Estimation of Genetic Correlation Between Dystocia with Production, Reproduction and Birth Weight Traits in Holstein Cattle of Iran using Bayesian Linear-Threshold Model

The parturition is a very important stage in the longevity of cows and related to future animal health. The health parturition and avoid dystocia are main issues that needed to attention in farms. Prolonged or difficult parturition called dystocia and effects on the profitability of herds, animal welfare and admissibility of the production system of consumers. Dystocia is the main cause of stillbirth, death of cattle and calves and decreasing fertility, also have a negative effect on the reproductive traits (such as higher days open and number of inseminations per conception). This situation can also lead to increasing risk of infertility, the outbreak of diseases after parturition, culling probability and cost of veterinary. Although dystocia is one of the most important problems in dairy cattle production system and had major economic losses in the dairy industry. Thus, the objective of this study was to estimate genetic and environmental correlations between dystocia and production traits (milk, fat and protein production), reproduction (calving interval, calving to first service, fist service to conception) and birth weight in Holstein cattle of Iran with Bayesian linear- threshold model.
In this study, data collected by Animal breeding center of Iran during 1989 to 2012 were used. The dystocia was considered as traits for the mother and the service sire was fitted for this trait as an additional random effect. After edition of records, dystocia (threshold with 5 scores) with other traits (linear) were analyzed as bivariate analysis by Gibbs sampling method via DMU software. Gibbs chains with 300000 iterations were generated, with an initial discard of 20000 samples and a sampling interval of 120 iterations. Therefore, each analysis 2500 samples of (Co) variance components were obtained. The convergence checking of the chains generated by the Gibbs sampler was done using graphical analysis and diagnosis tests available in the Bayesian output analysis program (BOA).
Maximum frequency of dystocia was related to unassisted calvings (80.35%) and only 19.65 % of calving were performed with assistance. Among calving that require to assistance, the highest number was for assistance with no damage (11.43 %) and 8.22 % of calvings require a lot of assistance. The posterior mean of heritabilities for milk, fat, protein, calving interval, calving to first service, first service to conception, birth weight and dystocia were 0.175, 0.120, 0.126, 0.050, 0.040, 0.004, 0.128 and 0.012, respectively. According to the estimated heritability, the genetic selection for production traits and birth weight can be somewhat effective, but it will not observe appropriate response for reproductive traits and dystocia. The genetic correlation between dystocia with production traits were estimated low and negative (exception of fat). Low genetic correlations between traits showed that these traits were not influenced by same genes. The highest genetic correlation was estimated between dystocia and birth weight that showing similar genes affected for these traits and dystocia was increased due to increasing of birth weight. The genetic correlation between dystocia with calving to first service and first service to conception were obtained positive and negative, respectively, indicating that dystocia can be increase calving to first service and decreased first service to conception. Increasing of calving to first service interval can be created opportunity for improvement of anatomical conditions of the animal, thus first service to conception could be decreased due to the improvement of the conception rate.
Recent study showed that estimated heritability for production traits and birth weight were high and it was low for reproduction traits and dystocia. The results indicated that improvement of environmental conditions was necessary for the improvement of reproduction traits and dystocia. The highest genetic correlation between dystocia and birth weight suggested that improvement of birth weight increases dystocia. Increasing of calving to first service and reducing first service to conception after dystocia is expected due to genetic correlation estimates for these traits with dystocia.