Study of early growth traits in Horro sheep using sizable records at Bako Agricultural Research Center, west Ethiopia

S Alemayehu, T Jembere¹ and G Duguma¹

Bako ATVET College, PO.Box 21
¹ Bako agricultural research center, PO. Box 03, West Shoa, Ethiopia
tjbakara@yahoo.co.uk

Abstract

Birth (BWt), age corrected three (WWt), six (6MWt) and yearling (YWt) weights recorded during the last 34 years (1978 – 2011) were analyzed in the present study. Pre (Pre-ADG) and post (Post-ADG) weaning average daily gains were also analyzed. The objective was to investigate if the early growth traits showed variability over years, parities, sexes and type of births. Fixed effects of year, parity, sex of lambs and type of birth were fitted as class variables. The data were analyzed using the general linear model of SAS.

The overall means for BWt, WWt, 6MWt, YWt, Pre-ADG and Post-ADG were 2.6 kg, 11.7 kg, 15.5 kg, 25.7 kg, 90.9 g, and 50.7 g, respectively. All of the studied traits showed variability by year of birth. Post-ADG was the only trait that was not influenced by parity of ewes whereas type of birth affected all except YWt and Post-ADG. In general, the current results did not differ from earlier findings, though larger data size was used. In turn, it was verified that Horro sheep breed have high early growth potential. In conclusion, consideration of fixed factors of year, parity, type of birth and sex of lambs remain crucial while planning to exploit the genetic potential of the breed through selection.

Keywords: age corrected weight, daily gain, post weaning, pre weaning

Introduction

Small ruminants (sheep and goats) are widely spread in the tropics and are important to subsistence, economic and social livelihood of a large population in these areas (Kosgey 2004).  In Ethiopia, they have national importance as they provide about 46% of the national meat consumption and 58% of the value of hide and skin production, which is one of the few items for earning foreign currency from exports (Kassahun et al 1991). Sheep are able to adapt to broad range of environments and are found in all agro-ecologies of Africa (Rege 1994). Ethiopia has at least 14 traditional sheep population (Gizaw 2008) with an estimated number of 26 million (CSA 2008). Sheep production is important agricultural enterprise in the country. They have special features like efficient utilization of marginal and small plot of land, short generation length, high reproductive rate, low risk of investment and more production per unit of investment as compared with cattle (Rege 1994; Dixit et al 2005). Additionally, their multipurpose role as source of income, meat, skin, manure and coarse wool or long hairy fleece, as means of risk avoidance during crop failure and their cultural function during festivals are widely appreciated (Yadesa 1999; Kosgey et al 2008). Of the total sheep population in the country, 75% is found in the highlands where mixed crop-livestock production systems dominate, which cover areas 1500 masl, while the remaining 25% of the sheep is found in the lowlands (DAGRIS 2006). Among the local highland sheep population, Horro and Menz are the most important breeds in Ethiopia. Menz sheep is raised for its meat and coarse wool (Mason 1969); whereas Horro sheep is raised for its meat only. Hence improvement of Horro sheep in one way or the other should target its weight.

Genetic and phenotypic parameter estimates for Horro sheep were evaluated using relatively small data set so far (Abegaz 2002; Jembere 2010). Horro sheep research was commenced in the 1977 at Bako agricultural research center (BARC) and from then onwards, data have been recorded. Former works utilized only part of these data and recommended that larger data set have to be used to assess the real potential of Horro sheep especially on early growth traits (Abegaz 2002; Jembere 2010). The early growth traits studied in the present work included birth weight (BWt), age corrected three month weight (WWt), age corrected six month weight (6MWt),  age corrected yearling weight (YWt), pre--weaning average daily gain (Pre-ADG) and post-weaning average daily gain (Post-ADG). The objective of the present work was to investigate if the early growth traits showed variability over years, parities of births, sex of lambs and types of birth.

Materials and methods

Location:

The study was conducted at BARC, located 250 km west of Addis Ababa at an altitude of 1650masl. It lies at about 09°6’N and 37°09’E. Administratively, it is found in Gobu Sayo district, East Wollega Zone, Oromia, Ethiopia.

Climate:

The area has a hot and humid climate and receives a mean annual rainfall of about 1220mm, of which more than 80% falls in the months of May to September. Mean monthly minimum and maximum temperatures are about 14°C and 28°C, respectively with an average monthly temperature of 21°C. The mean daily minimum and maximum temperatures are 9.4°C and 31.3°C, respectively. Potential evapotranspiration averages were 60 mm per month (Yadesa 1998).  Total annual rainfall (mm) and mean minimum and maximum annual temperature (degree Celsius) during the study periods are given in Figure 1 and 2, respectively. Total annual rainfall of BARC for the same period also is given in Figure 1. The trend of the total annual rainfall during the study period was found to be irregular. In similar fashion the mean minimum and maximum temperature of the study area during the study period is given in Figure 2. The mean minimum and maximum annual temperatures during the study periods for the study area did not show variability. The mean maximum annual temperature ranged between 25⁰C and 30⁰C and mean minimum annual temperature ranged between 10⁰C and 15⁰C.

Figure 1. Total annual rainfall (mm) of BARC during the study period over years.

Figure 2. Mean minimum (lower) and maximum (upper) temprature of BARC during the study periods by years.

Soils and vegetation:

The soil belongs to Alfisols series and it is clay in texture (Piccolo and Assefa 1983), reddish brown in color with pH ranging from 5.3-6 (Dawit and Leggesse 1987). The vegetation cover of the area is woodland and open wood grassland type. The dominant pasture species include Hyperhenia (Hyperhenia anamasa) and Sporobolus (Sporobolus prraminmidalis) grasses and the legume Neonotonia (Ninotonia wighti) (Lemma et al., 1993 as cited by Abegaz 1994). 

Breed description:
Horro sheep are widely distributed in the western part of Ethiopia in the area which lies within 35⁰ to 38⁰ E and 6⁰ to 10⁰N (Galal 1983). The color pattern of the Horro sheep is plain. Their coat color is brown, creamy white (tan), brown and white. Patchy and spotted coat color is also common. Plain white and solid black colors are rare. The breed exhibits facial profile difference between sex where almost all females have straight but in males it is slightly convex. The nature of the breeds’ tail is either hanging straight downward or twisted at the end (Edea 2008); are fatty and triangular with a relatively narrow base reaching just below the hock. Both sexes are pooled with semi- pendulous ear type. Picture of the breed is given hereunder (Photo 1).

Photo 1. Horro sheep: left: flock while grazing in their Homeland Horro District; middle and right: -Horro rams and ewes at BARC, respectively.

Often rams have mane between the head and the brisket and above the neck and the shoulder. The mean height at shoulder for adult males and adult females is 73±1.3 and 68±0.8 cm (Galal 1983), respectively. Based on the large geographical area which the Horro sheep breed is believed to inhibit and statistical report on the sheep residing in these areas (the then east and west Wollega, Illubbabor, Jimma and Kificho Shekicho zones), it can safely be assumed that the breed is not at a risk of extinction (Abegaz and Duguma 2002). The breed was reported to be the second largest in terms of population density amounting 3,409,300 next to Arsi-Bale sheep (Gizaw 2008). 

 Flock management and data:

The management of the flock was described in previous works (Abegaz 1994; Abegaz and Duguma 2000; Abegaz 2002; Jembere 2010). Birth (BWt), age corrected three (3MWt), six (6MWt) and yearling (12MWt) weights generated during the last 34 years (1978 – 2011) were analyzed in the present study. Birth weights (kg) were taken within 24 hours after birth. Individual WWt, 6MWt and YWt were adjusted to 90, 180 and 365 days using individual BWt and average daily gain from birth to WWt, 6MWt and YWt, respectively. The age corrected weights were calculated as:  

Where Adj.Wt.= age corrected 3MWt, 6MWt and 12MWt; Current weight=exact weight of sheep recorded at these ages; current age=exact age of lambs at measurement 3, 6 and 12 month weights; intended age was 90 days for WWt, 180 day for 6MWt, and 365 days for YWt.

Pre-ADG and Post-ADG average daily gains were also studied. Pre-ADG (g per day) was calculated as the difference in weight between weaning and birth, divided by age in days at weaning. Post-ADG (g per day) was calculated as the difference in weight between weaning and yearling, divided by age in days from weaning to yearling. The data were analyzed using the general linear model of Statistical Analysis System (SAS 2002).  

Results and discussion

All the growth traits studied showed variability by year of birth which could be due to the variability of total annual rainfall in the area during the study periods which in-turn affected growth of vegetation, quantity and quality of feeds for the sheep under study.

The overall mean for BWt, WWt, 6MWt, YWt, Pre-ADG and Post ADG were 2.6 kg, 11.7 kg, 15.5 kg, 25.7 kg, 90.9 g, and 50.7 g, respectively (Table 1). The BWt, YWt and Post-ADG of male lambs were significantly higher than that of female lambs but the rest of the growth traits did not significantly differ by sex of lambs. The significant effect of sex of lambs on 6MWt, 12MWt, and Post-ADG might be due to the fact that males might be busy attempting mating and probably due to the difference in the amount of growth hormone secreted by male lambs compared to female lambs in line with the advancement of the age of the animals.
 

Lambs born single had higher growth performance except for the Post-ADG. The weight of single born lambs was significantly higher than that of multiple born ones due to the fact that multiple born lambs had shared uterine environment, for instance in the case of BWt, whereas there was no competition for the uterine environment in the case of single born lambs. BWt of lambs born from the first parity was lighter than those born in the rest parities. In similar fashion, WWt, 6MWt and 12MWt from the first parity were lower than from the rest but were comparable with the last parities. However, the effect of parity was not manifested on Post-ADG. During the initial parities the uterine environment of the ewes is new and hence could have resulted in lower growth performance.

The BWt, WWt, and 6MWt, and YWt are given in Figure 3 and Pre-ADG and Post-ADG are given in Figure 4 for the different years. BWt was found to be stable for the different years due to the fact that it was more of affected by the maternal environment than physical environment. However, the WWt, 6MWt and YWt showed 'zigzag' pattern mainly following the rainfall pattern of the study area. In years with high rainfall, these growth parameters showed an improvement and declined otherwise. This was related to the growth of feeds and its availability to the sheep. The same pattern was observed in Pre-ADG and Post-ADG.

Figure 3. Birth weight (BWt), age corrected weaning weight (WWt), six (6MWt) and yearling weight (YWt) by year of birth of Horro sheep.

Figure 4. Least squares means of pre (Pre-ADG=Prew) and post (Post-ADG=Postw) weaning average daily gain by year of birth of Horro sheep.

Conclusion

• The early growth performances of Horro sheep were affected by year of births, type of birth, sex and parity.

  
  

• Improved growth performances were observed during years with high total rainfall. This was probably due to the fact that the amount of rainfall determined the feed availability and quality.

  
  

• The single born lambs always outperformed the multiple born lambs, even after weaning, probably due to the presence of moderate management to lambs at BARC. Due to this fact single born lambs resisted the weaning shock.

  
  

• The feed availability was found to be the most modulating factor of the early growth traits in Horro sheep which was affected by amount of rainfall.

  
  

• In general, the finding from the present study did not differ from earlier works and verified that Horro sheep have high early growth potential.

  
  

• Consideration of fixed factors of year, parity, type of birth and sex remain crucial while planning to exploit the genetic potential of the breed.

Acknowledgment

The authors are thankful to livestock research sector that has been generating the data and BARC for allowing us to use the data.

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Received 5 July 2016; Accepted 17 December 2016; Published 1 February 2017

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