Characteristics of spermatozoa and reproductive organs in relation to age and body weight in Swedish moose (Alces alces)

Knowledge of the reproductive biology of game species is vital for sustainable management. In moose (Alces alces), research in reproductive characteristics has focused on the female, whereas there are few studies in male moose. The aim of the present study was to investigate sperm morphology and chromatin integrity (SCSA), and their relationships with testicular and epididymal features, as well as temporal aspects with respect to the hunting season. In total, 143 male moose aged 1.5-11.5 years were sampled from 2008 to 2011. The proportion of normal spermatozoa (PNS) ranged from 1.5% to 82.0%, with a mean of 51%, and the %DFI (DNA fragmentation index) ranged from 2.5% to 36.7% (mean 9.5). PNS decreased temporally, and was positively associated with carcass and testes weight. Body weight and testes weight had positive effect on PNS regardless of age. No effect of any explanatory variables was observed on the DFI. The testis/body weight ratio of moose (0.033%) is among the lowest reported among mammals, indicating a less polygynous mating system than in roe deer and red deer. For reproduction success in moose, a high body weight in males is favorable, as is a balanced sex ratio. Thus, males should not be harvested prior to the time when the majority of females have passed their first oestrus of the season.