Some Genetic and Non-Genetic Factors Influencing Fertility of Different Sheep Breeds In Highland of North-Shewa, Ethiopia
Small ruminant specially, sheep are important for the subsistence, economic and social livelihood of small holder farmers in the developing countries and those residing in highlands of Ethiopia are no exception (Solomon et al., 2013; Mueller et al., 2017).Traditionally the sheep were/are selected for their adaptive traits which compromised with their productive, reproductive functions and existing environment (Solomon et al., 2008; Kosgey and Okayo, 2007). The overall improvement of the livestock is best sustained through within breed selection (Kosgey and Okeyo, 2007; Solomon et al., 2009, 2011; Philipson et al., 2011). However, the genetic improvement through within breed selection are a slow and tedious process and the other method of improvement can be through crossing them with some improved breeds (Solomon and Tesfaye , 2009; Tesfaye et al., 2013, 2016). Crossbreeding by using fast growing temperate sire lines has been suggested as rapid ways of breed improvement and such programs have been initiated in the past in many parts of the tropics and Ethiopia being no exception. These projects were initiated to improve the production and reproduction traits among the indigenous genotypes. However over the years several attempts of crossbreeding have not met with their appropriated goals as the introduced breeds were not adapted to the prevailing agro climate/s (Philipsson et al., 2011). The performance of the crossbreds at the farmers end are much below what was obtained on station studies , the traits which are adversely influenced were those associated with fertility (Tesfaye et al., 2013). In Ethiopia several exotic sheep breeds have been introduced over decades and Debre Birhan Agricultural Research Station had been established as the focal station for sheep research. Awassi breed was among the sheep breeds which were introduced from Israel in the year 1980, 1984 and 1994. They were introduced with an aim to improve the body weight of the Menz sheep (Rummel et al., 2005). Studies by Tesfaye et al., (2016) have indicated that the fertility among the Awassi rams reared in Ethiopia was lower than those reported from many Middle Eastern countries (Galal et al., 2008). Findings of a study by Solomon et al., (2007) indicated that there are around 14 breeds of sheep in Ethiopia, with within breed variations for most of the economical traits. The nicking ability of the Menz and Wollo ewes with those of Awassi rams have being studied (Solomon and Tesfaye, 20009; Tesfaye et al., 2013, 2016). Menz and Wollo ewes are small sized besides that they are poorly prolific (Solomon &Tesfaye, 2009; Tesfaye et al., 2013). The aim of selecting the Menz sheep was to access the within breed variations for improving their body weight (Solomon et al., 2008, 2009). The selection of the rams was based on their fitness which in turn is influenced by inbreeding, fertility and survival related traits among the closed nucleus flock (Solomon et al., 2013). The major challenges in the process of selection include identification of the genetically superior breeding stock (rams and ewes) and estimating the response to selection based on their breeding values of the trait of importance (Solomon et al., 2011). However, the underlying bottlenecks of the same are the difficulties associated with recording of the performance and reproduction related parameters of the animals themselves or their ancestors or progenies (Tesfaye et al., 2013). Besides the pedigree of these animals, which in most of the cases are not formally maintained by the reared or sometimes are remembered through recall methods thereby compromising on the quality of the data (Solomon et al., 2014). Studies by Petrovic et al., (2012) have indicated that the fertility related traits are lowly heritable and hence can be improved only through improving their management. Thus, in order to improve the weight of the Menz sheep raised in the Central highlands of Ethiopia it was decided to upgrade them using Dorper (from South Africa) and Awassi (from Israel). The introduced sheep breeds were reared at two government ranches, Debre Birhan Sheep Breeding and Multiplication Center (DBSBMC) and Amedguya Sheep Breeding and Multiplication Center. Presently nucleus stock of Awassi sheep are being maintained at these ranches with an aim to maintain the pure stock besides the crossbreeds are also being developed with Menz ewes as dam lines. The performances of these crossbreds are evaluated vis-a-vis those of the Menz sheep for traits such as yearling weight, survival and fertility (Solomon and Tesfaye, 2009; Tesfaye et al., 2016). However, it has been recorded in several studies that the fertility of the crossbred rams ( Awassi♂ x Menz♀) are/were lower when compared to their Menz counter parts (Tesfaye et al.,2013,2016). However, it was also recorded that the lambs born from the crossbreds Awassi ♂x Wolo ♀had better nicking abilities and had heavier body weights vis-a-vis those of the dam lines (Tesfaye et al., 2013, 2016) On farm and on station performances have indicated that the F1 (Awassi ♂x Menz♀) was much below the expectations with respect to their fertility traits which varied across the studied locations (Tesfaye et al., 2013). The values for the fertility traits for the Awassi rams were significantly lower than those reported from the Middle Eastern countries (Mohammed et al., 2006; Galal et al., 2008). Overall conception rate of the ewes are fallout of several hormonal attributes of both the sexes. Among the functions associated with the conception of the ewes are those associated with the semen related traits of the rams themselves besides several genetic and non-genetic factors (Foote, 1964; Duguma et al., 2002; Al-Samarrae, 2009; Tejaswi et al., 2016). Among the same are the various semen components viz. mass motility or individual motility of the sperms, acrosome integrity, the size of head, mid piece, length of the trail and other morphological functions associated with the same (Salhab et al.,2003, Ababneh et al., 2017) .The overall component of the semen and their fertilizing capacity is influenced by several genetic and non-genetic factors the latter being more important as the fertility traits are lowly heritable (Salhab et al., 2003; Mohammed, 2006; Casao 2010; Babiker, 2010). Studies by Yavarifard et al., (2015) have indicated that the fertility is also influenced by inbreeding among the flock, where the inbred rams have low fertility when compared to their non-inbred counterparts. Findings by Shamir et al., (2010) have indicated that inbreeding among Awassi sheep of the Ein Harod flock resulted in day blindness reared in Israel. Evaluating the performance of the traits particularly those related to fertility of different indigenous and exotic breeds of rams at each stage is impudent. Reproductive performance is one of the factors which determine the efficiency of the production among the sheep flock/s in the cool highlands of north Shewa, Ethiopia. In the region mentioned ahead sheep production is important as a means of livelihood and thus selection of rams’ breeds on the reproduction trait and pedigree record is essential in sheep breeding program.