Association between heterophil/lymphocyte ratio, a marker of 'resistance' to stress, and some production and fitness traits in chickens

1. A stock of cross-bred CD hens was divided into 'resistant' ( R) and 'sensitive' ( S) to stress on the basis of the heterophil/lymphocyte ( H/L) ratio using the lower 99% confidence limit method for selection. A first generation was produced from these R and S females mated with similarly selected R and S local Barred males. The association between 'resistance' and some production traits was investigated. 2. The proportions of R: S among CD females and Barred males was 51.2:48.8 and 52: 48, respectively. Mean H/L ratios for Barred males and females, respectively, were 0.87 +/- 0.03 and 0.83 +/- 0.03 ( P > 0.05). 3. Compared with the S group in CD females, the R group had greater egg production ( 59% vs 51%), egg weight ( 65.5g vs 62.6 g) and body weight at 39 weeks ( 115 g heavier). 4. The superiority of R in terms of proportion of fertile eggs, hatchability and the proportion hatched from those set amounted to 4.8, 6.1 and 5.4%, respectively. 5. The proportion of dead embryos in the R group ( 5.4%) was lower than in the S group ( 9.3%). 6. With the F1 generation the R chicks were heavier at hatching. 7. Percentage mortality of male F1 chicks, from hatching to 4 weeks and from 4 to 8 weeks, was lower in the R group. A similar, but non-significant, trend was noted for R females. 8. The progeny of the R group was heavier than the S progeny at 4 and 8 weeks and also the percentage dressed weight of males was greater at 8 weeks. The R group was heavier than the S group at 4, 8 and 12 weeks. 9. These results suggest that selection for general 'resistance', on the basis of the H/L ratio using the 99% lower confidence limit method of selection, is positively correlated with several important production and reproduction traits. Establishing resistant lines with high production rates seems feasible.