Reproductive performances of Ethiopian indigenous goat populations under different management conditions for assisting selective breeding schemes

ABSTRACT Profitable goat production is explained by an increased ratio of outputs (meat, milk, flees and skin) per production inputs (labour, feed and management costs). The productive potential of goats depends on their productive efficiency, which is associated with their reproductive rates. Moreover, the reproductive efficiency of individual breeding females determines the production potential of the flock. This paper reviewed the major reproductive performances of Ethiopian indigenous goat populations reported by several scholars under different management conditions. The evidence from the literature indicated that the reproductive performances of the Ethiopian goats ranged from 6.61 to 14.83 months, 11.82 to 28.46 months, 5.47 to 12.07 months, 1.00 to 2.15 kids and 4.72 to 10.2 years for pubertal age of females, age at first kidding, kidding interval, litter size at birth, and does’ average productive life, respectively. This indicates that there is considerable variation within and among the Ethiopian indigenous goat populations regarding the aforementioned reproductive parameters. Similarly, some reproductive traits including age at first kidding, kidding interval and litter size at birth have shown potential differences between management conditions. Hence, reproductive performances of the Ethiopian indigenous goat populations can be optimized using improved management, and within and between breed selective breeding schemes.


Introduction
Goats were among the first farm animals to be domesticated by humans (Aldridge et al. 2019;Mazinani and Rude 2020) and have a symbolic relationship with man that dates back 10,000 years (Aziz 2010;Muigai et al. 2018).Among 1003 million heads of goats in the world, 388 million heads are found in Africa (Kenfo et al. 2018).Ethiopia has 52.5 million heads of goats mainly (99%) of indigenous breeds (CSA 2021) that can be phenotypically grouped into twelve breeds and types (FARM-AFRICA 1996) and genetically into eight distinct breeds and types (Alemu 2004).Goats are primarily raised for meat, milk and dairy products, fleece and skin (Joshi et al. 2018;Muigai et al. 2018;Mazinani and Rude 2020), and have multifold socio-economic values for human populations, especially in rural and less favoured regions of the world (Skapetas and Bampidis 2016).
Goat production is efficient when there is an increased ratio of outputs or lifetime production of goats to production inputs (labour, feed and management costs).In turn, the lifetime production of goats is measured in terms of the main products obtained from them, i.e. meat, milk and fibre (Khan et al. 2019).The productive potential depends on the productive efficiency of goats (Khandoker et al. 2018), which is determined by the age at puberty, the age at first service, the age at first kidding, litter size, number of double and triple kiddings, and the weight of kids at birth (Simon et al. 2021).A high reproductive rate enhances the efficiency of goat production, which means more animals for sale as meat and a higher selection differential leading to a faster selection response (Khan et al. 2019).According to Bolacali et al. (2019), economical goat production particularly, objective production of goats for meat, milk and kids for sale, is highly influenced by the reproductive performances of goats.Hence, reproductive failure is the primary indicator of decreased flock productivity (Zewdie and Welday 2015).
Reproductive traits are fitness traits concerned with reproduction and viability (Joshi et al. 2018).In goats, the reproductive performances are considerably influenced by both genetic and non-genetic factors (Joshi et al. 2018;Bolacali et al. 2019;Mustefa et al. 2019;Suyadi et al. 2019;Zarazaga et al. 2019;Tesema et al. 2020).The breed of goat, rearing location, season, birth type, age, parity, health and nutrition are among the well-defined variables that affect goats' reproductive performances (Hasan et al. 2015;Keskin et al. 2017;Joshi et al. 2018;Luo et al. 2019. Tesema et al. 2020).Knowing the reproductive performances of goats is essential in designing an appropriate goat breeding program and for effective goat breeding management.In this regard, several scholars have reported the reproductive performances of Ethiopian indigenous goats under different management systems.Subsequently, some researchers, for instance, Dereje et al. (2015) and Zewdie and Welday (2015) reviewed some reproductive parameters of Ethiopian indigenous goats.However, the review works presented by those researchers were not exhaustive and did not incorporate some economically important reproductive parameters of goats such as the age at puberty, and the productive life of does.Above all, plentiful research outputs concerning the reproductive potential of native Ethiopian goats have been recently published.This needs timely review and documentation of the available literature regarding the key reproductive indicators of Ethiopian indigenous goats to make them easily accessible for use by researchers.Therefore, this paper aimed to review and document the reproductive potential of Ethiopian indigenous goat populations under different management conditions to aid selective goat breeding schemes in the country.

Age at puberty
Puberty is generally defined as the point of sexual development at which the animal becomes capable of reproduction (first ovulation in the female and first spermatozoa in the ejaculate of the male), but animals are not yet fully sexually mature at this stage (Hasan et al. 2015).Thus it can be defined as the time when the female goat showed the first sign of heat in her life (Khandoker et al. 2018).In female goats, the age at puberty can be described as the age of a doe showing the first estrus signs in her life, and it can be evaluated by giving close attention to the doe's behaviour towards mating (Hasan et al. 2015;Khandoker et al. 2018).Age at puberty is a major determinant factor in the lifetime productivity and reproductive efficiency of goats (Akhter 2019).The genetics of goats, the season of birth, management condition, environmental situation, availability of forages and plan of nutrition, presence of buck in the flock, birth weight and litter size at birth are among the well-defined variables that influence the timing of puberty onset in goats (Hasan et al. 2015).Shelton (1978) argued that most goats reach puberty at a relatively young age, however, there are considerable differences between genotypes.The reported average age at puberty of some Ethiopian indigenous goats under extensive management conditions is presented in Table 1.For Ethiopian indigenous goat populations under the extensive management condition, age at puberty ranges from 6.61 ± 1.23 months (Begashaw and Lemma 2017) to 14.83 ± 0.45 months (Gatew 2014) for female goats, and from 6.53 ± 1.22 months (Begashaw and Lemma 2017) to 18.61 ± 0.40 months (Tesfahun 2013) for male goats (Table 1).Khandoker et al. (2018) pointed out that female goats typically reach puberty at about 6 months of age, although some will become fertile sooner.Under the extensive management condition, doelings of Arab goats, and Oromo goats reach puberty at the age of about 7.9 ± 0.9 months and 8.3 ± 0.7 months, respectively (Sheriff et al. 2019).Debela et al. (2021)

Kidding interval
Kidding interval is the time interval between successive parturitions (two kidding) of the same doe (Suyadi et al. 2019;Hasan et al. 2015).It is one of the major components of the reproductive parameters of goats that greatly affect productivity (Deribe and Taye 2014) due to its considerable effect on goat population turnover rate and total lifetime productivity (Praharani et al. 2016).Kidding interval is highly influenced by both genetics (Praharani et al. 2016) and environmental factors i.e. nutrition and breeding practices (Abdalla et al. 2015).Begashaw and Lemma (2017) argued that the reproductive parameters of goats, more specifically the kidding interval of does and the weaning age of the kids, are significantly influenced by the feeding regimen, and management conditions of goats.In addition, Zewdie et al. (2022) also reported the kidding season, birth type and parity of does have a significant influence on the kidding interval of Arab goats.According to Zewdie et al. (2022), does kidding in the wet season, in their second to fourth parities, and those gave single birth had shorter kidding interval as compared to does kidding in cool and dry seasons, in their first parity, and those gave twin births.Table 3 shows the kidding interval of some Ethiopian indigenous goats under extensive and semi-intensive management conditions.Under the extensive management condition, from the Ethiopian indigenous goat populations, possible interkidding was observed for Abergelle goats (12.07 ± 2.73 months) (Jembere et al. 2019); whereas the shortest value was recorded for Woyito Guji goats (5.47 ± 0.96 months) (Zergaw et al. 2016).

Litter size at birth and kid mortality
Litter size or the number of kids in a litter is defined as the number of offspring produced at one birth by a doe, i.e. the number of kids per birth.The prolific characteristic of goats is influenced by genetic factors, and the doe's age when it reproduces (Adhianto et al. 2013).Besides genetic factors (the breed of the goats), the litter size of goats is affected by several factors including, age of the doe, the number of parities, birth seasons, body conformation and the total numbers of successful ovulation and embryonic mortality (Suyadi et al. 2019).In addition, Suyadi et al. (2019) also pointed out that the quantity and quality of the given feed and nutritional intake of the goats influence litter size due to its effect on body growth and reproductive hormone regulation in the animals' body.Furthermore, litter size in goats is largely influenced by ovulation rate and in turn, the ovulation rate is highly influenced by breed thus, an improvement could be achieved by selection (Hanrahan 1990).Goats commonly kid 2 kids per doe per kidding time except for some percentage of does having 3 or 4 kids per kidding (Adhianto et al. 2013).Khandoker et al. (2018) also stated the presence of single, twin or triple kidding.Abebe (2008) noted that the litter size of tropical goats varies between 1.08 and 1.75 kids with an average of 1.38 kids.The average litter size at birth of some Ethiopian indigenous goat populations reported under different management conditions is presented in Table 4.Under the extensive management system, the largest litter size at birth (2.15 ± 0.38) was reported for indigenous goats reared in the East Gojjam Zone of the Amhara region (Getaneh et al. 2022), whereas the lowest value (1.00 ± 0.170 kids) was reported for Abergelle goats (Jembere et al. 2019).The difference might be associated with agro-ecologies where these goat populations are raised, the former is reared in the mixed crop-livestock system, while the latter is raised in the semi-arid areas, which in turn is influenced by the availability, and types of feeds.Similarly, Abegaz et al. (2014) stated that some reproductive performances of goats including kidding interval, and litter size are relatively lower for Ethiopian indigenous goat populations found in arid and semi-arid areas, which is probably an adaptation to feed and water shortage.
One major factor that contributes to the low productivity of goats is early postnatal kid mortality.Early postnatal kid mortality is highly influenced by birth type (single, twins or triplets), season of birth, age of the dam, sex of the newborn kid, management condition (farmers negligence in caring for the newborn kids), kid birth weight, dam nutritional and other various forms of maternal and neonatal behaviours (Adhianto et al. 2013).Al-Dawood et al. (2020) also probed the effect of breed and kid sex on kids 'survivability.From a production standpoint, multiple births are desirable as it rises the number of kids produced per doe per unit of time thereby lowering the relative maintenance and production costs (Ensminger 2002).But, kid mortality is higher in twins/multiple births than in single births due to less milk production by the dam, insufficient to feed the newborn kids (Adhianto et al. 2013).

Productive life/stayability of does
Stayability or length of productive life (longevity/herd life) has been defined as the age of the animal or the number of lactations in the case of dairy females when it dies or it is culled (Serradilla et al. 1997;Pellerin and Browning 2012).Animals can withstand death or culling as a result of illness or reproductive failure (Pellerin and Browning 2012).In most cases, the functional longevity or length of productive life of breeding females refers to the time elapsed from the first parturition to the date of removal from the herd (Serradilla et al. 1997;Pellerin and Browning 2012).The decision of culling inefficient animals from the production cycle should be performed critically, as wrong and aggressive decisions may hinder farm profitability by rising replacement costs (El-Raghi et al. 2021).Goat production is affected by does' longevity as does with short production lives are costly due to loss of does at peak production age, biological and economical costs of young replacements, medical costs of illness, and lost salvage values in case of death (Pellerin and Browning 2012).
In addition, Pellerin and Browning (2012) stated that in goat production, a greater amount of marketable products (milk, meat and offspring) are expected to be produced by breeding females ensuring extended productive lives.Similarly, Pérez-Razo et al. (2004) pointed out that the long reproductive life of does is one of the most important components of profitable goat production.This is because, lengthening reproductive life may result in decreased replacement costs and lead to a heavier proportion of goats that is in later, high-producing kiddings (Pérez-Razo et al. 2004;Ferreira et al. 2020).Longevity or the productive life of does is influenced by several factors including, genetics, breed, herd health, management conditions and disabilities, and physical conditions associated with disease outcomes, i.e. parasitism, foot rot and emaciations   (Nugent and Jenkins 1992;Pérez-Razo et al. 2004;Pellerin and Browning 2012).In addition, the stayability of does is influenced by morphometric and type traits of goats including, body length, rump width, feet and legs soundness, udder and teat conformation traits of does (Ferreira et al. 2020).
The stayability or productive life of does from different breeds of goats under different management conditions has been reported by researchers in Ethiopia and elsewhere (Pérez-Razo et al. 2004;Pellerin and Browning 2012;Alemayehu and Kebede 2017;Ferreira et al. 2020;Getaneh et al. 2022;Yemane et al. 2022).Table 5 shows the reported average productive life of does for some Ethiopian indigenous goats managed under extensive management conditions.Under the extensive management condition, the longest productive life of does was reported for Short-Eared Somalie goats (10.2 ± 0.17 years) reared in the Siti zone of the Somali region, Ethiopia (Gatew 2014).Whereas, the shortest average productive life of does was reported for Woyto Guji goats (4.72 ± 0.08 years) reared in lowland areas of the South Omo zone, Ethiopia (Tesfahun 2013).

Conclusion
From this review, it can be concluded that under low-input management conditions, Ethiopian indigenous goat populations exhibited interesting reproductive performances.In addition, regarding the reproductive parameters, considerable variations are existed within and among the Ethiopian indigenous goat populations.The reproductive performances of Ethiopian indigenous goat populations varied across management conditions and production systems, as the highest values were recorded for goats raised in the mixed crop-livestock production system than those raised in the lowlands, which may be associated with differences in water and feed availability.Hence, improvement of the reproductive traits of Ethiopian indigenous goats can be achieved through improved management, and between and within breed selection while, considering the ecological advantages of the indigenous goat types in a particular production environment.

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

Table 1 .
Dea et al. (2019)019))talage of Arab goats, Felata goats and Gumuz goats doelings under the The age at puberty of some Ethiopian indigenous goats under the extensive management condition as reported by different scholars.Age at first kidding is defined as the age at which a doe gives birth to a kid for the first time(Abraham et al. 2019).It can be explained as a function of first pubertal age, age at first mating and conception, and successful completeness of pregnancy(Gatew 2014).It is one of the major reproductive performances of goats that indicate the overall productivity of the flock.Age at first kidding is a good indicator of sexual maturity in does and the lifetime production of does can be increased by decreasing age at first kidding(Deribe and Taye 2014).Goats' age at first kidding is highly influenced by both genetic and non-genetic factors, i.e. feeding, housing, health care, period and season of birth and other physical factors.The influence of efficient management improves a kid's birth weight thereby reducing the age at first sexual maturity and age at first kidding(Gautam et al. 2018).Abraham et al. (2019)reported that the age at first kidding of Begait goats under semi-intensive and extensive management conditions were 415.1 ± 9.01 and 444.3 ± 9.09 days, respectively.Dea et al. (2019)also reported the age at first kidding of Boer*Woyto-Guji F1 (50%) crossbred does under semi-intensive management conditions to be 12.91 ± 1.22 months, which is shorter as compared to most of the Ethiopian indigenous goats (Table2), and is influenced by the kids' birth type.

Table 3 .
The kidding interval (KI) of some Ethiopian indigenous goats under different management conditions as reported by different authors.

Table 4 .
Litter size at birth (LSB) of some Ethiopian indigenous goats under extensive and semi-intensive management conditions as reported by different scholars.

Table 5 .
The average productive life of does (PLD) for some Ethiopian indigenous goats raised under extensive management condition.