Investigation of the Use of Alternative Economic Indices and QTL-Assisted Selection for the Genetic Improvement of Production and Health Traits in Bangladeshi Dairy Cattle

Abstract

The study was undertaken to investigate the use of several economic indices including QTL assisted selection for the improvement of production and health trait of dairy cattle under Bangladesh conditions. Five traits (lactation milk, fat, protein yield, somatic cell score (SCS) and direct mastitis) were simulated over 14 generations, considering three selection objectives (selection for direct mastitis; milk SCS; and the combination of direct mastitis and SCS). In addition the selection objective for SCS was simulated incorporating marker/QTL information. Genetic gains per generation for different traits were calculated by plotting the average true breeding values (TBVs) and estimated breeding values (EBVs) over generation. Selection of replacement bulls and cows were based on total merit. The genetic gains based on TBVs and EBVs of cows for milk, fat and protein yield in three selection objectives with no QTL information were similar, but gains were higher with QTL-assisted selection implemented for SCS. Genetic gains of cows for different traits based on TBVs were higher than bulls, but reverse results were obtained for bulls. The genetic trends for all traits in cows were similar in all selection objectives. However, for bulls distinct differences were observed between the QTL and no QTL-assisted selection schemes and also between SCS and the combination of SCS and direct mastitis selection objectives. Higher correlations between TBVs and EBVs for lactation milk and fat yield for both cows and bulls were found under QTL-assisted selection compared to the no QTL-assisted selection schemes. The QTL-assisted selection scheme showed higher rates of genetic gain for lactation milk, fat and protein yields than no QTL-assisted selection. However, it does not affect SCS and index values from any of the selection objectives or selection schemes. The QTL-assisted selection scheme has a positive effect on milk production and mastitis control.