Flock dynamics of desert Barki sheep in relation to age structure.

Reproduction data of 8689 ewe records spread over 40 years (from 1960 to 2000) representing 2952 breeding Barki ewes were used in this study. The flock belonged to the Desert Research Center in Egypt. Flock dynamics of nine age groups (2-10 yrs) were assessed. Two parameters were used to evaluate flock dynamics, net reproduction rate (R(o)) (number of ewe- lambs reaching joining age and produced by each ewe during its lifetime in the flock) and intrinsic rate of increase (r(m)) (flock growth when no resource is limiting). Age of ewe had a highly significant (P < 0.01) effect on number of ewes lambing per ewe joined (E(PJ)), number of lambs born per ewe joined (L(BJ)), number of lambs weaned per ewe joined (L(WJ)) and number of ewe lambs reaching joining age per ewe joined (L(EJ.J)). All estimates tended to increase with dams age up to four years and decreased thereafter. The results of R(o) and r(m) showed that the studied flock must consist of 5 age groups to maintain its size and replace itself. It may be recommended to cull the breeding ewe at the age of 6 years to accelerate genetic improvement.