Ali Vojdan Hassan Kiyadeh; Mohammad Rokouei; Gholam Reza Dashab; Ahmad Reza Seyedalian; Hadi Faraji- Arough
Volume 21, Issue 2 , July 2019, , Pages 181-192
Abstract
This research was conducted with the aim of estimation of environmental factors affecting survival and estimate the genetic parameters survival from 1 to the last recording date in Zandi sheep. The survival records of 9558 Zandi sheep from 273 rams and 2328 ewes collected by Animal Breeding Center of ...
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This research was conducted with the aim of estimation of environmental factors affecting survival and estimate the genetic parameters survival from 1 to the last recording date in Zandi sheep. The survival records of 9558 Zandi sheep from 273 rams and 2328 ewes collected by Animal Breeding Center of Iran during the 25 years (1987 to 2011) were used in the analysis. The effective factors on survival and culling risk were estimated by Survival and cmprsk package. Estimation of variance components was performed by using of exponential distribution for censored dates by the fitting of model with additive genetic effect (model 1) and joint additive genetic and maternal permanent environmental of effects (model 2) under Bayesian approach and Gibbs sampling. A total of 1000000 samples with a burn-in of 100000 and a sampling interval of 75 were generated to estimate the posterior distribution of variance components. The results showed that year, month, birth weight, type birth, sex (P<0.001) and dam age (p<0.01) had significant effect on survival trait. the direct heritability of survival trait using models 1 and 2 was 0.184( 0.136-0.264) and 0.162( 0.120-0.202), respectively. the proportion of permanent variance to phenotypic variance was 0.046( 0.063- 0.031). According to the results of this study, genetic improvement of survival trait in zandi lamb is possible by genetic selection and the culling risk reduction is effective via management of environmental factors.
Maryam Arianfar; Mohammad Rokouei; Gholamreza Dashab; Hadi Faraji- Arough
Volume 20, Issue 3 , November 2018, , Pages 351-363
Abstract
The objective of this study was to compare some nonlinear functions (Wood, Dhanoa, Wilmink, Ali-Schaeffer, Cappio Borlino, Cobby – Le Du, Dijkstra, Rook, Gous and Nelder) to describe the milk production curve of Iranian Holstein cattle. A dataset consisted of 6079976, 4879486 and 3312416 test-day ...
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The objective of this study was to compare some nonlinear functions (Wood, Dhanoa, Wilmink, Ali-Schaeffer, Cappio Borlino, Cobby – Le Du, Dijkstra, Rook, Gous and Nelder) to describe the milk production curve of Iranian Holstein cattle. A dataset consisted of 6079976, 4879486 and 3312416 test-day milk yield records related to first, second and third three lactation periods, respectively, from 3550 herds collecting by the Animal Breeding Center of Iran from 1983 to 2017, were used. The average of test day milk records for three lactation was 31.17, 34.08 and 33.83 kg, respectively. The nlme package of R software (version 3.4.3) was used for fitting nonlinear functions. The nonlinear functions were compared using four goodness of fit criteria, including Akaike’s information criterion (AIC), Bayesian information criterion (BIC), Root mean square error (RMSE) and Durbin-Watson index (DW). The Rook function showed the best fit for the milk production curve shape for three lactations in Iranian Holstein cattle when compared to other functions. The Gous and Rook functions showed the highest accuracy in predicting peak time, peak yield and persistency of milk production parameters in different lactations, but in general, the Rook function has a high predictive value in estimating the milk curve parameter descriptors.Therefore, Rook function is recommended for describing the milk production curve of Iranian Holstein cattle.