CUMULATIVE INBREEDING IN COMMERCIAL WHITE LEGHORN LINES UNDER LONG-TERM RECIPROCAL RECURRENT SELECTION

1. Cumulative inbreeding attributable to selection in a finite population after long-term reciprocal recurrent selection (RRS) and modified RRS (MRRS) was studied in two White Leghorn lines. 2. Pedigree information was analysed for a period of 24 generations. In one generation, progeny of full-sib, half-sib and unrelated pureline as well as reciprocal cross-line matings were produced. 3. The structure of the two pure lines, which have been consistently used as part of the commercial cross, was documented in terms of numbers of sires and dams mated to produced sons and daughters, and variance of family size. On average, 87 sires and 870 dams per generation were mated to produce offspring. 4. Cumulative inbreeding values determined from pedigree data were compared with estimates from effective population size and variation of family size. 5. The increase in average inbreeding over 23 generations was 11.9% for line A and 10.8% for line B or 0.49% per generation, based on pedigree data. 6. Estimates from family structure were slightly higher: 12.6% for line A and 12.0% for line B or 0.54% per generation. 7. The increase in inbreeding appeared to be linear and independent of the selection method (MRRS compared to RRS).