Successful re-establishment of a rabbit population from embryos vitrified 15 years ago: The importance of biobanks in livestock conservation

Abstract

Genetic resource banks (GRB) are a valuable tool for maintaining genetic variability and preserving breeds from pathogens or catastrophe, enabling us to assess and correct breeding schemes, minimizing the impact of genetic drift and facilitating diffusion. This study tests their efficiency in re-establishing two extinct populations of a synthetic rabbit line selected for daily weight gain, using vitrified embryos from two generations (18th and 36th) separated by 15 years of genetic selection. The effect of long-term storage of vitrified embryos in liquid nitrogen was also evaluated. A total of 516 vitrified embryos using the same protocol were transferred into 54 recipients. The embryos had been maintained in liquid nitrogen during 2 different periods, (i) 1 year (301 embryos and 26 transfers, 36th generation) and (ii) 15 years (259 embryos and 28 transfers, 18th generation). A total of 80.0% (8/10 to 18th) and 60.0% (9/15 to 36th) of the foundational sire families were eventually re-established. Over approximately one year, animals within each population were crossed to produce the next generation and re-establish the original population size. Our study demonstrated that our GRB of embryos vitrified 15 years ago is a successful strategy to re-establish rabbit populations to continue the breeding programme.

Fig 1. Animals used in this study belonged to 2 Spanish commercial rabbit lines.

(A) Female and male from synthetic line R selected on individual daily weight gain between weaning (day 28) and end of the fattening (day 63) over 37 generations (B). Females used as recipient from maternal line based on New Zealand White rabbits selected since 1980 by a family index for litter size at weaning during 45 generations and donor from synthetic line R.

Fig 2. Rabbit embryos classified as excellent or good (presenting homogenous cellular mass, mucin coat, and spherical zona pellucida according to International Embryo Transfer Society classification).

(A) Compacted morulae at 100x. (B) Early blastocyst at 100x. Scale bar: 50 μm.

Fig 3. Experimental scheme design.