Reproductive performance of traditionally managed sheep in the south western part of Ethiopia

Belay Berhanu and Haile Aynalem

Jimma University, College of Agriculture and Veterinary Medicine, P.O. Box 307, Jimma, Ethiopia
berhanubelay@yahoo.com

Abstract

The study was conducted to assess the reproductive performance of ewes under village management condition in south western part of Ethiopia. The study was a monitoring study which took place for three years (1995-1997).

The overall least squares means for lambing interval (LI) and annual reproductive rate (ARR) were 262 ±53.4 days and 1.88 ± 0.44, respectively. The overall least squares means of age at first lambing and litter size were 404 + 65.40 day and 1.21+1.45 lambs, respectively. Lambing interval was significantly (P<0.05) influenced by parity of the ewe, type of birth and year of lambing. The ewes at their first, and six and above parity showed longer subsequent lambing interval than ewes at 2-5 parity. Ewes that suckled singles had shorter subsequent lambing interval than ewes which suckled twins (255+3.74 vs 283+5.72 days). Year of lambing and type of birth exerted a significant effect (P<0.05) on ARR. The ewes that dropped twins had higher ARR than ewes which dropped singles (1.52 Vs 2.56 lambs/ewe/year). Litter size was significantly (p<0.05) influenced by season of lambing and parity of the ewe. There was a tendency that, litter size increased with an increase of parity up to fifth parity and dropped at the sixth and more parities. The reproductive performance of ewes under village management condition is discussed in association with reports elsewhere in the tropics.

Key words: Ethiopia, ewes, monitoring study, non-genetic factors, village management

Introduction

The livestock sector is the component of the agricultural production system. Sheep production forms one of the major parts of the livestock production system in the South Western part of Ethiopia. Sheep serves as a main source of cash income, source of protein for resource poor segment of the society and manure as source of fertilizer to cultivate vegetables in the back yards. There are 24 million sheep in Ethiopia, mainly owned by smallholder farmers. Approximately 75% of sheep are kept on small scale mixed farming in the highland regions which are located at more than 1500 m above sea level and receive more than 700 mm of annual rainfall; while the remaining 25% are found in the lowlands (EMA 1981). Ethiopia is not only rich in sheep number, but also rich in sheep genetic diversity that has been developed by natural selection (Galal 1983).

The productivity of local sheep under village management condition is alleged to be poor. The lamb survival up to an age of yearling in the South Western part of Ethiopia was recorded at 50% and the weight at yearling was about 25 kg (Berhanu and Aynalem 2008a, 2008b). In Ethiopia most of the lambs are marketed at the age of less than one year and at the weight of 10-18 kg (Galal et al 1979). The lambs with higher growth performance and better condition score are sold to fetch a premium price whereas unthrifty ram lambs remain in a flock for breeding. These might contribute to poor performance of sheep in the village management condition.

The reproductive performance of sheep has been documented in the central highlands of Ethiopia and the age at first lambing, litter size, lambing interval and annual reproductive rate was estimated as 415 days, 1.33 lambs, 233 days and 1.80 lambs/ewe/year, respectively (Tekelye et al 1993).

The reproductive performance of sheep has not been documented in the southwestern part of Ethiopia. Reproductive performances of sheep together with, survival and growth traits are important determinants of productivity of sheep in a meat livestock farming systems (Wilson et al 1985). Sheep traits need to be recorded for genetic and management improvement. However, no detailed analyses of environment and management factors affecting reproductive performance have been documented in the southwestern part of Ethiopia. Therefore, this study assessed the effect of non-genetic factors on reproductive traits such as litter size, lambing interval, age at first lambing and annual reproductive rate under village management conditions to make sound recommendations for improvement of productivity of sheep.

Materials and methods  

Description of the study area

The study was conducted in the Jimma zone of the Oromia region from 1995 to 1997. Jimma zone is located 335 kms South-West of Addis Ababa. It lies at an altitude of 1710 m above sea level, 36⁰37^' E longitude and 7⁰55^' N latitude. Climatological data were obtained from the local meteorological station at Jimma. The minimum temperature is 11.8 ⁰C and the maximum temperature is 28 ⁰C. The annual rainfall averages about 1500 mm. The season is divided into three: the main rainy season (June-September), cool dry season (October-February) and short rainy season (March-May). The seasonal distribution of rainfall is 17.2% in cool dry season, 56.3% in the rainy season and 26.2% in short rains. The mean relative humidity is 68%.  The two districts considered in the present study were Dedo and Seka. Dedo district is characterized by small farm land and feed scarcity as compared to Seka District.

Animal management and data collection

A preliminary survey was conducted during early 1995 in which all livestock holdings, livestock composition of different species and husbandry practices of sheep were established in the region (Berhanu 1998). Based on this study two districts (Dedo and Seka) were selected. In each district three peasant associations were chosen and farmers who own sheep were consulted to involve their sheep in the monitoring study. Peasant association is the smallest administrative institution in Ethiopia. A total of 150 small holder farmers and 1000 sheep of different age groups were involved in the monitoring study. The data for this study was drawn from 388 lambing records of which 270 were from Seka district and 118 were from Dedo district. The ewes were kept under village management condition. The management of sheep was in such a way that during the wet and cropping season they were tethered for 6- 8 hours per day in road sides and pocket grazing areas (Berhanu 1998). During the dry season they were freely grazed on communal grazing area and crop aftermath. Animals were provided shelter during the night and routine monthly drenching against internal parasites was done. The sheep were tagged and data collectors who resided in villages monitored and followed births, deaths, sale and exits of sheep in the households of the villages. To assess reproductive traits, ewe parameters such as date of birth of the ewe, the type of birth of the ewe and the parity of the ewe were recorded. The reproductive traits of interest in these analyses were litter size, lambing interval, age at first lambing and annual reproductive rate. The annual reproductive rate was generated from litter size x 365/interval to the next birth. The reproductive traits were recorded for animals that gave birth during the monitoring period.

Data analyses

The traits studied were: Lambing interval (LI), annual reproductive rate (ARR), age at first lambing (AFL) and litter size (LS). The fixed effects fitted in the model for LI, LS and ARR were district (Dedo, Seka); season of lambing (main rainy season, post rain and dry season); year of lambing (1995, 1996, 1997); parity at lambing (1,.., >6); type of birth at lambing (single, twin). The fixed effects fitted for AFL were district, season of birth, year of birth, type of birth of ewe lamb and parity of dam of the ewe lamb. General linear model (GLM) procedures of SAS (SAS 2002) were used to analyze the data. The statistical model was:

Y_{ijklmn  =}  m+D_i+S_j+Y_k+P_l+L_m+e_ijklmn,

Where:

Y_ijklmn is a given reproductive performance trait,
m= overall mean;
Di is the fixed effect of the i^th District;
Sj is the fixed effect of j^th season of lambing;
Y_k is the fixed effect of k^th year of lambing;
Pl is the fixed effect of l^th Parity at lambing;
L_m is the fixed effect of m^th type of birth at lambing and
eijklmn is the random error attributed to the n^th lamb.

Results and discussion  

Fixed effects on lambing interval and annual reproductive rate

The least squares means and standard errors for the effects of district, season, year, type of birth and parity on LI and ARR of sheep are presented in Table 1. The explanatory power of the model was 0.16 for LI and 0.64 for ARR. This might point to the need for inclusion of more variables in the model to increase the accuracy of the model, particularly for analysis of LI. The CV was 20.0% and 24.4% for LI and ARR, respectively. The results of the present study with regard to the reproductive performances of the indigenous sheep concur with reports in the literature from the tropical regions (Wilson 1986, Fahumy 1990, Abassa 1995, Maria and Ascaso 1999, Mengiste 2008 and Fikrte 2008). The report in Ethiopia has also confirmed the results of the present study showing the lambing interval in the range of  199 days to 313 days (Abebe 1999, Mengiste 2008 and Fikrte 2008) . The results from this study is also in agreement with some estimates in Africa which has been estimated under village conditions that ranged from 254 to 366 days in the semi-arid zone and 214 to 322 days in the humid zone (Abassa1995). The ARR recorded in the present study (1.82±0.44) is more or less similar with the findings in the tropics (Adu et al 1985; Wilson and Durkin 1988 and Tekelye et al 1993). However, it was less as compared to reports of Wilson (1986b) that had reported ARR of 1.36 in Burkina Faso and 1.33 lambs per breeding ewe per year reported in Djallonke sheep (Fall et al 1982). The smaller ARR recorded in the latter studies were attributed to smaller litter size and long parturition interval of sheep.

Effect of district

District had no significant (p>0.05) effect on LI and ARR. This was in agreement with the study conducted in two locations (Bonga and Horro) of Ethiopia under village management condition for LI (Zewudu 2008). However, there was a tendency that, ewes raised in Seka district had a better LI and ARR than ewes rose in Dedo district.  The variation in reproductive rate between districts is associated to the differences in management practices followed and the availability of feed. The Seka district has a better land holding per farm accompanied by better supply of feed for the ewes that hasten reproductive rate.  The variation in reproductive rate among locations has been reported by a number of authors in the traditional management system. There is also some evidence suggesting that LI and ARR may show wide variability within ecological zones due to breed difference and management skills (Abbasa 1995).   

Effect of season

Season of lambing of ewe did not significantly (P>0.05) affect LI and ARR. However, there was a tendency that, the ewes that have lambed in post rains had shorter LI and higher ARR. The non-significant effect of season on ARR has also been reported by some workers (Sulieman et al 1990). However, contrary to the present study some workers have revealed the significant effect of season on LI (Sulieman et al 1990, Abebe 1999 and Mengiste 2008).   

Effect of year

Year exerted a significant (p<0.05) effect on LI and ARR. Ewes which had lambed in 1995 had longer subsequent LI than ewes which lambed in 1996. The ewes that lambed in 1995 had higher (2.5+0.04) ARR than ewes that lambed in 1996 (1.96+0.05). The ewes that lambed in 1995 had less LI of 16 day and higher ARR of 0.19 than ewes which lambed in 1996.  The present study is in agreement with the study conducted in Sudan Desert sheep (Sulieman et al 1990) and in Menz sheep of Ethiopia for LI (Niftalem 1990). The effect of year on LI and ARR might be attributed to the irregularity of management followed by the farmers and the variation in the amount and distribution of rain fall between years that has influence on herbage production and performance of ewe. The feed resources base in the two of the districts is mainly natural pasture contributing more than 80 % the feed resources that is mainly affected by amount and distribution of rain fall among years (Berhanu 1998). The effect of year on reproductive traits such as LI and ARR demonstrates the fact that, the sheep in the traditional sector needs supplementation through introduction of adaptive tree forage legumes to increase the feed resources base and reproductive efficiency of sheep. The provision of satisfactory nutrition and proper management in the tropics shortens LI and allows to attain three lambings in two years (Agyemang et al 1985 and Gautsch et al 1986).

Effect of type of birth

The type of birth had a significant (P<0.05) effect on LI and ARR. Ewes that have suckled singles were superior to ewes which lambed and suckled twines by 10.9% for LI and by 40.7% for ARR. The fact that, ewes that gave birth to twins to have longer LI than single bearing ewes might be due to longer period of recovery from lactation stresses. The magnitude of energy deficiency seems to affect those processes of follicular growth and development, leading to the first ovulation (Nett 1987).  The present study did not concur with the results reported on tropical sheep (Fall et al 1982, Sulieman et al 1990)

Effect of parity

The effect of parity at lambing was significant (p<0.05) on LI. The ewes in their middle parity (2-4) had shorter LI and the ewes in early (first parity) and later parities (beyond fifth) showed shorter LI. The effect of parity was not significant (p> 0.05) for ARR. However, there is a tendency that, the ewes in their early and late parity showed a smaller ARR than ewes in the middle parities. The effect of parity has also demonstrated an effect on lambing interval in Sudan sheep under station management condition but did not have effect on ARR (Sulieman et al 1990).  The effect of parity on LI has also been reported by some workers and showing that, as parity increases the lambing interval decreases (Gautsch 1987 and Mengiste 2008 ). The ewes in their middle parity may attain their physiological maturity, that have contributed to have shorter LI and higher ARR than ewes in their early and older ages which are not able to produce to their production capacity. The young ewes in their first parity are accommodating their own growth and reproduction for replacement and they are not in their mature status that has contributed to reveal longer subsequent lambing intervals and lower ARR.

Fixed effects on age at first lambing and litter size

Least squares means and standard errors for the effects of district, year, season, type of birth and parity on AFL and LS of sheep are presented in Table 2. The explanatory power of the model fitted was 0.34 and 0.26 for AFL and LS, respectively. The small explanatory power of the model elucidated the need to include more factors to improve the accuracy of the model. The CV was 16.2% and 18.2% for AFL and LS, respectively. The age at first lambing reported in this study is in agreement with other works in the tropics (Wilson 1986, Galina et al 1996 and Osaer et al 1999). The results obtained from the above authors were within the range of 437-465 days. The results of the present study are, however, shorter than the report of Agyemang et al (1991) and Gatenby et al (1997). In the first report it was revealed that AFL was 516±4 days and in the second report the value was18-21 months. The results of the LS of sheep in the present study are confirmatory to the results obtained by Valls (1983), Galina et al (1996) and Maria and Ascaso (1999).

Effect of district

District had not exerted a significant (p>0.05) effect on AFL and LS. However, there was a tendency that, the ewe-lambs raised in Seka district had shorter AFL and the ewes raised in Dedo district had more litter size.  However, this was not in agreement to the studies conducted in two locations of Ethiopian sheep ( Horro and Menze) and the variation was attributed to breed difference or environmental difference (Zewudu2008).  

Effect of season

Season of birth had significant effect (p<0.05) on AFL and LS. The ewe lambs born in the post rain and wet season had shorter AFL than lambs born in the dry season. The ewes which lambed during the post rain and wet season had more subsequent LS than ewes lambed during dry season. The ewe lambs born in the dry season were inferior to lambs born in post rains by 20.0 %. The difference in litter size between ewes which lambed in the dry season and those which lambed in post rains was 0.8 (6.7%). Lambs born during post rain and wet seasons reached sexual maturity at younger age than those born during the dry period. The present study is in agreement with the previous studies conducted else where in the tropics (Ortega et al 1981, Wilson and Murayi 1988, Galina et al 1996, Niftalem 1990 and Gbangboche et al 2006) with regard to seasonal effects on AFL. The effect of season might be associated with the availability of forages, where ewe lambs born in wet season grew fast and reached puberty and lambed at younger age. However, the effect of season was found non-significant on age at first lambing (Sulieman 1982, Fall et al 1982 and Mengiste 2008). Season of birth had effect on litter size and the present study agrees with the results of Galina et al (1996) who has reported the highest litter size in the wet season.

Effect of year

Year had significant effect (p<0.05) on AFL but did not have a significant effect (p>0.05) on LS.  The lambing that occurred in 1996 had lower (1.16+0.01) litter size than those which occurred in 1997 (1.29+0.03). There was also a tendency that, the ewe which lambed in 1997 had lesser (404 vs 425 days) AFL than the ewes lambed in 1996.  The significant effect of year on AFL might be attributed to the variation in feed supply which in turn is associated to variation in amount and distribution of rain fall. The effect of year on reproductive traits such as AFL have been reported by workers and was associated to the variations resulted mainly from variations in management of weaned ewe lambs (Sulieman et al 1990)

Effect of type of birth

Type of birth had no significant effect (p>0.05) on AFL. However, there was a tendency that, the ewe-lambs born as singles were having lesser AFL, than the ewe-lambs born as twines.  The present study is in agreement with study conducted in tropical sheep (Fall et al 1982 and Sulieman et al 1990). However, the present study did not confirm the earlier findings and showed that offspring of young and old ewes mature later than those from dams in the intermediate age groups (Wilson 1986).

Effect of parity

Parity of the ewe had significant effect (p<0.05) on AFL and LS. The lambs born in second to the fourth parity had shorter AFL than lambs born in the first, fifth and six or more parities. There was also a general tendency that litter size increased with an increase in parity up to fifth parity and dropped at the six and more parities. The highest litter size was recorded at the fifth parity (1.35+0.07) and the lowest litter size was recorded at first parity (1.04+0.04).  The present study is in agreement to a number of workers in the tropics  (Fahumy 1990, Sulieman et al 1990 and Solomon and Gemeda 2000).  Mean litter size of Horro sheep was reported to be 1.34  and litter size increased with parity from 1.26 at the first parity to 1.44 for parities five and above (Solomon and Gemeda 2000). A polynomial analysis of litter size in relation to parity in ewes showed also the increase in litter size to be linear from first to fourth parity (Sulieman et al 1990).  It can be justified that, the lambs born from multi-parous ewes had higher growth rate and reached sexual maturity at early age and this might be associated with better mothering ability of the ewes. It is well documented that the litter size improves with advance in age through increased ovulation rate, uterine capacity and maternal traits affecting reproduction efficiency of ewes (Fahumy 1990).

Conclusions

• The study has demonstrated that the non-genetic factors exerted a significant effect on reproductive performances of ewes.

  
  

• The results call for managerial effort to increase ARR and LS and reduce AFL and LI of ewes in order to improve the productivity of ewes in the South-western part of Ethiopia.

  
  

• The increase in reproductive efficiency could be offset by higher mortality of lambs unless the management system is not favoring the ewes and the lambs.

  
  

• Detailed analysis of the farming system, constraints identification and farmers’ participative intervention is suggested for an increase of sheep production in the villages of South Western part of Ethiopia.  

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Received 6 July 2009; Accepted 22 July 2009; Published 1 September 2009

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