Genetic improvement for production and health in broilers

The objective of present thesis was to optimize the genetic improvement of production and health traits in broilers. The genetic correlations among abdominal, subcutaneous, and intramuscular fat showed that there is a high genetic correlation between abdominal and subcutaneous fat (0.54), whereas the genetic correlation between abdominal and intramuscular fat is almost zero (0.02). Therefore selection for reduced abdominal fat does not change the intramuscular fat content and consequently meat quality. The genetic correlations were estimated on broilers of different ages (48, 63, and 70 d). The results indicated that increase in growth at 48 d was accompanied by increase in valuable parts (breast meat and back half); at 70 d it was accompanied by an increase in abdominal fat percentage. In addition, the genetic correlation of BW at 48 d between individual cage and group housing demonstrated a genotype by environment interaction for performance of birds in different housing systems. The present research showed that including indirect carcass measurements in the broiler breeding schemes resulted in improved genetic gain for breast meat percentage and reduced rate of inbreeding, which is desirable for long-term selection. The improved genetic gain resulted from increased accuracy of selection due to the own performance of selection candidates for carcass traits. The reliability of the indirect measurements influences the usefulness of these methods. The correlation between BW and ascites related traits in the cold conditions were estimated using mixture model analysis. The results indicated that the overall correlations between BW and ascites traits are dependent on the relative frequency of ascitic and non-ascitic birds in the population. Finally, estimated genetic parameters for production and health traits were used in a simulation to illustrate the consequences of including health related traits together with production traits in a sustainable breeding program. The results showed that a reduction of 6% of response in production traits was sufficient to offset the negative response in health traits.