Variation In Gestation Length Research Articles

Microsatellite Analysis Revealed Potential DNA Markers for Gestation Length and Sub-Population Diversity in Kari Sheep

Kari sheep inhabiting the Chitral district of Pakistan show variation in gestation length. In this study, we have analyzed the genetic differences between the three subtypes of Kari sheep (based on variation in gestation length) using microsatellite markers. Kari sheep samples were collected from their breeding tract and were characterized for gestation length and genetic diversity using microsatellite markers. A total of 78 Kari ewes were grouped into three categories based on gestation length (GL), i.e., Kari-S (with a shorter GL), Kari-M (with a medium GL), and Kari-L (with a longer GL). DNA from these samples was used to amplify 31 ovine-specific microsatellite loci through PCR. Of the total 78 Kari specimens, 24 were grouped in Kari-S (GL = 100.7 ± 1.8), 26 were from the Kari-M subtype (GL = 123.1 ± 1.0), and 28 were Kari-L (GL = 143.8 ± 1.5). Microsatellite analysis revealed an association of genotypes at two marker sites (MAF214 and ILSTS5) with variation in GL. A total of 158 alleles were detected across the 22 polymorphic loci with an average of 7.18 alleles per locus. Unique alleles were found in all three subtypes. The highest number of unique alleles was observed in Kari-L (15), followed by Kari-S (10) and Kari-M (8). The results indicated that Kari-S is a genetically distinct subtype (with higher genetic differentiation and distance) from Kari-M and Kari-L. The genetic uniqueness of Kari-S is important for further exploration of the genetic basis for shorter gestation length, and exploitation of their unique values.

Control of parturition in hyperprolific sows by using altrenogest and double administrations of PGF2α

The aim of the present study was to develop a protocol to reduce the variation in gestation length and synchronise the onset of parturition in sows by using altrenogest in combination with double administrations of prostaglandin F2alpha (PGF2α). In total, 188 Landrace x Yorkshire crossbred sows with parity numbers 3.1 ± 1.6 were included in the experiment. The sows were classified into two groups: CONTROL (n = 94) and TREATMENT (n = 94). CONTROL sows were allowed to farrow naturally, and TREATMENT sows were orally administered 20 mg/day of altrenogest starting when they entered the farrowing house (107.0 ± 2.0 days) until 113 (TREAT–113, n = 18), 114 (TREAT–114, n = 29) and 115 (TREAT–115, n = 47) days of gestation. The altrenogest-treated sows were administered PGF2α twice 6 h apart at 24 h after the withdrawal of altrenogest. The litters were randomly selected (25 and 26 litters from CONTROL and TREATMENT groups, respectively) to determine individual body weight at birth and at 24 h after birth. Gestation length of sows that farrowed naturally averaged 115.1 days (range 111–118), whereas gestation length of altrenogest-treated sows averaged 115.1–116.3 days (range 114–118). The colostrum yield of sows averaged 4.25 ± 1.19 kg and was not affected by the treatment (P > 0.05). Colostrum IgG in the CONTROL group was higher than in the TREAT–114 and TREAT–115 groups (P < 0.05) but did not differ significantly compared to the TREAT–113 group. The proportion of sows that farrowed during working hours (0700–1700 h) in the TREAT–113 group (72.3%) tended to be higher than in the CONTROL (46.4%, P = 0.053). The interval from the last altrenogest treatment until farrowing in the TREAT–113 group was longer than in the TREAT–114 and TREAT–115 groups (62.8, 40.7 and 34.6 h, respectively, P < 0.05). Similarly, the intervals from the first PGF2α administration to the onset of parturition in the TREAT–113 group (38.8 ± 3.8 h) was longer than TREAT–114 (21.9 ± 3.5 h, P = 0.002) and TREAT–115 (25.5 ± 3.7 h, P = 0.016) groups. However, the incidence of stillbirths in the TREAT–113, TREAT–114 and TREAT–115 groups was higher than in the CONTROL (16.4, 17.2, 11.8 and 5.8%, respectively, P < 0.05). In conclusion, altrenogest supplementation in combination with double administrations of PGF2α can reduce the variation in gestation length and synchronise the onset of parturition in sows. However, its side effects on the incidence of stillbirths should be considered.

Growth and reproductive performance of Rani breed of pig in various agro-climatic condition of Nagaland

The objective of the present study was to compare the growth and reproductive performance of Rani breed of pig in various agro-climatic condition of Nagaland. The present investigation was conducted at six locations, i.e. Dimapur, ICAR farm and Peren are low hill (300 m) area; Kohima and Wokha are mid hill (1000-1500 m) area and Kiphire district is high hill (2500 m) area. Body weight of male and female pig varied from 67 to 85 kg and 58 to 77 kg at 10 months of age. Body weight at 10 months of age was significantly higher in low hill (Dimapur, Peren and ICAR farm) area compared to high hill area (Kiphire) at all stages in male as well as female pig. Average daily weight gain was significantly higher at ICAR farm compared to other five locations in male and female pig. Age at first estrus and age at first mating was significantly higher at Kiphire. Estrus and mating occurred at significantly shorter age in pig at ICAR farm. There was no variation in gestation length across the different locations. Litter size at birth and litter weight at birth varied from 8 to 9 numbers and 9 to 10 kg. Litter size at weaning was significantly lower at Kiphire. Litter weight at weaning was significantly higher at ICAR farm. Significantly higher weaning to estrus interval was recorded at Kiphire. Pre-weaning mortality was recorded from 7 to 18% and it was highest at Kiphire district followed by Kohima and Peren. There was variation recorded in growth and reproductive performance of Rani breed at different location in Nagaland, however, the performance was better than pure exotic and indigenous breed.

Phenotypic relationships between gestation length and preweaning litter traits in rabbits.

A total of 135 kittens from 22 kindlings were used to determine the relationship between gestation length (GL) and some preweaning litter traits alongside the weight of their 12 dams. Average daily gain at 21 days (ADG21), average litter weight at birth (ALWB), kindling to weaning viability (KWV), litter size at birth{L.SB), litter size at 21 days (LS21), litter weight at 21 days(LW21), litter weight at birth (LWAB), and still birth number (SBN) when subjected to multiple regression analysis revealed non-significant t-test value with GL. However, Average litter weight at 21 days (ALW21) was highly significant (P&lt;0.01) suggesting that such can be used to predict GL. Weight of doe (WOD) was highly significant (P&lt;0.01) showing that such parameter is important for predicting GL. A high R2 value was obtained indicating that the variability in GL is explained by the linearity of the preweaning litter traits and WOD. However the correlation coefficient R, (0.89) revealed a high degree of association between the preweaning litter traits in the rabbits and the weight of doe in a linear form. The F-value was significant at P&lt;0.05 indicating that WOD and the preweaning litter traits in rabbits have significant contribution to the variation in GL. The correlations among traits were positive and significant for majority of the traits, which include live birth number (LBN), ADG21, ALW21, KWV, LS21, and LW21. However SBN had negative correlation with other traits.

Another look at returns to birthweight

We revisit the causal effect of birthweight. Because variation in birthweight in developed countries primarily stems from variation in gestational age rather than intrauterine growth restriction, we depart from the widely-used twin fixed-effects estimator and employ an instrumental variable – the diagnosis of placenta previa, which provides exogenous variation in gestation length. We find protective effects of additional birthweight against infant mortality and health capital loss, such as cerebral palsy, but in contrast to sibling and twin studies, no strong evidence for non-health long-run outcomes, such as test scores. We also find that short-run birthweight effects have diminished significantly over the decades.

Pregnancy and parturition in dromedary camels I. Factors affecting gestation length, calf birth weight and timing of delivery

In the present study, we evaluated the role of genetic, physiologic and environmental factors in affecting gestation length, calf birth weight and time of parturition in dromedary camels. Reproductive data were collected over a 10-year period at the world's first intensively managed, large-scale camel dairy farm. We hypothesized that environmental conditions (i.e. photoperiod) have a decisive effect on these reproductive parameters. The effect of various factors was tested with linear mixed models and variance component analysis. A total of 557 (13.1%) primiparous and 3691 (86.9%) multiparous parturitions were observed in 2,123 dromedaries. Parturitions had a pronounced seasonal distribution. The mean (±SE) length of gestation and mean (±SE) birth weight were 384.5 ± 0.17 days (n = 4,093, CV = 2.88%) and 34.5 ± 0.09 kg (n = 3,909, CV = 16.8%), respectively. All but one fixed factors (type of breeding) affected length of gestation and calf birth weight. Month of conception (27.1%), female camel (11.2%) and live-dead status of the calf (10.6%) were responsible for close to 50% of the variation in gestation length. At the same time, female camel (30.3%), parity (11.3%), year (6.9%) and month of parturition (6.2%) had the strongest relative influence on the variation in calf birth weight. Both reproductive traits showed a pronounced circannual variation. Mean length of gestation was longer by app. 18 days in dromedaries conceiving in November compared to those becoming pregnant in May. Average new-born weight was 4.4–4.9 kg higher in December compared to that in September and April. Dromedaries gave birth throughout the 24 h period, but most of the deliveries (n = 3,117, 74.1%) occurred from sunrise to sunset. The peak of deliveries was between 2 and 3 pm. Month of the year has a strong effect on the timing of deliveries. In contrast, the time from sunrise to parturition did not differ among the months. Peak of deliveries occurred 7–9 h after sunrise and the median of time from sunrise to parturition was 8 h and 24 min. These results give strong support to the original hypothesis. Seasonal changes were independent of nutritional factors, were associated with climatic conditions (i.e. photoperiod) and may reflect an endogenous circannual rhythm in foetal development. The dromedary camel could be a useful in vivo model to study the effect of the environment on feto-maternal communication, fetal development and timing of parturition.

Gestation length in red deer: genetically determined or environmentally controlled?

The red deer (Cervus elaphus) of European origin (e.g. subspecies scoticus, hispanicus, hippelaphus) is a medium sized (100-150kg mature hind weight) ruminant that exhibits highly seasonally patterns of autumn conceptions and summer births. Historic data indicate average (+/- s.d.) gestation length of 233-234 (+/- 2-4) days. Recently, however, there has been growing awareness that there is considerably greater variation in gestation length than earlier indicated and that there is a significant element of environmental, and possibly even social, control over the duration of pregnancy in this species. Imposition of variable levels of nutrition over late pregnancy of red deer hinds has been observed to influence fetal growth trajectory and gestation length, with no apparent effect on birth weight. This supports a hypothesis that under conditions of modest feed imbalance, variation in gestation length compensates for variation in fetal growth trajectory to ensure optimisation of birth weight. More recent studies on primiparous (24 month old) red deer hinds have identified surprisingly large variation in gestation length (193-263 days) compared with adult hinds (228-243 days), with earlier conceiving individuals within the primiparous cohort expressing significantly longer gestation than the later conceiving hinds, resulting in a higher level of calving synchrony than expected from known conception dates. This introduces an intriguing hypothesis of social indicative effects on parturition timing to promote within-cohort birth synchrony. Collectively, these data debunk the commonly held notion that gestation length of red deer is genetically fixed within strict limits. A review of the literature points to this as possibly a common phenomenon across a range of non-domesticated ruminant species but this conclusion is not supported by numerous conflicting studies on domestic sheep and cattle.

Induction of parturition by double administration of prostaglandin F2α in sows reduces the variation of gestation length without affecting the colostrum yield and piglet performance.

The objective of the present study was to investigate whether double intra-vulvo submucosal administration of prostaglandin F2α (PGF2α) could improve farrowing synchronization compared to single administration, and the effects of the induction of farrowing on colostrum yield and piglet performances. In total, 91 sows were randomly assigned to one of three groups: i) treatment with a single or ii) double administration of PGF2α or iii) control group without any treatment. A synthetic analogue of PGF2α was administrated via the intra-vulvo submucosal route on day 114 of gestation, at 0800 hr (single administration) or at 0800 and 1400 hr (double administration). The animals were monitored during the farrowing process. The time interval from the first administration of PGF2α to the onset of parturition was compared between groups. The proportion of sows that farrowed within 32 hr of induced parturition was higher in the double administration group than in the single administration group (100 vs. 84.4%, P=0.046). The duration of farrowing was higher in single administration sows than in control (241.1 vs. 169.5 min, P=0.004) and tended to be higher than in double administration sows (241.1 vs. 190.3 min, P=0.088). Birth interval of piglets born after double administration of PGF2α was shorter than those born after a single administration (14.6 and 20.1 min, P=0.024). In sows, the induction of parturition using a double administration of PGF2α reduces variation in gestation length and significantly increases the proportion of sows with an early response to PGF2α.

Genetic and environmental causes of variation in gestation length of Jersey crossbred cattle

Aim:The objective of this study was to investigate the effect of genetic and non-genetic factors and estimate the genetic parameter for gestation length (GL) of Jersey crossbred cattle.Materials and Methods:The data included the 986 parturition records on Jersey crossbred cattle maintained at the Eastern Regional Station of ICAR-National Dairy Research Institute, Kalyani, West Bengal, India during 36 years (1978-2013). The data were analyzed applying mixed model least square technique considering the fixed effects of genetic group, season of calving, period of calving, parity of animal, birth weight, and sex of calf born from animal. The effect of sire was included as a random effect in the model.Results:The genetic group of animal, season of calving, parity of animal, and birth weight of calf born were found to be a significant source of variation in the GL, whereas the period of calving and sex of calf did not affect this trait. Cows with <50% and >62.5% Jersey inheritance had the shortest and longest GLs, respectively. Cows calved in summer and rainy season had shorter GL than those calved in the winter season. Older cows in 4th parity carried calves for longer days than the cows in 1st parity. The increase in calf birth weight significantly (p<0.01) contributed to a linear increase in GL value in this study. The heritability estimate of GL was 0.24±0.08.Conclusion:It can be concluded that selection for lower GL without distressing future growth of calf can be used to reduce calving difficulty, but a very small standard deviation of GL limits the benefit. Moreover, more accurate prediction of calving date will help in better management and health care of pregnant animals.

Factors affecting gestational length in the Mangalarga Paulista breed

The Mangalarga Paulista is a Brazilian horse breed that originated from a cross between Andalusian and Alter Real horses, and despite its national importance, no data exist regarding their gestational length. This study was conducted to determine the variation in gestation length and the influence of factors such as the sex of the foal, maternal age and parity, stallion and mating period. Retrospectively, data from 208 gestations of Mangalarga Paulista foals located in Piracaia, SP, Brazil, during the period from 1991 to 2012 were analyzed. The mean gestational length was 343.08 ± 0.66 days, with a range between 317 and 404 days. Gestation of mares carrying colts had a tendency to be longer than mares carrying fillies. Maternal parity significantly affected gestational length, with longer gestation for primiparous mares until the third gestation, shorter pregnancies between 4th and 8th gestation, and longer thereafter. Regarding mating period, mares that were mated at the end of the breeding season (January and February) had shorter pregnancies (P < 0.05). These results are of significant clinical and economic relevance for the equine industry, so that the monitoring of gestation and parturition can be performed effectively.

Is preterm birth a human-specific syndrome?

Human preterm birth (PTB), a multifactorial syndrome affecting offspring born before 37 completed weeks of gestation, is the leading cause of newborn death worldwide. Remarkably, the degree to which early parturition contributes to mortality in other placental mammals remains unclear. To gain insights on whether PTB is a human-specific syndrome, we examined within- and between-species variation in gestation length across placental mammals and the impact of early parturition on offspring fitness. Within species, gestation length is normally distributed, and all species appear to occasionally give birth before the ‘optimal’ time. Furthermore, human gestation length, like that of many mammalian species, scales proportionally to body mass, suggesting that this trait, like many others, is constrained by body size. Premature humans suffer from numerous cognitive impairments, but little is known of cognitive impairments in other placental mammals. Human gestation differs in the timing of the ‘brain growth spurt’, where unlike many mammals, including closely related primates, the trajectory of human brain growth directly overlaps with the parturition time window. Thus, although all mammals experience early parturition, the fitness costs imposed by the cognitive impairments may be unique to our species. Describing PTB broadly in mammals opens avenues for comparative studies on the physiological and genetic regulators of birth timing as well as the development of new mammalian models of the disease.

Voluntary food intake of pregnant and non-pregnant red deer hinds

Efficient farmed venison production under New Zealand lowland conditions requires early calving to better align lactation with pasture availability. However, hinds that conceive early in the breeding season have a longer gestation length than those conceiving later, negating some of the gains achieved by early conception. This variation in gestation length may relate to seasonal imbalances in hind nutrient uptake influencing foetal growth. However, little is known about food intake cycles of pregnant hinds and whether they exhibit the photoperiod-induced voluntary food intake (VFI) reduction over winter seen in younger age classes and adult stags. This study investigated the effect of pregnancy status on VFI of red deer hinds. In addition, concentration of leptin and ghrelin circulating in the body was measured throughout the study to ascertain if these hormones are indicative of hind energy status. Seven pregnant (P) and seven non-pregnant (NP) hinds were housed indoors in individual pens from April to November where they were offered daily an ad libitum pelleted ration. On average, P hinds gained 75g/day and NP hinds lost 27g/day (P=0.02) in autumn. Mean live weight (LW) of both groups then steadily increased for the remainder of the study with no significant difference between groups. Mean body condition score (BCS) change of P and NP hinds was similar in autumn and winter, but whereas that of P hinds decreased in spring, that of NP hinds increased (P=0.02). Pregnancy status of the hinds had no significant effect on mean VFI throughout the trial except for the last 5 days before parturition when VFI of P hinds decreased dramatically (P=0.001). VFI of both groups of hinds was significantly higher in autumn (P=0.03) and spring (P=0.01) than in winter and for every 0.1MJME/kgLW0.75/day increase in mean VFI during the study period, gestation length decreased by 6.4 days (r2=0.51; P=0.04). Pregnancy status had no significant effect on plasma concentration of either leptin or ghrelin at any of the sampling times and there was no significant association of either leptin or ghrelin with VFI. However, leptin plasma concentration was positively associated with BCS (r2=0.41; P=0.008). This study showed that VFI of pregnant hinds was depressed during winter and early spring, and was negatively associated with gestation length. A reduction in BCS of pregnant hinds indicated that they were in a moderate energy deficit during the final third of gestation.

Short communication: Prepartum plasma insulin-like growth factor-I concentrations based on day of insemination are lower in cows developing postpartum diseases

Because peripartal production diseases are prevalent in dairy cows, early recognition is crucial. Several studies reported metabolic variables as risk predictors for subsequent diseases. To improve on-farm testing and application of those methods, the sampling procedure should take into account variation in gestation length. Furthermore, additional variables indicating cows at risk of any production disease should be sought. Therefore, the objective was to characterize differences between cows with and without postpartum production disease (retained fetal membranes, ketosis, hypocalcemia, abomasal displacement, metritis, mastitis) by prepartum measurement of serum nonesterified fatty acid (NEFA) and plasma insulin-like growth factor (IGF)-I concentrations relative to the artificial insemination (AI) that established pregnancy. Blood was collected from 41 Holstein Friesian cows on 235 to 241, 242 to 248, 249 to 255, 256 to 262, 263 to 269, 270 to 276, 277 to 283, and 284 to 290 d after AI. Health status was assessed daily for 3 wk after calving; 25 cows (66%) had at least one production disease. Cows developing postpartum diseases had higher mean serum NEFA concentrations (450±26μmol/L; mean ± SE) and lower plasma IGF-I concentrations (78±6 ng/mL) prepartum compared with healthy cows (259±19μmol/L and 117±8 ng/mL, respectively). In conclusion, because of substantial variation among cows in gestation length, blood samples should be collected and studies performed on risk prediction relative to AI rather than expected date of calving. As the somatotropic axis is one of the key regulators of metabolic adaption for onset of lactation, IGF-I might be a useful variable to differentiate between cows susceptible to production diseases and cows that are able to adapt adequately within the transition period and remain healthy.

Spontaneous abortion and preterm labor and delivery in nonhuman primates: evidence from a captive colony of chimpanzees (Pan troglodytes).

BackgroundPreterm birth is a leading cause of perinatal mortality, yet the evolutionary history of this obstetrical syndrome is largely unknown in nonhuman primate species.Methodology/Principal FindingsWe examined the length of gestation during pregnancies that occurred in a captive chimpanzee colony by inspecting veterinary and behavioral records spanning a total of thirty years. Upon examination of these records we were able to confidently estimate gestation length for 93 of the 97 (96%) pregnancies recorded at the colony. In total, 78 singleton gestations resulted in live birth, and from these pregnancies we estimated the mean gestation length of normal chimpanzee pregnancies to be 228 days, a finding consistent with other published reports. We also calculated that the range of gestation in normal chimpanzee pregnancies is approximately forty days. Of the remaining fifteen pregnancies, only one of the offspring survived, suggesting viability for chimpanzees requires a gestation of approximately 200 days. These fifteen pregnancies constitute spontaneous abortions and preterm deliveries, for which the upper gestational age limit was defined as 2 SD from the mean length of gestation (208 days).Conclusions/SignificanceThe present study documents that preterm birth occurred within our study population of captive chimpanzees. As in humans, pregnancy loss is not uncommon in chimpanzees, In addition, our findings indicate that both humans and chimpanzees show a similar range of normal variation in gestation length, suggesting this was the case at the time of their last common ancestor (LCA). Nevertheless, our data suggest that whereas chimpanzees' normal gestation length is ∼20–30 days after reaching viability, humans' normal gestation length is approximately 50 days beyond the estimated date of viability without medical intervention. Future research using a comparative evolutionary framework should help to clarify the extent to which mechanisms at work in normal and preterm parturition are shared in these species.

Gestation length variation in a wild ungulate

Summary 1. In species inhabiting a seasonal environment, timing of birth may be highly correlated with fitness. However, we know little about the relative effects of conception date and gestation length in determining birth date in wild mammalian populations. 2. Here, we tested for variation in gestation length using long-term data from a wild ungulate population (red deer, with observations running from 1971 to 2007). High March temperatures during gestation were associated with shorter average gestation length (a decrease of 0·77 days for every degree warmer), but we found no significant correlations with female age, recent reproductive history or offspring sex. 3. We also tested whether early or late conceiving females adjusted gestation length to give birth closer to an optimum time. Simply fitting conception date as a fixed effect in a model of gestation length is not statistically sound as errors in determining conception date could drive an observed negative covariance; consequently we also approached this problem using a novel technique of bivariate models. We found that late conception was indeed correlated with shorter gestation length, but this was not repeatable within females, suggesting either that the observed association may have been a statistical artefact or that gestation length adjustment may only be apparent on the rare occasions that females conceive outside an optimum time window. 4. Although there were no consistent differences between females in gestation length, there were differences between males in the gestation lengths of females with whom they mated. This possibly reflects a local environment effect, grouping females who were primarily in the same area during conception and gestation. 5. We conclude that observed variation in birth date is predominantly due to systematic variation in conception date as opposed to gestation length. Additionally, we highlight the broad range of reproductive tactics utilized by a number of closely related species, and consequently the difficulties inherent in cross-species comparisons of gestation length.

Age‐related gestation length adjustment in a large iteroparous mammal at northern latitude

1. There is considerable interest in patterns of age-dependent reproductive effort and reproductive timing of large iteroparous mammals living in strongly seasonal environments. Due to lack of data on both timing of mating and birth, there is generally little insight into whether variation in gestation length play a role for life-history patterns observed for large mammals at northern latitudes. 2. Based on data on both timing of mating and birth of 88 female reindeer (and paternity confirmed with DNA fingerprinting), we explore the view that adjustment of gestation length plays a role in the reproductive tactic. 3. Observed gestation lengths of reindeer varied between 211 and 229 days (mean of 221 days). Consistent with a dynamic view of gestation length, variation could be predicted from life-history traits. Gestation length was longer for male than female offspring, which is expected in polygynous species where males benefit more from extra allocation of maternal resources. Gestation length increased with maternal age both due to direct effects and indirect effects linked to earlier mating of older, heavier females. Early mating females increased gestation length. A relatively small effect of female age on birth mass operated through variation in gestation length. 4. Our analysis supports the view that adjustment of gestation length is a part of the reproductive tactic of large mammals in northern environments.

Effect of weaning regimen on energy profiles and reproductive performance of beef cows1

The effect of shifting calf-weaning age on profiles of energy status (BW, BCS, and rib and rump fat) and reproductive performance of beef cows was evaluated in a 3-yr study. Pregnant and lactating crossbred beef cows (n = 408), mainly of Angus and Hereford breeding, were stratified by age and by sex and BW of their calves and assigned randomly into 2 treatments: weaning at approximately 180 d (early weaning) and normal weaning 45 d later (control). Cows were managed together on native range pastures and supplemented with harvested forage during the winter months. Cow BW, BCS, rib fat, and rump fat were measured periodically from early weaning through the next breeding. Reproductive performance was evaluated by calving intervals (CI), days from initiation of breeding to calving (BCI), retention in the herd, and adjusted 205-d weaning BW of the subsequent calf. Early weaned cows had greater (P < 0.001) BW at normal weaning than control cows, but the overall pattern of cow BW did not differ (P > 0.05) among treatments. Peak and nadir BCS occurred at precalving and postcalving periods, respectively and were greater (P < 0.001) at each period in early weaned than in control cows and in cows > or =5-yr-old than in younger cows. Patterns for rib fat and rump fat were nearly identical to those of BCS except for the 3-way interaction (P < 0.001) of treatment, age, and period on rump fat. Mean CI (372.4 +/- 2.1 d) and BCI (299.7 +/- 1.9 d) were not affected (P = 0.42) by treatment but varied (P < 0.001) with age of the cow. Age of cow accounted for 16% of total variation in CI and 12% of total variation in gestation length (P < 0.001). The intervals were longer (P < 0.001) in primiparous cows than in older cows. Early weaning decreased risk of culling in cows and thereby increased (P < 0.05) overall persistence by 11% over control cows. Earlier weaning of cows in the previous year increased (P < 0.001) weaning weight of the subsequent calf by 8.6 kg per cow per yr. Shifting weaning time increased storage of consumed energy as evidenced by increased rump fat, for use later during high-energy demand, ultimately improving overall productivity of the cow-calf system.

Gestation length in red deer: genetically determined or environmentally controlled?

The red deer (Cervus elaphus) of European origin (e.g. subspecies scoticus, hispanicus, hippelaphus) is a medium sized (100-150kg mature hind weight) ruminant that exhibits highly seasonally patterns of autumn conceptions and summer births. Historic data indicate average (+/- s.d.) gestation length of 233-234 (+/- 2-4) days. Recently, however, there has been growing awareness that there is considerably greater variation in gestation length than earlier indicated and that there is a significant element of environmental, and possibly even social, control over the duration of pregnancy in this species. Imposition of variable levels of nutrition over late pregnancy of red deer hinds has been observed to influence fetal growth trajectory and gestation length, with no apparent effect on birth weight. This supports a hypothesis that under conditions of modest feed imbalance, variation in gestation length compensates for variation in fetal growth trajectory to ensure optimisation of birth weight. More recent studies on primiparous (24 month old) red deer hinds have identified surprisingly large variation in gestation length (193-263 days) compared with adult hinds (228-243 days), with earlier conceiving individuals within the primiparous cohort expressing significantly longer gestation than the later conceiving hinds, resulting in a higher level of calving synchrony than expected from known conception dates. This introduces an intriguing hypothesis of social indicative effects on parturition timing to promote within-cohort birth synchrony. Collectively, these data debunk the commonly held notion that gestation length of red deer is genetically fixed within strict limits. A review of the literature points to this as possibly a common phenomenon across a range of non-domesticated ruminant species but this conclusion is not supported by numerous conflicting studies on domestic sheep and cattle.

Genetic study of gestation length in andalusian and arabian mares

The length of gestation in Andalusian, or Spanish Purebred (SPB) and Arabian (AB) mares reared in Spain was analysed, based on 766 spontaneous full-term deliveries appertaining to 141 mares of SPB breed and 72 mares of AB breed in 31 breeding seasons. The data were obtained from the Yeguada Militar de Jerez de la Frontera stud farm in Cádiz, Spain. The mean length of gestation was of 336.8 ± 0.48 days in the SPB mares and 340.3 ± 0.63 days in AB mares. To assess the accurate prediction of time of birth the potential effect of a number of factors was investigated. The influences of the breed, mare, month and year of mating, age of the mother, number of births and sex of the foal were statistically significant. The factor have the greatest influence over the gestation length was the mare itself, with a correlation among consecutive births of around 0.4. The effect of inbreeding, both of the mare and foal, was negligible. Gestation length shortened as the breeding season progressed: in both breeds, a delay of 1 month in mating corresponded to a decrease of 3 days in the gestation length. According to our results, gestation length decrease as the mare gets older, with the shortest gestation periods when the mare is 10–12 years old, and from this point on, it slowly increases. The gestation period shortens as the 4th or 5th birth approaches, and then gets progressively longer. The range of variation in gestation length due to the number of births to the mare is of 2.9 days for the AB mares, and 2.2 days for SPB mares. The heritability for the gestation length for AB and the SPB breeds was 0.2, with a repeatability of 0.36 and 0.37, for SPB and AB breeds, respectively. With the data from both breeds, and using a classical approach, the response to selection was estimated if mares with extreme gestation lengths were culled, i.e. lengths which are under 310 days, or over 360 days. According to our results, in the case of SPB, a decrease of 14–45% would occur in the number of extreme gestation lengths, while in the AB breed, this value would decrease from 2 to 39%.

Delayed embryonic development in the Indian short-nosed fruit bat, Cynopterus sphinx

The unusual feature of the breeding cycle of Cynopterus sphinx at Varanasi is the significant variation in gestation length of the two successive pregnancies of the year. The aim of this study was to investigate whether the prolongation of the first pregnancy in C. sphinx is due to delayed embryonic development. The first (winter) pregnancy commences in late October and lasts until late March and has a gestation period of about 150 days. The second (summer) pregnancy commences in April and lasts until the end of July or early August with a gestation period of about 125 days. Changes in the size and weight of uterine cornua during the two successive pregnancies suggest retarded embryonic growth during November and December. Histological analysis during the period of retarded embryonic development in November and December showed a slow gastrulation process. The process of amniogenesis was particularly slow. When the embryos attained the early primitive streak stage, their developmental rate suddenly increased considerably. During the summer pregnancy, on the other hand, the process of gastrulation was much faster and proceeded quickly. A comparison of the pattern of embryonic development for 4 consecutive years consistently showed retarded or delayed embryonic development during November and December. The time of parturition and post-partum oestrus showed only a limited variation from 1 year to another. This suggests that delayed embryonic development in C. sphinx may function to synchronize parturition among females. The period of delayed embryonic development in this species clearly coincides with the period of fat deposition. The significance of this correlation warrants further investigation.