THE OPTIMUM TIME FOR SINGLE ARTIFICIAL-INSEMINATION OF BLUE FOX VIXENS (ALOPEX-LAGOPUS) WITH FROZEN-THAWED SEMEN FROM SILVER FOXES (VULPES-VULPES)

During the breeding season of 1991 a total of 608 blue fox vixens aged 1 to 6 years ( 2.3 +/- 0.1 years, mean +/- SEM ) from 2 farms were artificially inseminated intrauterine once with frozen-thawed silver fox semen (1m1 dose containing a total of 150 million spermatozoa). The vixens were allocated to 3 different groups according to the time of insemination. Vixens in Group 1 (n = 203), Group 2 (n = 198), and Group 3 (n = 207) were inseminated on the first, second or third day after the peak value of vaginal electrical resistance, respectively. An overall conception rate of 75% (456 of 608) and 6.0 +/- 0.1 (mean +/- SEM) cubs per litter was obtained. Conception rates and mean litter sizes were significantly different between groups of vixens with respect to day of insemination (P = 0.02, Chi-square, Kruskall-Wallis Test). Vixens inseminated on the second day (Group 2) had the highest conception rate (81%) and the largest mean litter size (7.0 +/- 0.2 cubs) of the three groups, while those inseminated on the third day (Group 3) had the lowest conception rate and mean litter size (70%, 5.4 +/- 0.3 cubs).