Factors affecting growth performance of sheep under village management conditions in the south western part of Ethiopia

Berhanu Bela and Aynalem Haile

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 growth performance of lambs under village management condition in Jimma, Ethiopia from 1995 to 1997.

The overall mean body weight at birth, at weaning (180 days) and up to a year (360 days) was recorded to be 2.45, 18.8 and 25.4 kg, respectively.  The overall mean growth rate up to weaning weight (180 days) and up to one year old (360 days) was 92.3 and 68.3 g/day. The non-genetic factors such as season, yea, sex, parity, litter size and district were considered in this study. The main factors had a significant effect (at least p<0.05) on weight for age and weight gains recorded. A consistent significant effect of sex and birth type (single/twin) (p< 0.05) was observed for weight for age and growth rates. The males were heavier than females, by 7.11% and 10.2 % for 180 days and 360 days weight, respectively. The twins were lighter than singles by 20.1 % and 8.32% for 180 days and 300 days weight, respectively. The effect of parity was significant (p<0.05). The lambs born to ewes at first parity had lower weight for ages and weight gains compared to subsequent parities. The lambs born in land scarce area (Dedo district) had lower weight gains than lambs born in Seka (land better area). Differences were significant (P<0.05) and weight gain recorded at 180 days were 85.3 and 90.9 g/day for Dedo and Seka lambs, respectively.

The variation in growth performance of sheep in different districts could provide base line information to set a long-term genetic improvement plan by election. The results are discussed in comparison with data obtained from elsewhere in the tropics.

Key words: lambs, none-genetic factors, weight for age, weight gain

Introduction

Sheep are a major component of the livestock production system in the South Western part of Ethiopia. The sheep production system is characterized by a small flock size and free grazing. The feeding management practice basis mainly on communal grazing lands in wet season and crop residues in the dry season. Traditionally, sheep are kept on crop-livestock mixed farms and are considered as a sideline business by their owners and are given marginal care. They are handled by village children during the cropping season and are allowed to browse and scavenge freely along roadsides and pockets of grazing lands. Due to poor health management and inadequate nutrition, the productivity of these animals remains less than optimal (Wilson and Murayi 1988). The lambs are marketed at the age of less than one year and at a weight of 10-18kg (Galal et al 1979). The practice of castration and fattening are not frequently exercised in South Western part of Ethiopia, though there is a lucrative market for fattened and castrated sheep.

Sheep also serve as a source of cash income to pay for school fees to children, and purchase of goods such us salt and sugar for family consumption. They also serve as a source of protein, predominantly slaughtered during festive and religious occasions.

The performance of sheep under village management is not recorded in the South Western part of Ethiopia. With-in ecotype variation under village management conditions has also not been recorded. Little evidence has been documented of sheep performance under on-farm management condition in the central highlands of Ethiopia (Tekeleye et al 1985 and Abebe et al 2000). On-farm sheep performance evaluation in Ethiopia is narrow in coverage and does not represent the village management conditions. Choice of breeds for improving the output from sheep should depend on the amount of information available on them. This situation has necessitated undertaking a monitoring study of the performance of sheep in villages before planning a wider genetic improvement plan.

The sheep in the villages are not selected for growth performance traits. They have been subjected to natural selection essentially for survival in their various ecologies, with their associated feed, parasite and diseases problems (Williamson and Payne 1978).

Growth performance is a key production indicator. It has implications in the reproductive efficiency of sheep. Fast growth performance allows sheep to breed early and contribute more lambs in their lifetime. Fast growth rate entails reaching market weight early and brings a quicker income to the farmer. It is from these perspectives that this study was conducted. The objective of this study was to assess the performance of lambs for growth traits and to investigate the effect of non-genetic factors on growth traits under village management conditions.

Materials and methods  

Description of the study area

The study was conducted in the Jimma zone of the Oromia region from 1995 to 1997. The 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, 56.4% in the rainy season and 26.3% in short rains. The mean relative humidity is 68.0%.  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

The area is a mixed crop-livestock production system, where sheep are a major component of the livestock production sub-system.  Sheep were shepherd for 8 or 9 hours per day in communal grazing area in the wet season and crop after-math in the dry season. The vegetation in the grazing land included mainly Andropogon, Hyparrhenia, Trifolium species, browses and shrubs. The sheep were drenched with anti-helminthics every month during weighing.  Lambs were naturally weaned at the age of about 5-6 months.

Data collection

A preliminary survey was conducted during 1994 in which all livestock holdings, the livestock composition of different species and husbandry practices of livestock were recorded in the region (Berhanu 1998). For the present study two districts were selected. In each district three peasant associations were selected and farmers who own sheep were consulted to involve their sheep in the monitoring study. Farmers who showed interest in the research were advised to bring sheep to the communal grazing area for growth performance measurements. More than 30 farmers owning sheep were included in the monitoring study at each site.  More than one thousand sheep were identified with plastic ear tags and were visited every month by the research team for recording. Weights were taken by means of a spring balance and a sling every month. Enumerators residing in these villages took the birth weight within 12 hours of birth.

Data analyses

The traits analyzed were birth weight, weight at the interval of 60 days (0, 60, 120, 180 (assumed to be weaning weight), 240, 300, 360 days weight and Average Daily Body weight Gain (ADG) from (0- 60, 0-120, 0-180, 0-240, 0-300 and 0-360 days).  Data were analyzed using the General Linear Model (GLM) procedures of SAS (SAS 2002). Fixed effects fitted in the model included the effects of district (Dedo, Seka); sex (male, female); parity (1- >6), type of birth (single, twin); season of birth (main rainy season, short rains and dry season); year of birth (1995, 1996, 1997) and two-way interactions between the main effects. Interactions effects were not retained in the final model as their effects were not significant in preliminary analysis. Tukey Kramer test was used to separate means of effects with three or more levels which were significant in the least squares analysis of variance (SAS 2002).

The statistical model was explained as follows:

Y_ijklmno = μ + D_i + S_j + Y_k + P_l + L_m +X_n +e_ijklmno;

where

Y_ijklmno is the weights and ADG of the n^th lamb;
μ is the overall mean;
D_i is the fixed effect of the i^th district;
S_j is the fixed effect of j^th season; Y_k is the fixed effect of k^th Year of birth;
P_l is the fixed  effect of l^th Parity;
L_m is the fixed effect of m^th type of birth;
X_n is the fixed effect n^th of sex;
e_ijklmno is the random error.

Results and discussion  

Body weights and fixed effects

Least squares means and standard errors of body weight at different ages are given in Tables 1 and 2. 

The  R² (the explanatory power of the model) was in the range of 11.3% for 240 days weight to 27.3% for 300 days weight, where as the CV was in the range of  13.9% at 300 days weight to 23.3% for 60 days weight. The overall least squares means of body weights presented in Table 1 and 2  concur well with reports by various authors in Ethiopia (Galal et al  1979; Abebe et al 2000). However, the weights reported were higher than those reported from West Africa on Djallonke sheep, 1.9 kg for BWT and 10.2 kg for WT90 in improved village flocks located in the Ivory Coast (Armbruster et al 1991); 2.2 ±0.02 kg for BW and 9.1 ± 0.05 kg for WT80 in participating farms of an open nucleus improvement programme in the Ivory Coast (Yapi-Gnaor´e et al 1997); 12.7 kg for WT90 to WT100 and 15.1 kg for WT180 (Poivey et al 1982).

Effect of district

The effect of district was significant (p< 0.05) for weights at birth, 60, 180, 300 days age. It was consistently observed that, the lambs born in Seka district were heavier than lambs born in Dedo district. The lambs born in Seka district were superior to lambs born in Dedo district by 4.62% and 13.7% for weights at 180 and 300 days age, respectively. The variation in growth traits among locations also concurred with previous results that had compared performance of sheep in different locations (Gatenby et al 1997; Gautsch 1992; Mukasa-Mugerawa et al  2000). Mukasa-Mugerewa et al (2000) showed significant difference between Horro and Menz lambs in birth weight (2.4 vs 2.1kg).  In the present study the lambs born in land available area (Seka) showed higher growth rate indicating that feed is available for lambs and lactating ewes. It can also be argued that morphologically Seka sheep are larger in size and have a better condition score and are liked by consumer in Jimma market than Dedo sheep. The variation recorded in growth performance between districts could be an asset and gives a direction to improve the genetic potentials of local sheep with a long-term selection effort.  These will render a hope that  tropical sheep show a variation and genetic improvement through selection could be a long term strategy in the tropics with an organized and planned genetic improvement effort. In this regard, Boujenane et al (1998) reported a wide variation in weight, at birth and at subsequent weight among lambs born at different locations, emphasizing the importance of adequate genetic variation in breed comparison studies. The study can give also a direction to improve local breeds through conservation-based with-in breed selection with a participation of small holder farmers in communities.

Effect of season

Seasonal variation has not exerted significant effect (p<0.05) on most of the weights except for birth, 120 days and 300 days weights. The effect of season on growth performance was not clear cut and consistent. For 120 days weight, the lambs born in the dry season were superior to lambs born in post rain and wet season. The lambs born in the dry season were superior by 6.72% as compared to lambs born in the wet season for weight at 120 days age. The lambs born in post rain and wet season were superior to lambs born in the dry season for weight at 300 days.  The lambs born in the wet season were superior to lambs born in the dry season by 8.51% for weight at 300 days age.  The effect of season on weight for age is in accordance with a number of reports in the tropics (Agyemangy et al  1991; Nawaz and Khalil 1998). The effect of season is associated with difference in feed and disease situation. When lambing occurred during wet season there is high incidence of parasite infestation impairing growth performance.    

Effect of year

The effect year was significant (p<0.05) on weight 60 days, weight at 120 days and weight at 180 days. The lambs born in year 1996 were significantly heavier for traits showed a significant effect.  The lambs born in 1996 were superior to lambs born in 1997 by 6.12 % for weight at 60 days age, where as the lambs born in 1996 were also superior to lambs born in 1997 by 8.91% for weight at 120 days age. The influence of year on growth for weight of lambs could be the result of changes in management, incidence of disease, herdsman’s skills and environmental factors. However, Wilson (1986) reported a non-significant effect of year on birth weight and pre-weaning traits.

Effect of parity

The effect of parity had consistently showed a significant effect (p<0.05) on growth performance in the present study.  The lambs born from ewes in their earlier parity (1-2) were consistently lighter than lambs born at later parities (>3). The differences in weights between parities was narrow for weights recorded at later stages (300 and 360 days weights) than weights recorded at earlier ages (60 and 120 days weights). The lambs born from ewes in their fifth parity were superior to the lambs born in the first parity for 60, 120 and 180 days weights by 16.5%,  10.5%, 7.13%, respectively.  It can be said that, in this study the lambs born from primiparous ewes were lighter than lambs born from multiparous ewes. The trend is that, as parity increased growth performance increased up to fifth parity and a decrease in growth performance was observed at sixth parity. Lambs born to ewes at first and six parities and above had lighter weight for age compared to second to fifth parities.  Lambs born from ewes at 4 and 5 parities revealed the best performance for growth traits.  These results are in agreement with the studies carried out elsewhere in the tropics (Fall et al 1982; Adu et al 1985; Wilson and Murayi 1988; Movarogenis and Constantinou 1986; Nawaz and Khalil 1998). It seems reasonable to argue that the ewes after their six parities could be culled for better productivity of the flock (Solomon et al 1996).

Effect of litter size

The effect of litter size was consistently significant (p<0.05) for all weight except for weight at 240 days. The lambs born as single were heavier than the lambs born as twines.  The effect of litter size on growth traits diminishes as the age of lambs advanced.  The lambs born as singles were heavier by 15.1%, 19.4%, 19.7%, 9.40% and 7.14% as compared to lambs born as twins for weight at 60, 120, 180, 240 and 300 days weight, respectively.  The fact that singles were heavier than twins is in agreement with the results of other authors in the tropics (Mavarogenis and Louca 1979; Adu et al 1985; Movarogenis and Constantinou 1996; Nawaz and Khalil 1998; Rastogi 2001). Single born lambs had higher birth weight than twins and triplets, hence a better chance of survival. Twins and triplets on the other hand had lighter average birth weight and were more subject to physiological starvation (Nawaz and Khamil 1998).

Effect of sex

Sex had consistently exerted a significant effect (p<0.05) on all weights. The males were  heavier as compared to females in all the weights considered in the present study. The difference in weight between sexes is pronounced as age advances. The males were superior to females by 4.63%, 6.61%, 10.0% and 10.12 at 60, 120, 300 and 360 days weight, respectively.  Male lambs had higher weights than females after and before weaning and such differences have been documented by a number of investigators (Adu et al 1985; Mavorogenis and Constanntinous 1986; Movarogenis and Constantinou  1986; Nawaz and Khalil 1998; Rastogi 2001).  The larger weight of males in comparison to female lambs could be due to the hormonal differences in their endocrinological and physiological functions (Ebangi et al 1996).    

Body weight gains and fixed effect

Least squares means for growth rates are shown in Tables 3 and 4.

The growth rate of lambs decreased as age advances.  The results on weights gains recorded in this study are in accordance with research findings elsewhere in the tropics (Gatenby et al 1997; Wilson 1986; Gauch 1992; Mukasa-Mugerewa et al  2000). The average daily gain found in this study was higher than values reported by Vallerand and Branckaert (1975), Rombaut (1980) and Poivey et al (1982) between 30 or 60 days, and higher than 69.6 g for ADGs from 0 to 80 (Yapi-Gnaor´e et al 1997) and lower than the reports of El-Fadili et al (2003) in Timahdit sheep as estimated at 181 g for ADGs from 30 to 90 days. The differences between the growths  rates of lambs reported in the present study and literature could be attributed to the management, the level of genetic makeup, the incidence of diseases, herd’s man skill and other factors.

Effect of district

The effect of district was significant (p<0.05) for weight gains between 0-60 day, 0-180 days and 0-300 days.  The lambs born in Seka district gained higher weight compared to lambs born at Dedo district.  The lambs born in Seka district were heavier to lambs born in Dedo by 10.7%, 6.61% and 10.7% for gains between 0-60, 0-180 and 0-300 days, respectively.  The variation in growth rates among locations has concurred with previous results that had compared performance of sheep in different locations (Gatenby et al 1997; Gautsch 1992; Mukasa-Mugerawa et al  2000). Mukasa-Mugerewa et al (2000) showed significant difference between Horro and Menz lambs in pre-weaning growth rate (67 vs 61g/day).

Effect of season

The effect of season was significant (p<0.05) for weight gains between 0-120 and 0-300 days. The lambs born in the wet season were lighter than lambs born in dry and post rainy season on weight gains between 0-120 days, where as the lambs born in the dry season has lower weight gain compared to the lambs born in wet and post rainy season.  The lambs born in the wet season were lighter by 7.83% as compared to lambs born in the dry season at 0-120 days.   The lambs born in the wet season were superior to lambs born in the dry season by 10.51% for weight gains between 0-300 days.

Effect of year

The effect of year was significant (p<0.05) for weight gains between 0-60, 0-120 and 0-180 days.  The lambs born in 1996 were superior to the lambs born in 1995 and 1997. The lambs born in 1996 were superior to lambs born in 1995 by 9.62%, 11.1% and 13.9% for weight gains between 0-60 days, 0-120 days and 0-180 days, respectively. 

Effect of parity

Parity of dam exerted a significant (p<0.05) effect on lamb weight gain at some stages (0-60, 0-120 and 0-300 days). Lambs born from ewes in their first parity had significantly lower weight gains to 60, 120 and 300 days compared to lambs born from second to fifth parity ewes.  The lambs born from dams in their first parity were lighter by 18.0%, 9.63% and 5.63% as compared to lambs born from the third parity for weight gains from birth to 60, 120 and 300 days age of lamb, respectively.  

Effect of litter size

Litter size had a significant effect (p<0.01) on weight gain of lambs at all age intervals except for 0-360 days.   The single born lambs grew faster than twins. The weight gain of singles was superior to those of twines by  15.8%, 19.5%, 18.1%, 8.03% and 6.82% for weight gains from birth to 60, 120, 180, 240 and 300 days, respectively.  The difference in weight gains between singles and twines decreased as age advanced.

Effect of sex

Male lambs were heavier than females. The weight gain differed significantly (p< 0.01) between sexes at all stages except weight gains up to 60 days. The males grew faster than females by 7.72%, 6.81%, 6.43%, 10.6% and 11.1% to 120, 180, 240, 300 and 360 days, respectively. The weight gain difference between sexes was pronounced as age advanced. The differences in weight gains have been documented by a number of investigators (Adu et al 1985; Mavorogenis and Constanntinous 1986; Movarogenis and Constantinou  1986; Nawaz and Khalil 1998; Rastogi 2001).  The larger weight gain of males in comparison to female lambs could be due to the hormonal differences in their endocrinological and physiological functions (Ebangi et al 1996).

Conclusions 

• The study was conducted to investigate the growth performance of lambs under village management conditions in Jimma, Ethiopia.

  
  

• The variability observed in growth performance between lambs located in the two districts suggested that genetic diversity exists which could be exploited for genetic improvement. This can be organized through ram progeny testing in order to identify sires for producing fast growing lambs. These programs (possibly nucleus breeding schemes) should involve the faster  growing weaner lambs selected from ewes with high rearing ability in farmers flock within the same eco-regions.

  
  

• Preweaning lamb growth rate should be emphasized because it is an indicator of dam milking ability.

  
  

• It is recommended that, a selection program should be organized to improve the local sheep by identifying the traits which have greater impact in economic return of the small ruminants.

  
  

• The study can give also a direction to improve local breeds through conservation-based with-in breed selection with a participation of small holder farmers in communities.

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

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