Direct and maternal genetic parameters and genetic trends for some body weights and growth traits in barki sheep

الملخص EN

Body weight records of 3189 Barki lambs progenies of 186 sires and 1748 ewes were obtained from Barki sheep flock maintained at Ras Elhekma (from 1963 to 1972) and Maryout (from 1973 to 2004) research stations which belong to the Desert Research Centre in order to assess direct and maternal genetic parameters and genetic trends to evaluate the breeding strategies implemented for improving growth performance in Barki sheep.

The present study dealt with body weights at birth, BW ; weaning, WW and yearling, YW as well as average daily gain from birth to weaning, DGBW and from weaning to yearling, DGWY.

Data were analyzed by fitting a direct- maternal animal model using the MTDFREML program to estimate direct and maternal expected breeding values and correlations.

Breeding values were plotted against year of birth to obtain genetic trends for the studied traits.

Results indicated the importance of maternal effects on the studied body weights and growth traits in Barki sheep.

Maternal correlation coefficients (either genetic or environmental) were positive and higher than the corresponding phenotypic and direct ones.

Genetic trend analysis for the studied traits indicated, on one hand, that there is virtually no difference between direct and maternal breeding values and hence genetic trends across the examined years which reveal that maternal genetic effects are of importance and probably have the same impact as the direct genetic effects.

On the other hand, two distinct trends were clearly illustrated in which the positive genetic trends in body weight exhibited till 1975- 1976 and then dropped and remained constant, thereafter.

This time probably coordinated when the sheep flock had just moved from Ras Elhekma to Maryout research station.

At Ras Elhekma research station, genetic progress achieved in the studied traits appeared to be generally significant and positive but of little magnitude throughout the examined years with slightly higher maternal genetic improvement compared with the respective direct genetic one.

However, the annual direct and maternal genetic trends were generally negative, not significant and almost zeros at Maryout research station.

Such no or minor genetic response exhibited for the studied traits during the evaluated years might be a result of lacking effective directional selection, management system applied and incompatible environmental conditions.

Likewise, it could probably be attributed to neglecting the maternal influences either genetic or environmental throughout the implementation of breeding program which used to depend entirely on direct genetic effects.

Implications of including both direct and maternal effects into the breeding program to improve growth performance in Barki sheep have been discussed.