Genetic and non-genetic effect on fertility trait of different ram breeds reared in the highland of North-Shewa, Ethiopia

Shenkute Goshme, Sandip Banerjee¹, Mourad Rekik², Aynalem Haile² and Tesfaye Getachew²

Debre Birhan Agricultural research center P O BOX 112, Debre Birhan Ethiopia
shenkutegoshme@yahoo.com
¹ Hawassa University, Collage of Agriculture, P O Box 05, Hawassa, Ethiopia
² International Centre for Agricultural Research in the dry Areas (ICARDA), Addis Ababa, Ethiopia

Abstract

The aim was to investigate genetic and non-genetic factors influencing fertility of rams. The fertility study encompassed 155 rams of different breed mated to 14,357 ewes over several years, seasons, locations and genotypes. Data were obtained from Amedguya Sheep Breeding and Multiplication center (ASBMC), Debre Birhan Sheep Breeding and Multiplication center (DBSBMC). The influences of genetic and non-genetic factors on fertility trait of the rams were analyzed using non-parametric tests. Animal model were used for the estimation of genetic parameters using WOMBAT^®. The fertility rate of Awassi, Awassi x Menz, Menz and Dorper rams were 45.4, 53.4, 84.8 and 70.6% respectively. Fertility rate among the Menz rams was not influenced by season, contrary to the Awassi, Awassi x Menz and Dorper rams. Heritability estimates for fertility of Awassi, rams were 0.1. It can be concluded that, Awassi rams and Awassi x Menz crossbred had lower fertility across seasons and location studied. These indicated that further investigation would be needed to identify the cause of low fertility in Awassi breed.

Key words: fertility, heritability, Awassi, Menz, Dorper

Introduction

Sheep are the most important for the subsistence, economic and social livelihood of small holder farmers in the developing countries and those residing in the highlands of Ethiopia are no exception. However available indigenous sheep breeds are unimproved, less productive and reared under traditional system. Genetic improvement within the existing livestock can be achieved either through within breed selection (which is a very slow process) or through crossing the native breeds with exotic breeds which are fast growers and have a higher production capacity. Crossbreeding by using fast growing temperate sire lines with local breeds has been considered as fast way of genetic improvement and widely used in developing countries. Many breeds like Merino, Romney, Hampshire, corriedale, Awassi and Dorper were imported in Ethiopia since 1940s. However, over the years many attempts of crossbreeding in tropical developing countries have not met with their desired goals as the introduced breeds were not fitting to small holder situation (Getachew et al 2016), unable to adapt the prevailing agro climate (Philipsson et al 2011) and lack of proper crossbreeding plan. Awassi and Dorper are still in use in Ethiopia while the remaining introduced breeds were destocked in different times. Awassi sheep was introduced from Israel in the year 1980, 1984 and 1994, with an aim to improve the meat and coarse wool production of the Menz sheep (Rummel et al 2005). Studies by Getachew et al (2016), have indicated that the fertility among the Awassi rams reared in Ethiopia is lower than those reported from many Middle Eastern countries (Galal et al 2008). The performances of these crossbreds are evaluated regarding to those of the Menz sheep for yearling weight, survival and fertility traits (Gizaw and Getachew, 2009; Getachew et al 2016). However, it has been reported that the fertility of the crossbred rams (Awassi_♂ x Menz_♀) was lower than Menz purebred rams (Getachew et al 2013).

Studies reported by Yavarifard et al (2015), have indicated that fertility is also influenced by inbreeding among flocks, 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. The productivity of the farmers is much more dependent upon how well adapted and how productive the ewes are than the rams. It is the ewes more than the rams that determine the conception rate, how many lambs will be born, and whether the lambs get started off with a good milk supply. Increasing the number of lambs marked per ewe per year is major way to improve the efficiency of meat production in sheep. Evaluating the performance particularly, related to fertility of different indigenous and exotic ram breeds at each stage is essential. 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. As the fertility traits are lowly heritable the non-genetic factors influencing the traits need to be identified to improve the fertility among the flock (Petrovi et al., 2012). Differences in fertility have been reported between rams within a breed and among rams of same age between breeds. The overall fertility levels in rams are a culmination of both genetic and non-genetic factors Therefore the objective of the study was to assess the causes associated with the fertility trait of the rams of different genotypes reared in the study areas.

Material and methods

Description of the study area and breeding program

The study was conducted at Amedguya and Debre Birhan in the cool highland of North Shewa, Ethiopia. Debre Birhan was located at latitude of 9 ^ᵒ 36’N and longitude 39^ᵒ 38’E. The area is located at 130 km northeast from Addis Ababa with the altitude of 2780m above sea level and the mean annual rainfall of the area ranges from 781-1279mm and the minimum and maximum temperature were 7.3ᵒc and 23.7ᵒc respectively and relative humidity 68% (center data). Amedguya was located at 315 km from Addis Ababa with the altitude of 2970m above sea level and the mean annual rainfall of the area ranges from 900-100mm.The climate for both location was characterized by bimodal rainfall consists of long rain season (June-September), short rain season (February-May) and dry season (October-January) (Fekadu, 2015).

Animals and their management

A total of 155 rams of different breed were used to assess their fertility and estimate genetic parameter for fertility trait. Fertility of the rams was defined as the percentages of ewes conceive among the total numbers of ewes in the flock. The genotypes of the rams evaluated were Awassi, Menz, Awassi x Menz and Dorper whereas the genotypes of ewes were Awassi, Menz, 50% Awassi x 50% Menz and 75% Awassi x 25% Menz. The fertility of the rams was assessed from the data collected of a total of 14357 ewes mated to the 155 rams. The genotype of ewes were 9464 Menz, 3388 50% Awassi x 50%menz, 344 washera, 616 Dorper, 171 Awassi x Menz (75%), 161 Pure Awassi and 212 Bonga, whereas genotype of rams were 85 pure Awassi, 25 Menz, 20 Dorper and 18 Awassi cross Menz. The body condition score of the ewes were 2.5-3.5 and the age of the ewes also 1.5-6 years old. The average number of ewes per mating pen per rams was 30 ewes and they stay in mating pen for two estrus cycle of ewes. The data were obtained from Amedguya Sheep Breeding and Multiplication center (ASBMC), Debre Birhan Sheep Breeding and Multiplication center (DBSBMC) and DBARC. The data pertains to several years which varied across the genotypes while for Awassi rams the data pertained to records from 2001-2016 whereas for Menz and Dorper 2010-2016 and 2012-2016 respectively.

Data from Awassi rams breed were used for genetic parameter estimation. The structure of data used for genetic parameter estimation included pedigree data (animal identification number, sire, dam), fixed effects (year of birth, season of birth, sire breed, ewe breed and location) and a dependent variable (ram fertility). The feeding of animals was depending up on the availability of natural grazing land. This means that the grazing land during long rainy season is covered with a variety of forages species like clover and local lotus, in this time there is no supplementation for the sheep. Supplementary feed (commercial concentrate and hay) were provide during dry and short rain seasons while they were not feeding their animal during long rain seasons. Feeding activities were based on the age, sex and weight of animals.

Statistical Analysis

Ram fertility was analyzed using FREQ procedure of SAS software (SAS Institute, 9.0). Testing the relationship and association between breed and fertility was using chi-square test. Genetic parameters for fertility were estimated by restricted maximum likelihood (REML) procedure and single animal model using WOMBAT software (Meyer, 2007).

Conception rate was recorded repeatedly for each Awassi sire. A repeatability animal model was employed to estimate genetic variance components for Awassi rams.

The repeated measurement animal model used to estimate variance components was

Y_i = X_ib_i + Z_ia_i + Wpe_i+e_i

Where Y_{i =} is a vector of observations,

b_i= is a vector of fixed effects for trait i (year, season, location and ewe breed),

a_i= is a vector of random animal effects for traiti,

pe_i= is permanent environmental effects for trait i and non- additive genetic effect

e_{i =} is a vector of residual effects for trait i,

X, Z, W= incidence matrix of relating records to fixed, animal and permanent environmental effects, respectively. Note that the vector ai only include additive random animal effects consequently, non-additive genetic effects are included in the pe term. It is assumed that the permanent environmental effects and residual effects are independently distributed with means of zero and variance σ²_pe and σ²_e , Respectively. Heritability and repeatability were estimated based on

Where,   σ²_ɑ   = additive genetic variance, h² = heritability, r = repeatability,

σ²_p = phenotypic variance, = permanent environmental variance,

σ²_e = residual variance

Results

Rams breed effect on conception rate of ewes

Means of seasons and breed on conception of ewes are presented in Table 1. There was a difference (p<0.001) in fertility in overall mating seasons. Long rainy season had higher conception (p< 0.001) across all the genotypes than the dry and short rainy seasons. The results indicate that the fertility was highest (p <0.05) among the Dorper rams during the long rainy season with the values being lowest among the Awassi rams x Menz ewes. The study further indicates that during the dry and short rainy season the fertility of the Menz rams were higher than the Awassi and Dorper rams. When we compare the effects of seasons across the genotypes it transpires that the value for the Awassi rams were lower across seasons i.e. from Long rain to dry, the A x M rams had lower fertility during the long rains while the values improved during the short rainy season. Among the Menz rams there were no differences in fertility across the seasons, while there was a sharp decline (p<0.05) in the fertility of the Dorper rams across seasons from long rain to the short rain.

Effect of season and location on fertility of Awassi rams

Means of Awassi ram’s on conception of ewes in different location and season are presented in Table 2. It transpires from the study that there are differences across seasons (p<0.05) in the fertility of the Awassi rams reared in the two locations. The study shows that at Debre Birhan and Menz district the fertility was higher (p<0.05) in the long rainy season while it was lowest during the short rainy season. The results also indicate that the fertility was higher at Debre Birhan (during the long rainy season), while the reverse was true during the other two seasons.

Fertility of Awassi rams in different ewe breeds

Means of ewe breeds on conception of by using Awassi ram are presented in Table 3. The results indicate that there were no differences in conception across the genotypes (of the ewes) when it came to nicking with the Awassi rams.

Estimation of genetic parameters influencing the fertility traits of Awassi ram

Estimate of variance components and genetic parameters influencing the fertility of the rams are presented in Table 4. The results indicate that the estimated additive genetic variance and phenotypic variance of the rams was very low. The result further indicates that environmental factors were 0.05 which indicating their adaptability towards the studied areas. Repeatability and heritability of this trait was 0.38 and 0.1 respectively.

Discussion

The results in the present study show that the conception of the ewes varied by breed group which can be ascribed to several factors the quality of the semen of the rams (Afolayan et al 2014). The differences in conception of the ewes mated to the Awassi rams too varied across the locations, which can be ascribed to the genotype by environment interaction and the status of the ewes mated to the rams (David et al 2015). The genetic variation relating to fertility of rams was recorded and the capacity of fertilizing varied across the genotypes Menz (84.85%), Dorper (70.62%), Awassi x Menz (53.36%) and Awassi (44.11%). The findings also indicated that the fertilizing capacity of the Awassi rams (irrespective of the locations) was below the 45.44% reared at in Debre Birhan ranch and 43.38% reared at Amedguya (Menz) ranch. The findings indicative of the low fertility of the Awassi rams which is in close accordance with the findings of Getachewe et al (2013). The low fertility of Awassi rams may be attributed to inbreeding within the flock. Awassi breeds were highly inbred when compared to Menz sheep, which ranged between 1 to 2.6 % (Getachew et al 2015). High inbreeding within the Awassi flock too has been reported by Shamir et al. (2010) who observed that inbreeding resulted in day blindness among Awassi sheep flock at EinHarod. Studies by David et al (2015) indicated correlation between fertility of rams and fecundity of ewes, which indicated that there was strong correlation between spermatozoa motility and fecundity of ewes and mass motility and is also associated with fertility.

The conception of the ewes mated to rams of the different genotypes varied across the season which can be attributed to temporary environmental effect on the levels of testosterone and spermatogenesis. Studies by William and Walker, (2011) have also indicated that the spermatogenesis is influenced by genotype by environmental interaction and hence an environment favorable for a particular genotype would result in better fertility and conception. The result indicates that there is association between genetic and environment. The findings are in close agreement with the observations of (David et al 2015). The results indicated that there were genotype by environmental interaction relating to the conception of the ewes mated to Awassi rams across seasons and locations. The results also indicate that the conception (of the ewes) mated to Awassi rams was much below the desired levels, which can be attributed to the adaptability of the rams (Getachew et al 2013). The fertility of Awassi rams during the long rain season was higher than short rain and dry season respectively. This is due to seasonality of breeding and better availability of forages thereby assisting in the availability of vitamins. Based on such changes, rams continue to produce viable and fertile spermatozoa and exhibit sexual behavior throughout the years. The findings further justifies the observations from indicating suboptimal conception across different genotypes of the ewes mated to the Awassi rams, this can be further attributed to the nicking effect or the quality of the rams themselves. Findings from studies by (Afolayan et al 2014) indicated that the rams with poor semen parameters and which are highly inbred can have suboptimal fertilizing capacity thereby affecting the overall conception of the ewes.

The results refer to the heritability estimates indicate that the values was low and lower values reported among the Awassi rams, this can be ascribed to poor adaptability of the Awassi rams in the studied agro climate which is evident from the high environmental variance (Yavarifard et al 2015). Since heritability is influenced by many other environmental factors. Higher environmental variance influenced the total phenotypic variance influencing the heritability of the trait (Vleck et al 2004; David et al 2008). Lower adaptability also results in poor genotype by environmental variance (genotype by environment) and which consecutively will influence the overall fertility of the rams (Afolayan et al 2014). The estimated heritability for fertility traits as obtained in this study is in close agreement with the results of Vleck, (2004) for Colombia and Polypay rams. According to Vleck, (2004) because, of low genetic correlation between sexual performance score and number of lambs born (ewe reproductive traits), selection and use of rams with high sexual performance scores would not be expected to result in much indirect response for improved reproduction of ewes. The observations as mentioned ahead are contrary to the present observations as sexual performance score may not be expressed as fertility among the rams. The results indicate that Menz rams had a better fertility rate when compared to Awassi, AxM and Dorper in all season and years, which may be attributed to better genotype by environment interaction. The results further indicate that conception (of the ewes) mated to the Awassi rams too varied across the locations, which might be ascribed to their adaptability to the environment where they were reared. The fertility among the Awassi rams were the lowest followed by AxM, while Menz rams were superior in natural mating and followed by Dorper rams. The effects of seasons varied across the genotypes its influence was more for the Awassi rams which had lower fertility across all the seasons. Season did not influence the fertility of the Menz rams. Fertility rate of rams were influenced by genotype and all non-genetic factors. Menz rams had higher fertility rate than all other breeds in all seasons.

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Received 25 February 2020; Accepted 13 April 2020; Published 1 May 2020

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