Determination of genetic and environmental factors affecting growth curve and sire evaluation with the aspect of curve parameters in pırlak lambs

Determination of genetic and environmental factors affecting growth curve and sire evaluation with the aspect of curve parameters in Pırlak lambsIn this study, it was aimed to obtain the growth curves of Pırlak lambs with different mathematical models, to detect the effects of different environmental and genetic factors and and to investigate the possibilities of utilization of curve parameters for sire ram evaluation.Bertalanffy, Brody, Gompertz and Logistic models were applied to live weight, wither height, body length, chest depth, front chest width, rump width, chest circumference and shank circumference measurements of 328 Pırlak lambs born in Afyon Kocatepe University Research and Application Center in 2008 and 2009. Non-linear regression method were utilized for curve fitting and coefficient of determination (R2) was used for fitting criterion. The highest R2 values for live weight, wither height, body length and chest depth, front chest width and rump width, chest circumference and shank circumference were found in Brody as 95,58%; Bertalanffy and Brody as 93,00%; Brody as 90,52% and 91,28%; Bertalanffy as 89,84% and 93,67%; Brody as 94,06% and Bertalanffy as 84,94%, respectively. The effects of birth year, birth month, birth type, gender and age on the growth curves were significant (P<0,05).Genetic parameters were estimated by using REML procedure and WOMBAT computer program. Best direct, maternal and total heritabilities for the curve parameter A were detected with Logistic model. These values were found to be 0,25±0,25; 0,16±0,1 and 0,33±0,21 for live weight; 0,32±0,35; 0,24±0,16 and 0,45±0,28 for wither weight; 0,24±0,46; 0,19±0,19 and 0,34±0,39 for body length; 0,37±0,39; 0,20±0,14 and 0,47±0,33 for chest depth; 0,29±0,40; 0,15±0,17 and 0,36±0,33 for front chest width; 0,36±0,41; 0,27±0,18 and 0,49±0,33 for rump width; 0,22±0,02; 0,11±0,09 and 0,27±0,04 for chest circumference and 0,32±0,83; 0,54±0,40 and 0,58±0,65 for shank circumference, respectively. Best direct, maternal and total heritabilities for the curve parameter B were determined with Bertalanffy model. These values were calculated as 0,02±0,04; 0,96±0,02 and 0,50±0,03 for live weight; 0,27±0,32; 0,39±0,16 and 0,47±0,27 for wither weight; 0,13±0,19; 0,53±0,10 and 0,39±0,16 for body length; 0,14±0,22; 0,70±0,11 and 0,49±0,18 chest depth; 0,24±0,32; 0,58±0,14 and 0,53±0,26 for front chest width; 0,31±0,53; 0,42±0,27 and 0,52±0,44 for rump width; 0,23±0,29; 0,58±0,15 and 0,52±0,24 for chest circumference; 0,30±0,58; 0,43±0,28 and 0,51±0,50 for shank circumference, respectively. Best direct, maternal and total heritabilities for the curve parameter k were determined with Brody model. These values were 0,30±0,49; 0,32±0,20 and 0,47±0,41 for live weight; 0,28±0,33; 0,22±0,14 and 0,39±0,28 for wither weight; 0,31±0,47; 0,21±0,18 and 0,42±0,40 for body length; 0,30±0,35; 0,20±0,15 and 0,40±0,30 chest depth; 0,29±0,39; 0,15±0,16 and 0,37±0,33 for front chest width; 0,29±0,49; 0,19±0,20 and 0,38±0,42 for rump width; 0,32±0,39; 0,21±0,16 and 0,43±0,32 for chest circumference; 0,32±0,42; 0,29±0,18 and 0,47±0,35 for shank circumference, respectively. Significant (P<0,05) genetic correlations ranging from 0,710±0,332 to 0,888±0,081 were found between A and B for wither height, front chest width, rump width, chest circumference and shank circumference by Gompertz model. Significant (P<0,05) genetic correlations between A and k for live weight and wither height were ranged from -0,642±0,318 to -0,678±0,288 by Logistic model. In this model, genetic correlations between A and B for front chest width, rump width, chest circumference and shank circumference were significant (P<0,05) and among 0,648±0,260 and 0,998±0,002. Genetic correlations between birth, six month and yearling weights were significant (P<0,05) and changed from 0,519±0,248 to 0,864±0,120. Significant (P<0,05) or approached to significant (P<0,10) total heritabilities ranging from 0,27±0,07 to 0,54±0,23 for growth curve parameters of different body measurements and immature weights indicated that some genetic progress in these traits may be obtained and these results should be considered in the selection of stud rams.