BREEDING OF DJUNGARIAN HAMSTERS (PHODOPUS-SUNGORUS) - INFLUENCE OF PARITY AND LITTER SIZE ON WEANING SUCCESS AND OFFSPRING SEX-RATIO

The reproduction of 368 breeding pairs of Djungarian hamsters (Phodopu s sungorus) has been recorded and evaluated during 5 consecutive years . Three-hundred-and-eight pairs (=83.7%) were successful breeders givi ng birth to 2113 litters (up to 13 per dam) with a total of 12,591 off spring (mean: 6.0 +/- 2.2 [+/- SD] per litter). One-hundred-and-fifty dams delivered within 25 days after pairing, indicating a breeding suc cess in the first oestrous cycle of 40.8% of all pairs (95% confidence interval: 35.7%-46.0%). The average number of offspring was higher in the 2nd than in the first litter, reaching a maximum in the 3rd (6.8 +/- 2.0), and decreasing thereafter. The loss of offspring (mean: 24.2 %) was higher in older parents and influenced by the number of offspri ng per litter, indicating that experience and stress contribute to bre eding success. A small, but significantly higher number of females was recorded only when no loss of offspring occurred until weaning (femal es: 2.36 +/- 1.75; males: 2.16 +/- 1.63, P<0.001). There was no indica tion of a shift of the offspring sex ratio towards favouring females w ith increased litter numbers, in contrast to the predictions of the Tr ivers-Willard hypothesis, at least with respect to the species and the breeding conditions as described in this report. Since all breeders w ere kept under long-day type photoperiods (16L:8D), no signs of season ality in breeding outcome were noted.