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  • Author: R. A. MEAD x
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Western forms of the spotted skunk breed in late September, at which time daylength is decreasing. Early cleavage and tubal transport are normal but implantation is delayed for approximately 220 days and further embryonic development is greatly retarded (Mead, 1968). Corpora lutea involute soon after their formation and progesterone secretion is minimal during embryonic diapause (Mead & Eik-Nes, 1969a). The vulva enlarges in late April, at which time daylength is increasing, progesterone levels increase and embryonic development proceeds rapidly. Nidation is initiated a few days after luteal recrudescence and parturition occurs 29 to 31 days after implantation. These findings suggest that delayed implantation may result from insufficient gonadotrophin secretion during the preimplantation period.

The duration of the preimplantation period of the spotted skunk can be significantly shortened by increasing daylength

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R. A. Mead and S. Neirinckx

Summary. Three doses of FSH were tested for their ability to induce oestrus in ferrets. A dose of 0·25 mg, administered twice daily, induced oestrus and breeding in most females within 6–13 days. Addition of 5 i.u. hCG during the final stages of follicular development enhanced the percentage of females with implantation sites (85%), and 23% of the ferrets so treated gave birth to kits, none of which survived for more than 3 days. This may have been due to insufficient prolactin secretion and thus inadequate luteal maintenance and milk production, as these females were maintained on a short-day photoperiod.

Keywords: ferret; oestrus, induction of; pregnancy; anoestrus; implantation; FSH; hCG

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R. Ravindra, Kiran Bhatia and R. A. Mead

Summary. The present study reports steroid metabolism by corpora lutea (CL) obtained from skunks with diapausing embryos ('delay' CL) and with activated embryos (activated CL). CL from both reproductive periods were incubated with various radioactive precursors. Control incubations without any tissue or with 50 μl of packed skunk blood cells were also conducted simultaneously. Incubation of skunk CL with [3H]pregnenolone for 3 h resulted in 36% of the precursor accumulating as progesterone. Metabolism of [3H]dehydroepiandrosterone (DHEA) to androstenedione proceeded with approximately the same amount of product accumulating (34–46%) as was observed in the conversion of pregnenolone to progesterone. These results suggest that Δ5 isomerase, 3β-hydroxysteroid dehydrogenase, is the most prominent enzyme in skunk CL. Metabolism of [3H]pregnenolone to 17α-hydroxypregnenolone and [3H]progesterone to 17α-hydroxyprogesterone occurred at low rates (1–7%), suggesting the presence of C2l steroid 17α-hydroxylase in skunk CL. Aromatase activity, as estimated by measuring accumulation of oestradiol-17β from [3H]testosterone, was demonstrated in activated CL. These results suggest that skunk CL appear to metabolize steroids in a manner similar to CL of other mustelids such as the ferret and American badger.

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B. D. Murphy and R. A. Mead

Department of Biology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada S7N 0W0 and Department of Biological Sciences, University of Idaho, Moscow, Idaho 83843, U.S.A.

Oestrogen has been shown to be necessary to precipitate implantation in the rat and mouse (see review by Nalbandov, 1971). Progesterone alone can initiate implantation in most other mammals studied to date, and oestrogen either facilitates or has no effect on the nidatory process (Nalbandov, 1971; McLaren, 1971). Recent studies on hormonal control of implantation in ferrets (Wu & Chang, 1972, 1973) indicate that progesterone alone will support implantation (as indicated by uterine swellings) on Day 13 in ferrets ovariectomized on Days 8 or 10. However, implantation was usually delayed in ferrets ovariectomized on Days 6 or 7 and treated with progesterone or progesterone + oestrogen.

This study was designed to investigate further the role of oestrogen in inducing implantation in ferrets by administration of specific antiserum to

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J. B. Kaplan and R. A. Mead

The western spotted skunk is a seasonally breeding mammal: most copulations occur in late September and early October. This study was performed to characterize the seasonal changes in concentrations of testosterone and in ejaculate quality. Captive males (n = 22) were maintained on a natural photoperiod for 15 months. Semen samples were collected by electroejaculation; testis size was measured; and blood samples were collected. Of 110 electroejaculation attempts, 104 (95%) resulted in successful fluid collection and 101 (97%) samples contained spermatozoa. Significant increases (P < 0.05) in serum testosterone concentration, testis size and ejaculate volume were observed from August to November. Mean concentration of testosterone in serum ranged from 0.15 ± 0.05 ng ml−1 in mid-January to 6.42 ± 1.79 ng ml−1 in early October. Mean testis size ranged from 1.22 ± 0.25 cm2 in February to 2.68 ± 0.08 cm2 in October. Mean ejaculate volume ranged from 11 ± 3 μl in March to 129 ± 22 μl in October. Seasonal changes in the number of spermatozoa per ejaculate or motility of spermatozoa were not observed. Mean number of spermatozoa per ejaculate was 8.14 ± 0.85 × 106 spermatozoa (n = 97); motility was 56 ± 2.4% (n = 93); semen pH was 7.76 ± 0.20 (n = 6); osmolarity was 394 ± 13 mmol kg−1 (n = 10); and 70.3 ± 1.5% of the spermatozoa were morphologically normal (n = 47). Concentration of testosterone in serum was highly correlated with testis size (r = 0.484, P < 0.001, n = 137), but none of the semen characteristics was found to be correlated with either concentration of testosterone in serum or testis size (P > 0.05). These data suggest that concentration of testosterone in serum, testis size and ejaculate volume increase seasonally as photoperiod decreases.

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R. A. Mead, S. Bremner and B. D. Murphy

Summary. A highly localized increase in permeability of uterine blood vessels in the immediate vicinity of implanting blastocysts was first detected on the morning of the 12th day of pregnancy (290 h post coitum). The amount of extravasated dye which accumulated at implantation sites continued to increase through the evening of Day 13 (321 h p.c.). Blastocyst expansion, as indicated by small uterine swellings, preceded a detectable change in vascular permeability by about 10 h, suggesting that the timing of increased permeability is closely associated with initial blastocyst attachment to the uterine epithelium.

The results do not support the hypothesis that prostaglandins are required for increased uterine vascular permeability as two doses of indomethacin (4 and 8 mg/kg body wt) administered 5 times/day failed to decrease endometrial vascular permeability. However, the 8 mg dose did cause a significant reduction in size and number of uterine swellings and delayed or inhibited attachment of the trophoblast to the uterine epithelium in 2 of 5 ferrets. These findings suggest that prostaglandins play an important role in the process of implantation that is unrelated to decidual formation as the ferret is an adeciduate species.

Keywords: ferret, implantation, uterine vascular permeability, indomethacin

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R. A. Mead, S. Neirinckx and N. M. Czekala

Summary. In laboratory conditions, in a natural photoperiod, testicular redevelopment began in late December. Maximal testis size was attained by the end of February. Testicular regression began in mid-May and was complete by the end of August. Oestrus was first observed in late March and continued throughout April. Females mated for the first time between 30 March and 8 April. Mating generally coincided with peak concentrations of urinary oestrone conjugates and when vaginal lavages contained >90% cornified epithelial cells. Blastocyst implantation occurred by Day 13 and the post-implantation period was 29 days. Gestation ranged from 39 to 43 days and first parturition occurred in mid-May. Concentrations of urinary oestrone conjugates and free progesterone were elevated during the first half of pregnancy, reaching maximum values at mid-pregnancy, and then gradually declined as parturition neared. Litter size of primiparous females averaged 6·8 young/female. Females that were pseudopregnant or lost their litters shortly after birth, and several with weaned kits, exhibited a second oestrus.

Keywords: steppe polecat; oestrous cycle; testis; pregnancy; urinary steroids