Effect of Genetic Connectedness on the Selection Results of Breeding Pigs

Two pig populations were simulated with Monte Carlo method; each consisted of 5 boars and 50 sows per generation. Genetic connectedness between herds was established by randomly selecting 1 or 2 boars from one population to mate sows of the other population. Breeding pigs were selected within populations according to animal model BLUP. The benefits of genetic connectedness between herds were examined. The results showed that, the average coefficients of inbreeding decreased, while the cumulative selection responses of populations increased, and the higher response occurred randomly in the two populations at generation 5 with the increase of the genetic connectedness between herds. Selection response was affected by genetic connectedness and trait heritability, the lower heritability and higher connectedness, the better selection results. When the number of exchanged litters between populations per generation was 6 litters, the selection results reached a reflection point; if the number of exchanged litters between populations increased further from this point, neither the increase of the cumulative selection responses nor the decrease of coefficients of inbreeding was significant.

Comparison of Estimated Genetic Connectedness among Three Herds of Chinese Holstein Cattle

Estimating genetic connectedness among herds is important for the accuracy of dairy cattle genetic evaluation. When selecting between animals raised in different herds, the accuracy of their genetic evaluations can be influenced by the degree of connectedness among these herds. In this study, two methods were used to measure genetic connectedness, CR （genetic connectedness rating ） and GLt （total number of direct genetic links between group）, among herds from Beijing, Shanghai, and Tianjin. Genetic connectedness between the herds from Beijing and Tianjin was 23.95%, between Beijing and Shanghai was 17. 10%, and between Shanghai and Tianjin it was 14.28%. Genetic connectedness between herds from Beijing and Tianjin was the highest and that between Shanghai and Tianjin was the lowest. The correlation coefficient for the two methods was 0. 808. Some suggestions for improved genetic evaluation of dairy cattle were also discussed.

Study on the Measures of Connectedness Between Herds

Pig breeding is generally conducted among many herds, so EBV comparisons across populationsare necessary. Genetic connectedness is required for reliable between-farm animal EBV comparisons.Five quantitative overall connectedness measures among populations have been proposed so far,coefficient of connectedness(γ*), coefficient of determination (CD) and overall indices ofprecision, connectedness rating, number of direct genetic links between subpopulations due tocommon sires and dams (GLt), and average genetic covariance (AGC) are reviewed and theirproperties are discussed in this paper. It is recommended to use AGC at present for measuringgenetic connectedness between herds.