Genetic variability of functional longevity in five rabbit lines

Abstract

The objectives of this study were to analyse the differences in the genetic determination of functional longevity in five Spanish lines of rabbits and to check how different systematic factors might affect this genetic determination. Four of the lines were maternal (lines A, V, H and LP), these lines were established selecting base generation animals according to different criteria, but in the subsequent generations all of them were selected for litter size at weaning. The other is the paternal line R, this line was constituted by selecting animals with an outstanding daily growth rate. The trait analysed, length of productive life, was the time in days between the date of the first positive pregnancy test and the date of culling or death of a doe. Four models extended from the Cox proportional hazard model were used to analyse data of each line separately and jointly. The complete model (Model 1) included the fixed effect of year-season (YS) combination, positive palpation order (OPP), that is, reproductive cycle, physiological status of the doe (PS) at service and number of kits born alive (NBA) in each kindling as time-dependent factors. The inbreeding coefficient was fitted as a continuous covariate and the animal’s additive genetic effect was also fitted to the model (Model 1). The other models were identical to Model 1 but excluding OPP (Model 2) or PS (Model 3) or NBA (Model 4), which were explored to assess the consequence on additive variance estimates of not correcting for these animal-dependent factors. Estimated effective heritabilities of longevity were 0.07 ± 0.03, 0.03 ± 0.02, 0.14 ± 0.09, 0.05 ± 0.04, 0.02 ± 0.01 and 0.04 ± 0.01 for lines A, V, H, LP, R and for the merged data set, respectively. Removing the PS from the model led to an increase in the estimated additive genetic variance in all lines (0.17 ± 0.05, 0.05 ± 0.03, 0.29 ± 0.19, 0.29 ± 0.20, 0.07 ± 0.04 and 0.05 ± 0.02 for lines A, V, H, LP, R and the merged data set, respectively). The highest hazard of death and/or culling was observed during the first two parities and decreased as the order of parity progressed. Does non-pregnant-non-lactating had the highest risk of death or culling. The does that had zero kits born alive incurred the highest risk, and this risk decreased as the NBA increased. In conclusion, the consideration of longevity as selection criterion for the studied rabbit lines is not recommended.

Genetic analysis of functional longevity in a complete diallel crossing experiment involving four maternal rabbit lines

“…This result was in accordance with previous reports by EL Nagar et al. (2020) who stated that the L rabbit line had a longer functional longevity than the A, V, H and R rabbit lines. Also, Theilgaard et al.…”

“…In this regard, however, El Nagar et al. (2020) showed that, in a single farm, with the same purebred lines as were used in this study, they followed a similar lifetime risk pattern. This risk decreased as the order of positive palpation increased.…”

“…However, EL Nagar et al. (2020) reported that the inbreeding did not seem to have an unfavourable effect on longevity for the A, V, H, L and R rabbit lines. Moreover, the crossbred does have a higher production level than purebred does which, with time, could increase the risk of culling or death.…”

“…However, EL Nagar et al. (2020) stated that the greatest risk of culling or death associated with low litter sizes could be linked to underlying pathological and/or stress disorders, since no voluntary culling for production reasons was practiced in the experimental farm.…”

Functional longevity in five rabbit lines founded on different criteria: Comparison at foundation and at fixed times after selection

“…The economic weight of doe replacement rate as an estimation of the economic weight of longevity is relatively low (−0.29 €/percentage unit) compared with other traits like, for example, efficiency in the use of feed or prolificacy (Cartuche et al., 2014). However, until now, in the computation of this weight, some relevant factors associated with management, welfare and ethics are not properly defined in the farm benefit function (EL Nagar et al., 2020). With the aim of creating a maternal line outstanding for its longevity, Sánchez et al.…”