Study of performance and estimation of genetic parameters of reproductive traits in Makooei sheep using linear and threshold models

Reproductive traits in sheep are the most important traits affecting profitability. These traits have categorical nature, but in practice the continuous distribution of traits is analyzed. In addition, to have true and accurate pedigree records, applying the appropriate model for analyzing the characteristics of high precision in the estimation of genetic parameters will be evaluated.Accurate prediction of animals breeding values is one of the best tools available to maximize the response to a selection program. Development of effective genetic evaluation and improvement programs requires knowledge of the genetic parameters for these economically important production traits. many studies, LS is analyzed by linear models, and the variance components are obtained by REML methods. Compared to linear models, non-linear models have disadvantages in goodness of fit or predictivty and they are time consuming in computation, which might be prohibitive for routine calculations The main objective of this study was to obtain effects of genetic estimates of reproductive traits in Makooei sheep using repeatability linear and threshold models that are necessary to develop an efficient selection strategy for improvement of reproduction. For this purpose, were estimated using linear and threshold univariate animal model on the data of 4319 records of 1629 ewes, collected during 1996 to 2014 in rearing and improvement of Makooei sheep for conception rate, number of lambs born, number of lambs alive at weaning, number of lambs born per ewe exposed and number of lambs born per ewe exposed traits. The model was included fixed effects (year and age of ewe) and random effects additive genetic of ewe, permanent environmental of ewe and residual. The overall mean of traits were as 0.93 for conception rate, 1.16 for number of lambs born, 0.98, for number of lambs alive at weaning, 1.07 for number of lambs born per ewe exposed and 0.91 for number of lambs born per ewe exposed. The heritability coefficient of traits were estimated as 0.05, 0.11, 0.06, 0.08, and 0.04 respectively, resulted from linear analysis and 0.12, 0.20, 0.15, 0.18 and 0.10 respectively, resulted from threshold analysis. The estimation of repeatability coefficient of traits were as 0.09, 0.16, 0.18, 0.15 and 0.12 respectively, for linear analysis and 0.48, 0.51, 0.34, 0.50 and 0.41 respectively for threshold analysis. The results of this study showed that, using threshold models for analyzing reproductive traits in genetic evaluations, comparison with linear models, caused relatively increasing genetic parameters and accuracy of evaluations.