Determination ofinfluences of some genetic and environmental factors on fertility and preweaning growth traits and estimation of selection indexes for these traits in pirlak sheep

In this study, it was aimed to investigate the effects of some genetic and environmental factors on the fertility and pre-weaning growth characteristics of Pırlaks, and establish selection indices by estimating genetic parameters related to these traits to improve the yield characteristics. The data were collected from the four Pırlak elite herds in the project of ''Improvment of Pırlaks in Public Hand'' conducted by the General Directorate of Agricultural Research and Policies among 2015 and 2016. Birth rate was found to be 1,13 per ewe. Least square means for birth weight, 60th, 75th, 90th, 105th, 120th and 130th days weights were 3,757; 14,248; 16,346; 18,556; 20,355; 21,299 ve 25,189 kg respectively. In the study, least square means of lambs for 60th, 75th, 90th, 105th, 120th and 130th days backfat thickness were 1,605 mm; 1,715 mm; 1,997 mm; 2,175 mm; 2,529 mm and 2,720 mm respectively. Least square means of lambs for 60th, 75th, 90th, 105th, 120th and 130th days eye muscle depth were 1,515 cm; 1,608 cm; 1,726 cm;1,809 cm; 1,814 cm and 2,014 cm respectively. Least square means of lambs for 60th, 75th, 90th, 105th, 120th and 130th days eye muscle width were found to be 4,339 cm; 4,532 cm; 4,974 cm; 5,272 cm; 5,467 cm and 5,668 cm respectively. Least square means of lambs for 60th, 75th, 90th, 105th, 120th and 130th days eye muscle area were 4,510 cm2; 5,165 cm2; 6,006 cm2; 6,615 cm2; 6,961 cm2 and 8,149 cm2 respectively. The effect of geographical region and birth time on the litter size was significant (P <0,05). The effects of the geographic region, birth time, sex, birth type, birth weight, age of dam and weaning age on live weight, backfat thickness, eye muscle depth, eye muscle width and eye muscle area of lambs examined in different growth periods were insignificant in a given periods but in some periods those effects were found to be significant (P <0,05) at different levels. The total heritabilities of yield characteristics were analyzed using the Wombat program. For litter size, birth weight, 60th, 75th, 90th, 105th, 120th and 130th day live weight of total heritability were calculatedas 0,30 ± 0,11; 0,94 ± 0,15; 0,19 ± 0,09; 0,29 ± 0,12; 0,33 ± 0,13; 0,49 ± 0,15; 0,23 ± 0,10 ve 0,30 ± 0,15 respectively. The total heritability of backfat thickness, eye muscle depth, eye muscle width and eye muscle area were found for 60th day 0,14 ± 0,13; 0,025 ± 0,09; 0,23 ± 0,14 ve 0,15 ±0,13; for 75th day0,22 ± 0,11; 0,18 ± 0,10; 0,87 ± 0,19 ve 0,16 ±0,11; for 90th day 0,52 ± 0,15; 0,15 ± 0,09; 0,99 ± 0,19 ve 0,09 ±0,07; for 105th 0,18 ± 0,09; 0,09 ± 0,07; 0,30 ± 0,11 ve 0,12 ± 0,07; for 120th 0,23 ± 0,10; 0,19 ± 0,10; 0,10 ± 0,08 ve 0,18 ± 0,09 and for 130th day 0,04 ± 0,11; 0,23 ± 0,14; 0,10 ± 0,12 ve 0,25 ± 0,14 respectively. The selection indexes constructed using by birth weight of lambs (X1) and live weight of lambs at 90th day (X2) as follows: I = 0,777 X1 + 0,386 X2 ; live weight of lambs at 90th day (X1) and eye muscle depth of lambs at 90th day (X2) as follows: I= 0,418 X1 + 0,066 X2 and live weight of lambs at 90th day (X1) and backfat thickness of lambs at 90th day (X2) as follows: I = 0,238 X1 + 0,290 X2. As a result, it has been determined that the effects of different environmental factors should be taken into consideration in a selection program, and it is concluded that the genetic parameters of different characteristics have the potential to increase reproductive and growth performance for Pırlak's and the established selection indexes could be accelerate the improvement.