Selection efficiency for growth performance of Menz sheep in a community-based breeding program

Aschalew Abebe, Sandip Banarjee¹, Shenkute Goshmie, Asfaw Bisrat, Ayele Abebe, Shanbel Besufikad, Tesfaye Zewdie and Solomon Gizaw²

Debre-Birhan Agricultural Research Center, P O Box. 112. Debre-Birhan, Ethiopia
aschalew1978@gmail.com
¹ Hawassa University, Collage of Agriculture, P O Box 05, Hawassa, Ethiopia
² ILRI (International Livestock Research Institute) P O Box 5689, Addis Ababa, Ethiopia

Abstract

The study was undertaken to evaluate the efficiency of selection on growth performance of Menz sheep under a community-based breeding program (CBBP) from the period of 2009 – 2017. A total of 3996 lamb records (ram lambs 2025/ ewe lambs 1971) were used to evaluate the phenotypic and genetic factors affecting the growth traits of Menz sheep. REML in Wombat and General linear model on SAS (version 9.0) were used to evaluate selection efficiency for growth of Menz sheep. The least squares means and standard errors on phenotypic growth weight for birth, weaning age, six month age and yearling age were 2.58±0.004, 8.99±0.02, 13.28±0.02 and 19.94±0.06 kg, respectively. The effect of sex was significant (p<0.001) only for birth weight and no significance effect (p>0.05) was observed for weaning, six month and yearling weights. All growth traits were not affected by fixed effect of parity and birth type in this particular study. However, birth season and birth year had a great influence (p<0.0001) on all growth traits. The genetic trend on estimated breeding values (EBV) was not consistent across years and varied between sexes. The highest EBV for weaning, six month and yearling were recorded for the year 2013 and the lowest in 2009 (at weaning and six month) and 2015 (at yearling).The female EBV (at weaning, six month and yearling) was higher than male for the current (2017) and base population (2009).The responses to selection as compared to base population (2009) for birth, weaning, six month and yearling weight were – 0.00446Kg, + 0.11Kg, + 0.54Kg and + 0.75Kg respectively. This study indicates that improvement in body weight for Menz sheep through CBBP is possible; however, the response to selection varied across years and its pattern was irregular for the implemented years due to the problem on selection of breeding rams (lower availability of breeding rams) and management effect.

Keywords: estimated breeding value, response to selection, wombat

Introduction

Rearing of small ruminants is an integral part of the animal agriculture especially under small holder farming condition in the tropics (Kosgey et al 2006). They play multifarious roles in the livelihood of the rearers and also those who are tangibly or intangibly associated with livestock husbandry and allied activities, this is more true for the residents of the developing and yet to develop countries (Kosgey et al 2006).). Small ruminants are distributed across all the agro-ecological zones of Ethiopia (Gizaw et al 2008a; CSA 2018).

In the highlands of Ethiopia, sheep are an integral part of the socio cultural and economic livelihood of the agrarian society (Shapiro et al 2017). In the highlands of Amhara region, Ethiopia, sheep account for one of the major livestock species and sheep husbandry is one of the major sources of livelihood for the resource challenged members of the society (Gizaw et al 2008a). The highland and midlands are the most important market segment for sheep and contribute immensely to the mutton value chain (Shapiro et al 2017; CSA 2018)

Indigenous sheep breeds have an advantage over exotic breeds in improving the livelihood of the smallholders and pastoralist under low input agro-pastoral and pastoral production system (Kosgey and Okeyo 2007). This may be is attributed to their ability in effectively utilizing the available feed resources, most of which are obtained from the degraded grasslands unsuitable for the agronomic activities (Baker and Rege 1994) and also well adapted to the prevailing agro climate, traditionally selected for their adaptive traits with the overall production coming from the sheer numbers that are being raised (Hassen et al 2002; FAO 2010; Mirkena et al 2012), however, the productivity of indigenous livestock (especially under the smallholder production system) is generally low due to scarcity of feed both in quality and quantity, occurrence of frequent droughts, high incidences of diseases and parasites, genetic makeup (breed), insufficient infrastructure and associated reasons (Samson and Frehiwot, 2014; Kosgey and Okeyo 2007). And also genetic improvement techniques are also limited by lack of proper identification, paucity of reliable records (performance, pedigree etc), low education and scattered settlements which makes difficult the scientific selection methods as practiced in the developing countries (Jaitner et al 2001).

In Ethiopia, “Community based breeding programs" (CBBP) were initiated for Afar, Menz, Bonga and Horro sheep (Mirkena et al 2012). The programs were designed with the notion to improve targeted breeds without disturbing the prevailing genetic resources in their respective breeding tract (Kosgey and Okeyo 2007; Gizaw et al 2011; Mirkena et al 2012). This in turn provides opportunities for the implementation of breeding strategies that helps to improve livestock production and conserving native livestock genetic resources (Gizaw et al 2011). The CBBP for the Menz sheep was initiated in the year 2009 to improve the productivity of the Menz sheep through within breed selection so as to improve the income of the smallholder farmers’ by selecting genetically superior breeding stock (Gizaw et al 2011; Mirkena et al 2012).

In the past on the CBBP, the growth performance in Menz sheep (Gizaw et al 2014a) were evaluated but regular monitoring and periodic evaluation of a breeding program needed as a feedback for the programs. Therefore, the present study was carried out to evaluate the efficiency of selection on growth for Menz sheep under CBBP.

Materials and methods

Description of the study area

The study was conducted in Menz Gera woreda, which is one of the five woredas in Northen Shoa zone of Amhara National Regional state. The study area was located between 39^°- 44^°E longitude and 10 ^° - 24^°N latitude with an altitude of 3354 meters above the mean sea level. The average temperatures of the study area vary between 5 to 18°C and an average annual rainfall is 980mm.

The Menz area is characterized by a low in-put sheep-barely production systems with bi-modal rainfall pattern and the main rainy season is from June to September and erratic and unreliable short rainy season is expected in February and March (Tesfaye 2008).

Organization of community for sheep breeding program

At the beginning, farmers were organized informally for sheep breeding program and then CBBP of Menz sheep was set up in 2009 in Dargegn village with the plan of improving the productivity and income of smallholder farmers through genetic improvement of animals. Initially, the sheep breeding cooperative was started with a provision of 45 breeding rams, which had the highest estimated breeding value from the nucleus flock of Debre Birhan Agricultural Research Center (DBARC). The cooperative was formed by having 50 farmers with 17 breeding rams groups for 1005 breeding ewes. One breeding ram group comprised of 1 to 4 farmers based on the numbers of breeding ewes owned by the members. The allocated breeding rams to each breeding ram group run all the year round with the breeding ewes in the communal grazing land for ensuring the optimal usage of breeding rams.

The cooperative obtained legal entity in 2012 and was named as “ Tebab and Merchet selective sheep improvement and fattening cooperative ” and launched with an initial capital of 5000.00 ETH Birr. The sheep cooperative offer dividends on 2 round (68,367.00 ETH Birr) for the members and it has a capital of 42,374.57 ETH Birr in cash (in their bank account) besides 18 breeding rams. The cooperative provided credit up to 5000.00 (five thousand) ETH Birr for different purposes (for buying agricultural input such as fertilizer, seed, land and oxen).

Ram selection criteria and practices

After the initial provision of breeding rams originated from nucleus flock DBARC, it was observed that the selection criteria of the farmers differed from those of the scientific communities’ elsewhere. Therefore, the initially distributed rams (after service period of 2 year) were replaced by the young rams, which were considered best through participatory discussions with the stakeholders (cooperative members). The farmer’s preferences for different traits were identified during selection process and were primarily based on the body conformation, coat color, tail and testicle arrangement, horn shape, pelvic shape, pedigree information (oral) and wool production. Progenies of the best candidate rams were evaluated for selection by the researcher at different age (six month and yearling stage) based on estimated breeding value. The sheep cooperative committees determine the price of selected best breeding rams and paid for the owner.

Distribution of selecting breeding rams to ram groups

After selection of breeding rams, the committee and members in the group were responsible for care and upkeep of the breeding ram and a system of rotating the rams between the different ram groups was carried out based on a designed plan. During distribution of the breeding rams the enumerator was obliged to maintain the records (i.e. identification number of breeding ram assigned for ram group members). The record from the earlier ram group (assigned breeding ram information) after service period (2 years) was not checked with the new ram group members (newly assigned breeding ram) thus consequences a members of one ram group were able to have related family ram at different years. This often leads to development of full and half sib families of the rams and in such a case there are high chances of inbreeding within the population.

Sampling and data collection

The data for growth and reproduction of the lambs/rams were collected from 2009 to 2017 with a total of 5340 sheep, (3996 lambs (male (2025) and female (1971)), 144 rams, 1200 ewes). Furthermore data pertaining to the performance of parental grand sires (2505), parental grand dams (2460), maternal grand sires (982) and maternal grand dams (1040) too were included in the study. The data included in the study pertained to the birth weight, weaning weight, six month weight and yearling weight, year of birth and season, sex, birth type and parity.

Data Analysis

The effect of non genetic factors (sex, type of birth, parity, birth year and season) on growth performance of Menz sheep were analyzed and means were compared using the GLM procedure of SAS 9.0 (SAS, 2002) by the following model

Yjklmn = µ + Aj + Bk+ Cl+ Dm + En + ejklmn

Where;

• Y_jklmn = is the an observation
• µ= is the mean of population
• A_j= is the fixed effect of j^th birth year (j= 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017)
• Bk= is the fixed effect of k^th sex (k= male, female)
• C_l= is the fixed effect of l^th season (l= Long rainy season, Short rainy season, Dry season)
• D_m= is the fixed effect of m^th parity of dam (m= 1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
• E_n= is the fixed effect of n^th birth type (n= Single, Twin)
• e_jklmn= is the random error

The genetic trend as response was calculated by estimating the breeding values of lambs born from selected rams taking year zero lambs (born from unselected farmers’ rams) as a reference or base. The Breeding values were estimated using REML method using the software WOMBAT (Meyer, 2012).

The 3-month, 6-month and 12 month records were adjusted to a standard 90-day, 180-day and 365-day weights were calculated using formula developed by Inyangala et al (1991).

Where, W₂, W₃ and W₄ = weight at a given age

W₁= birth weight

D = number of days between weighing date and date of birth

(WWT= Weaning weight; SMWT = Six month weight; YLWT= Yearling weight)

Variance components and BLUP of breeding values for birth and 3-month, 6- month weights and 12 month weights were obtained from the solutions for the random animal genetic effect in a multi-trait individual animal model analysis.

Y_ijklmn=µ+A_i+ B_j +C_k +D _l + E_m + F_n + e_ijklmn

Where;

• Y_ijklmn = is th overall observation
• µ= is the mean of population
• A_i= is the random animal effect
• B_j= is fixed effect of j^th year on growth (j= 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017)
• C_k= is the fixed effect of k^th parity of dam (k= 1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
• D_l = is the fixed effect of l^th sex (l= male, female)
• E_m = is the fixed effect of m^th birth season (m= Long rainy season, Short rainy season, Dry season)
• F_n = is the fixed effect of n^th birth type (n= singe, twin)
• e ijklmn= is the random error e ijklmn

The variance components were extracted for male and female differently to compare them, due to this, some pedigree information may reduced thus the overall mean might be affected or reduced.

Response was estimated based on the yearly trends in mean performance levels of the lambs born each year based on the changes in EBV over years.

R=EBV_yt+1 – EBV_yt

Where;

R = Response to selection for growth traits

EBV_{yt +1} = Estimated breeding value for growth traits of later year

EBV_yt = Estimated breeding value for growth traits former year

Result

Efficiency of selection on the growth performance of Menz sheep reared under CBBP

Phenotypic growth performance of menz sheep reared under CBBP

The study pertaining to the growth of the Menz sheep under CBBP indicates that birth weight of male lambs was higher (p<0.05) compared to female lambs (table 1). The findings also show that there was no difference (p>0.05) in birth weight of the lambs due to the parity of the ewes. The study further shows that there were differences (p <0.001) in birth weight due to years, where birth weight was higher among the lambs born in 2017 while the converse was true for the lambs born in 2009. Differences (p<0.001) were also recorded across the season of birth on the trait with body weight of the lambs born in the long and short rainy being lower than those born in the dry season. The trend was more or less similar for weaning, six months and yearling weight. The weaning weight, six months weight and yearling weight was lowest ( p<0.001) among the lambs born in 2009. The study further indicates that weaning weight did not differ between lambs born between 2009 and 2010. The weight at weaning, six months and yearling too varied across the years with the values being highest among the lambs’ born in 2011. The study further indicated that the weaning weight and yearling weight were highest (p<0.001) among the lambs born in the long rainy season, while the study also indicates that it was highest (p<0.001) among the lambs born during the short rainy season.

Genetic performance on growth or estimated breeding value

The BLUP (best linear unbiased predictors) result pertaining to the estimated breeding values (EBV) for growth related traits (weaning, six and yearling weights) of Menz lambs are presented in Figure 1. The findings showed variation across the years for the traits. The BLUP results for the weaning weight indicated that the EBV too varied between years with the values being highest during 2013 for weaning, six months, and also yearling weight. The study further showed that the EBV was lowest in the corresponding year (2014) the effect of which was also observed in the yearling weight for the year 2015. However, the EBV values for weaning weight and weight at six months, showed an improvement in 2015 while the yearling body weight rebounded back from a negative value to show an improvement in the year 2016. Thereafter all the traits showed an improvement in the following year (2017).

Figure 1. Estimated breeding values trends of Menz lambs born from the selected rams across the years in the studied population (WWT = Weaning weight, SMWT = Six month weight, YLWT= Yearling weight)

The results pertaining to the EBV of the lambs born in 2016/2017 (irrespective of both the sexes) vis-a-vis those of 2009 are presented in Figure 2. The findings indicated that the EBV values differed across the sexes with higher values population of the EBV with sex, ewe lambs were better achiever than ram lambs across all the growth weights (birth, weaning, six month and yearling weight).

Figure 2. The average estimated breeding value for base and current animals along with sex

The findings showed that the EBV values of the lambs born in 2017 improved over those of the base population (2009) for weaning, six months and yearling weights, with highest change was observed in the yearling weight. The findings from Figure 2 indicated that the EBV too were higher among the ewe lambs as compared to those of the ram lambs, both for six months and yearling weight. The findings also showed that the EBV for yearling weight of the ram lambs was lower than the six months weight for the same year. However the trend for the ewe lambs for the same age was higher.

The response to selection for body weights of the lambs reared in the CBBP under low-input smallholder systems are represented in Figure 3. The findings showed an oscillating trend in all the parameters over the studied years. The response to selection (R) for weights across the studied ages (weaning weight, six months and yearling weight) showed high R in the years 2010 and 2013 and thereafter, however the R values too followed similar trend as EBV with the values of all the three parameters (weaning weight, six months weight and yearling) being lowest in 2014, which resulted to a drastic reduction in R values for yearling weight of the lambs in the following year (2015). The R values for yearling weight of the selected in the year 2016 reflected the trend in R of weaning and six months weight as observed in the previous year. The response to selection from a base population (2009) for birth, weaning, six month and yearling weight were – 0.00446Kg, + 0.11Kg, + 0.54Kg and + 0.75Kg respectively.

Figure 3. Trends for annual response to selection for the growth traits (R1 = Response to selection for birth weight, R2 = Response to selection for weaning weight, R3 = Response to selection for six month weight, R4 = Response to selection for yearling weight)

Discussion

Efficiency of selection on growth performance of Menz sheep under CBBP

Our findings on birth in the current study is in close agreement with the findings of Yilmaz et al (2007) and Al-Bial et al (2012); Ghafouri and Notter (2016) in the Afshari, Black Bangal and Norduz sheep as well as in Menz sheep (Gizaw et al 2014a). The differences as observed may be ascribed to the Rensch's law which supports the differences between sexes as ascribed to sexual dimorphism (Rensch 1950; Fairbairn 2007; Polak and Frynta 2009). The findings also showed that there was no difference ( p>0.05) in birth weight, weaning weight, six months weight and yearling weight due to parity of the ewes; it may be ascribed to the higher numbers of single born lambs who have enough uterine space for proper growth (Babar et al 2004). The present findings are also in close accordance with those of (Ali et al 2006) who reported that effects of parity on birth weight of the lambs is generally prominent among the prolific breeds of sheep in Rambouillet sheep. However, the findings differ from those of (Ebangi et al 2004) from Fulbe sheep.

The findings also indicated that the birth weight of the lambs born as single did not differ significantly (p>0.05) from those born as twins, which may be misleading at this stage as the numbers of twin born were proportionately very few, the present finding is in agreement with the observations of Abebe (1999) on Menz sheep. The present findings however contradict with the reports of several researchers (Yilmaz et al 2007; Berhanu and Haile 2009; Al-Bial et al 2012) who reported that the single born lambs weigh more than the twin born counter parts. This may be attributed to the fact that the single born lambs do not have to share the uterine space and also the nutrient, as the multiple births have to do. The effects of years too was (p<0.05) on the birth weight of the lambs, which can be ascribed to the type of feed received by the dams besides the allied factors viz. diseases and other types of stresses which an ewe often encounters during the gestation period (Ebangi et al 2004; Zaffer et al 2015; Chakraborty et al 2015). The results pertaining to the effects of seasons on the birth weight too are significant and are in close accordance with the findings of Yohannes et al (1998) and Germinus et al (2017) who reported that the ewes reared on grazing encountered different feedstuffs across the seasons which often vary in quality and quantity and thereby influences the weight of the growing fetus (Inyangala et al 1991; Yohannes et al 1998). The results regarding the differences in weaning weight across the years can also be ascribed to the type of feed (both in quality and quantity) received by the dam (Oftedal 1984; Yohannes et al 1998). This invariably will influence the lactation yield and the milk available for consumption by the lambs (Inyangala et al 1991; Regan et al 2015). This may be also responsible for the differences in weight lambs which can vary both across the years and also within years, the carry over effects of the amount of milk consumed by the lambs and their composition, too can have a carryover effect towards the six month and also yearling weight of the sheep (Yohannes et al 1998). Studies by (Buncha et al 2014) have also indicated that for compensatory growth to be effective the quality of the feed has to be exceptionally good with adequate in quantity. This is besides the fact that the animals themselves are free from any endo and ecto parasites besides other diseases (Coltman et al 2001).

Our findings in the present study indicated that the EBVs of the lambs born in 2017 was improved compared to base population (2009) for weaning, six months and yearling weights, with highest change observed in the yearling weight. Figure 2 indicated that the EBV too was higher among the ewe lambs as compared to those of the ram lambs, both for six months and yearling weight. The findings also showed that the EBV for yearling weight of the ram lambs was lower than the six months weight for the same year. However, the trend for the ewe lambs for the same age was higher.

The response to selection was better achievement till 2013 on all growth traits (birth weight, weaning weight, six month weight and yearling weight) due to the good breeding value of provided rams to the CBBP from DBARC that served as a jump-start Gizaw et al (2014a). While in the lower number or limitation on availability of candidate rams during screening (Gizaw et al 2014a), occurrence of drought and high mortality (liver fluke) on the year as well as the farmer preference dependency on selected rams color affects the selection process of best breeding animal, even take on breeding rams body weight below the average of the population mean thus consequences on irregular pattern in the response to selection evaluation across the implemented year.

Conclusion

• The selection efficiency for phenotypic growth performance of Menz sheep was better for all growth traits, however regular increment on growth traits was not observed.
  
  
• The efficiency of selection on genetic performance of growth was differ in EBV and the response to selection trend was irregular in the implimented year.
  
  
• Therefore, better management on the animal and record keeping on distribution and selection of breeding rams is needed and the breeding objective requests for oestrus synchronization by hormonal method to get sufficient candidate rams.

Acknowledgement

The author would like to thank the Amhara Agricultural Research Institute, Debre-birhan Agricultural Research Center livestock researchers for their unlimited support during the data collection and School of Animal and Range Sciences, College of Agriculture, Hawassa University.

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