Onset Of First Estrus Research Articles

Characteristics of estrous cycles in gilts treated with gonadotropins after estrus or treatment with a progestogen

A combination of eCG (400 IU) and hCG (200 IU) (P.G. 600; Merck Animal Health, Summit, NJ, USA) stimulates puberty in gilts, but variation in the estrual response exists among farms. We hypothesized that some of the variability is a consequence of gilts that have commenced cycling being inadvertently treated. The objective of experiment 1 was to determine the effect of intramuscular (im) P.G. 600 on estrous cycles in sexually mature gilts. Gilts in treatment 1 (n = 16) received P.G. 600 at the onset of daily boar exposure. Gilts in treatments 2 to 5 (n = 16 per treatment) were allowed to express a natural first estrus and were then treated with P.G. 600 during the first estrous cycle as follows: treatment 2 at Day 6, treatment 3 at Day 12, and treatment 4 at Day 18 of the estrous cycle. Treatment 5 gilts received no P.G. 600. The proportion of gilts displaying a normal estrous cycle (18–24 days) was greater (P < 0.05) for treatments 4 (100%) and 5 (100%) compared with treatments 1 (73.3%) and 3 (60%), with treatment 2 having a value (87.5%) that was not different from the other groups. For treatment 3, 33% of gilts displayed an increased interestrus interval that averaged 32.5 days. Concentrations of progesterone remained elevated 20 days after the onset of first estrus in treatment 3 gilts, which supports the concept that P.G. 600 administered at Day 12 of the estrous cycle induced follicular growth, ovulation, and formation of CL that functioned for approximately 15 days, increasing the length of the estrous cycle. It is common for swine producers to have groups of replacement gilts that include both cycling and prepubertal animals, or individuals, the cycling status of which is unknown. The objective of experiment 2 was to evaluate a system using a combination of a progestogen (Matrix; Merck Animal Health) and P.G. 600 to synchronize estrus in replacement gilts. Crossbred gilts, assumed to be a mix of cycling and prepubertal females, were allocated to one of four treatments (n = 12 per treatment): treatment 1, Matrix (15 mg/day) fed for 14 days and im P.G. 600 24 hours after the last feeding of Matrix; treatment 2, Matrix for 7 days and P.G. 600; treatment 3, P.G. 600 only; and treatment 4, im water only. The percentage of gilts in estrus within 7 days after im treatment was the greatest (P < 0.02) and days to estrus the least (P < 0.05) for gilts receiving Matrix for 14 days and P.G. 600 (treatment 1, 91.7% and 5.4 ± 1.9 days; treatment 2, 50% and 9.2 ± 2.0 days; treatment 3, 33% and 13.8 ± 2.1 days; and treatment 4, 50% and 9.1 ± 1.9 days). The results of these experiments suggest that P.G. 600 administered to gilts that have already obtained puberty may cause abnormal estrous cycles and demonstrate to swine producers the need to correctly classify replacement gilts as prepubertal or cycling before administering the product. The use of Matrix and P.G. 600 in combination has potential as an effective strategy for synchronizing estrus in a mix of prepubertal and mature, cycling gilts.

Sex-specific impact of prenatal stress on growth and reproductive parameters of guinea pigs

Body condition and reproductive maturation are parameters of reproductive success that are influenced by sexual hormones rising in the circulation during the time of puberty. Various endocrine systems can be programmed by conditions experienced during early life. Stress for instance is supposed to be capable of influencing fetal development, leading to adjustments of offspring's later physiology. We examined whether prenatal stress (induced by exposure to strobe light) during early- to mid-gestation was capable of affecting later reproductive parameters in guinea pigs (Cavia aperea f. porcellus). Therefore, we measured the levels of testosterone and progesterone from the age of day 12-124 in prenatally stressed (PS, n=20) and unaffected control animals (n=24). Furthermore, we determined the timing of puberty and growth. Body weight development revealed significantly faster growth in PS females compared to control animals. The onset of first estrus was slightly earlier in PS females, however not significantly so. Cycle lengths and levels of progesterone differed between groups over the course of time with higher progesterone levels and more constant cycles among PS females compared to control females who displayed marked differences between first and subsequent cycles. Levels of testosterone did not differ between groups. We conclude that prenatal stress accelerates growth and maturity in females, but not in males.

Follicle Development during Luteal Phase and Altrenogest Treatment in Pigs

Synchronization of the oestrous cycle of gilts using altrenogest treatment has been found to increase ovulation rate. The current experiment investigated if the increase in ovulation rate after altrenogest treatment is related to increased follicle size at the end of altrenogest treatment compared with late luteal phase follicles. Crossbred gilts (n = 15) received altrenogest during 18 days [20 mg Regumate (Janssen Animal Health, Beerse, Belgium)], starting 5-7 days after onset of first oestrus. Control gilts (n = 15) did not receive altrenogest. At days 10-12 of the oestrous cycle [i.e. in the presence of corpora lutea (CL)], average follicle development was 2.51 +/- 0.20 mm (assessed with ultrasound) in altrenogest-treated gilts and 2.58 +/- 0.16 mm in control gilts (p > 0.10). During the last days of altrenogest treatment (i.e. when CL had gone into regression), average follicle size had increased to 3.01 +/- 0.31 mm (p < 0.05). Subsequent ovulation rate was 16.6 +/- 1.7 in altrenogest treated gilts and 15.1 +/- 1.2 in control gilts (p < 0.05). Altrenogest treatment resulted in increased follicle size after regression of the CL, showing that suppression of follicle growth by altrenogest alone is less severe than suppression by endogenous progesterone (either with or without altrenogest). Altrenogest treatment also resulted in a higher ovulation rate. However, it is unclear if the increased follicle size and higher ovulation rate after altrenogest treatment are causally related, as the relation between the two on an animal level was not significant.

Early exposure to oxytocin affects the age of vaginal opening and first estrus in female rats

Neonatal exposure to exogenous oxytocin (OT) can have long-term effects on the subsequent expression of adult behavior and physiology. Here, we test the prediction that early postnatal exposure to OT can affect the timing of sexual maturation in females, as indicated by the age of vaginal opening and the onset of first estrus. To test this hypothesis, female Sprague–Dawley rats received one of four treatments beginning on the day of birth and continuing for the next 6 days. Three groups received an intraperitoneal injection of one of the following: OT (1 μg/g), an OT antagonist (OTA, 0.1 μg/g) or isotonic saline (vehicle control). The fourth group was handled but not injected. Females were then examined to determine the day of vaginal opening and first estrus. The potential effects of OT on body weight were also measured, with females being weighed on postnatal days 1–7, 70, 91 and 136. Treatment with OT significantly delayed the age of vaginal opening and the onset of first estrus. There was no effect on weight. Results indicate that early exposure to OT can affect the timing and development of female sexual maturation.

Interleukin-5 transgene expression and eosinophilia are associated with retarded mammary gland development in mice.

Eosinophils are prevalent in the female reproductive tract, where they may contribute to regulation of development and maintenance of epithelial integrity. The present study examined the effects of constitutive interleukin-5 (IL-5) expression and overabundance of eosinophils on the development and function of the mammary gland, uterus, and ovary in mice. Eosinophils were up to 13-fold and 4-fold more abundant in the uterus and mammary gland, respectively, in female IL-5 transgenic (IL-5Tg) mice than in wild-type (Wt) animals. Eosinophils were present in large numbers in regressing corpora lutea in IL-5Tg mice but not in ovaries from Wt mice. Postpubertal mammary gland development was retarded in IL-5Tg mice, with impaired terminal end bud formation and an altered pattern of epithelial cell proliferation across the mammary fat pad coincident with disrupted ductal branching and extension. By 10 wk of age, the ductal tree was complete in both genotypes. Onset of first estrus was also delayed in IL-5Tg mice, but once IL-5Tg mice reached puberty, serum estrogen content across the cycle and estrous cycle duration were normal. The histology of uterine tissue and epithelial cell turnover were unchanged. Capacity to mate and achieve pregnancy was not affected by maternal IL-5 transgene expression, although at Day 18 of gestation, a modest decrease in the fetal:placental weight ratio was observed. Furthermore, parturition and ability to lactate and nurture postnatal pup development were not compromised. These data demonstrate an effect of IL-5 overexpression on ductal morphogenesis during postpubertal mammary gland development that is consistent with a direct regulatory role for eosinophils in these events, but these data also show that eosinophil excess does not have long-term consequences for adult reproductive function.

Effects of injection of hCG during the estrous cycle on follicle development and the inter-estrous interval

Pseudopregnancy in pigs can be induced by the administration of a single dose of hCG at Day 12 of the estrous cycle. However, the resulting length of pseudopregnancy can be extremely variable. In this study, it was investigated whether time of hCG administration (day of the cycle) and degree of follicle growth after hCG administration were related to the length of inter-estrous interval (pseudopregnancy). In the first experiment, groups of cyclic gilts were given 1500 IU hCG at either Day 11 (D11; n=14) or Day 12 (D12; n=14) after onset of estrus, or not treated (Control; n=13). Follicle development was assessed daily using transcutaneous ultrasonography. Follicle size in the Control gilts remained relatively constant between Days 11 and 17, whereas in the treated gilts, follicle size increased (P<0.001) within 4 days (D11) and 2 days (D12) after treatment. The inter-estrous interval was increased (P<0.01) in the hCG-treated gilts (34.7 ± 6.3 and 37.6± 11.1 days in the D11 and D12 gilts, respectively), compared to Controls (22.3 ± 5.2 d). About two-thirds of the treated gilts returned to estrus between Days 32 and 39 after onset of first estrus. No relationships were found between follicle development after treatment and length of the inter-estrous interval. In a second experiment, 16 cyclic gilts were treated with 1500 IU hCG at Day 12 and Day 15 of the estrous cycle. Follicle development was assessed at Days 12, 15 and 18. At Day 18, average follicle size was 8.4 ± 2.0 mm. The inter-estrous interval was 39.7 ± 5.4 days and 14 of 16 gilts returned to estrus between Days 34 and 44 after onset of first estrus. Again, no relationships were found between follicle development after treatment and the duration of the inter-estrous interval. We conclude that, based on the duration of the inter-estrous interval, administration of hCG during the luteal phase induced a short pseudopregnancy. However, the induction of accessory corpora lutea or follicular luteinization cannot be discounted.

The nature of the metabolic signal that triggers onset of puberty in female rats

These experiments examined the effects of different refeeding stimuli on reproductive activity as measured by the onset of first estrus in prepubertal, food-restricted female rats. Such rats were placed on a restricted food intake until day 50 of age to maintain a weight of 80–90 g, and to suppress onset of puberty (normal time of puberty: 37 ± 1.4 days of age). In Experiment 1, rats were refed at different daily caloric intakes from day 50 through day 62. First estrus was observed in all rats, with highest caloric intake after 5.7 ± 0.6 days of refeeding. Progressively fewer rats achieved first estrus, and the time to first estrus increased as the caloric intake per day decreased. These results suggest that the highest caloric intake most closely resembles an ad lib diet in such realimented rats. The second experiment determined the duration of an ad lib food stimulus needed to initiate first estrus. Similarly growth-restricted rats were refed (on Day 50 of age) ad lib meals of 67.2 ± 0.1 kcal, presented for periods of 12, 24, 48, or 72 h. The majority of rats (6 of 7) achieved first estrus when the ad lib meals were presented for 72 h, but progressively fewer rats achieved first estrus when such meals were presented for less time. These data indicate that an extended ad lib food stimulus (72 h) is necessary to cause onset of cycling in the majority of food-restricted, prepubertal female rats.

Growth and sexual development of Etawah-cross kids from does of different levels of milk production

The experiment was conducted to evaluate growth and sexual development of female Etawah-cross kids of the progeny of the does with low (Group L), medium (Group M) and high (Group H) milk production. The does were fed King grass ( Pennisetum purpureophoides) (about 2% DM of liveweight) and 400 g/head of concentrate. The amount of concentrate was increased to 600 g/head during the last two months of pregnancy period and during lactation. Kids were weaned at four months of age. Thereafter, they were reared in group and were fed King grass and concentrate. The animals were weighed every two weeks. A mature vasectomized buck were joined in each group to detect the onset of first oestrus (puberty). When kids reached puberty and had a liveweight of about 20 kg, they were mated with intact buck. Ovulation rate, progesterone profiles and fertility were observed. The results showed that pre-weaning growth rates of kids in all three groups were not significantly different (67.0 vs 74.9 vs 70.5 g/day, P>0.05). At six and 12 months of ages, Groups L and M had almost the same liveweight which were higher than Group H. Consequently, Groups L and M reached puberty about 3 - 6 weeks earlier than Group H. The average liveweight at puberty was 19.9, 18.2 and 18.8 kg for Groups L, M and H, respectively, or at about 57.1-69.8% (average 63.2%) of mature liveweight. The pregnancy rate following first mating was relatively high (67-73%) and all does were pregnant in the following mating. Average ovulation rate at conception were low (1.1) in all groups. It was concluded that differences in milk production of the does did not significantly affect post-weaning growth and sexual development and performances of kids. Other factors at certain age or growth phases might be more important to affect growth and reproduction of Etawah-cross goat, and this may warrant further study. Key words : Growth, reproduction, Etawah-cross does

Controlled neonatal exposure to estrogens: a suitable tool for reproductive aging studies in the female rat.

The present study was designed to determine whether the modification of exposure time to large doses of estrogens provided a reliable model for early changes in reproductive aging. Silastic implants containing estradiol benzoate (EB) in solution were placed into 5-day-old female Wistar rats and removed 1 day (Ei1 group) or 5 days (Ei5) later. In addition, 100 micrograms [corrected] EB dissolved in 100 microliters corn oil was administered s.c. to another group (EI). Control rats received either vehicle implants or 100 microliters corn oil. Premature occurrence of vaginal opening was observed in all three estrogenized groups independently of EB exposure. However, females bearing implants for 24 h had first estrus at the same age as their controls and cycled regularly, and neither histological nor gonadal alterations could be observed at 75 days. Interestingly, they failed to cycle regularly at 5 mo whereas controls continued to cycle. On the other hand, the increase of EB exposure (Ei5, EI) resulted in a gradual and significant delay in the onset of first estrus and in a high number of estrous phases, as frequently observed during reproductive decline. At 75 days, the ovaries of these last two groups showed a reduced number of corpora lutea and an increased number of large follicles. According to this histological pattern, ovarian weight and progesterone (P) content gradually decreased whereas both groups showed higher estradiol (E2) content than controls. This resulted in a higher E2:P ratio, comparable to that observed in normal aging rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Short luteal phases and ovulations without oestrus in primiparous Borana ( Bos indicus) cows in the central highlands of Ethiopia

The incidence of short luteal phases and ovulations without oestrus was investigated in 42 primiparous Borana cows. Based on calving body weight, cows were allocated to either a control group with grass hay only or to a supplement group with a concentrate ration. Within nutritional groups, cows were further assigned to either milked or partially suckled groups. Cows were under continuous observation and vasectomised teaser bulls used in oestrus detection. Blood samples were collected twice weekly commencing on Day 30 postpartum until pregnancy for determination of plasma progesterone levels. A progesterone concentration of above 1 ng ml −1 was taken as a cut-off value between luteal and non-luteal phases and oestrous cycles of 17 days or less were considered as short. By 150 days postpartum, ovarian cyclic activity had commenced in 64.3% of the cows while 35.7% remained anoestrous. The mean (±SEM) postpartum anoestrous interval for the cyclic cows was 104 ± 19 days. Progesterone profiles revealed that up to the first detected oestrus, 97 ovulations occurred and 72% were not accompanied by behavioural signs of oestrus, indicating that an average of 2.6 oestrous periods per cow were silent. Differences in intervals between calving to onset of first oestrus based on visual detection and progesterone concentrations ranged from 5 to 21 days in 22.2%, 24–43 days in 44.4%, 44–63 days in 11.2% and 83–166 days in 22.2% of the cows. Short luteal phases with a mean duration of 10 ± 2 days and a range of 7–14 days were detected in 55.6% of the cows. There were no nutritional and suckling influences on the incidence of ovulation without oestrus and short luteal phases. Progesterone concentrations, however, were significantly ( P < 0.01) lower in short than in normal oestrous cycles. It was concluded that although short luteal phases occurred in a relatively larger proportion of cows, it was not an exclusive prerequisite for the establishment of normal oestrous cycles. The commencement of ovarian cyclic activity in 78% of the cows before Day 63 postpartum also suggests that ovulations without oestrus rather than postpartum anoestrus could be more responsible for extended calving intervals in Zebu cattle. The physiological basis and significance of ovulations without oestrus and short luteal phases in the fertility of Zebu cattle thus need further investigation.

Effect of naloxone on gonadotrophin secretion at various stages of development in the ewe lamb

Spring-born crossbred ewe lambs were raised in a natural photoperiod and saline (N = 6) or naloxone (1 mg/kg) in saline (N = 6) was injected (i.m.) every 2 h for 6 h at 5, 10 and 15 weeks of age and for 8 h at 20, 25 and 30 weeks of age. Blood samples were taken every 12 min during treatment periods. Naloxone had no effect on time to first oestrus (controls 235 +/- 6 days, naloxone 242 +/- 7 days). Mean serum LH concentrations and LH pulse frequency were elevated by naloxone in ewe lambs at 20, 25, and 30 weeks of age (P less than 0.05). The only FSH response to naloxone was a depression of mean serum concentrations at 30 weeks of age (P less than 0.05). LH pulse amplitude was elevated at 5 weeks of age in all ewe lambs and declined thereafter to a nadir at 30 weeks of age in control, but not in naloxone-treated animals (P less than 0.05). LH pulse frequency was elevated at 10 weeks of age in control ewe lambs and in all animals at 30 weeks of age (P less than 0.05). FSH pulse frequency declined from 5 weeks of age in control ewe lambs (P less than 0.05), with very few pulses noted in 25- and 30-week-old animals. We conclude that (1) opioidergic suppression of LH, but not FSH, secretion developed at 20 weeks of age in the growing ewe lambs used in the present study, with no obvious change in suppression before the onset of first oestrus: (2) pulsatile FSH secretion occurred in the young ewe lamb but was lost as the lamb matured: (3) attainment of sexual maturity was preceded by an elevation in LH pulse frequency.

Intermittent stimulation and delay of puberty by urinary chemosignals and social contact in wild stock female house mice (Mus Domesticus)

A sequence of six experiments using wild stock house mouse ( Mus domesticus) tested the effects of intermittent stimulation with either the urinary chemosignal released by grouped female mice or social contact from grouped females on the age of first vaginal oestrus in young females. Weanling female mice were exposed to bedding soiled by grouped females or cages containing grouped females for 15 min periods, then removed for a prescribed period, and placed again in a cage with soiled bedding or grouped females. The nature of the exposure to the puberty delaying effect, the number of total exposures each day, the total length of exposure to the stimulus, and the total time period over which the exposures occurred were varied. None of the treatment regimes employed here with soiled bedding from grouped females resulted in delays in the onset of first oestrus in test females. Young females exposed to grouped females for 6 or 8 exposures in a 4 h period, 6 or 8 exposures in an 8 h period, or 8 exposures in a 12 h period were significantly delayed in attaining puberty relative to control females that were exposed to cages containing clean bedding. These results are in contrast to earlier findings involving chemosignals that accelerate first oestrus wherein young females exhibited the capacity to accumulate the exposures to the urinary chemosignals from males, females in oestrus and pregnant or lactating females. Direct exposure to the grouped females on an intermittent basis can provide stimulation that is cummulative and results in delays in the onset of first oestrus.

Acceleration and delay of sexual maturation in female house mice (Mus domesticus) by urinary chemosignals: mixing urine sources in unequal proportions.

Urine from male mice, from estrous female mice, and from pregnant or lactating female mice accelerate first vaginal estrus in females, whereas urine from grouped female mice delays first estrus. Nine experiments were used to test the effects of treatment of young female mice with urinary chemosignals that influence the onset of first estrus using unequal proportions of urine from the different sources. At ratios of 10-20 parts acceleratory chemosignal to 1 part delay chemosignal the acceleratory effect overrides the delay chemosignal, and the mice attain first estrus at earlier ages than controls. Ratios of about 4 to 1 up to 7 to 1 result in mean ages for puberty that are not accelerated or delayed relative to controls. Over a modest range of actual dose amounts of urine, the ratio effects are the same regardless of the actual quantities of urine employed in treating test females.

Reproduction in Wild Canids, Canis-Familiaris, From the Eastern Highlands of Victoria

Reproduction was studied in a group of wild canids collected over four years from the eastern highlands of Victoria. While births were recorded from March to September inclusive, 78% of them took place in the winter months of June-August, with the peak occurring in July. A single breeding season each year was indicated for most, with a mean prenatal litter size of 5.5 (range 2-9). Sexually mature males were fertile throughout the year, although they exhibited a significant increase in testes weight, epididymides weight, and number of active seminiferous tubules for the months of April-June, which corresponded to the peak period of oestrus in females. The onset of first oestrus in females was variable, occurring when they were 1-4 years old, with only 36% of those less than 2 years old sexually mature. Sexual maturity in males was also variable. For animals of 10 kg (weight at initial onset of spermatogenesis) or heavier, spermatogenesis had commenced in only 63% of those less than two years old, but increased to 97% of those more than three years old. Overall this sample of canids displayed reproductive characteristics, such as a seasonal breeding season, considered typical of dingoes. However the possibility of slight changes to the original dingo breeding patterns through hybridization with domestic dogs is discussed.

Ano-genital distance as a factor in determining puberty acceleration in mice.

The daily exposure of newly born female mice to the urine of lactating mice with a small ano-genital distance accelerated the onset of first oestrus while the urine from donors with a large ano-genital distance was without effect in advancing puberty. The rate of growth of the mice exposed to the urine of lactating mothers was greater than that of a control sample but it was only those mice exposed to the urine of lactating females with a small ano-genital distance which continued to grow, after the cessation of treatment at 21 days of age, at a faster rate. There was no difference in the mass of the uterus when the mice were killed when adult but there were significant age-dependent differences in the mass of the ovaries and adrenal glands. The mice exposed to the urine from lactating mothers (with both large and small ano-genital indices) had smaller ovaries than the control mice while the adrenal glands of mice exposed to the urine of lactating mothers with a large ano-genital index were of greater mass than those of the control mice and mice exposed to mothers with a small ano-genital distance. Exposure to the urine of lactating mothers had no effect on the subsequent activity of the mice when tested in an automated activity recorder. The results confirm that urine from lactating mothers accelerates the onset of puberty and suggests that the effects are restricted to the urine from mothers with a small ano-genital index.

Plasma prolactin, LH, FSH and estrogen excretion patterns in gilts during sexual development.

Plasma prolactin (PRL), luteinizing hormone (LH) and follicle stimulating hormone (FSH) were measured by radioimmunoassay in groups of eight gilts sampled every 20 min for 6 h at about 2-wk intervals between 15 and 192 d of age. The PRL levels were high at 15 and 28 d, declined at 40 d just after weaning and then rose slowly until 192 d of age. The number of LH pulses during 6 h was higher between 83 and 125 d than at the other periods. Magnitude of LH pulses was highest at 15 d, constant from 54 to 125 d, fell at 137 d and remained low until 192 d. Plasma FSH was high from 15 to 125 d, with a maximum at 54 d. It declined slowly until 168 d and did not change thereafter. Estrogen excretion was estimated from urine excretion of estrone (E1; conjugated plus nonconjugated E1) per 24 h from 40 d until puberty in three gilts and at 156 and 174 d in two other animals. The E1 excretion increased with age and four levels were described before peak values with the onset of first estrus. The first increase in E1 excretion occurred between 68 and 110 d, when antral follicles appeared in the ovaries. It was subsequent to the highest levels of FSH and concomitant with the increased frequency of LH pulses. The drop in levels of both gonadotropins after 125 d probably corresponded to the development of the negative feedback as a result of greater ovarian activity in these gilts.

Role of the vomeronasal organ and prolactin in the acceleration of puberty in female mice.

Young female mice were grouped on Day 21 after birth and subjected to removal of the vomeronasal organ. Soiled bedding from intact adult males failed to advance the onset of first oestrus in these lesioned mice compared to the various control groups. Vomeronasal organ lesions of prepubertal females also prevented increases in uterine weight following exposure to soiled bedding for 48 h on Day 23 when compared to controls. Lowering prolactin by injections of bromocriptine for 48 h on Day 26, but not Day 23, advanced the onset of puberty in intact and vomeronasal organ-lesioned females. Elevating prolactin by injections of domperidone were without effect on the early onset of oestrus when compared to sham-injected controls. It is concluded that marked similarities exist in both the receptor system and neuroendocrine mechanism of male pheromone action observed in prepubertal females and that seen in the adult.

Attainment of puberty in female pigs: Clinical appearance and patterns of progesterone, oestradiol-17β and LH

The object of the study was to investigate the clinical and endocrine patterns of progesterone, oestradiol-17β and LH during the peripubertal period in female pigs. Crossbred gilts were penned in groups at an age of 10–12 weeks and boars were kept in adjacent pens during the entire experimental period. Daily oestrous checks started at 4.5 months of age and the gilts were slaughtered after their third heat. At the age of 4.5–5 months a permanent catheter was inserted in the cephalic vein and blood samples were collected from the gilts once daily until either the first or second oestrus. In three gilts hourly blood samples were taken during their first and second oestrus, beginning at early pro-oestrus. The gilts showed their first oestrus at the average age of 183 days. No corpora lutea from earlier ovulations were observed in gilts laparoscoped after their first detected oestrus. During the 30-day period before first oestrus the mean daily progesterone levels varied between 32 and 329 pmol/l. The average levels of oestradiol-17β varied between 15.6 and 30.8 pmol/l. There was no tendency for the oestradiol-17β level to rise before onset of first pro-oestrus. The average levels of LH varied between 0.15 and 0.94 μg/l. The statistical analyses revealed no significant relationship between the level of the hormones studied and onset of first oestrus. The mean progesterone levels during the first and second oestrous cycles were almost identical, however. Oestradiol-17β increased gradually during pro-oestrus, reaching maximum levels before onset of oestrus and thereafter decreasing sharply to values around 30 pmol/l. The oestradiol-17β levels were higher at the second than at the first pro-oestrous period. The concentrations of plasma LH rose sharply with declining plasma levels of oestradiol-17β. The duration of elevated plasma LH levels (> 1 μg/l) was, on average, 26 h and the LH levels were higher during the first oestrus than during the second oestrus. The first rise in progesterone was observed 11–29 h after the LH levels had decreased to concentrations below 1 μg/l.

Changes in Plasma Hormone Concentrations Associated with the Onset of Puberty in the Gilt2

Hormonal changes during the follicular phase of gilts exhibiting their first estrus were examined in response to either relocation and boar exposure or treatment with pregnant mare serum gonadotropin (PMSG). In the first experiment, blood was collected from nine gilts from 6 d before to 6 d after the onset of first estrus. Mean estradiol-17 beta (E2 beta) concentrations increased from d -6 to a peak on d -2 of 20 pg/ml (d 0 = of estrus) and then declined gradually over the next 6 d until basal levels (2.4 pg/ml) were reached. Mean concentrations of luteinizing hormone (LH) fluctuated between .5 to 1 ng/ml before d 1.5 and after d 1.5, with the ovulatory surge occurring on either d -1 or d 0 and averaging 6.2 ng/ml. Progesterone (P) concentrations were less than .3 ng/ml until formation of corpora lutea, while concentrations of glucocorticoids (CORT) ranged from 7.4 to 24.5 ng/ml. In Exp. 2, blood was collected every 6 h from d -2 to d 14 from eight gilts that were exposed to boars on d 0. Four of the gilts exhibited estrus and had a hormonal profile similar to that of gilts in Exp. 1. Concentrations of E2 beta were elevated in two gilts after exposure to a boar, but concentrations of LH were not altered. The remaining two gilts had basal concentrations of E2 beta and LH throughout the blood sampling period. In Exp. 3, blood was sampled from five gilts twice daily for 8 d following the administration of 1,000 IU PMSG. Estrus was exhibited by all gilts on the fifth day after PMSG. Circulating concentrations of total estrogens peaked on -1 while concentrations of LH peaked on d 0. Concentrations of P were low until after estrus and CORT levels displayed a diurnal pattern throughout. The results indicate that the hormonal profiles during the pubertal follicular phase of gilts induced by relocation and boar exposure or PMSG are similar. Furthermore, no changes were observed in P concentrations immediately before or during the pubertal follicular phase, suggesting that progesterone priming may not be prerequisite to puberty in gilts.

Regulatory effects of urinary pheromones on puberty in the mouse.

Application of 0.03 mI/day of adult male mouse urine to the oral-nasal grooves of postweanling female mice accelerated the onset of first estrus by 4-6 days relative to animals similarly exposed to tap water. Exposure to male urine for 3 successive days between the ages of 2 1-29 days was su cient to induce earlier puberty. The older the mouse at the time of first exposure to male mouse urine, the faster its subsequent sexual development. Exposure to male urine tended to shorten the interval between vaginal opening and first estrus indicating that the pheromone does not “trigger” puberty, but instead accelerates the process of sexual maturation. Puberty was hastened by exposure to urine from either preputialectomized male mice or adult male rats, indicating that the preputial gland does not contain the priming pheromone and that the pheromone is not unique to the male mouse. Urine from castrated male mice was ineffective. In contrast to the acceleratory effect of male urine, urine from grouped adult female mice retarded sexual maturation. The urine of both sexes of adult mice therefore contain pheromones that affect sexual development of the female, but the pheromones are opposite in their regulatory effects on puberty. Relationships between body weight and puberty were not consistent among the three experiments and the data do not support the concept of a causal relationship between puberty and body weight, although under some conditions they are indeed correlated.