Evaluation of Phenotypic and Morphometric Characteristics in Community Based Breeding Program of Gumer Sheep

MATERIALS AND METHODS

Description of the study area: The study was conducted in the Gumer district, which is geographically located in Gurage Zone SNNPR, Ethiopia. The study was carried out at the South Agricultural Research Institute of Worabe Agricultural Research Center from 2015-2020. The geographic coordination of the district is 7°55ʹN 38°05ʹE with an altitude range of 2500-3000 m above sea level. According to the world metrology organization, the maximum and minimum temperature of the district is 26 and 12°C with an average of 19°C and the average annual rainfall is 1226 mm. According to personal observation and discussion with elder people in the area, the rainy season ranges from May to November and the dry season extend from December to April. The production system in this area is mixed crop-livestock and suitable for cereal production due to suitable weather conditions.

Breeding program and animal management: All CBBPs (Abeke, Denber, Enjefo and on-station) were established in 2014. Gumer sheep is not a seasonal breed, lambing is observed all year round. The founder stocks of sheep were tagged for identification with a plastic ear tag and the lambs were tagged before weaning. The ear tag contained information on the code of the CBBP, the Identification Number (ID) of the animal and year of birth or registration. The data recorded for each lamb included their sex, Birth Weight (BWT), Weaning Weight (WWT), Six Months Weight (SMWT), Yearling Weight (YWT), coat colour pattern, animal ID, sire ID, dam ID, birth date, birth type, parity, CBBP name and owners name. The selection of male lambs was carried out separately within each CBBP based on their Estimated Breeding Value (EBV) at SMWT. Lambs with undesirable traits like white and black coat colour were culled regardless of their EBV. The maternal selection for Gumer sheep CBBP was not undertaken due to the small flock size per household. The total flock size for Gumer CBBP participants of 153 members was 520 sheep. This indicates that the average flock size for each household of the area was 3.42. The reason for the lower flock size is the selling of their sheep due to shortage of grazing land and fear of predators like a hyena. Flocks were kept in animal a house which is shared with kitchen during night and midday. The houses were made of wooden walls and covered by mud with straw corrugated with grass or corrugated iron. The major feed resources were pasture, crop residues and kitchen leftovers.

Data collection: Bodyweight (BW) data used for this study were BWT, WWT, SMWT and YWT. Similarly, Average Daily Gains (ADGs) like ADG from birth to weaning weight (ADG₁), ADG from weaning to 6 month (ADG₂) and ADG from 6 month to yearling (ADG₃) were collected. ADG was calculated as:

Where:

When referring to WWT, SMWT and YWT, these are age-corrected traits such that, for example:

where, wwt is the three months weight recorded at approximately three months and age is the recording date minus birth date in days. SMWT and YWT are calculated similarly.

The total BW data used for this study were 988, 854, 708 and 404 for BWT, WWT, SMWT and YWT, respectively. Data sizes for ADGs used for the current study were 853, 711 and 572 for ADG₁, ADG₂ and ADG₃, respectively whereas 678 data of ewe were used for prolificacy traits evaluation. A suspended weighing scale 50 kg capacity with an accuracy of 100 g was used to record BW. Linear Body Measurement (LBM) data were collected from mature 85 male and 200 female sheep by using the purposive sampling technique. These LBMs BW, Body Length (BL), Height at Wither (HW), Heart Girth (HG), Horn Length (HL), Tail Length (TL), Scrotal Circumference (SC), Tail Circumference (TC) and Ear Length (EL).

Data analysis: The effect of non-genetic factors like a year of birth (6 levels: 2015-2020), sex (2 levels), litter size (3 levels: single, twin and triple), birth season (2 levels: dry and wet), animal coat colour (8 levels) and CBBP (4 levels) were analyzed by using general linear model procedures of the Statistical Analysis System (SAS). Both BW and ADGs at different ages were considered as response factors and subjected to the adjusted Tukey-Kramer method when significant in SAS. Similarly, the non-genetic factors for prolificacy traits included lambing year (6 levels: 2015-2020), CBBP (4 levels) and lambing season (2 levels). The correlation between LBM traits was estimated as the ratio of the estimates of the covariance between traits one and two to the product of the square roots of the estimates of variance for traits one and two⁵. A stepwise regression procedure was used to determine the best fitting regression equations for the prediction of the live body weight of both sexes. Regression equations were calculated and the highest adjusted coefficient of determination (R²_adj) was used to establish the accuracy of the equations. The following regression model was used for estimation BW from LBM:

Where:

RESULTS

Growth rate traits: The overall least square Mean±SE for BWT, WWT, SMWT and YWT of Gumer sheep were 2.09±0.02, 11.63±0.20, 15.76±0.42 and 21.14±0.64 (kg), respectively (Table 1). The effect of birth year, CBBP and litter size was significant (p<0.0001) for BW traits (Table 1). Whereas birth season except for WWT, sex except for BWT and coat colour pattern fixed effects were not significantly affected BW of Gumer sheep. Similarly, the overall least-square Mean±SE for ADG₁, ADG₂ and ADG₃ were 105.31±2.21, 47.71±5.16 and 20.82±4.48 g/day, respectively (Table 2). The effect of birth year and CBBP of animals was significant (p<0.0001) for all ADGs. Gumer sheep ADGs were not significantly affected by sex, litter sizes except for ADG₁ and the coat colour pattern of the animal (Table 2).

Prolificacy trait of Gumer sheep: The overall least square Mean±SE for litter size of Gumer sheep was 1.65±0.02 lambs and the Coefficient of Variation (CV) was 31.24% (Table 3). The percentages of twins and triplets were 70.34%. This trait was statistically significant (p<0.0001) variation across different CBBPs but non-significant across lambing year and season. The lower litter size performance was recorded from the on-station of Gumer site which is related to poor management in the station. Flushing the ewe at least three weeks pre-mating is important to increase litter size which was not implemented at this sheep station. The overall prolificacy of this sheep population was higher than any other indigenous and some exotic sheep breeds.

Linear body measurements of Gumer sheep: Mature BW for male and female of Gumer sheep was 29.13±0.971 and 26.11±0.454 kg, respectively and statistically significant between sexes of sheep (Table 4).

Similarly, both EL and HL were significantly different for male and female sheep. Most ewes are prolific and have a large frame which may be the reason for related and non-significant traits like BL, HG and HW between male and female sheep. Also, farmers share their food for their prolific ewes than breeding sires result in related body size for both sexes of sheep.

Correlation between body weight and linear body measurements: The BW had the highest correlation with BL (0.892) followed by HG (0.861) and HW (0.792) for male sheep (Table 5). The EL of male sheep had a non-significant association with BW. The BL of male sheep had the highest correlation with HW (0.777) and HG (0.768) but no association with EL. Similarly, BW of female sheep had highly correlated with HG (0.602) followed by BL (0.296) and EL (0.289) but HW and TL had a non-significant correlation (Table 5). Unexpectedly TL of female sheep was negatively correlated with BL and HG.

Prediction of body weight estimation equation: The best regression model for live weight estimation to be used by farmers without the use of a weighing scale for the Gumer sheep population was determined separately by sex. It indicated that BW is estimated by morphometric measurements which included HG and BL for male sheep but HG alone was an important trait for female sheep. The model for BW estimation for male sheep was Y = -42.29+0.46 HG+0.53 BL with R²_adj = 0.87 and for female sheep Y = -16.11+0.40 HG with R²_adj = 0.50. The accuracy was expected because HG was linked to the chest and abdominal area which dominate the volume of BW than the chest to the base of the tail known as BL.

DISCUSSION

The studied BW showed a fluctuating trend over the years of 2015-2020. Numerically the value of BW for BWT and WWT is higher during the initial year of CBBP (Table 1). Whereas, the efficiency of the enumerator was poor during the initial period and the number of observations for the mentioned year was few which lead to difficulty to recorded BW being higher. Possible reasons for the fluctuating trend of BW may be the number of recorded data differences, enumerators record-keeping know how variation through time, a variation in environmental conditions and the availability of forage and feeding over the last 6 years (2015-2020). The performance of Gumer sheep was comparable with other local sheep breeds such as sheep ecotype of Jimma zone, Afar, Washera, Farta, a cross of Wahera and Farta and Atsbi highland sheep breeds reported as 8.98±0.24-14.8±0.22 kg for WWT, 13.7±0.30-23.8±0.16 kg for SMWT and 16.9±0.45-26.9±3.98 kg for YWT^6-8, respectively. Results showed that BWT was significantly higher for on-station but the least for WWT, SMWT and YWT. The main reason for lower BW from on-station was poor animal management like feeding, supplementing during the dry season and health care. Enjefo CBBP had higher WWT, SMWT and YWT among CBBP cooperatives. This performance comparison of the same breed at on-farm and on-station breeding programs indicated that management at the farmers level organized by CBBP was comparatively better. It incurs low cost and better performance than the on-station breeding program. It leads to focus on CBBP as a best breed improvement program in the study area than governmental station site. Bodyweight gain after SMWT was relatively lower than Bonga and Karangploso sheep which were 98.7±2.40 and 93.29±26.73 g/day, respectively^9,10. Litter size had a significant effect ( p< 0.001) on BWT, WWT and SMWT (Table 1). It shows that a uniform trend was exhibited in BW among singles, twins and triplets wherein the BW of single born lambs was higher and triplets lower. The higher body weight in single born lambs may be as a result of the optimum nutrition during both pre and postnatal stages of growth. The superiority of BW of singles over multiple born lambs after weaning was lost due to the decline of maternal effect⁸.

Numerically the value is increasing trend for litter size across 6 lambing years (2015-2020) but statistically not significant (Table 3). Even though the selection was based on SMWT EBV of ram lamb that didn’t influence the prolificacy trait of Gumer sheep. This may be as a result of twins and triplet dam and sire dominating flock. It had an opportunity to increase for the future when we consider it as a selection criterion. Litter size is one of the major non-genetic factors which have a multifaceted influence as it regulates both reproduction and production in sheep 11 . The current result of the twinning rate was higher than Bonga and Horo sheep breeds reported as 39.9 and 36%, respectively¹². The litter size of Gumer sheep obtained in this study was higher than local sheep breeds such as the local ecotype of Jimma zone, Bonga, BHS, Menz, Washera, Horro and Atsbi highland sheep breeds reported in the range of 1.02-1.45±0.01^6,8,13-15. Additionally, the Gumer sheep breed had a higher litter size than West African Dwarf Djallonke sheep, Iranian Afshari, Red Masai and Tumelie-Dorper cross sheep breed reported in the range of 1.05-1.4±0.5^7,16-18. Rekik et al.¹⁹ reported that litter size can be increased by improving the nutrition management of the pre-mating. According to Thompson²⁰, a kilogram increase of ewes BW at mating could improve twining by about 3%.

Gumer sheep is mainly known for its uniform coat colour of plain brown-black and brown-black with white and these colours are preferred by farmers. The percentage of these colours among the CBBP population was nearly 71.5% (Table 1). These colours determine the market price of sheep. The other types of coat colours which are not preferred by farmers viz, white, grey and black were introduced due to the continuous flow of animals from markets.

The value of LBMs for mature male and female sheep of the current study was in agreement with the report of¹. The higher LBMs of males than females might be due to hormonal differences in growth. Gumer sheep have a better frame of HG than indigenous sheep found in south Ethiopia (Kemata and Hadiya, Wolita, Gamogofa and Sidama and Gedio) which is 70.9±1.6, 72.8±7.1, 73.0±6.5 and 72.1±1.5 but related by BL, HW and other morphometric traits¹. Additionally, Gumer sheep have large SC than above mentioned South Ethiopian sheep breeds which were 22.5±2.5, 23.5±2.3, 20.5±3.4 and 20.6±3.0 cm. These variations may be the effect of both genotype and environment in different areas. Naturally, animals raised in the mountain and high rainfall available region tend to be shorter than dry areas due to leaching of some important minerals.

The correlation between the independent variable of morphometric traits was less than 0.90 which suggest that there is no multicollinearity. Similarly, Ibrahim et al.²¹ explained that the correlation of independent variables which had below 0.90 indicate no multicollinearity. The correlations of BW with BL and HG of the current research was aligned with previous research for female Batur sheep²¹.

The regression equations are unique for every category of livestock and vary according to the area, sex, age and breed. Information on the weight of sheep is important for medication, marketing, breeding and supplemental feeding. Under traditional farm conditions where access to a weighing scale is unavailable other options are mandatory. The most widely used method for estimating the weight of sheep under farm conditions are using a regression equation developed from LBMs for the breed because it is practical, faster, easier and cheaper where the resources are insufficient¹. Using spring balance to measure live body weight need labour to lift up the animals 8. In the current study, both HG and BL are important to determine the BW of male sheep but HG alone is sufficient for female sheep. This is in agreement with the regression equation determined for Washera, Farta and across of Washera and Farta sheep breeds⁸.

The implication of this study was to expand the CBBP breed improvement strategy to further improvement for both the growth and prolificacy traits of Gumer sheep. The significant effect of non-genetic factors namely, a birth year, CBBP and litter size of lambs for the BW suggests considering them during EBV determination for selection. A significant correlation between LBMs and BW guarantee the application of using the regression equation to predict live body weight. To get clear within breed variation genetic parameter estimation is important. Therefore, we recommended estimating genetic parameters and evaluating genetic gains across years by using breeding values of selection traits.

CONCLUSION

The BW of Gumer sheep was in increasing trend and positively influenced by CBBP. Within variation of the population was high which indicated the possibility for further improvement through selection for both BW and prolificacy traits. Heart girth is comparatively the primary variable for the prediction of BW for both sexes. The best and accurate prediction equations of Gumer male and female sheep were Y = -42.29+0.46 HG+0.53 BL and Y = -16.11+0.40 HG, respectively. However, if this sheep is raised under varying agro-ecological conditions and different management options, it is logical to expect variation in estimator and accuracy of body weight.

SIGNIFICANCE STATEMENT

This study discovers the possible animal breeding program option, effect of non-genetic factors and method of animal breeding program evaluation. This study will help the researcher and policymaker to uncover the critical area of breed improvement in the low input-output production system. Thus, a new approach of CBBP for breed improvement programs with the full participation of the community at every stage of the program.

ACKNOWLEDGMENTS

The authors acknowledge the financial donor of the South Agricultural Research Institute (SARI) and the farmers for providing their animals and precious time for this study. This research was done by using an annual budget for the last 6 years (2015-2020) nearly 400-500 USD.