The aim of this study was to determine the effect of artificially extended daylight applied during pregnancy on reproductive performance in farmed mink. The material consisted of 536 female Black (or “short NAP”) mink aged 2 years. To analyse the reproductive performance, we selected females mated twice during the period 13 to 17 March. Energy-saving bulbs of 11 watts each (equivalent to traditional 60-watt bulbs) were placed above the cages of the females. The experiment involved two groups of females: the control group (n = 258) were females kept under natural daylight throughout pregnancy; the females of the treatment group (n = 278) were additionally subjected to extended photoperiod - up to 16 hours of light per day, applied from 20 March to 15 April. Selected reproduction indicators were analysed among the groups. The extended daylight applied during pregnancy of mink positively influenced many of the analysed indices. The duration of diapause and related total length of gestation decreased, the litter size - both at birth and at weaning - significantly increased. Pre-weaning mortality of young and the proportion of nonbreeding females slightly decreased as a result of the treatment, which from the practical point of view might be seen as a beneficial effect; however, these parameters are shaped by other factors than photoperiod. The whelping season was both commenced and completed earlier among females subjected to extra light during pregnancy, which improved the organization of work on the farm. Artificial illumination of pregnant mink in Poland’s climate can be applied with great success and introducing this treatment to the mink breeding technology on a permanent basis should be seriously considered.

The aim of the study was observation of the effect of light modulation on blood testosterone levels and libido in male American mink. The study was performed on 64 Black Velvet male mink on a farm located in the north-west of Poland. Day length was modified using artificial lighting placed above mink cages. Two variants of lighting programs were applied to males: (I) from 8 of February and (II) from 12 of February. In order to measure blood testosterone concentration samples were collected from males of the experimental groups and the control groups (animals kept under natural light conditions). As a result of the experiment, the males subjected to extended lighting were found to have had slightly higher libido than those outside the treatment, although no strong or clear effect of lighting on the pattern of testosterone levels in male mink has been found. It remains unexplained whether slightly, non-significantly higher libido of the experimental males is related to the applied modulation of photoperiod. In order to unambiguously clarify the effect of day light modulation on the results of males sexual activity, further studies should be performed on a larger population and possibly using modified extended lighting programs.

The aim of the study was to analyse the effect of a male mink single-dose hCG stimulation on the libido during the mating season and on blood testosterone levels after the season. The material involved males of American mink. The treatment-group males were administered a dose of 100, 150 or 200 U of hCG. Blood was collected twice, approx. 2 weeks prior to and on the completion of the mating season. The group receiving 100 U hCG had the highest percentage of males effectively copulating with females within the first 24 hours after stimulation, whereas males stimulated with a dose of 200 U hCG showed the lowest libido over the same period. On the other hand, males of the group stimulated with 150 U hCG mated to the highest number of females throughout the mating season. The mean plasma testosterone concentration in all the studied males on 18 February was 12.44 ng/ml. The drop in testosterone concentration at the end of the mating season was significant.