ارزیابی عوامل محیطی موثر بر زنده مانی بره های بلوچی از تولد تا شیرگیری

Abstract

Lamb survival is one of the major factors affecting overall sheep productivity. Lamb survival affected by environmental effect such as management, birth-type, year, season of birth, dam-age, maternal behavior, genotype of parents, and birth-weight. The data comprised 9989 records were collected from 1989 to 2009 in Iranian Baluchi sheep at Abbasabad sheep breeding station. Four binary traits created, value 0 was assigned for lambs dead and 1 for lambs alive at certain ages. Cumulative survival to day 10, 30, 60 and 90 (weaning) was calculated. Birth-weight, litter-size, birth-type, dam-age and birth-year considered in analysis. Statistical analyses of cumulative lamb survival at 10, 30, 60 and 90 days after birth analyzed by application of logistic model with binary response variable. Analysis of variance for cumulative survival each trait separately were analyzed using SAS with a linear model. The fixed effects of the model included dam-age, birth-year, birth-type, herd and sex. From 9989 lambs born at Abbasabad station over the period 1989-2009, There were 5147 (51.5%) lambs born as male and 4847 (48.5%) female which that 5583 (56%) lambs as singles 4239 (42%) as twins and 167 (2%) as triplet. Among the singles, 79 (1.5%) were dead at 10days after birth, 229 (4.1%), 373 (6.68%), 435 (7.8%) died at 30, 60 and 90 days after birth respectively. The results indicated survival of male lambs less than female at from birth to weaning, single and twin born lambs were more survival than triplet at each age. Lamb born from ewes 2 years old or in first parity had lowest survival compared with other parities. The least survival occurred in first parity as result of lack of maternal experiences of ewes at that stage. Average birth weight all lambs was 4.28 ± 0.7 Kg. male lambs had heavier birth weight than female lambs (4.4 ± 0.7 vs. 4.1 ± 0.6) also single born lambs (4.6 ± 0.6) heavier than twin or triplet born lambs 3.8 ± 0.6 , 3.3± 0.6 respectively . Linear and quadratic of birth-weight had significant effect on survival at 10, 30, 60 and 90days after birth. There was a curvilinear relationship between birth-weight and survival from birth to weaning. Survival for during birth to weaning maximized at 5 Kg although average birth-weight in this study was 4.3 Kg. Optimum birth-weight for survival of single, twin and triplet born lambs were 7, 5 and 4.3 Kg with (0.93, 0.93 and 0.92 %) survival compared average birth-weight at single, twin and triplet (4.6, 3.8 and 3.3 Kg) with (0.92, 0.92 and 0.91 %) survival. Female lambs had greater survival rate than male lambs at the same weight (1 to 2 %) Survival was maximized at 7 Kg birth weight for female (94 vs. 91.5% at average birth-weight) and male at 5 Kg which was only slightly heavier than average birth weight of 4.4 Kg.