Mean Gestation Length Research Articles

The effect of genital mycoplasmas on human fetal growth.

The relation between maternal genital colonization by mycoplasmas and fetal growth was examined in a study of 195 women. Swabs were taken from the endocervix on three occasions during pregnancy and once post partum. Ureaplasma urealyticum organisms (ureaplasmas) were recovered from 42.7 per cent of Caucasian women and from 34.6 per cent of Asian women at their first antenatal visit. These isolation rates remained similar throughout pregnancy, although there was a decrease in isolation after delivery. Mycoplasma hominis was recovered from 6.5 per cent of Caucasians and from 11.5 per cent of Asians at their first antenatal visit and these rates remained fairly constant during pregnancy and after delivery. Caucasian women colonized by ureaplasmas had a longer mean length of gestation (p less than 0.025) than non-colonized women. Furthermore, the colonized women gave birth to infants who had a statistically significant greater mean birth weight and a greater mean birth weight-for-dates than those of the non-colonized Caucasians. There was no correlation between gestational length, birth weight, or birth weight-for-dates and genital colonization of Asian mothers by ureaplasmas or M. hominis. It is clear the ureaplasmas are not associated with low birth weight in our population.

Effects of forced exercise during gestation on farrowing and weaning performance of swine.

Forty-three gilts and 24 sows were tethered throughout gestation, and one-half were forced to walk on a treadmill 15 min daily 5 days a week. Exercised and nonexercised dams farrowed 10.0 and 10.2 pigs (P greater than .05) and weaned 8.1 and 7.9 (P greater than .05), respectively. Birth weight of pigs born alive from exercised and nonexercised dams averaged 1.6 and 1.5 kg (P greater than .05); weaning weights were 8.5 and 8.2 kg (P greater than .05), respectively. Sows farrowed 12% more pigs (P less than .05) than gilts and weaned 17% more pigs (P less than .05) that were 12% heavier at birth (P less than .01) than those of gilts. Forced exercise did not improve (P greater than .05) reproductive performance as measured by numbers of pigs farrowed and weaned or by birth and weaning weights. Mean length of gestation was not significantly affected by age of dam or exercise treatment. The interval between birth of first and birth of last pig per litter averaged 154 and 151 min (P greater than .05) for exercised gilts and sows, respectively, and 170 and 161 min (P greater than .05) for those not exercised.

Factors affecting gestation length in dairy cattle

Data were collected through a special record keeping system for 2,254 herds that used artificial insemination, 37% of which were enrolled in Dairy Herd Improvement Associations. Information was available on a total of 35,162 gestations, consisting of 24,367 Holstein, 5,849 Guernsey, 2,872 Jersey, 1,667 Ayrshire and 407 Brown Swiss pregnancies resulting in single births plus 930 multiple births. Breeds, twinning, sex of calf, parity of the cow and time of day on which estrus occurred were associated with differences in gestation length. Month of insemination had no effect. Mates and sires of the cows both affected gestation length slightly, but significantly. Selection of sires for high milk production of their daughters over a 23-year period appears to have had little, if any, effect on gestation length, as the mean gestation length has increased only one day, from 278 to 279 days for Holsteins during that time.

The effect of age at first mating on litter characteristics in the native nigerian pig

Thirty primiparous gilts of the local breed, which has a very small size, were used in an experiment to study the effect of breeding age (3, 5, 7, 9, 11 and 13 months) on weight at breeding, gestation length, litter size, birth weight, and weaning weight. Increase of breeding age involved increase in breeding weight. Gilts in the three-month age group showed heat but none of them became pregnant at mating. Gilts in age groups from 5 up to 13 months became pregnant after breeding. The mean gestation length ranged between 113 and 114 days and seemed not to depend on the age at breeding. There was no significant difference among the various age groups in litter size (4 or 5 piglets). However, birth weight (between 0.6 and 1.1 kg) and weaning weight tended to increase with increase in age at mating.

Characteristics of the menstrual cycle in nonhuman primates. III. Timed mating in Macaca arctoides.

Analysis of five years of reproductive data from Macaca arctoides showed the mean menstrual cycle length was 29.9 +/- 4.4 days. Using timed mating, a conception rate of 16.3% was observed. The highest conception rate occurred after matings on day 11 of the cycle. Eight pregnancies went to term and the mean gestation length was 172.4 days. The sex ratio was 137.8 males per 100 females in fetuses obtained on day 100 post-conception.

Genital mycoplasmas and birth weight in offspring of primigravid women

The relationship between colonization of pregnant women by Ureaplasma and Mycoplasma and the outcome of pregnancy in a study of 104 women is reported. There were eight abortions but no multiple births or stillbirths. Excluding abortions, the mean gestational length was 39.6 weeks and the corrected mean birth weight was 3.28 kilograms. There was no relationship between maternal colonization by genital mycoplasmas and reduction in birth weight of the offspring, but five of the eight women who aborted harbored Ureaplasma, suggesting an increased trend toward abortion in women harboring Ureaplasma.

Serum relaxin concentrations in pigs with parturition delayed by progesterone administration.

Two groups of pregnant pigs were administered four sc injections of 25 mg progesterone each day from day 110 through day 113 (P4) or from day 110 through day 115 (P6) of gestation. In control pigs, which received only corn oil, the mean gestation length was 113.8 days and the mean incidence of live births was 87%. P4 had a mean gestation length of 115.7 days and a mean incidence of live births of 49%. These values did not differ significantly from controls. P6, however, had a longer mean gestation length (P < 0.01) of 118.1 days and a lower mean incidence of live births (P < 0.001) of 3% than controls. Progesterone treatment did not influence the time of occurrence of the relaxin surge which normally takes place during the 2 days immediately preceding parturition. The mean days of gestation on which maximal relaxin concentrations were obtained for controls, P4, and P6 were 113.0, 112.9, and 112.6, respectively. The mean time interval between maximal relaxin levels and parturition was 22.5 h for controls. Longer time intervals of 70.0 h (P < 0.05) and 136.5 h (P < 0.001) were obtained with P4 and P6, respectively. Progesterone treatment also did not influence the onset of lactation, which was recorded as the time when milk could be readily expressed from the teats. The mean days of gestation on which the onset of lactation was observed for controls, P4 and P6 were 113.8, 114.4, and 113.1, respectively. In all cases the onset of lactation occurred within 24 h following the surge in serum relaxin levels. (Endocrinology102: 471, 1978)

The length of gestation period of Ayrshire cows when mated with bulls of other breeds

SUMMARYLeast squares analyses were undertaken on 1519 gestation lengths of cows mated to Beef Shorthorn, Hereford, Charolais, German Simmental or British Friesian bulls. Gestation length was influenced largely by breed of sireand byindividual sires within breeds. Approximately 100 calvings are required to give a mean value with a standard error of 0·50 day. Heritability of gestation length was estimated to be 0·24±0·05. It is recommended that Artificial Insemination organizations survey and publish the mean gestation lengths of their bulls and that dairy farmers modify, where necessary, pre-partum feeding in the light of this information.

Aspects of reproduction in New Zealand dairy herds 1. Gestation length

Abstract Extract In New Zealand dairy cattle, the average gestation length is commonly accepted as 282 days. This is slightly longer than that reported in European and American studies of Jersey and Holstein or Friesian cattle (Anderson and Plum, 1965 Anderson, H. and Plum, M. 1965. Gestation length and birth weight in cattle and buffaloes: A review. J. Dairy Sci., 48: 1224–1235. [Crossref], [PubMed], [Web of Science ®] , [Google Scholar]; O'Conner et al., 1968 O'Conner, L. K., Wood, P. D. P. and Smith, G. F. 1968. A note on the differences between geographical areas in the gestation length and birth weight of British Friesian calves. Anim. Prod., 10: 125–128. [Google Scholar]). A feature of these reports and previous New Zealand studies is the differing variation associated with the mean gestation lengths. Part of this may be due to sex, season, breed of sire, age of dam and unspecified herd effects, but is largely the result of excluding or including abnormal gestation periods. The criteria for determining normality have been rather arbitrary in most cases. Abnormally short and long gestation periods may result from disease or from incomplete data recording for conception dates.

Changes in the concentrations of urea, glucose and some mineral elements in the plasma of the ewe during induced parturition

Four Finnish Landrace X Dorset Horn ewes were each given an intramuscular injection of 15 mg of dexamethazone on day 142 of gestation. Four ewes with the same fetal numbers were used as controls. Administration of the corticosteroid reduced the mean gestation length from 146-5 to 143-3 days and had no effect on the pre-lambing concentrations of Na, Cl, Ca P and Mg in the maternal plasma or on blood pH. There was a slight but significant (P less than 0-05) decrease in plasma K before lambing in the treated ewes. Plasma urea and glucose concentrations were not affected by treatment. There was a significant increase in the plasma concentration of glucose in both groups of ewes immediately after parturition.

Factors affecting calving difficulty and gestation length in cows mated to Chianina bulls and factors affecting the birth weight of their calves

SummaryImported semen from 10 Italian Chianina bulls was used to inseminate beef and dairy cattle throughout England and Southern Scotland. A total of 2134 records of calving performance were subjected to least squares analyses. Dystocia score was significantly affected by county of birth, parity of dam, sire, type of birth, birth weight (P &lt; 0·001), season of birth and sex of calf (P &lt; 0·01). There were no significant effects of breed or size of cow. Serious dystocia was encountered in 3% of calvings, with the incidence for individual sires ranging from 1·7% to 6·7%. Arithmetic mean gestation length was 284·2 days and it was significantly affected by county, sire (P &lt; 0·05), sex of calf (P &lt; 0·01), and type of birth (P &lt; 0·001). Arithmetic mean birth weight of the calves was 41·2 kg and this was significantly affected by all main effects studied except season of birth and type of herd.

Reproductive Biology of Ototylomys (Cricetidae)

Reproductive biology of the Neotropical climbing-rat, Ototy- lomys, is described, based on the examination of 86 offspring of animals live- trapped from Campeche, Mexico. Animals were maintained in the Michigan State University Live Animal Colony. Vaginal smears were collected from Ototylomys kept in 14 hours of light and 10 hours of darkness. The average interval between comified cell periods was 8.8 ? 0.5 days. A postpartum estrous was observed for all littering females, as evidenced by the presence of sperm in vaginal smears taken within 24 hours after the discovery of new litters. Females mated as early as 29 days and males as early as 175 days. Gestation period was 52.8 ? 2.1 days. No statistical difference was found between the mean gestation lengths of lactating and nonlactating females. Both minimum and maximum extremes in gestation lengths were observed in lactating females. Embryos were first detected by palpation on day 14 of gestation. The fetal head was initially distinguishable at 28 days. Average litter size of 2.4 young consisted of 46 males and 40 females. The standard measurements, in millimeters, on day one were as follows: total length, 119.5 - 0.9; tail length, 47.1 - 0.8; hind foot, 16.4 ? 0.2; ear, 9.4 ? 0.2; weight, 10.2 ? 0.3 grams. The least variance over time was observed in the length of head and body. At birth, head and body length was 46.4 percent of adult body length. No statistical differences were found between males and females. For approximately 30 days after birth, the very precocial neonates adhere tenaciously to their mother's inguinal teats. The largest number of individuals initially responded to loud noises by day two and had opened their eyes by day six. Hearing preceded eye opening in all but four cases. Ototylomys reach 50 percent of adult body length by day two and 90 percent by 58 days of age. The reproductive biology of Ototylomys was judged to be primitive in form and best adapted for scansorial living. Early efforts to evaluate the possible evolutionary significance of reproduc- tive biology were made by Mossman (1953) and Keys (1958). They proposed that the internal mechanisms of implantation and subsequent development of placental membranes occurred under uniform internal conditions and with little influence from external environment. These characteristics would be more conservative than the usual morphological criteria in current use and therefore may be more evolutionarily significant. Within the cricetid genus, Peromyscus, Layne (1968) found that body size and environment were the most influential factors governing gestation length and postnatal development. To further elucidate evolutionary and reproductive relationships found in rodents, I have examined the reproductive biology of Ototylomnys. The re- sults are described herein and compared to the reproductive biology of other cricetid rodents as reported in the literature. Ototylomys belongs to an assemblage of Neotropical cricetine rodents of obscure ancestry. Ototylomys has been placed in the subfamily Neotominae

Reproductive biology of PMSG-primed immature female rats.

The reprodutive performance of PMSG-pnimed immature female rats (8 lU PMSG at 30 days of age)was studiedto determinewhether theyaresuitablemodelsorsubstitutes foradultanimalsin studies of reproduction. Pseudopregnancy, induced by cervical stimulation on day 33, lasted 12 days as indicated by leukocytic vaginal smears. Decidual cell reaction was elicited by uterine trauma on day 5 of pseudopregnancy, and resulted in a fifteen-fold increase in the mean weight of the traumatized horn within 4 days. PMSG-treated immature rats can conceive, maintain viable fetuses to term, and deliver live pups in a normal mannner (mean length of gestation: 24.2 days; mean litter size: 7.1 pups). Serum levels of progesterone, 20o-dihydroprogesterone (20�-DHP), LH, and FSH were measured by radioimmunoassay in samples taken at 3-day intervals between days 6 and 21 of pregnancy. Progesterone decreased from 86.7 ng/ml on day 6 to 69.7 ng/ml on day 9, was elevated to 111.4 ng/ml on day 12, and decreasedto 64.4ng/mlon day 21.20a-DHP increasedfrom 7.2ng/mlon day 6 to a peak of 14.5 ng/ml on day 15, and decreased significantly to 5.8 ng/ml on day 18. Serum LU and FSH did not vary significantly. These hormone profiles are similar to those reported by others in adult pregnant rats. Implantation was delayed in PMSG-pnimed pregnant rats by bilateral ovariectomy on day 3 and

Nutritional influences in industrial societies.

Evidence that maternal undernutrition contributes to the problem of low birth weight in industrial societies will be discussed in the following categories: (1) epidemiological associations, (2) clinical studies of growth-retarded babies, (3) maternal dietary studies, and (4) pathologic findings in perinatal deaths. Epidemiological Associations Mean Birth Weight. —As summarized by Rosa and Turshen, 1 quite large differences between populations occur with respect to mean birth weight. In contrast, differences in mean length of gestation are minor. Thus, between-population variance in mean birth weight reflects principally differences in rate of fetal growth. It is a central problem of perinatal medicine to know the relative contributions of heredity and environment to the variance in fetal growth rate, and, among the environmental factors, to know the effect of maternal undernutrition. Within industrial societies, similar though less obvious differences are seen in the mean birth weight. For example, mean weight at term for male

Reproduction in the Two Species of Grey Kangaroos, Macropus Giganteus Shaw and M. Fuliginosus (Desmarest). Ii. Gestation, Parturition and Pouch Life.

Over a 10-y period, eastern and western grey kangaroos were bred in enclosures. All western subspecies interbred, and western males bred with eastern females to give hybrid young, but never the reverse cross. Hybrid males were sterile but females readily backcrossed with western males. Mean gestation lengths were: eastern greys, 36.41 � 1.63 days; western greys, 30.56 � 2.55 days; hybrids, 34.09 � 0.81 days; backcrosses, 31.58 � 0.93 days. Births occurred throughout the year in both species, but those of western greys were more concentrated in the summer months. Gestation length did not vary with month of year. Parturition in one backcross female is described. Young weighed just over 800 mg at birth and could reach 1000 mg within 24 h. With a free choice, they preferred an anterior to a posterior teat, but when one teat was already being suckled, they chose either the anterior or the posterior teat on the opposite side. The sex ratio was close to unity in all groups, the overall value being 102B : 100@. If dropped from the pouch, young of all groups over 200 days old (mean minimum age 243.86 � 19.74 days) were usually capable of standing and regaining the pouch. Eastern and western young left the pouch for the first time at mean ages of 283.86 � 24.70 and 298.40 � 34.29 days respectively,and left it finally at about 320 days old in both species. Within the western species, pouch life was significantly longer in the subspecies ocydromus than in either fuliginosus or melanops. The intervals between parturitions in lactating females was close to 1 year (variation between species was probably significant). The mean interval in eastern females undergoing embryonic diapause did not differ significantly from that in western females not doing so; in western females it did not differ significantly between fuliginosus and ocydromus, but did so between melanops and both the other subspecies. Lactation usually exceeded 18 months. Mortality of pouch young accounted for 17% of known births, mostly within the first few days after birth. Accidental injury and coccidiosis were the major causes of death in the first months after leaving the pouch.

Influences on Birth Weight and Gestation Period of Holstein-Friesian Cattle

The effects of genetic group for milk yield, breeding management, nutrition of cow, sex of calf, year and season of birth, parity, and sires within genetic groups on birth weights and gestation length were studied in 341 Hoistein-Friesian single-born calves.Least squares means and error standard deviations for birth weight and gestation length were 44.9 kg±4.5kg and 276.7 days±3.7 days. Season and year of birth did not influence both traits significantly. Male calves were 3.6kg heavier than females, but they did not differ significantly in gestation length. Calves from second and third carvings were heavier than those from first parturitions and gestated for a significantly longer time. Cows under heavy grain feeding dropped calves that were 1.8kg heavier than those under average feeding conditions; no differences in their mean gestation lengths were detected. Calves resulting from early postpartum breedings were 1.2kg lighter than those from late breedings, but their gestation lengths were not affected differentially. Calves from the high genetic group were gestated 3.4 days longer than those in the low group though they did not differ in their mean birth weight. Sires within genetic groups were a significant source of variation for gestation length in both groups, but only sires within the low group had a significant effect on birth weight. Interactions between genetic×reproduction and genetic×nutrition×reproduction were significant on birth weight whereas nutrition×sex and genetic×nutrition×reproduction interactions were significant for gestation length.A multiple regression equation for birth weight selected by a stepwise procedure included the dummy variables nutrition of cow, breeding management, sex, parity, and a second-order term in parity (squared multiple correlation = .40). The equation for gestation length included genetic group for milk yield and age at calving (squared multiple correlation .17). Sire groups accounted for 7.6 and 13.6% of the phenotypic variance of adjusted birth weight and gestation length. Paternal half-sib heritabilities were .30±.16 and .54±.22 for birth weight and gestation length.

The influence of anencephaly upon intrauterine growth of fetus and placenta and upon gestation length.

SummaryIn order to determine the influence of anencephaly upon the intrauterine growth of fetus and placenta, and upon gestation length, 147 pregnancies with anencephaly were analyzed and compared with a control group.There appeared to be a lower rate of intrauterine growth of the fetus and of the placenta in the anencephalic group. The birthweights of the anencephalic infants were much lower than those of the control group, but showed a steady increase which continued beyond term so that a birthweight level was achieved which was similar to that reached by the control group at term. The placentae of the anencephalic group showed a decreased weight in a high percentage of the cases, although this trend was less pronounced than for the birthweights.The mean gestation length was significantly shorter in the anencephalic group than in the control group. Spontaneously born anencephalics from pregnancies with no hydramnios had a mean gestation length which was not significantly different from that of the control group. The distribution over the maturity periods differed significantly, however, in the high percentage of prematurely and postmaturely born anencephalic infants.Short gestation length in anencephaly, on the one hand, is not due solely to hydramnios or to maternal factors; absence of hydramnios, on the other hand, is not invariably associated with prolonged gestation. Our observations do not support the suggestion that the anencephalic fetus might be the human analogue to the hypophysectomized lamb, nor that the pituitary‐adrenal axis, of importance in the initiation of labour in sheep, plays the same role in humans.

Serum post‐albumins and fertility in dairy cattle

SummaryBlood samples from 180 Guernsey cows and 599 Holstein cows were typed for post‐albumins (Poa). The genotypes were compared for breeding efficiency, mean return interval, anestrus interval, service interval, gestation length and lactation length. Poa SF cows had a significantly shorter (P &lt; 0.01) mean return interval than SS cows. The effect is associated with order of insemination, but is independent of lactation number. None of the other parameters showed genotypic differences.

Cyclicity and gestation length ofMacaca fascicularis

Menstrual cycle records were kept on all of the females in the colony for a period of 14 months. The mean cycle length was 30.8 days; the median, 33 days; and, the mode, 28 days. Cycles ranging from 27 to 32 days in length comprised 66.4% of all cycles. Regular cycles were scored on the basis of menses beginning within 2 days of a projected date based on an average of 6 previous cycles. Regular cycles were observed in 6.24% of the cases. The mean cycle length for regular cycles was 29.2 days. Forty-five percent of all females had regular cycles at least 70% of the time. The duration of menstrual flow for 150 cycles averaged 2.8 days. Menses ranged from 1 to 8 days in length, with 90.7% of the cases ranging from 1 to 4 days in length. For a given duration of menses, the percentage of cases of light flow increased as the end of the menstrual period was reached. The mean gestation length of 3 pregnancies was 164.4 days, with implantation bleeding beginning on day 19 of pregnancy and lasting from 4 to 9 days.

Effect of pre- and post- natal nutrition on the growth of beef cattle I. The effect of nutrition and parity of the dam on calf birth weight

The influence of submaintenance (low plane) nutrition during the last trimester of pregnancy, and parity of the dam, on calf birth weight was studied in Hereford cows.The submaintenance ration (3.5 kg Rhodes grass hay per head per day) significantly (P &lt; 0.01) reduced the mean calf birth weight by 6.8 kg to 24 1 kg, and the mean length of gestation by 5.4 days to 277.3 days, compared with an above-maintenance (high plane) ration (3.5 kg each of Rhodes grass hay and barley grain per head per day). Dam nutrition, however, did not influence the number of retained placentae, calf mortality, or the incidence of dystocias. Dam parity did not significantly influence calf birth weight or length of gestation, but significantly (P &lt; 0.05) reduced the number of retained placentae of second parity cows. There were no significant differences between sexes in mean birth weight or mean gestation length. The regression of calf birth weight on dam weight just prior to calving was significant (P &lt; 0.05) for high plane cows: y = 20.248 + 0.023x, r = 0.40. The regression of calf birth weight on length of gestation was significant for both high(P &lt; 0.05) and low(P &lt; 0.01) plane cows: y = –28.343 + 0.210x, r = 0.40, and y = -41.015 + 0.235x, r = 0.42 respectively.