Effect of genetic and environmental factors on the growth performance traits of Pak-Awassi sheep

Present research was carried out to investigate the genetic characteristics of Pak-Awassi Sheep with respect to the growth performance traits and estimation of the genetic parameters. The 10 years (2004-2013) data regarding the growth performance traits of Pak-Awassi sheep maintained at livestock experimental station Nabisr, Umar Kot, Sindh were utilized for the current study. The result for genetic parameters heritability for birth weight and yearling weight was observed low, while correlation and regression coefficient was observed medium and positive for birth weight and yearling weight. The effect of season was observed significantly higher on lambing rate of Pak-Awasi sheep. It is concluded that winter season has significant effect on lambing rate, while the low heritable traits can be improved with better management and selection practices.


Introduction
At present Pakistan has 28 sheep breeds and Sindh possess about 16% to total sheep population of Pakistan [1].Small ruminant especially sheep is well known for serving multipurpose animals for milk, meat and wool.Pak-Awassi sheep breed is cross of Awassi sheep of Lebanon and Kachhi native breed of Sindh, that is why this breed is well known for serving multipurpose sheep for milk, meat and wool purpose.
Pak-Awassi sheep commonly found in Tharparkar district of Sindh.Information regarding the genetic factors and their influence on the productive traits is of interest to farmers as well as the animal breeders, because influence of genetic factors helps to improve animal production and also in the planning of herd management program [2, 3].The concept of genetic parameters such as heritability, correlation and regression estimates are essential for planning of efficient breeding programs and to predict the response to selection, high values of genetic factor can cause improvement of productive traits of selected animals [3, 4].

Material and methods
The available Ram-wise data of 10 Ram's with total 14 animals of each Ram of Pak-Awassi sheep was brought under the study.The data regarding growth traits including birth weight and yearling weight was maintained and collected for period of 10 years 2014 to 2013 on especially designed profroma.The data was collected from livestock experimental station Nabisr, Umar Kot, Sindh, Pakistan.

Genetic analysis
The estimation of genetic parameters heritability, correlation and regression coefficient was analysed according the formula as suggested by (Becker, 1985) [3].

Season of lambing
The seasons of lambing were divided into two seasons, i.e. summer (Aprilto September) and winter (October-March).

The Ram-wise data for birth weight and yearling weight of Pak-Awassi sheep
The Ram-wise results for birth was observed higher in Ram-Tag: 2 (3.742±0.148ab ), while it was observe lower in Ram-Tag: 17 (3.601±0.145d ).The Ram-wise results for yearling weight was found in Ram-Tag: 18 (38.264±1.540a ), whereas it was observed lower in Ram-Tag: 3 (37.027±2.519abc ) details are mentioned in Table 1.

Results of heritability (h 2 ) and correlation coefficient estimates for birth weight and yearling weight
The results of heritability (h 2 ) estimates for birth weight and yearling weight of Pak-Awassi sheep was observed low.While the correlation coefficient estimates was observed positively high among birth weight and weaning weight, details are given in Table 2.

of regression coefficient estimates between birth weight and yearling weight
The results of regression coefficient estimates are presented in graph.The graph shows a positive and strong relationship between both traits of Pak-Awassi sheep, details are present in Graph 1.

The results for the effect of season on the lambing rate of Pak-Awassi sheep
The season wise lambing results of Pak-Awassi sheep showed that higher lambing rate was observed in winter season (October to March), while lower lambing rate was found in summer season (April to September), details are presented in Table 3.

Heritability and correlation and regression coefficient
In current investigation the results of heritability was observed lower as compared to study conducted by [8, 9], who reported high heritability estimates for birth weight and yearling weight Kachhi and Pak-Awassi sheep breed respectively.The same statement repeated by [10, 11], they had also mentioned high heritability for birth weight and yearling weight in Suffolk and Karadi sheep breeds.The results of correlation and regression coefficient showed positive and high correlation and regression coefficient between birth weight and yearling weight of Pak-Awassi sheep.The findings of our study are in agreement with the research conducted by of [11-13], they had been reported higher as well as positive correlation and regression coefficient between birth weight and yearling weight of Awassi, Karadi and indigenous Ethiopian Horro sheep breeds.The same results also observed by [6, 7], they have also reported high and positive correlation as well as regression coefficient between birth weight and weaning weight of Turkish Awassi and cross breed sheep.The findings of our study are opposition to the results of [14] in Barki and [15], they reported lower correlation and regression coefficient between birth weight and yearling.The mention difference may because of different seasons and different feeding process and availability of fodder.Low observation of correlation and regression may be due to inbreeding depression, while high positive correlation as well as regression estimates showed increase in one traits will positively affect or increase other trait.

Effect of season on lambing rate and birth weight and yearling weight
The effect of season on lambing rate as well as on the birth weight and yearling weight in current study was found significant.The observation of current results are in opposition of results of [16,17], they reported that season was observed nonsignificant effect of season lambing rate, birth weight and yearling weight of Baluchi sheep breed in Baluchistan.The different among study may be due to dry arid land and climatic conditions and their effect of Baluchistan province.The findings of current study are in agreement with the results of [6, 18], they had reported higher significant effect of season on lambing rate and birth weight and yearling weight of Madras red sheep breed.The similar statement reported by [3, 19] they reported higher lambing rate in winter and lower in summer season, while birth weight and yearling weight was also observed higher in winter as compared lower in summer season.The different among researchers is due difference of breed their genetic diversity and climatic condition such as hot, humid and cold season has greater effect on the lambing rate and growth traits of animals.

Conclusion
It was concluded the genetic and nongenetic parameter has greater effect on the growth traits of Pak-Awassi sheep.Due to low heritability results it is concluded to improve low heritable traits with the help of management and feeding practices of farm due to better management and feeding effect of non-genetic factors can also be overcome.

Results for effect of season of lambing on the birth weight and yearling weight Season of lambing No. of observation
Juma KH, Alkass JE, Amir A & Fahim T (1998).Factors affecting on yearling weight in indigenous Iraqi sheep.Proc.6 ltl World Cong., Genetics Applied to Livestock, Armidale, Australia 11-16 January 24: 220-222.10.Gürsoy O (2005).Small ruminant breeds of Turkey.In Characterization of Small Ruminant Breeds in West Asia, North Africa, Vol 1: West Asia,