The study of survival distribution function in Lori-Bakhtiari lambs from birth to yearling age

Data set used in this study were 6800 records of lamb’s length life and survival rate from 263 sires and 1839 dams collected from 1989 through 2009، from the Lori-Bakhtiari stud flock at Shooli station in Shahrekord. The frequency distribution for causes of culling and survival distribution function of lambs to yearling age were estimated by SAS. The results showed that 50. 47 percent of total lambs removed from the flock up to 1 year old of age. The most causes of removing lambs from the flock were extera-fattening lambs، mortality due to illness، experimental slaughter and bad phenotype، respectively. The accumulative survival from birth to yearling age of lambs was 78. 68 percent. The regression coefficient of survival from age of lamb up to yearling showed that the survival rate decreased by 0. 076 percent per day. The overall lambs mortality up to yearling age was 21. 32 percent، which occured 5. 84% in first triplet months، 8. 43% in second triplet months، 6. 23% in third triplet months and 0. 82% in fourth triplet months of life lambs، respectively. The most mortality rate occurred in first، fifth، fourth، sixth and ninth month of life lambs، respectively. Recommended to decreasing mortality rate in lambs، the managerial factors and rearing system of lambs should be improve in second and third triplet months by coplementarity feeding، because mortality rate in second and third triplet months of life lambs were higher than first triplet months.