Joint analysis of health and production traits

The objective of the study was to investigate the relationship between health and production traits in chickens. The data were obtained from a closed, fully pedigreed, commercial broiler line. Records included measurements of body weight (BW), residual feed intake (RFI), percent breast meat (PBM), and two health traits (H1 and H2) from 13,665 birds and 1,524 hens with progeny records. Production traits were recorded as continuous and health traits were recorded as binary (1 or 0). After data editing, 13,632 records remained for analysis. For the health traits there were no extreme case problems observed in the 28 contemporary groups. Two analyses were conducted: 1) a threshold-linear mixed model for the joint analysis of BW, RFI, PBM, and H1; and 2) a threshold mixed model for analysis of H2. The mixed model included fi xed effects of contemporary group (fl ock-week of hatch-parent’s fl ock) and sex (not included in the model for H2); and random additive effects of bird and residual. A separate analysis for H2 was required since BW, RFI, PBM, and H1 were considered missing for these birds. In analysis 1, each bird had a valid observation for BW and H1, however, a bird which had RFI did not have PBM and vice versa. Thus a large number of birds had at least one missing observation in the fi rst analysis and missing records for RFI and PBM were predicted based on the model parameters. Heritability estimates obtained for BW, PBM, RFI, H1, and H2 were 0.38, 0.55, 0.30, 0.14, and 0.12, respectively. Genetic correlations obtained from analysis 1 for BW with PBM, RFI and H1 were 0.08, 0.14 and -0.20, respectively; PBM with RFI and H1 was 0.38 and 0.08, respectively; and RFI with H1 was 0.03. The results suggest that as RFI is increased, BW and PBM were also increased. However, it would appear that as BW is increased, the health of the bird is decreased for H1. Residual correlations around -0.20 were reported between H1 with PBM and BW with RFI and 0.57 between BW with PBM. Given that H2 was analyzed separately, breeding values for birds in both analyses were correlated in order to obtain an approximation of the genetic correlation between BW, RFI, PBM, and H1 with H2. Correlations between H2 with BW, PBM, and RFI ranged from -0.03 to -0.04. A positive correlation of 0.05 was obtained for H2 with H1. The correlations were close to zero indicating that no defi nitive conclusions could be drawn for the relationship of H2 with the other traits using breeding values. In conclusion, the heritability estimates for the health and production traits of interest suggest that genetic improvement could be made. However, the relationship between these traits varies with the health traits having little to no relationship with the production traits. The fl uctuation in these relationships could be due to the large number of missing records for PBM and RFI.