The Effect of Low Environmental Temperature on the Reproductive Cycle of Female Mice

Abstract

Breeding stocks of mice of strain 0A2G have been studied at environmental temperatures of \m=-\3\s=deg\and 21\s=deg\C. The mean age of opening of the vagina was 33 days at \ m=-\ 3\ s=deg\ C, 26 days at 21\s=deg\C. The mean body weight at opening was 13 g in both temperatures. The vaginal smear of typical oestrus appeared at a mean age of 61 days at \ m=-\ 3\ s=deg\ C, 38 days at 21\ s=deg\ C; it was preceded by variable numbers of anomalous smears containing squamous cells. The mean length of the oestrous cycle was 8\m=.\5 days at \m=-\3\s=deg\ C, 4\m=.\8 days at 21\s=deg\C. Females transferred from 21\s=deg\to \m=-\3\s=deg\C had longer cycles at first, but tended to return to normal after some months. The interval between parturitions had two modes, at about 3 and 6 weeks respectively: most intervals were around 6 weeks at \m=-\3\ s=deg\ C, 3 weeks at 21\s=deg\C. There was evidence of a negative correlation between the numbers weaned in successive parturitions, when the interval between parturitions was near the minimum. The slowing of the reproductive cycle at \m=-\ 3\ s=deg\ C may be attributed to the prior demands of catabolism; but this does not account for the recovery of the mice transferred from warm to cold.Mice of several strains have been bred for many generations in an environment kept at -3°C , and compared with parallel stocks at 21°C. The mice in the cold environ¬ ment have a much increased metabolic rate and a higher mortality between birth and weaning at 3 weeks; they also build better nests and begin to breed later. Other effects vary with the strain of mouse. The evidence for these statements has been given by Barnett [1956], Barnett, Coleman & Manly [1959], and by Barnett & Manly [1956. Here we are concerned with the effect of cold on the opening of the vagina, the oestrous cycle and the interval between parturitions; and we show that in mice of strain A 2G all these are markedly influenced by a cold environment. METHODThe mice used were of strain A2G, supplied by Glaxo Laboratories in 1953. All pairs used for the maintenance of the stock, or for studies of reproduction, were littermates. They were kept as permanent breeding stocks in each of two constant tem¬ perature rooms, one at 21°C and the other at -3°C. All the mice reported on here had been conceived, born and reared in one of these rooms. All mice had cotton wool in which to nest. Details of the conditions in which they were kept have been given by Barnett [1956]. The observations on vaginal opening and oestrous cycles were made on mice of the eleventh to seventeenth generations in the warm room and of the eighth and ninth generations in the cold.Members of mated pairs were kept always together. Young were removed from

Effect of heterosis on performance of mice across three environments.

“…Biggers et al (1958) reported that 7% of 4-wk-old female offspring of pregnant strain TO mice at 5°C had vaginal introitus, compared with 23% at 21°C. Bamett and Coleman (1959) reported similar findings with three mice strains (A, A2G, C57BL) breeding at -3 and 21°C. Mean age at vaginal opening for their female offspring at -3' C was 33 d, compared with 26 d at 21°C.…”

Chemical Signals in Vertebrates 4

“…A number of factors can influence the timing of female mouse puberty, including genetics (Drickamer, 1981), social conditions and non-social environmental factors (e.g., diet, temperature, photoperiod) (Laurie, 1946;Barnett and Coleman, 1959;Drickamer, 1975a,b;. Investigations of the social conditions that affect puberty in house mice have yielded evidence for a series of chemosigna1s contained in the urine that retard or accelerate sexual development in young females.…”

Conception and Parturition of Mice at Two Temperatures

“…It would be conventional to try to explain our observations on both lactation delay and the failure of post-partum conceptions at -3°C by endocrine changes. But Barnett 8c Little (1965) have brought evidence that the repro¬ ductive performance of A2G female mice at -3°C is limited by the amount of food they can eat; and Barnett & Coleman (1959) have suggested that the reproductive cycle of female mice at -3°C resembles that of mice on a low plane of nutrition. It is, therefore, at least plausible that the crucial factor is the supply of metabolites from food.…”

“…Mice, Mus musculus, breeding in rooms kept at -3°C , have been compared, in previous work, with controls at 21°C. The age at which the vagina opens and the first oestrus are later in the cold; the oestrous cycles may be longer; and the age of first parturition is later (Barnett & Coleman, 1959, 1960. For one strain 296 S. A.…”