Gonadotrophins and sex steroids during pregnancy and natural superfoetation in captive brown hares (Lepus europaeus)

Abstract

In brown hares, which are induced ovulators, sexual behaviour occurs episodically at the beginning of pregnancy. From Day 34 (length of pregnancy is 41 days), the frequency of sexual chases followed by mating, ovulation and fertilization increased and 59% of pregnant females presented a natural superfoetation. The pattern of circulating luteinizing hormone (LH), follicle-stimulating hormone (FSH), oestradiol and progesterone was studied in 13 pregnant females left permanently with a male, and in 10 females isolated from males around Day 20 of pregnancy. In the 2 groups FSH concentrations were high at the beginning and end of pregnancy. All females presented a peak value of FSH in the last 4 days of pregnancy, regardless of mating stimuli. This peak value was higher for females left permanently with a male than for isolated ones. Oestradiol concentrations fluctuated between 20 and 100 pg/ml, without any clear correlation with sexual behaviour, stage of pregnancy or profiles of other hormones. Prepartum matings occurred when progesterone values were still greater than 50 ng/ml; they were followed by a transient rise in LH and by a periovulatory progesterone secretion, with values above 100 ng/ml in the morning after mating. Such modifications of LH and progesterone were not detected before Day 34, suggesting that mating stimuli are not able to induce an LH surge at the beginning of pregnancy. After Day 34, mating can induce an LH surge, ovulation and superfoetation.

The concept of superfetation: a critical review on a ‘myth’ in mammalian reproduction

“…Therefore, it was concluded that Graafian follicles developed prior to parturition and may be responsible for oestrus activity and mating (Caillol et al , 1991 a ). Increased mating behaviour may be required to stimulate the pituitary‐hypothalamic‐gonadal axis to overcome the inhibition caused by an active pregnancy (Caillol, Mondain‐Monval & Rossano, 1991 b ). The precise mechanism by which ovulation occurs during pregnancy is still unknown (Caillol et al , 1991 a ).…”

Female Receptiveity, Embryonic Diapause, and Superfetation in the European Badger (Meles Meles: Implications for the Reproductive Tactics of Males and Females

“…Confirmed reports of natural superfetation during normal reproduction of a species resulting in successful parturition are extremely rare in eutherian mammals. Apart from the American mink, and possibly the European badger, superfetation has only been reported in the casiragua Proechimys semispinosus (Weir 1974), the North African gundi Ctenodactyles gundi (Gouat 1985), the brown hare Lepus europaeus (Caillol et al 1991), and possibly the common tenrec Tenrec ecaudatus (Poduschka 1996). However, superfetation in these four species, which occurs without embryonic diapause, is characterized by a second estrus just before parturition of the fetuses that developed from the first set of ova.…”

Seasonal variations in the morphometric analysis of the testis, testosterone production, and occurrence of pathological spermatozoa in the brown hare (<i>Lepus europaeus</i>)

“…The uterine enlargement (Calliol et al, 1989a), increased progesterone (Calliol and Martinet, 1976;Calliol etal., 1991) and estradiol (Caillol et al, 1989a(Caillol et al, , 1991Semizorova et al, 1990) levels in the blood of females have been reported. In males, growth of testicles and increased blood testosterone levels (Calliol et al, 1989b) during the reproductive cycle have been described.…”