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Certain Aspects of Reproduction in a Herd of Silver Foxes

1946; University of Chicago Press; Volume: 80; Issue: 786 Linguagem: Inglês

10.1086/281323

1537-5323

Oliver P. Pearson, Charles F. Bassett,

Reproductive Physiology in Livestock

(1) The reproductive behavior of the herd of silver foxes at the U. S. Fur Animal Experiment Station, Saratoga Springs, N. Y., was studied from 1930 through 1944. Some of the observations extended over the entire period, while others were collected only in recent years. (2) The mean mating date of the adult vixens was February 12th with a standard deviation of 9.9 days; and of yearlings, February 21st with a standard deviation of 12.0 days. The yearlings mated later than the adults every year, but not always by the same length of time; the average was 8 days later. (3) The mean mating date of the adult herd differed by more than 2 weeks in different years. No close correlation could be found between the mean mating date of the herd and temperature of the months from September to February. (4) There was a slight tendency for early-whelped vixens to breed earlier in their first breeding season than late-whelped vixens. This tendency was less distinct in the second season and absent in the third. (5) There was a moderate tendency for a vixen to mate at the same part of the season each year. The coefficient of correlation between the time of estrus in the yearling year and the mean mating date in subsequent years was + .45 ± .07. (6) The mean duration of 524 copulations was 26.49 ± .46 minutes. Both males and females tended to remain coupled longer as adults than as yearlings. Individual males showed a definite tendency to remain coupled the same length of time in several copulations; females showed only a slight tendency. There was no correlation between duration of copulation and litter size. (7) There was a definite tendency for the vulva of adult vixens to swell to the same size during proestrus in successive seasons. Vulvar size was correlated with the reproductive capacity of the vixen. (8) There was a strong tendency for certain vixens to destroy their litters year after year. (9) Litters whelped by yearlings were as large as those whelped by the same vixens in their second and third years. There was possibly an increase in the fourth year. There was some tendency for individual adult vixens to have the same sized litter in several seasons, but the correlation between litter size in the yearling year and subsequent years was low and of questionable significance. (10) There was no tendency for the litters sired by an individual male to be of the same size, nor did sisters tend to bear litters of the same size. (11) Failure to mate was more frequent among year-lings than among the same vixens in their adult years.