GENETIC, PHENOTYPIC AND ENVIRONMENTAL TRENDS TOWARDS IMPROVING BODY WEIGHT IN BARKI SHEEP

ABSTRACT
Genetic, phenotypic and environmental trends for some body weights at birth (BW), 120 days (W120), 360 days (W360) and at 480 days (W480) were estimated to evaluate the breeding plan implemented in Barki sheep flock of the Desert Research Centre. The study also investigated the effects of various environmental factors on these traits. The data set employed in this study was obtained from 3192 records of lambs progenies of 186 sires reared at two research stations; Ras Elhekma (from 1963 to 1972) and Maryout (from 1973 to 2004). Animal breeding values, heritabilities and both genetic and phenotypic correlations for studied body weights were also estimated. Genetic and phenotypic trends were calculated by regression of breeding and phenotypic values on birth year respectively. Environmental trend was attained by subtracting genetic trend from the phenotypic one. Results indicated that average least square means of males had significantly heavier body weights compared with females for the studied body weights. As age of dam increased, body weights tended to be significantly heavier for BW and W120. Ras Elhekma research station exhibited heavier BW, W120 and W360 as well as lighter W480 compared with Maryout research station. The heritabilities of the studied body weights tend to increase as age increased. Genetic correlations among W120, W360 and W480 were greater with higher magnitude than those of phenotypic ones. Least squares means of animal breeding values for birth year were found to range from 3.50 kg to 3.68 kg, from 17.19 kg to 20.24 kg, from 30.46 kg to 37.27 kg and from 35.26 kg to 43.08 kg for BW, W120, W360 and W480, respectively during the examined study period. Genetic, phenotypic and environmental trends for the studied traits exhibited substantial irregular fluctuations among the examined years and being of higher magnitude in Ras Elhekma than in Maryout research station. Ras Elhekma research station had obviously positive genetic trend for BW (15 gm/ year), W120 (189 gm/year), W360 (448 gm/ year) and W480 (521 gm/ year) as well as negative phenotypic trend for BW (-18 gm/ year), W120 (-702 gm/year), W360 (-322 gm/year) and W480 (-345 gm/ year). Positive genetic trends appeared in Ras Elhekma research station indicate genetic improvement in Barki sheep flock reared in this location. The declines in the studied phenotypic traits observed in the Barki sheep flock during the examined period might be attributed to the negative and higher magnitudes of the environmental trends which might reflect some environmental inadequacies such as diseases, insufficient feeding and harsh climatic conditions.