A comparative study among four maternal lines of rabbits (A, V, H and LP) was conducted. Data for this study were collected during the program of selection of these lines from September 1980 to March 2011. The main objective of this work was to compare doe longevity (length of productive life, LPL) in four lines selected for litter size at weaning but founded on different criteria. The analysed trait was defined as the time in days between date of the first positive pregnancy diagnosis and date of culling or death. The comparison has been done at their foundation time using the complete pedigree file and the complete data set of the performances from their foundation until March, 2011.The number of does with records was 12693 and the pedigree involved 14805 animals. The second objective of this study was to compare the lines at fixed times, during the last three year-seasons shared by at least three of them. The fixed times of comparison were from March, 1997 to September 1998 (period 1) for A, V and H lines, and from September, 2009 to March, 2011 (period 2) for A, V and LP lines. Survival analyses were carried out with a Cox proportional hazard model. The effective heritability for LPL was 0.16. The relative risk (RR) for the contrasts A vs V, A vs H and A vs LP was 3.40, 3.43 and 5.56 at foundation, respectively. RR for the contrasts A vs V and A vs H was 1.42 and 1.32, respectively, during the first fixed period of comparison. RR for the contrasts A vs V and A vs LP was 1.41 and 1.71, respectively, during the second fixed period of comparison. The line A had a risk of death or culling greater than the other lines in all comparisons. No significant differences either between V and LP lines or between V and H lines have been founded in any comparison. In general the differences between lines at fixed times were smaller than those at their foundation. Along the generations of selection for litter size, the differences of longevity between lines tend to decrease, due to the action of the natural selection in the lines of lower longevity. The foundation criterion is important to define the initial longevity of the lines. |
