Postpartum Estrus Research Articles

Consequence of Dam Genotypes on Productive and Reproductive Performance of Dairy Cows under the Rural Condition in Bangladesh

The main objective of the present study was to evaluate the consequence of dam genotypes on productive and reproductive performance of different cross-bred dairy cows under field condition. A total of 313 dairy cow's information were collected from 33 Artificial Insemination (AI) Sub-centers/Points from the District AI center of greater Rajshahi district for a period from 1993 to 2002. The information of the productive and reproductive parameters were analyzed from questionnaires answered by 33 field assistant (artificial inseminator) and owner's of cow in respective of AI Sub-Center/Points as well as from reading the AI and 100% progeny collection Registers. In general, the mean birth weight, age at puberty, age at first fertile service, age at first calving, gestation length, post-partum heat period, days open, wastage day, service per conception, milk production per day, peak milk production per day, lactation length, lactation yield, dry period, weaning period and calving intervals were 18.8 kg, 27.9 month, 29.2 month, 38.7 months, 278.7 days, 139 days, 160 days, 20.3 days, 1.62, 5.13 L, 10.45 L, 282 days, 1445 L, 146 days, 10.65 months and 438 days, respectively. Dam genotype of dairy cows were divided into 5 groups according to their genetic composition. LxF, SxSL, L, LxSLxF and LxSxSL of dam genotype had significant effect on all the productive and reproductive performances of the dairy cows except on age at first calving, gestation length and weaning period. The genotypes of dam's of cows like LxF and LxSL showed a better performance under field condition at greater Rajshahi district and poor performance were recorded in L and LxSxSL of dam genotype. The experiment reflects that the LxF and LxSL genotypes of dam showed the better productive and reproductive performances of dairy cows under rural condition in Bangladesh.

Meadow voles, Microtus pennsylvanicus, have the capacity to recall the “what”, “where”, and “when” of a single past event

Some non-human animals may possess the ability to recall the "what", "where", and "when" of a single past event. We tested the hypothesis that male meadow voles possess the capacity to recall the "what", "where", and "when" of a single past event associated with mate selection in two experiments. Briefly, male voles were allowed to explore an apparatus that contained two chambers. One chamber contained a day-20 pregnant female (24 h prepartum). The other chamber contained a sexually mature female that was neither pregnant nor lactating (REF female). Twenty-four hour after the exposure, the males were placed in the same apparatus, which was empty and clean. At this time, the pregnant female would have entered postpartum estrus (PPE), a period of heightened sexual receptivity. Males initially chose and spent significantly more time investigating the chamber that originally housed the pregnant female (now a PPE female) than the chamber that originally housed the REF female. Male voles also explored an apparatus containing a chamber with a PPE female and one chamber containing a REF female. Twenty-four hour later, males were placed into an empty and clean apparatus. The males did not display an initial choice and they spent similar amounts of time investigating the chamber that originally housed the PPE female (now a lactating female) and the chamber that originally housed the REF female. The results of these and additional experiments suggest that male voles may have the capacity to recall the "what", "where", and "when" of a single past event, which may allow males to remember the location of females who would currently be in heightened states of sexual receptivity.

Interaction of calf suckling, use of oxytocin and milk yield with reproductive performance of dairy buffaloes

Calf suckling and oxytocin injections are commonly used for pre-milking stimulus in dairy buffaloes under field conditions. A study was conducted to investigate effect of these treatments on reproductive performance. Fifty one Nili-Ravi buffaloes were monitored from parturition up to 150 days postpartum through rectal examination. Data on milk yield, body condition score (BCS) and reproductive parameters were recorded weekly. Postpartum ovulation interval (POI) was determined by presence of an ovulation depression or a very soft corpus luteum haemorrhagicum and was confirmed through milk progesterone levels (MPL). Suckling was used to stimulate milk let down, and where the calf had died, injection of oxytocin was resorted to. Milk samples were analyzed for MPL using radioimmunoassay (RIA) and fat; and milk yield was converted to 4% fat corrected milk (FCM). The mean postpartum uterine involution length (PUI) was 34.30 ± 1.33 days. Mean POI was 59.37 ± 4.76 days and mean postpartum estrus interval (PEI) was 69.03 ± 6.03 days. Suckling period averaged 26.40 ± 5.57 days and correlated with POI ( r = 0.19, P < 0.01) and PEI ( r = 0.23, P < 0.01). POI was shortest in buffaloes suckled for one month ( P < 0.05). Oxytocin was used with a mean dosage of 7.50 IU, delaying placental expulsion time (PET) and POI but shortening PEI. BCS shortened PET, POI and PEI ( P < 0.01). Mean FCM was 14.50 ± 0.20, ranging from 2 to 35 kg/d; and was higher in estrus group; correlating positively with POI ( r = 0.31, P < 0.01). MPL were 1.37 ± 0.17 ng/ml and increased after ovulation, remaining greater than 1.5 ng/ml from Day 4 to 14 of the estrus cycle, followed by a rapid decline up to next estrus. BCS in buffaloes resuming oestrus was constantly higher than those failing to resume ovarian cyclicity. Live weight, prepartum was 510.0 ± 5.9 kg with a loss of 3.7 ± 2.12 kg, 30 days postpartum. The present study suggests a lower reproductive efficiency of dairy buffaloes under the peri-urban farming system reflected by ovarian cyclicity in 68.63% buffaloes within 150 days postpartum and silent estrus in 51.5% of the cases. Increasing suckling duration and use of oxytocin delayed POI, however, POI was shortest in buffaloes suckled for one month. The high yielding buffaloes also manifested better reproductive cyclicity; while moderate yielder showed shorter ovulation intervals and higher conception rate.

Comparison of medial preoptic, amygdala, and nucleus accumbens lesions on parental behavior in California mice (Peromyscus californicus)

We have previously shown that medial preoptic area (MPOA) lesions disrupt parental behavior in both male and female California mice ( P. californicus). In the present study, we compare the effects of lesions in the MPOA, with those in the basolateral amygdala (BA) and nucleus accumbens (NA) on male and female parental behaviors in the biparental California mouse. A male or multiparous female from each male–female pair was given an electrolytic or sham lesion in the MPOA, BA, or NA and tested for parental responsiveness. Since female P. californicus show postpartum estrus, they were likely pregnant during parental testing. MPOA lesions produced deficits in both male and female parental behaviors, and BA lesions disrupted male, and to a lesser extent, female parental behavior. NA lesions produced mild effects on pup-retrieval in males and no effect on parental behavior in females. However, NA lesions incompletely destroyed the NA shell, the region most relevant for maternal behavior in rats, and should be investigated further. These results support a role for the MPOA and BA in both male and female parental behaviors.

Artificial insemination in the anoestrous and the postpartum white rhinoceros using GnRH analogue to induce ovulation

The objective of this study was to develop AI and to achieve first time pregnancy in a nulliparous rhinoceros. For this, one 24-year-old irregular cycling female white rhinoceros was selected, which had never been mated. The endocrine function was monitored by faecal and serum pregnane analysis. Ultrasound determined the optimal day for AI by measuring follicle sizes of 2.0, 2.6, 3.0, 3.2 cm on days −6, −4, −1, 0 of the induced oestrous cycle, respectively. AI was performed and ovulation induced when a pre-ovulatory-sized follicle was present using GnRH analogue, deslorelin. Fresh semen was deposited in the uterine horn using a patented AI catheter overcoming the hymeneal membrane and torturous cervical folds non-surgically. Moreover, ultrasound monitoring of the uterine involution and ovarian activity on days 16, 26, 30 postpartum facilitated the induction of and the AI on the first postpartum oestrous in a rhinoceros using GnRH analogue. Two consecutive pregnancies were achieved by AI for the first time in the rhinoceros. Pregnancies were diagnosed by elevated serum and faecal 20-oxo-pregnane concentrations. In addition ultrasound measured biometric parameters of the two foetuses on days 86 and 133 of gestation. Two female calves were born after 490 and 502 days of gestation, yet one calf was stillborn. AI in rhinoceros might now be used as assisted reproduction technology tool to boost critically small captive rhinoceros populations.

Female Meadow Voles, Microtus pennsylvanicus, Experience a Reduction in Copulatory Behavior During Postpartum Estrus

AbstractIn many small mammalian species, females undergo postpartum estrus (PPE), mate, and become pregnant soon after delivering a litter. Mating during PPE implies a trade‐off between attending to the new litter and leaving that litter to mate. We tested the hypothesis that copulatory behavior is faster when a female mates during PPE than when it mates outside of PPE, during male‐induced estrus (MIE), a time when it is not lactating. We compared several variables of copulatory behavior in female meadow vole mating during both PPE and MIE. Females in PPE received significantly fewer intromissions, with shorter intervals between intromissions. Each ejaculatory series was also shorter for females in PPE. As a consequence, the total amount of time devoted to copulation was much shorter for females in PPE than for those in MIE. These data support the hypothesis that female meadow voles are able to reduce their copulatory behavior during PPE.

Paternal care in rodents: Weakening support for hormonal regulation of the transition to behavioral fatherhood in rodent animal models of biparental care

Male rodents that are naturally paternal, like all females, must inhibit infanticide and activate direct parental behavior as they become parents. Males, however, alter their behavior in the absence of parturition, postpartum ovulation and lactation, and therefore do not experience the hormone dynamics associated with such conditions. Paternal males might nevertheless use the same hormones to activate pre-existing maternal behavior pathways in the brain. Positive and inverse associations between prolactin, sex steroids (estradiol, testosterone, progesterone), glucocorticoids, oxytocin and vasopressin and paternal behavior are reviewed. Across biparental rodents ( Phodopus campbelli, Peromyscus californicus, Microtus ochrogaster, and Meriones unguiculatus), as well as non-human primates and men, hormone–behavior associations are broadly supported. However, experimental manipulations (largely restricted to P. campbelli) suggest that the co-variation of hormones and paternal behavior is not causal in paternal behavior. Perhaps the hormone–behavior associations shared by P. campbelli and other paternal males are important for other challenges at the same time as fatherhood (e.g., mating during the postpartum estrus). On the other hand, each paternal species might, instead, have unique neuroendocrine pathways to parental behavior. In the latter case, future comparisons might reveal extraordinary plasticity in how the brain forms social bonds and alters behavior in family groups.

On-farm characterization and present status of North Bengal Grey (NBG) cattle in Bangladesh

SummaryNorth Bengal Grey (NBG) cattle are an important indigenous cattle genetic resource found mainly in the northern part of Bangladesh. The study was undertaken at Bogra Sadar, Shibgonj and Kahalu Upazila (sub-district) in the Bogra district. The physical and morphological characteristics, and the productive and reproductive performances of NBG cattle were studied. The coat colour of these animals is deep grey to white. The coat colour of the neck region in adult bulls was found to be generally ashy with a range of shades.The body is small, compact and less fleshy. Ear length and ear width were 18.0±0.17 and 11.0±0.21 cm, respectively. The head length average was 38.0±0.56 cm, the head width 16.0±0.17 cm, the foreleg length average 65.0±0.64 cm, the hind leg length 71.0±0.64 cm, the tail length average 71.0±0.67 cm, the horn length average 9.0±0.39 cm, the horn diameter 10.0±0.37 cm, the average teat length 5.0±0.18 cm, the teat diameter 6.0±0.22 cm, the distance betweenthe front teats 7.0±0.13 cm and the distance between the rear teats 7.0±0.13 cm. Body length, height at wither and heart girth in adult cows were 105.0il.20, 94.0+1.12 and 127.0±1.52 cm, respectively.The recorded highest peak milk production per day was 3.5±0.18 kg, lactation length was 219±6.1 days, and the dry period was 180±6.8 days. The average birth weight of calves was 18.4±0.52 kg and mature live weight of cows 241.0±4.0 kg. The age at first heat was 869±29.6 days, age at first calving 1191±19.7 days, gestation length 281±1.3 days, calving interval 442±7.4 days, postpartum heat period 110±4.2 days and the number of services per conception 1.4±0.6. About 54% of total cattle population was NBG cattle in the surveyed area of Bangladesh. The results indicated that the productive and reproductive performance of NBG cattle was better than other non-descript indigenous cattle of Bangladesh. The study further revealed an obvious need for more in-depth and objective information on wider samples of this type of indigenous cattle in order to assess the future need for conservation and improvement programs to be undertaken.

Seasonal changes in cortisol and progesterone secretion in Common hamsters

In this study, we investigated endocrine factors and behaviour in free-living Common hamsters ( Cricetus cricetus) during reproductive and non-reproductive periods of the annual cycle. We applied a non-invasive method to gain information on seasonal changes in adrenocortical activity in male and female hamsters by analysing faecal glucocorticoid metabolite concentrations (FCM). In addition, plasma progesterone concentrations were monitored in females throughout the non-hibernation season. The animals were live-trapped from spring emergence until the onset of hibernation in autumn. Reproductive status was determined at capture and blood and faecal samples were collected. During behavioural observations, agonistic and sexual interactions were recorded. FCM concentrations were significantly higher in males than in females during the reproductive period. In males, a pronounced increase in FCM during the reproductive period coincided with high frequencies of intrasexual aggression. In females, FCM levels remained relatively constant. Aggressive behaviour in females increased during the reproductive period, but was much less frequent than in males. Females, which successfully raised a second litter after a postpartum oestrus and concurrent lactation and gestation had lower FCM levels than individuals, which lost their second litter after parturition. As expected, plasma progesterone concentrations were low before and after the reproductive period. During gestation, levels peaked and remained elevated during lactation. The results of this field study provide insight in critical periods associated with reproduction in male and female Common hamsters.

Endocrine Profile Comparisons of Fat Versus Moderately Conditioned Mares Following Parturition

The influence of progesterone, luteinizing hormone (LH), and estrogen on the mare's estrous cycle has been well researched and documented, but other endocrine profiles have not received as much attention. To evaluate endocrine concentrations in fat-conditioned (body condition score [BCS] of 7–8) versus moderately conditioned mares (BCS of 5–6), 24 mares were allotted to and maintained in respective groups from late gestation until pregnancy was confirmed after breeding on the second postpartum estrus. Serum concentrations of thyroxine (T4), insulin-like growth factor-1 (IGF-1), and leptin were assayed to characterize circulating blood concentrations. Additionally, LH and progesterone serum concentrations were assayed to evaluate the estrous cycle status of the mares. Leptin and progesterone concentrations were not different (P > .05) between the groups. Nevertheless, serum concentrations of T4 were higher (P < .01) and IGF-1 concentrations lower (P < .01) in moderately conditioned as compared with fat-conditioned mares during times of ovulation and the interovulatory period. Furthermore, serum concentrations of LH were found to be different between the groups only when the estrous cycle approached the second ovulation (P < .0001). Results of this study suggest that mares maintained in a BCS of 5 or greater are similar in terms of reproductive efficiency. Although the circulating serum concentrations of T4 and IGF-1 are different after parturition, their influence does not affect reproductive capabilities of mares with a BCS of 5 or greater.

Postpartum Ovarian Activity and Serum Estradiol‐17beta Level in Thai Crossbred Native Mares

To study the postpartum ovarian activities for investigation of first postpartum oestrus, twenty-five Thai crossbred native mares were monitored after parturition by oestrous detection, transrectal palpation and reproductive ultrasonography. Blood samplings were also taken for estradiol-17beta (E2) analysis. The first ovulation occurred within 20 days postpartum in 92% (23/25) of the mares. The mean intervals of foaling to first oestrus and to first ovulation were 10.3 +/- 2.9 and 13.4 +/- 2.6 days (mean +/- SD) respectively. Serum E2 increased from 7.0 +/- 2.9 to a peak of 10.8 +/- 3.3 pg/ml (mean +/- SD) at 2 days before ovulation. In conclusion, from the study, it can be stated that the postpartum breeding management should be considered after day 10 postpartum by careful examination of ovarian activity with various methods. However, the uterine condition should be also estimated associated with the ovarian activity after parturition which may increase breeding performance and foal production.

Effects of levonorgestrel on ovulation and oestrous behaviour in the female tammar wallaby

Subcutaneous hormone implants are a useful method for managing overabundant marsupials in restricted enclosures in Australia. Levonorgestrel induces long-term infertility in the kangaroo, tammar wallaby and koala, although the contraceptive mechanism of levonorgestrel is unknown for any marsupial. In the present study, it was investigated if insertion of a single levonorgestrel or control implant at the time of reactivation of the diapausing blastocyst affected the subsequent post-partum oestrus or the preceding follicular development. Twenty levonorgestrel-treated and 16 control animals were autopsied the day before birth and the accompanying post-partum oestrus (Day 25), and 10 levonorgestrel-treated and five of the nine control animals were autopsied 3-4 days (Days 29-30) after the expected birth and oestrus. Peripartum behaviour was observed and birth and mating times were recorded. Levonorgestrel treatment did not prevent follicular growth because there was no significant difference between treatment and control animals in the size of the dominant follicle at Day 25. None of the levonorgestrel-treated females autopsied at Days 29-30 had ovulated (n = 10), in contrast to controls, where four of the five that were autopsied had ovulated. Mating occurred in eight of nine control animals but in only three of 10 levonorgestrel-treated females. Males showed a more sustained period of interest in the three that were mated than in the controls, and mating took place significantly later after birth (36 v. 10 h; P = 0.038). Follicular growth and development was not blocked in any female but only one-third of the animals mated and none ovulated after levonorgestrel treatment. These results suggest that levonorgestrel inhibits the preovulatory surge of luteinising hormone.

Factors Concerning Early Embryonic Death in Thoroughbred Mares in South Korea

A total of 384 Thoroughbred mares were investigated to determine and evaluate the features of early embryonic death at nine equine farms on Jeju Island, South Korea, from 2001 to 2003. Overall, 771 matings for 384 mares resulted in 376 pregnancies 15 days after ovulation. Subsequently, 12.2% (46/376) of these early conceptuses were lost within 45 days after ovulation. Furthermore, about three quarters of the 46 embryonic deaths occurred between 16 and 25 days after ovulation. The incidence of embryonic death was highest in the barren (17.2%), more than 15 years old (15.4%), and more than 10 parities (18.2%) groups compared with the other groups (9.1-16.9%). Mares mated in March, April, and during the first estrus postpartum had higher embryonic death rates, (19.6%, 17.2%, and 24.6%, respectively). Mares with abnormal fluid and cysts in the uterus (18.0%) or multiple embryonic vesicles (23.1%) had higher embryonic death rates than those with normal uterine conditions (9.8%) or single embryonic vesicles (10.5%). The condition of mares, such as breeding condition and the environment of the embryo or fetus, are the major factors in relation to occurrence of early embryonic death.

Reproduction in the short‐nosed fruit bat in relation to environmental factors

AbstractThe reproductive pattern of the short‐nosed fruit bat Cynopterus brachyotis in a tropical dry evergreen rainforest in Thailand (13°N) is characterized by seasonal bimodal polyoestry with postpartum oestrus. The first lactation period occurred in March–April, but the timing of the second varied between years: September–October in 1998 and July–August in 1999. Females may experience reproductive delays after the second parturition. Females attained sexual maturity at 6–7 months of age and gave birth for the first time at about 11–12 months, and are able to produce two young a year. Females born in April gave birth as early as March the following year. Those born in August–September first gave birth in July–August the following year. Males attained sexual maturity when they were a year old. Testis size was significantly positively correlated with photoperiod. The body weight of mature males varied cyclically, was higher during breeding periods and was significantly correlated with testis size. The first parturition coincided with the onset of the annual rains and the second occurred in the middle of the rainy season. Both lactation and weaning periods correspond with high food availability. A significantly higher percentage of reproductive females, earlier parturition, greater synchrony of lactation, higher body mass of lactating females, more abundant, larger and heavier juveniles, and heavier mature males were recorded in 1999 compared with 1998. The El Niño Southern Oscillation resulted in a prolonged and severe drought early in 1998, and induced mast fruiting in 1999 that led to higher reproductive success. Photoperiod may regulate the reproductive rhythm in male C. brachyotis, although experimental studies are required to verify this.

Reproductive biology and postnatal development in the tent‐making batArtibeus watsoni(Chiroptera: Phyllostomidae)

AbstractIn this study we investigated the reproductive patterns and postnatal development in the tent‐making batArtibeus watsoni. We sampled two populations in the Golfito Wildlife Refuge and Corcovado National Park, south‐western Costa Rica, from June 2003 to March 2005. Most females were pregnant during the months of January and June, and most were lactating in March and July, indicating that this species exhibits seasonal bimodal polyoestry, with the first parturition peak occurring in February–March and the second in June–July. Additionally, we observed a postpartum oestrus following the first parturition, but not after the second. Females entered oestrus again in November–December and had a gestation period ofc. 3 months. A female‐biased sex ratio of neonates was observed during the second parturition period, and young were born at 32 and 56% of their mothers' body mass and length of forearm, respectively. Adult proportions in length of forearm were attained faster than adult proportions in body mass, and sustained flight was only possible after 35 days of age, when pups had achieved 100 and 80% of adult length of forearm and body mass proportions, respectively. Weaning and roosting independence occurred when young werec. 30–40 days old, and young females appeared to remain close to their place of birth, at least for their first mating period, whereas adult males were never recaptured near their birth site. In addition, sexual maturity was reached in as little as 3 months in females born during the first parturition period, whereas females born during the second birth period in June–July seemed to reach maturity at 6 months of age. Our results show thatA. watsonibelongs to the faster lane of the slow–fast continuum of life‐history variation in bats, which may be attributed primarily to its roosting and feeding ecology.

First postpartum estrus and pregnancy in the female collared peccary ( Tayassu tajacu) from the amazon

The onset of sexual cycle postpartum was described in the collared peccary ( Tayassu tajacu). Serum progesterone and 17β-estradiol profiles, vaginal smears and external genitalia were analyzed in 20 animals housed with their piglets during the first postpartum month. The appearance of external genitalia showed no variation in any of the females: a shallow, reddish vulva, and vaginal mucus were constant features throughout the study. Based on hormonal profiles and vaginal smear cell patterns, 16 (80%) of the 20 peccaries showed signs of estrus and were considered cycling. The remaining four females (20%) did no show signs of estrus confirmed by low levels of progesterone (0.9 ± 0.4 ng/mL) during the first postpartum month. In the cycling peccaries, a serum 17β-estradiol peak (53.4 ± 8.1 pg/mL) was observed on Day 7 ± 1 postpartum, along with a linear increase in progesterone concentration from 3 (4.3 ± 2.6 ng/mL) to 11 (30.8 ± 4.9 ng/mL) days after this estradiol peak. Proportions of the different cells of the vaginal epithelium also changed in these females: superficial plus intermediate cells amounted to 76% of the cell total between Days 6 and 9 postpartum, corresponding to the estradiol peak. Nine (56%) of the 16 cycling females mated, indicated by the presence of sperm cells in their vaginal smears, and 6 (67%) became pregnant, reaching term. Non-pregnant cycling females ( n = 10) showed a steady decrease in serum progesterone concentration from 11 to 23 days after the estradiol peak, when basal levels were attained and a new estradiol peak registered, indicating the resumption of cyclicity in these females. The time interval between the two estradiol peaks was 23.5 ± 2.1 days in these females. In pregnant females, progesterone concentrations continued to rise to levels of 60 ng/mL ( n = 6) 23 days after mating. These findings indicate that the lactating collared peccary female can become cycling and fertile during the early postpartum period, and that a predominance of superficial plus intermediate vaginal cells can be taken as the first sign of estrus.

The amount of time that a meadow vole, Microtus pennsylvanicus, self-grooms is affected by its reproductive state and that of the odor donor

Many hypotheses have been put forth to account for differences in the amount of time that animals engage self-grooming when exposed to conspecifics or their odors, but most ignore the possibility that self-grooming may be associated with olfactory communication between groomers and conspecifics. As yet, we do not know the function of self-grooming and why animals do so when they encounter the odors of conspecifics. The present experiment tests the hypothesis that the amount of time that a meadow vole, Microtus pennsylvanicus, self-grooms is affected by the reproductive state of the odor donor and its own reproductive state. The findings support the hypothesis. Male voles spent more time self-grooming when they were exposed to bedding scented by female voles in postpartum estrus (PPE) compared to that of female voles in other reproductive states and female mice. PPE female voles spent more time self-grooming when they were exposed to bedding scented by testosterone-treated male voles than either to that of gonadectomized male voles and male mice. PPE female voles spent more time than OVX+E and more time than OVX females self-grooming when they were exposed to bedding scented by testosterone-treated male voles. GX+T male voles spent more time than GX male voles self-grooming when they were exposed to bedding scented by PPE female voles. The results suggest that individuals self-groom more in the presence of an odor of a highly receptive potential mate than that of a less receptive mate.

Similarities between female meadow voles mating during post-partum oestrus and raising two concurrent litters and females raising only one litter

In many species of small mammals, females undergo post-partum oestrus soon after delivering a litter, becoming pregnant while suckling the previous litter. Females raising two concurrent litters need to allocate many more resources to reproduction than females raising only one litter. Consequently, there may be differences between litters raised concurrently or singly. We investigated this issue in the meadow vole, Microtus pennsylvanicus, a species in which most females in the wild reproduce during post-partum oestrus. Specifically, we tested the hypothesis that the development of pups in two concurrent litters differs from that of pups in a single litter. To test this hypothesis, we measured the following variables for concurrent and singly reared litters: gestation length; litter size; sex ratio; bodyweight of males and females at different ages; total litter weight at weaning; growth rates; and intra-litter variation in body mass. Except for bodyweight of males at 60 days of age, which was higher in the first of the concurrent litters, none of the variables differed among the litters. These results indicate that females are able to adjust to differing loads of maternal care to provide equivalent resources to concurrent litters and singly reared litters.

Non-invasive Monitoring of Estrous Cycle, Pregnancy and Postpartum Estrus by Enzyme Immunoassay for Fecal Progesterone in Addax (&lt;i&gt;Addax nasomaculatus&lt;/i&gt;)

Non-invasive Monitoring of Estrous Cycle, Pregnancy and Postpartum Estrus by Enzyme Immunoassay for Fecal Progesterone in Addax (&lt;i&gt;Addax nasomaculatus&lt;/i&gt;)

Immunoreactive Insulin-Like Growth Factor in Plasma during Pre- and Post-Partum Periods of Thoroughbred Mares from which the Newborn were Removed: its Pattern, Physiological Function and Relation to Other Hormones

Plasma concentrations of immunoreactive (ir-) insulin-like growth factor I (IGF-I) were measured in 9 pregnant mares from 30 days before foaling to Day 7 after ovulation of the first post-partum estrus (foal heat) in order to characterize its pattern and investigate its possible role in mares during that time. A marked increase in plasma concentrations of ir-IGF-I was observed during the last month of pregnancy. After foaling, ir-IGF-I sustained its high concentration for the first week after parturition and it gradually decreased thereafter. Throughout the observation period of the current study, a significant positive correlation between ir-IGF-I and FSH (r=0.58, p<0.05) was found. The significant increase in ir-IGF-I and FSH shortly prior to parturition may be responsible for the rapid resumption of ovarian activity in mares and the initiation of foal heat in thoroughbred mares. Statistically significant positive correlation between ir-IGF-I, FSH and ir-inhibin levels observed in the current study confirm the previous suggestion that ir-inhibin secreted during late pregnancy in mares may be biologically inactive.