Banche delle risorse genetiche suine: alcuni criteri di ottimizzazione.

The criteria for optimizing the number of semen doses and cost of semen banks for pig genetic resources are discussed. We assume the storage of semen to re-establish the breed in case of extinction by recovering 98% of its genome, and the storage of semen from 25 boars, corresponding to 2% loss of heterozygosity. The number of doses was analysed according to the number of fertile females for double AI (f), which is the function of conception rate, number of born alive and survival rate at breeding age. Conception rates of 35, 50 and 65%, 6 to 10 born alive and 50 to 70% survival rate at breeding age are considered. With f=1 and the creation of two storage sites, we need to store 600 semen doses per breed, with 70% reduction of the costs compared to the 2080 semen doses previously suggested. With f>1 for breed reconstruction, it is possible to use a very small number of females and semen doses. This however implies that not all founder boars will be used at each backcross generation, with risk of loss of genetic variability. Two different reconstruction schemes with f values of 1.5 and 2 are analysed. Loss of genetic variability is estimated by means of founders genome equivalents, allelic diversity and average relationship. A decrease of 2% of founders genome equivalents and an increase of 15% of average relationship are observed only with the scheme with f=2. Costs for the creation of a semen bank were analysed according to the number of semen doses to be stored, from 150 (f=1.5) to 1040 (f=0.67), and to boar training period for semen collection (8 or 23 weeks). Costs varied from 16 636 Euro for 150 semen doses and 8 weeks of training period to 46 675 Euro for 1040 semen doses and 23 weeks of training period. Assuming a more realistic f value of 1, the reduction of semen doses from 2080 to 600 allows to save 25 050 Euro per breed.