Abstract
Data collected on 2550 Kurdi lambs originated from 1505 dams and 149 sires during 1991 to 2015 in Hossein Abad Kurdi Sheep Breeding Station, located in Shirvan city, North Khorasan province, North-eastern area of Iran, were used for inferring causal relationship among the body weights at birth (BW), at weaning (WW), at six-month age (6MW), at nine-month age (9MW) and yearling age (YW). The inductive causation (IC) algorithm was employed to search for causal structure among these traits. This algorithm was applied to the posterior distribution of the residual (co)variance matrix of a standard multivariate model (SMM). The causal structure detected by the IC algorithm coupling with biological prior knowledge provides a temporal recursive causal network among the studied traits. The studied traits were analyzed under three multivariate models including SMM, fully recursive multivariate model (FRM) and IC-based multivariate model (ICM) via a Bayesian approach by 100,000 iterations, thinning interval of 10 and the first 10,000 iterations as burn-in. The three considered multivariate models (SMM, FRM and ICM) were compared using deviance information criterion (DIC) and predictive ability measures including mean square of error (MSE) and Pearson's correlation coefficient between the observed and predicted values (r(y, )) of records. In general, structural equation based models (FRM and ICM) performed better than SMM in terms of lower DIC and MSE and also higher r(y, ). Among the tested models ICM had the lowest (36678.551) and SMM had the highest (36744.107)DIC values. In each case of the traits studied, the lowest MSE and the highest r(y, ) were obtained under ICM. The causal effects of BW on WW, WW on 6MW, 6MW on 9MW and 9MW on YW were statistically significant values of 1.478, 0.737, 0.776 and 0.929 kg, respectively (99% highest posterior density intervals did not include zero).
Highlights
In livestock species, body weight of domestic animals at different ages has deterministic effects on the profitability of breeding enterprises
The importance of considering the maternal effects for genetic evaluation of the body weights of several sheep breeds have been well documented in the literature (Abegaz, Van Wyk, & Olivier, 2005; Rashidi et al, 2008)
Applying inductive causation (IC) algorithm, a model with temporal recursive causal relationships detected among the studied growth traits in Kurdi sheep which favored on fully recursive and standard multivariate models in terms of lower deviance information criterion (DIC)
Summary
Body weight of domestic animals at different ages has deterministic effects on the profitability of breeding enterprises. These traits may be considered as efficient selection criteria for developing breeding programs (Tosh & Kemp, 1994). Mutton is the main source of animal protein in Iran and approximately 40 percent of red meat supplied through sheep production which does not satisfy the increasing demand of consumers. Increasing production efficiency in any sheep breeding system is required (Rashidi, Mokhtari, Jahanshahi, & Abadi, 2008). Developing an appropriate selective procedure considering breeding values requires accurate estimates of genetic parameters obtained under multivariate models
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