Folliculogenesis, onset of puberty and fecundity of mink (Mustela vision Schreb) selectively bred for docility or aggressiveness

It has been suggested that selective breeding of animals for docile behavior is correlated with early onset of puberty and improved fertility. We wished to test the hypothesis that mink bred for docility would show earlier onset of puberty and greater fecundity than mink bred for aggressiveness. We used farm-raised, 7-mo-old mink females that had been selectively bred for 7 to 10 generations on the basis of behavior towards humans. Onset of puberty was estimated once (between 15 and 20 December) by vaginal smears and was said to start wtih preponderance of cornified epithelial cells in the cytological specimen. Fecundity was measured by litter size and rate of folliculogenesis, with and without hCG stimulation, by histomorphometric examination of ovaries and uteri. A total of 43/100 (43%) docile females achieved proestrus and estrus as compared to 16/136 (12%) of the aggressive ones. Overall pregnancy rate, survival to 5 d after whelping and litter size did not differ between the docile and aggressive females. Docile females showed significantly higher numbers (P < 0.05 and < 0.001) of growing, maturing and atretic follicles than the aggressive ones, however the latter showed a highly significant (P < 0.001) folliculogenic response to hCG. The response of the ovary of aggressive females to hCG is particularly dramatic because in most aggressive females the ovaries contained none or only few follicles of any kind. The inhibition of folliculogenesis in aggressive mink is similar to that reported in Silverblue and Sapphire mink homozygous for the Stuart factor. The paradoxical response to hCG may be an indication that selective breeding for aggression may be correlated with the disturbance at the early stages of folliculogenesis which creates a deficiency of follicles that are sensitive to LH-type stimulation.     

The effects of a low dose of cabergoline on induction of estrus and pregnancy rates in anestrous bitches

This is the first report of successful induction of normal estrus and ovulation in breeder bitches with as a low dose as 0.6 microg/kg/day of cabergoline formulation marketed for use in women. Sixty-one pure breed bitches from various breeds were used in the study at their already determined periods of anestrus. Twenty-four dogs formed the control group, while 37 bitches were administered with two different doses of cabergoline (recommended dose group, n=10, 5 microg/kg/day and low dose group, n=27, 0.6 microg/kg/day). Induced estrus rates and mean treatment and proestrus durations of dogs in these two dose groups were compared. At the second phase of the study, the effects of 500 IU human chorionic gonadotropin (hCG) administered on days 1 and 3 of estrus induced by the low dose of cabergoline, on the duration of behavioral estrus, ovulation rates, pregnancy rates and the number of offspring were investigated. For this purpose, the dogs with signs of proestrus (22/27) following the treatment in the low dose group were assigned into two subgroups. Five hundred IU of hCG (Pregnyl, Organon, Turkey) was intramuscularly administered to eight of these dogs [low dose (hCG+) group] on days 1 and 3 of estrus. The remaining 14 dogs were not treated with hCG [low dose (hCG-) group]. An aqueous solution of cabergoline (Dostinex, Pharmacia, Italy) was orally administered until 2 day after the onset of proestrus or for a maximum of 42 days. Blood samples were taken daily from all treatment and 11 control bitches during the first five days of behavioral estrus to measure progesterone concentrations. In the recommended dose and low dose groups, estrus was induced between days 8-45 and 4-48 (mean: 23.63+/-14.33 and 24.41+/-14.31 days), in the ratio of 80.0 and 81.5%, respectively (p>0.05). In both dose groups, post-treatment interestrous intervals were significantly shorter than both those of the control group and their own pre-treatment interestrous intervals (p<0.05). Ovulation rates, pregnancy rates and mean number of offspring delivered by the dogs in the recommended dose, low dose (hCG-), low dose (hCG+) and control groups were found to be similar (p>0.05). However, the mean duration of behavioral estrus of the dogs in the low dose (hCG+) group was found to be significantly longer compared to dogs in all other groups (p<0.05). In both dose groups, no correlation could be found between the anestrus stages and treatment durations (p>0.05). Shortly, it has been concluded from the study that (1) normal and fertile estrus can be induced more economically in bitches during different stages of anestrus using as a low dose of 0.6 microg/kg of cabergoline formulation marketed for use in women, and that (2) hCG injections on days 1 and 3 of the estrus induced by this method has no positive effects on the ovulation rates, pregnancy rates and the number of offspring per pregnancy.     

Noninvasive monitoring of female reproductive hormone metabolites in the endangered European mink (Mustela lutreola)

This study examined the reproductive physiology of female European mink (Mustela lutreola) to augment the available information on estrus, ovulation, and pregnancy with the long-term goal of supporting ex situ breeding management of this highly endangered species. Fecal reproductive hormone metabolites were measured using EIAs for estrogen and 20-oxo-pregnane metabolites. Seasonal hormone profiles were established. A comparison of hormone fluctuations in pregnant and nonpregnant females showed that both estrogen and 20-oxo-pregnane metabolites were significantly elevated during gestation, which is 42 days in length. Delayed implantation or embryonic diapause does not occur in this species. Litter size was correlated with 20-oxo-pregnane levels but not with estrogen concentrations. During lactation, 20-oxo-pregnane metabolite levels remained higher than in nonpregnant females. The breeding season was characterized by peaks in vaginal cornified cells and fecal estrogen metabolite levels. Up to four peaks in estrogen levels were identified and confirmed that European mink are seasonally polyestrous. The results of 20-oxo-pregnane measurements indicated that hCG can be applied to induce ovulation. With the establishment of this noninvasive method, we present a new tool to support population management of this species.     

Estrus induction and synchronization in canids and felids

Indications for estrus induction in the dog and cat include potential missed breeding opportunities or conception failure, the treatment of primary or secondary anestrus, out-of-season breeding (feline) and synchronization of ovulation for embryo transfer programs. Reported methods for estrus induction in bitches and queens include the use of synthetic estrogens (diethylstilbesterol), dopamine agonists (bromocriptine and cabergoline), GnRH agonists (lutrelin, buserelin, fertirelin, deslorelin, and leuprolide), exogenous gonadotropins (LH, FSH, hCG, PMSG, and human menopausal gonadotropin) and opiate antagonists (naloxone). These methods vary widely in efficacy of inducing estrus as well as in the fertility of the induced estrus. The applicability of some of these methods for clinical practice is questionable. This review will summarize published reports on estrus induction in canids and felids, both wild and domestic, and provide an update on research using a long-acting injectable deslorelin preparation in bitches.     

Estrous Cycle,Folliculogenesis, and Brain Catecholamines after Stimulation of the Sexual System by Choriogonadotropin in Female Minks Selected for Behavior

The content of hypothalamic dopamine (DA) and noradrenaline (NA) is determined and ovary function (folliculogenesis) in various states of estrous cycle is studied in non-selected (control) immature (7-month old) standard female minks and in similar females of aggressive and quiet behavioral types (the 18th generation of selection) in norm and at the 7th day after single intramuscular injections of chorionic gonadotropin (CG). At the 7th day after the CG administrations, the control females were distributed by their estrous cycle state as follows: anestrus (A)— 47.2%, anestrus-proestrus (AP)—10.0%, proestrus (P)—8.5%, proestrus-estrus (PE)—14.3%, and estrus (E)— 20.0%. In the female minks selected for behavior, there was a significant increase of percentage of estrous females: to 84.6% in the aggressive ( p < 0.001) and to 58.4% in the quiet type animals ( p < 0.01). The number of growing and maturing (at the early stage) follicles in intact females of aggressive behavior was lower than in control and in females of the quiet type. However, the number of Graafian vesicles in ovaries of aggressive and quiet females did not differ and exceeded control. The stimulation by CG enhanced the differences between the ovaries of selected animals. In control females at the 7th day after CG injections there was a tendency for a decrease of the DA and NA content with development of estrus (A→AP→P). The hypothalamic DA concentration was higher in intact females of the aggressive type than in the quiet females ( p < 0.05). In animals of the aggressive type, stimulation of the sex system decreased the DA level. No correlation between sexual function and DA and NA levels was found in females of the quiet type. However, differential analysis of NA in these females with different reactions of vaginal epithelium to CG stimulation (A, AP vs P, PE, E) indicates correlation of catecholamine level with sexual function. Thus, selection of minks for aggressive behavioral type produces an increase of the hypothalamic catecholamine level, which, in turn, is one of factors inhibiting sexual function.__________Translated from Zhurnal Evolyutsionnoi Biokhimii i Fiziologii, Vol. 41, No. 3, 2005, pp. 266–271.Original Russian Text Copyright © 2005 by Klochkov, Alekhina, Trapezov, Petrenko.     

Induction of estrus in bitches with normal and persistent anestrus using human menopausal gonadotropin (hMG)

Human menopausal gonadotropin (hMG) was administered intramuscularly to 10 bitches during apparently normal anestrus (n = 7) or persistent anestrus (n = 3). Each dog received a 75-IU dose of hMG (75 IU LH and 75 IU FSH; 1 to 7 units/kg) daily for nine days. Nine bitches responded with obvious signs of proestrus within 3 to 9 days. Of these, 3 bitches exhibited a weak proestrus while 2 exhibited a normal estrus and ovulation but failed to become pregnant The remaining 4 bitches became pregnant at the induced cycle and produced normal litters at 72 to 85 d after the start of treatment, including 1 bitch that had been treated at 24 mo after the last estrus. In 2 cases, treatment resulted in ovulation following 25 or 34 mo of chronic pubertal anestrus, 1 of which became pregnant. The results suggest that hMG can be a useful gonadotropin preparation for inducing estrus in dogs.     

Response of the mink reproductive system to hormonal stimulation in october as a prognostic criterion of folluculogenesis and fertility

The responsess of the mink reproductive systems in October to a single intramuscular injection of chorionic gonadotropin (CG, Profasi R, Italy) at doses of 10, 20, 50, and 100 IU was studied. The estrous cycle state, folliculogenesis, and reproductive parameters of the female minks were estimated. To evaluate functional polymorphism in the reproductive system of the females in response to the CG injection, a dose of 20 IU was chosen. On the sixth day after administration of this dose of CG, the females (n = 185) were distributed according to the stages of the estrous cycle as follows: anestrus—71 animals (38.4%), anestrus-proestrus—37 (20.0%), proestrus—30 (16.2%), proestrus-estrus—14 (7.6%), estrus—33 (17.8%). In the females of the “anestrus-proestrus” and “proestrus” groups as compared with the other groups as well as with control, a statistically significantly higher fertility was revealed. The study of folliculogenesis in the females with different parameters of the estrous cycle in November demonstrated the high level of fertility to be due to ability of these females to produce, under influence of the CG injection, the maximal number of mature follicles. A high heritable responsiveness of the reproductive system of the females to the CG injection (coefficient of realized heritabilityh = 0.64; the calculation made on the data for the sisters) indicates that this method may be an additional criterion in the selection of females for fertility.     

In vitro DNA synthesis by isolated preantral to preovulatory follicles from the cyclic mouse

In recent studies, we have shown that the smallest preantral follicles in the cyclic hamster increase DNA synthesis in the periovulatory period in response to surge levels of FSH. The current investigation was designed to determine whether the same phenomenon occurs in the cyclic mouse. Intact mouse follicles were isolated with watchmaker forceps (stages 4-6) or by enzymatic digestion (stages 1-4) at 0900 h and 1500 h on each day of the 5-day estrous cycle. The isolated follicles were classified into 6 stages: stages 1 and 2: follicles with 1 and 2 layers of granulosa cells; stage 3: follicles with 3 or more layers of granulosa cells and formation of theca; stages 4-6: incipient, small, and preovulatory antral follicles. The follicles at each stage were incubated for 3 h with [3H]thymidine. DNA content in stages 1-4 of follicles remained unchanged during the estrous cycle; for stages 5 and 6, DNA content was higher on the afternoon of proestrus than on other days of the cycle. Incorporation of [3H]thymidine for stages 1-3 (preantral follicles) started to increase at 1500 h of proestrus and peaked at 0900 h on estrus, whereas for stages 4-6, DNA synthesis peaked on proestrus (1500 h) and then fell by the morning of estrus. Thus, the rate of DNA replication in preantral and antral mouse follicles were different. Similarities and differences in folliculogenesis between mouse and hamster are discussed. These results suggest that DNA synthesis and the growth of all stages of follicles in the cyclic mouse may be associated with changing levels of periovulatory gonadotropins.     

Profiles of oestradiol-17 beta and progesterone and follicular development during the reproductive season in mink (Mustela vison).

Plasma concentrations of oestradiol-17 beta and progesterone were studied in yearling mink females. The blood samples were collected from 2 March until 13 April in females not subjected to mating and in females mated on two consecutive days, early or late in the breeding season, or with 8-9 days between matings. Peaks in oestradiol-17 beta were recorded on the day of first mating, in relation to the second wave of growing follicles, and in early April, around the time when implantation should have occurred. Significant rises in progesterone were recorded from 17 to 21 March and were slightly later in females mated late in the season. Histological studies of ovaries from unmated females revealed that the number of 'active' follicles exceeded the number of degenerated or luteinized follicles until 7 April, after which the number of degenerated follicles increased rapidly. Degeneration was followed by luteinization. On 15 April, ovaries were collected from two females having 15 luteinized follicles each. These females had increased plasma concentrations of progesterone. These studies indicate that, in female mink, peaks in oestradiol-17 beta coincide with the first mating as a result of the copulatory act and that unmated females appear to experience a luteal phase in the absence of ovulation.     

The postpartum buffalo. II. Acyclicity and anestrus

Prolonged postpartum acyclicity (absence of ovarian cyclic activity) and anestrum (absence of overt estrous signs) are major sources of economic loss to buffalo breeders. Studies on the epidemiology of these two problems are highly recommended to achieve successful control. Review of the available literature on controlled studies in dairy buffaloes revealed that first ovulation as detected by rectal palpation and progesterone analysis occurred between 28-71 and 24-55 days, respectively, after calving. Postpartum estrus in the same studies occurred between 44 and 87 days. Reports concerned with data compiled from breeding records of research stations, breeding farms and small holders where estrus is a subjective measure, gave much longer periods. Also data from Egypt, India and Pakistan indicate that only 34-49% of buffaloes showed estrus during the first 90 days after calving and 31-42% remained anestrus for more than 150 days. In swamp buffaloes both postpartum ovulation and estrus are more delayed than in dairy buffaloes. The role of suckling, nutrition, body condition score at calving, milk yield, parity, season of calving and other minor factors were discussed. First postpartum ovulation is frequently followed by one or more short estrous cycles (<18 days). Long anovulatory and anestrous periods due to prolonged inter-luteal phase were reported to occur after short cycles. Also long anestrous periods due to cessation of cyclic activity (true anestrus) for 3 or more weeks and prolonged luteal activity for 28 days or more were described to occur in about 25 and 8-11% of the buffaloes, respectively, after the first or second ovulation. These cycle irregularities certainly impose difficulties on estrus detection programs in postpartum buffaloes. Four main forms of anestrus i.e. true anestrus (inactive ovaries and small and medium sized anovulatory follicles), subestrus, prolonged luteal activity and ovarian cysts in addition to pregnancy are reviewed in this article. Differentiation between true anestrus and subestrus is particularly important in buffaloes because of their weak estrous signs. However, the accuracy of a single rectal palpation of the ovaries is limited with an overestimation of the frequency of true anestrus due to misdiagnosis of the corpus luteum. The possible causes are discussed.     

Seasonal effects on fertility and ovarian follicular growth and maturation in camels (Camelus dromedarius).

Camels are said to be seasonal breeders, but the extent to which season interferes with food supply to affect ovarian function is not fully documented. Hence, the three aims of this study were: (1) to define the breeding season of camels maintained in semi-arid conditions in southern Morocco; (2) to relate the proportion of females with active ovaries (i.e., with follicles > 5 mm), with ovulatory (11-17 mm) or cystic (> 18 mm) follicles to age and body conditions score; (3) to study the consequences of the interactions between age and body conditions score on the proportion of females ovulating and conceiving; and (4) to compare follicular maturation, using in vitro steroidogenesis by intact follicles as a marker during the transition into the breeding season (October) and peak breeding season (March). There was a clear breeding season in the two flocks studied, since over 80-90% of the matings occurred during the period from mid-November to mid-April. Collection of ovaries at slaughter (n = 238) demonstrated a significant seasonal effect on the proportion of females with active ovaries (increasing from 73.5% in October-December to 89% in January-May), but no changes in the proportion of females with ovulatory follicles. Lean females (BCS < 2.5) had a delayed initiation of ovarian function in October-December. In addition, the proportion of females with cystic follicles was also affected by season (peaking during April-May). Neither age nor body condition modulated the frequency of cysts. Finally, the proportion of females conceiving increased steadily as season progressed (peaking at 57% in April-May). Body condition score did not affect this proportion, but young females (< or = 5 years old) had a low ability to conceive. Morphological features of large follicles were unaffected by season. Ovulatory follicles contained around 10(7) granulosa and theca cells. In vitro testosterone output by intact follicles was unrelated to follicle size and season. In vitro oestradiol output increased with increasing follicle size and was larger in follicles obtained during peak breeding season than at its initiation. This may indicate that early breeding season follicles display a low aromatase activity in their granulosa cells. Whether the low oestradiol output of early breeding season follicles is resulting in the low fertility observed at this period remains to be determined.     

Adrenal function in different phases of the estrous cycle in the domesticated silver fox, Vulpes fulvus

Experiments were made on silver foxes from a population which had been selected for 10 to 15 generations for the domestic behaviour and on animals from a control, unselected population. In females from both populations, studies were made of the level of 11-OHCS in the blood serum, in vitro production of 11-OHCS, the size of fascicular zone in the adrenal cortex, the volume of cellular nuclei and nucleoli, as well as the reaction of the adrenals in vitro to 2 doses of ACTH (1 and 5 units/g of the adrenals) during anestrus, proestrus and estrus. In control females, all the characters investigated significantly increased from anestrus to proestrus. In domesticated females, no changes in the production of 11-OHCS in vitro or changes in morphological features of the fascicular zone were observed in the course of estrous cycle. During proestrus, the adrenals of the domesticated animals were not able to increase the production of 11-OHCS in vitro after application of ACTH. The decrease in the reactivity of the adrenals to the effect of ACTH is presumably the main cause why in unselected females the adrenal are not activated during proestrus. Therefore, in the course of selection for the domestication type of behaviour, species specific dynamics of activation of the adrenals during estrous cycle is lost.     

Effects of PMSG and ram contact on the reproductive performance of progestagen-treated ewes during breeding and anestrous seasons

The objective of this study was to evaluate the efficacy of combinations of PMSG treatment and ram contact on the reproductive performance of progestagen-treated ewes during three different times of the year, Febraury (early anestrus), July (late anestrus) and October (breeding season). A total of 109 multiparous Dorset ewes was used. Ewes were treated with intravaginal progestagen pessaries for 12 days, injected with 500 IU PMSG at pessary removal and either isolated from rams prior to mating (n = 12, February; n = 12, July; n = 8, October) or exposed to rams during pessary treatment (n = 17, February; n = 12, July; n = 8, October). A third treatment group (n = 18, February; n = 6, July; n = 8, October) received pessaries and ram exposure but no PMSG. An additional treatment of progestagen pessaries alone was included in October (n = 8). There were no differences among treatments in their ability to induce estrus at different times of the year, but incidence of estrus tended (P < 0.10) to be lower for PMSG treatment during the July breeding. During February, the use of pessaries with PMSG treatment increased (P < 0.05) conception and lambing rates, whereas ram contact was without any beneficial effects. The trend was reversed during July breeding, when ram contact increased (P < 0.05) fertility of progestagen-treated ewes compared with other treatment combinations. Pessaries alone were sufficient to attain acceptable levels of fertility and fecundity in October.     

Inhibin activity and secretion of gonadotropin during the period of follicular maturation

To evaluate the relative contributions of the ovarian inhibin and estradiol-17 beta (E) on the regulation of FSH secretion, inhibin and E in ovarian venous plasma (OVP) and FSH and LH in peripheral plasma were simultaneously measured using superovulating rats with special reference to follicular maturation. By the transplantation of a pituitary gland from adult male rats under the kidney capsule between 1100 and 1200 hr on diestrus-1 in cyclic rats, superovulation was successfully induced on the morning of the next estrus without any additional treatment with human chorionic gonadotropin (hCG). The number of maturing follicles capable of ovulating in response to hCG significantly increased at 12 hours after the grafting as compared with sham-operated controls and further increases occurred until the afternoon of proestrus. In the superovulating rat, first and second surges of FSH were completely blocked and an LH surge was also partially suppressed during the periovulatory period when surges of FSH and LH were normally observed in controls. Contents of FSH as well as LH in the animal's own pituitary gland were suppressed significantly after the grafting as compared with controls. A marked increase in inhibin activity in OVP of rats with a pituitary transplant occurred concomitantly with an increase in the number of follicles capable of ovulating whereas E levels in OVP did not so. Inhibin activity in OVP at each point was much higher in the pituitary grafted rats than in controls but this was not true for E levels. These results suggest that ovarian inhibin derived from the maturing follicles rather than E may be a primary factor for regulation of FSH secretion, and high levels of endogenous inhibin can suppress synthesis of LH as well as FSH in the pituitary gland of the female rat.     

Ultrasound and endocrine evaluation of the ovarian response to a single dose of 500 IU of eCG following a 12-day treatment with progestogen-releasing intravaginal sponges in the breeding and nonbreeding seasons in ewes

A standard dose of 500 IU of eCG is commonly given to progestogen pre-treated anestrous ewes for induction of estrus. Twelve seasonally anestrous and 12 cyclic Western White Face ewes were treated for 12 days with intravaginal sponges impregnated with medroxyprogesterone acetate (MAP). In trials in both the breeding and nonbreeding seasons, six randomly selected ewes were given 500 IU of eCG at sponge removal to determine the effects of low dose of eCG on ovarian antral follicular dynamics and ovulation. Ultrasound scanning and blood sampling were done daily. Treatment with eCG did not have marked effects on antral follicular growth. All ewes ovulated, except for five of six control anestrous ewes. Luteal structures and progesterone secretion were confirmed in all but the control anestrous ewes. In the breeding season, peak progesterone concentrations were greater (P<0.05) in eCG-treated compared to control ewes. Daily serum estradiol concentrations were greater in the periovulatory period in eCG-treated compared to control ewes (treatment-by-day interaction; P<0.05), particularly in anestrus. Progestogen-treated ewes ovulated follicles from several follicular waves, in contrast to ovulations of follicles from the final wave of the cycle in untreated, cyclic ewes. Anestrous ewes exhibited more frequent follicular waves and FSH peaks compared to cyclic ewes after a progestogen/eCG treatment. In conclusion, 500 IU of eCG given after 12 days of progestogen treatment had limited effects on the dynamics of ovarian follicular waves. However, eCG treatment increased serum concentrations of estradiol during the periovulatory period, particularly in anestrous ewes; this probably resulted in the synchronous estrus and ovulation in anestrous ewes.     

Effect of breeding season on fertility of sheep following estrus synchronization and fixed-time artificial insemination under field conditions in semi-arid tropical region

Accelerated lambing system is heavily reliant on reproductive technologies meant to enable off the season breeding in sheep. Therefore, the present study was programmed to assess the effect of breeding season (BS) on fertility of sheep following estrus synchronization (ES) and fixed time artificial insemination (FTAI). A total of 248 and 365 ewes were synchronized and inseminated during the BS (Febuary–March and July–September) and non-breeding season (NBS) respectively, during 2012–14. Synchronization of estrus was done by AVIKESIL-S, intra-vaginal progesterone sponges kept in situ in vagina for 12 days. 200 IU eCG was administered intramuscularly on 12th day after sponge withdrawal. FTAI was performed twice in ewes exhibiting signs of estrus at 48 and 56h after sponge removal, using liquid chilled semen of Patanwadi/Malpura rams containing 100 million sperm. Breeding season had no significant (p<0.05) effect on estrus synchronization. The estrous responses during the BS and NBS were 84.68% and 83.29% respectively. The lambing percentage during BS was 66.67%, which is significantly (p<0.05) higher than the lambing percentage of NBS (57.57%). Although, the lambing percentage in NBS maneuvered ewes were lower than the BS ewes but still the technology can be used to offset the effect of anestrus and to augment production in sheep.     

Sexual characteristics of female dogs during successive phases of the ovarian cycle

Five female beagles were examined periodically throughout their second biannual cycle of proestrus, estrus, metestrus, and anestrus for fluctuations in several physiological and behavioral charateristics. Physiological measures included plasma levels of estradiol and progesterone as well as the vulvar swelling and vaginal bleeding that begin with proestrus and continue in estrus. Behavioral tests revealed changes in female receptivity, attractivity, and proceptivity. Estradiol increased prior to the onset of proestrus and declined during estrus. Progesterone levels were low during most of proestrus, increased from the beginning to the end of estrus, and remained elevated during the first month or more of metestrus. While they were in proestrous females were not receptive but they and their vaginal secretions were highly attractive to males. Attractivity remained high throughout estrus and declined abruptly in the next 24 hr. Receptivity increased over the first 3 days of estrus and continued at a high level until the last 3 days during which it decreased slightly, and then dropped nearly to zero within the next 24 hr. “Sexual reflexes” of the vulva, tail, and hindquarters followed the same course of changes described for attractivity. Proceptive behavior, including seeking proximity to caged males and display of solicitation responses during mating tests was characteristic of females during proestrus and estrus but uncommon or absent in other phases of the cycle. It is hypothesized that in the natural cycle, attractivity and proceptivity develop during proestrus as a consequence of rapidly increasing secretion of estrogen. The onset of receptivity is due to synergistic action of estrogen and progesterone. Estrogen secreted during proestrus primes the system, and progesterone secreted just before and during estrus activates it. Termination of receptivity is thought to be due to the marked decline in estrogen, to inhibition by high concentrations of progesterone, or to a combination of these factors.     

Comparison of two sources of gonadotropin for estrus synchronization in does

Two sources of gonadotropin, combined with norgestomet implants and cloprostenol, were compared to induce estrus in 137 lactating dairy goats during the period of transition from anestrus to estrus. Does received either reagent-grade PMSG or commercially available hCG/PMSG product labeled for use in swine. Of the does treated with hCG/PMSG, 63 of 70 (90%) became pregnant compared with 50 of 66 (76%) does treated with reagent-grade PMSG. The pregnancy rates were significantly associated with the source of gonadotropin (P = 0.047). No difference in estrus response or litter size was detected; however, more does in the PMSG group appeared to have an extended interval from implant removal to breeding than did the hCG/PMSG-treated does. The results of this study indicate that the hCG/PMSG combination product is a satisfactory source of PMSG for extra-label use with norgestomet implants and cloprostenol to synchronize estrus in transitional period does.     

Stimulation of folliculogenesis in domestic cats with human FSH and LH

Folliculogenesis in response to exogenous stimulation by human urinary follicle stimulating hormone (huFSH) and human menopausal gonadotropin (hMG) was evaluated in the domestic queen (Felis catus). The role of LH and/or FSH in folliculogenesis was examined by measuring concentrations of estradiol 17beta (E(2)) and progesterone (P) in the serum. Additionally, changes in the number and size of follicles from before the administration of exogenous hormones to surgical oocyte collection were monitored. Findings indicated that in queens receiving huFSH or hMG followed by human chorionic gonadotropin (hCG) to induce ovulation, the numbers of follicles from 1 to 3 mm increase with statistical significance (P<0.005) from before the initiation of treatment to surgical collection of oocytes. Although E(2) concentrations in cats receiving hMG increased above baseline by the third exogenous hormone injection, mean E(2) concentrations did not increase in the groups that received both huFSH and hCG, or hCG only, until after the administration of hCG. This suggests that the exogenous administration of LH contained in both hMG and hCG was necessary for E(2) to rise to levels associated with estrus.