1.30	Extensive	Crop-livestock	A. Berhe et al. (2019)
Local sheep in Arba Minch	12.81 ± 0.14	Extensive	Crop-livestock	Bekele et al. (2019)
Bonga	12.81 ± 0.14	Extensive	Crop-livestock	Bekele et al. (2019)
Doyogena	12.81 ± 0.14	Extensive	Crop-livestock	Bekele et al. (2019)
Washera	15.47 ± 0.47	Extensive	Crop-livestock	Taye et al. (2011)
Menz	24.8 ± 0.52	Semi-intensive	Absent	Lemma et al. (2014)
Local sheep in West-shoa	14.29 ± 0.08	Extensive	Crop-livestock	Neme et al. (2016)
Farta	15.71 ± 0.4	Extensive	Crop-livestock	Amane et al. (2014)
Local sheep in Meket area	16.04 ± 0.14	Extensive	Crop-livestock	Demeke et al. (2020)
Local sheep in Gidan area	15.57 ± 0.14	Extensive	Crop-livestock	Demeke et al. (2020)
Local Wollo-highland sheep	12.3 ± 0.1	Extensive	Crop-livestock	T. Amare et al. (2017)
Abera sheep	12.9 ± 0.26	Extensive	Crop-livestock	Marufa et al. (2017)
Black Head Somalie	23.56 ± 3.63	Extensive	Pastoral	Ferew (2008)
Local sheep in Alaba Zone	12.43 ± 0.10	Extensive	Crop-livestock	Talore (2009)
Local sheep in Gurage Zone	13.8 ± 0.4	Extensive	Crop-livestock	Kerga (2021)
Begait	12.40 ± 1.61	Extensive	Crop-livestock	Tsigab (2018)

4.3. Lambing interval (LI)

The interval between two consecutive parturitions of sheep is termed as lambing interval. It is one of the main components of reproductive parameters in sheep and serves as an important indicator of reproductive efficiency in a flock (Abate, 2016; Ampong et al., 2019). A shorter lambing interval provides a better opportunity to enhance ewes’ lifetime productivity by increasing the number of lamb crops per ewe (Marufa et al., 2017). Lambing interval is con­siderably influenced by several factors, such as genetics/breed of sheep, management practices, agro-ecology, season of lambing, mating management (continuous vs. controlled), nutrition, lactation, ewe parity, birth type/number of lambs in the previous lambing, and ram used for mating purposes (Ampong et al., 2019; Asmare et al., 2021; Lakew et al., 2014; Mekuriaw et al., 2013; Taye et al., 2011; Vlahek et al., 2022).

Vlahek et al. (2022) reported shorter lambing intervals for ewes with advanced parities, ewes lambing in spring and summer seasons, and for single-born ewes than for ewes at the first parity, ewes lambing in autumn and winter seasons, and multiple-born ewes, for intensively managed Romanov sheep in Croatia. Similarly, Taye et al. (2011) reported a significant influence of rearing location, year and season of birth, ewes parity, and number of lambs born in the previous lambing on the lambing interval of traditionally managed Washera ewes in Amhara region, Ethiopia. According to Taye et al. (2011), ewes born single lambs at the fifth parity and lambed during the wet season had the shortest lambing interval than their multiple born, lower parity and dry season lambed counterparts. Some of the factors (year and season of birth) influencing ewes’ lambing interval are associated with the availability of feed and nutrition planning during parturition and lactation (Ampong et al., 2019; Berhanu & Aynalem, 2009; Marufa et al., 2017; Taye et al., 2011; Vlahek et al., 2022). Other factors affecting lambing interval are related to the growth need of the ewe itself (parity), which requires a longer recovery time after lambing, and the production of more milk to feed the newborn lambs (litter size), which may require the mobilization of body reserves of the ewe lambing. These may inturn require a longer recovery time from lactation stress, and subsequent prolonged postpartum breeding and longer lambing interval (Berhanu & Aynalem, 2009; Getachew et al., 2013; Lakew et al., 2014; Taye et al., 2011).

The reported lambing intervals for some Ethiopian indigenous sheep breeds are presented in Table 4. Under extensive management condition, the minimum and maximum lambing intervals were reported for local Wollo highland sheep (6.1 ± 3.0 months) (T. Amare et al., 2017), and BHS sheep (10.46 ± 2.58 months) (Ferew, 2008), respectively. Conversely, under semi-intensive management condition, the longest lambing interval was reported for Tumelie sheep (9.57 ± 0.08 months) (Lakew et al., 2014) as compared to Washera sheep (8.77 ± 0.36 months) (Mekuriaw et al., 2013), and Menz (8.9 ± 0.28 months) sheep (Lemma et al., 2014). The impact of management conditions on the lambing interval has been reported. For instance, the lambing interval of Washera sheep in extensive management was 10.1 ± 0.34 months, while it reduced to 8.77 ± 0.36 months under the semi-intensive management condition (Mekuriaw et al., 2013).

Table 4. Lambing interval (LI) of some Ethiopian indigenous sheep breeds under different management conditions and production systems.

Sheep breed	LI (month)	Management condition	Production system	Reference
Tumelie	9.57 ± 0.08	Semi-intensive	Absent	Lakew et al. (2014)
Local sheep in Bensa area	9.59 ± 0.1	Extensive	Crop-livestock	Kenfo et al. (2018)
Bonga	8.9 ± 2.1	Extensive	Crop-livestock	Edea et al. (2012)
Horro	7.8 ± 2.4	Extensive	Crop-livestock	Edea et al. (2012)
Menz	9.0 ± 0.9	Extensive	Crop-livestock	Haile et al. (2014)
Chacha Local	8.53 ± 0.29	Extensive	Crop-livestock	Getachew et al. (2013)
Menz	8.67 ± 0.29	Extensive	Crop-livestock	Getachew et al. (2013)
Menz	13.77 ± 5.30	On-station		Getachew et al. (2015)
Wollo Local	7.57 ± 0.31	Extensive	Crop-livestock	Getachew et al. (2013)
Menz	8.50 ± 1.83	Extensive	Crop-livestock	Mengistu (2008)
Afar	9.02 ± 2.41	Extensive	Pastoral	Mengistu (2008)
Washera	8.77 ± 0.36	Semi-intensive	Absent	Mekuriaw et al. (2013)
Washera	10.1 ± 0.34	Extensive	Crop-livestock	Mekuriaw et al. (2013)
Local sheep in South Western Ethiopia	8.73 ± 1.78	Extensive	Crop-livestock	Berhanu and Aynalem (2009)
Local sheep in Ray kobo district	9.12 ± 0.50	Extensive	Crop-livestock	Deribe, Teseme, et al. (2021)
Washera	9.2 ± 3.5	Extensive	Crop-livestock	Asmare et al. (2021)
Gumuz	10.4 ± 1.2	Extensive	Crop-livestock	Asmare et al. (2021)
Local sheep in Southern Ethiopia	8.97 ± 0.01	Extensive	Crop-livestock	Hussein (2018)
Begait	6.79 ± 1.56	Extensive	Crop-livestock	A. Berhe et al. (2019)
Local sheep in Arba Minch Zuria	7.52 ± 0.08	Extensive	Crop-livestock	Bekele et al. (2019)
Bonga	7.52 ± 0.08	Extensive	Crop-livestock	Bekele et al. (2019)
Doyogena	7.52 ± 0.08	Extensive	Crop-livestock	Bekele et al. (2019)
Washera	8.95 ± 0.21	Extensive	Crop-livestock	Taye et al. (2011)
Menz	8.9 ± 0.28	Semi-intensive	Absent	Lemma et al. (2014)
Local sheep in west-shoa	8.83 ± 0.44	Extensive	Crop-livestock	Neme et al. (2016)
Farta	9.31 ± 0.34	Extensive	Crop-livestock	Amane et al. (2014)
Local sheep in Meket area	9.14 ± 0.11	Extensive	Crop-livestock	Demeke et al. (2020)
Local sheep in Gidan area	8.66 ± 0.16	Extensive	Crop-livestock	Demeke et al. (2020)
Local Wollo-highland sheep	6.1 ± 3.0	Extensive	Crop-livestock	T. Amare et al. (2017)
Abera sheep	9.6 ± 0.24	Extensive	Crop-livestock	Marufa et al. (2017)
Black Head Somalie	10.46 ± 2.58	Extensive	Pastoral	Ferew (2008)
Local sheep in Alaba	9.19 ± 0.08	Extensive	Crop-livestock	Talore (2009)
Local sheep in Gurage zone	8.3 ± 0.17	Extensive	Crop-livestock	Kerga (2021)
Begait	6.94 ± 2.07	Extensive	Crop-livestock	Tsigab (2018)

4.4. Litter size at birth

Litter size, or the number of lambs born in a litter, is defined as the number of offspring produced at one birth by ewe lambing or the number of lambs born (alive or dead) per lambing event (Mchugh et al., 2016). In sheep, ovulation rate and litter size are important reproductive parameters with high economic values, as they are crucial factors for efficient sheep production (Abdoli et al., 2016). Prolificacy/litter size, fertility/number of lambings per year, and fecundity/number of lambs produced per year are among the measures of the reproductive ability of sheep (Abdoli et al., 2016). Reproductive traits in sheep, such as fertility, have low to moderate heritability estimates and selection based on phenotype, and estimated breeding values (EBVs) derived from them may no longer improve the traits. Hence, the inclusion of genetic information of genes linked with fertility traits may efficiently enhance selection responses (Abdoli et al., 2016). In economical sheep production, litter size is a key reproductive trait as it regulates both reproductive and productive traits (Assan, 2020b). Among the productive traits, litter size affects birth weight and subsequent lamb growth (Assan, 2020a; Hagan et al., 2014; Kramarenko et al., 2021), lamb survivability (Abdelqader et al., 2017; Assan, 2020b; Getachew et al., 2015; Mchugh et al., 2016), and milk yield and composition (Assan, 2020b).

Litter size and prolificacy in sheep are greatly affected by several genetic and non-genetic factors. Sánchez-Dávila et al. (2015) reported a significant effect of ewes parity, year of birth, and type of breeding ram on the litter size of Saint Croix hair sheep raised under semi-arid condition in Mexico. Similarly, Đuričić et al. (2019) reported the effects of environmental temperature, rainfall, and season on litter size and other reproductive traits of Romanov sheep in the continental part of Croatia, as the highest litter size was recorded for ewes lambed in winter (January-February). Schmidová et al. (2016) also reported a considerable influence of ram use on the litter size of their mates in a highly prolific Romanov breed of sheep, and concluded that there is a possibility of enhancing litter size through direct selection of the service ram effect. Substantial effects of breed, birth year, postpartum ewes’ body weight, agro-ecology, and rearing location have been reported for Ethiopian sheep breeds (Asmare et al., 2021; Bekele et al., 2019; Taye et al., 2011). Conversely, some studies have reported a non-significant effect of parity, season of birth (Lakew et al., 2014; Mekuriaw et al., 2013; Taye et al., 2011), breed (Lakew et al., 2014), management, and birth year (Mekuriaw et al., 2013) on litter size of some sheep breed in Ethiopia.

The average litter sizes at birth for some Ethiopian indigenous sheep breeds under diverse management conditions are presented in Table 5. Under extensive management condition, the smallest litter size at birth has been reported for local sheep in Raya Kobo district (1.01 lambs) (Deribe, Teseme, et al., 2021), while the corresponding highest value was recorded for Washera sheep (2.4 ± 1.5 lambs) raised in the mixed crop-livestock production system (Asmare et al., 2021). The litter size of Washera sheep in extensive management surpasses that of semi-intensively managed Romanov sheep (1.61 lambs) in Croatia (Đuričić et al., 2019). However, under semi-intensive management condition, the smallest litter size at birth was recorded for Washera sheep (1.03 ± 0.01 lambs) at Adet research center (Mekuriaw et al., 2013), while the highest litter size at birth was reported for Horro sheep (1.16 ± 0.01 lambs) at Debreberhan sheep research station (Berhan & Arendonk, 2006). Almost all the values reported under semi-intensive management condition were below the values reported under extensive management condition (Table 5). It contradicts the assumption that improved management induces multiple births. The dis­crepancy may be attributed to inappropriate or inconsistent concentrate supplementation of the breeding flock, which may result in the breeding ewes maintaining a poor body condition score (BCS) that is not within the range of 3-3.5 (Vatankhah et al., 2012).

Table 5. Litter size at birth (LSB) of some Ethiopian indigenous sheep breeds under different management conditions and production systems.

Sheep breed	LSB (number)	Management condition	Production system	Reference
Tumelie	1.18 ± 0.02	Semi-intensive	Absent	Lakew et al. (2014)
Local sheep in Bensa area	1.25 ± 0.24	Extensive	Crop-livestock	Kenfo et al. (2018)
Washera	1.03 ± 0.01	Semi-intensive	Crop-livestock	Mekuriaw et al. (2013)
Washera	1.05 ± 0.09	Extensive	Crop-livestock	Mekuriaw et al. (2013)
Horro	1.16 ± 0.01	Semi-intensive	Absent	Berhan and Arendonk (2006)
Menz	1.14 ± 0.01	Semi-intensive	Absent	Berhan and Arendonk (2006)
Local sheep in South-western Ethiopia	1.21 + 1.45	Extensive	Crop-livestock	Berhanu and Aynalem (2009)
Local sheep in Raya-kobo	1.01	Extensive	Crop-livestock	Deribe, Teseme, et al. (2021)
Washera	2.4 ± 1.5	Extensive	Crop-livestock	Asmare et al. (2021)
Gumuz	1.7 ± 0.6	Extensive	Crop-livestock	Asmare et al. (2021)
Begait	1.33 ± 0.47	Extensive	Crop-livestock	A. Berhe et al. (2019)
Local sheep in Arba Minch	1.50 ± 0.08	Extensive	Crop-livestock	Bekele et al. (2019)
Bonga	1.5 ± 0.08	Extensive	Crop-livestock	Bekele et al. (2019)
Doyogena	1.5 ± 0.08	Extensive	Crop-livestock	Bekele et al. (2019)
Washera	1.19 ± 0.02	Extensive	Crop-livestock	Taye et al. (2011)
Local sheep in West-shoa	1.19 ± 0.42	Extensive	Pastoral	Neme et al. (2016)
Farta	1.08 ± 0.01	Extensive	Crop-livestock	Amane et al. (2014)
Abera sheep	1.5 ± 0.003	Extensive	Crop-livestock	Marufa et al. (2017)
Horro	1.34 ± 0.01	On-station	Absent	Abegaz et al. (2002)
Tumelie	1.09 ± 0.01	Semi-intensive	Crop-livestock	Tesema et al. (2020)
Local sheep in Alaba zone	1.51 ± 0.04	Extensive	Crop-livestock	Talore (2009)
Local sheep in Gurage zone	1.49 ± 1.15	Extensive	Crop-livestock	Kerga (2021)

4.5. Productive life of ewes and lifetime lamb crop

The productive life/longevity of an ewe is a trait of great economic interest in sheep farming due to its potential to reduce the rate of culling and costs of replacement for breeding females (Abdelqader et al., 2012; Mclaren et al., 2020). The productive life/longevity of an ewe can be defined as the age of the ewe (in years) at the last recorded lambing event (Mclaren et al., 2020), or it is the number of days between the first lambing of the ewe and its culling or death (Abdelqader et al., 2012). In sheep farming, increasing functional longevity not only reduces the need to carry non-productive replacement, but also limits costs due to health problems in animals (Milerski et al., 2018). Furthermore, ewe’s longevity plays a considerable role in the economics of sheep production as the number of lambings, and the number of lambs per sheep is increased with the extended productive life of ewes (Kern et al., 2010). Ewes’ longevity is a lowly heritable, and sex-limited trait (Lee et al., 2015; Scholtens et al., 2018), which is expressed later in life and is hence difficult to quantify in young animals (Milerski et al., 2018).

The longevity or productive life of ewes are considerably influenced by various genetic and environmental factors, in addition to management decisions (Milerski et al., 2018). For instance, Kern et al. (2010) reported a significant (P < 0.001) effect of breed, farm, age at first lambing, and number of lambs on the length of productive life of ewes in the German Whiteheaded Mutton, German Blackheaded Mutton, Texel, and Suffolk sheep breeds in northern Germany. According to Kern et al. (2010), a shorter age at first lambing (<395 days) was associated with the lowest relative culling risk (0.56). In a separate study, the influence of genetics, location and year of birth, weaning weight, smaller live weight, poor body condition score (<2.0), fluctuation in environmental weather conditions, parasite burden, and fly strike on the mortality of adult ewes (∼660 days) managed under extensive Australian conditions was reported (Doughty et al., 2018). In addition, Mclaren et al. (2020) observed the effect of breed and production systems on ewes’ longevity on sheep farms in Ireland, Norway, and the UK and concluded that the application of a specific solution to select ewes for a longer productive life in different sheep flocks. Likewise, the substantial influence of prolificacy, prior protein gene (PrP) haplotype, muscularity, and back-fat thickness on ewes’ longevity have been reported for Suffolk sheep in the Czech Republic (Milerski et al., 2018). Furthermore, ewes’ parity, litter weight at weaning age, and year were found to significantly affect ewes’ longevity in Ethiopian sheep breeds under on-station (Menz sheep) and on-farm (Awassi × Menz sheep) management conditions (Getachew et al., 2015).

The average productive life of ewes and the number of lamb crops per ewe lifetime for some indigenous Ethiopian sheep breeds are shown in Table 6. Under extensive management condition, the longest productive life was reported for local ewes raised in West Shoa zone (10.53 ± 1.32 years) (Neme et al., 2016) whereas, the shortest value was reported for Washera ewes’ (6.6 ± 1.8 years) raised in the mixed crop-livestock production system in Northwest Amhara (Asmare et al., 2021). Conversely, shorter productive life of ewes was reported for Menz sheep (5.32 ± 2.10 years) under on-station condition (Getachew et al., 2015). Regarding lifetime lamb crop, the highest value was reported for Local sheep in Gurage zone (17.0 ± 0.4 lambs) (Kerga, 2021) whereas, the smallest number of lambs per ewe’s lifetime has been reported for BHS sheep (8.18 ± 2.27 lambs) (Ferew, 2008). The lifetime lamb crops of some Ethiopian sheep breeds were not consistent with their productive life, as some of the sheep breeds, typically those raised in the mixed crop-livestock production system, have delivered a high number of lambs within a short period of ewes’ productive life, which may be associated with either the prolific nature of the sheep breeds or their management conditions (Table 6).

Table 6. The average productive life of ewes, and the number of lamb crops per ewe’s lifetime of some Ethiopian indigenous sheep breeds under extensive management condition.

Sheep breed	PLE (year)	LTLC (number)	Management condition	Production system	Reference
Local sheep in Bensa area	8.1 ± 0.11	8.69 ± 0.185	Extensive	Crop-livestock	Kenfo et al. (2018)
Bonga	7.45 ± 2.73	12.2 ± 1.80	Extensive	Crop-livestock	Edea et al. (2012)
Horro	7.91 ± 3.10	15.3 ± 4.3	Extensive	Crop-livestock	Edea et al. (2012)
Menz	Absent	9.31 ± 2.56	Extensive	Crop-livestock	Mengistu (2008)
Afar	Absent	12.06 ± 4.29	Extensive	Pastoral	Mengistu (2008)
Washera	6.6 ± 1.8	12.2 ± 4.5	Extensive	Crop-livestock	Asmare et al. (2021)
Gumuz	6.7 ± 1.4	9.8 ± 2.7	Extensive	Crop-livestock	Asmare et al. (2021)
Begait	7.71 ± 1.87	14.54 ± 3.53	Extensive	Crop-livestock	A. Berhe et al. (2019)
Doyogena	9.8 ± 0.16	11.7 ± 0.30	Extensive	Crop-livestock	Bekele et al. (2019)
Local sheep in West-shoa	10.53 ± 1.32	Absent	Extensive	Crop-livestock	Neme et al. (2016)
Local sheep in Meket area	7.46 ± 0.01	8.92 ± 0.14	Extensive	Crop-livestock	Demeke et al. (2020)
Local sheep in Gidan area	7.72 ± 0.08	9.77 ± 0.11	Extensive	Crop-livestock	Demeke et al. (2020)
BHS sheep	9.12 ± 1.6	8.18 ± 2.27	Extensive	Pastoral	Ferew (2008)
Local sheep in Gurage zone	Absent	17.0 ± 0.4	Extensive	Crop-livestock	Kerga (2021)
Menz	5.32 ± 2.10	Absent	On-station	Absent	Getachew et al. (2015)
Begait	8.28 ± 1.88	11.78 ± 3.92	Extensive	Crop-livestock	Tsigab (2018)

Note: PLE: productive life of ewes; LTLC: lifetime lamb crop.

5. Conclusion

Ethiopia is home to a vast sheep population that possesses a diversified gene pool. These sheep populations are managed by different ethnic communities within diverse agro-ecologies and production systems for multiple economic and social uses. This situation creates social and geographical barriers to gene flow among the sheep populations. Consequently, phenotypically variable sheep subpopulations that were not previously recognized, have been developed in the country over time. This review also indicate that the reproductive chracteristics of Ethiopian indigenous sheep breeds varied within and between the sheep breeds, as well as across different management conditions. Therefore, the reproductive characteristics of Ethiopian indigenous sheep breeds can be improved through management intervention, and within and between breed selection. However, most of the reproductive traits are lowly heritable, sex-limited, and traits that can be expressed later in the animal’s life, which makes it difficult to quantify these traits in young animals and to apply direct selection to the traits. This calls for the need to identify and include the genetic bases of the traits in the selection decisions to enhance the reproductive characteristics of Ethiopian indigenous sheep breeds.

Authors’ contributions

MG: Conceptualized and designed the review, did all of the necessary literature searches, and drafted the paper, MT: Conceptualized and designed the review, and revised the paper critically. KA, AH, and TG: Revised the paper critically. All authors have been approved the final version of the paper to be published, and agreed to be accountable for all aspects of the work.

Acknowledgments

The authors acknowledge the Ethiopian Ministry of Education for supporting the first author in attaining his Ph.D. study.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

Data sharing is not applicable to this article as no new data were created or analyzed in this review.

Additional information

Funding

This work was supported by the Ministry of Education of Ethiopia.

Notes on contributors

Mezgebu Getaneh

Mezgebu Getaneh, the first author, is a Ph.D. student in Animal Genetics and Breeding at Bahir Dar University, Ethiopia. He is working his Ph.D. thesis research on the phenotypic characteristics, genetic bases and economic values of reproduction traits in Ethiopian indigenous sheep breeds. His research interest include genetics, molecular animal breeding, the economics of livestock production traits, phenotypic and molecular characterization of economically important animals, and performance evaluation and improvement of livestock.

Mengistie Taye

Mengistie Taye (PhD) is an Associate Professor of Agricultural Biotechnology at Bahir Dar University, Ethiopia.

Kefyalew Alemayehu

Kefyalew Alemayehu (PhD) is a Professor of Animal Genetics and Breeding at Bahir Dar University, Ethiopia.

Aynalem Haile

Aynalem Haile (PhD) is a Principal Scientist at the International Center for Agricultural Research in the Dry Areas (ICARDA), Addis Ababa, Ethiopia.

Tesfaye Getachew

Tesfaye Getachew (PhD) is a Researcher of Animal Genetics and Breeding at the International Center for Agricultural Research in the Dry Areas (ICARDA), Addis Ababa, Ethiopia.