Induction of twinning in Holstein and Japanese black cows by ipsilateral frozen embryo transfer

Induction of twinning by ipsilateral nonsurgical transfer of two frozen-thawed Japanese Black bovine embryos to each of 20 Holstein and 26 Japanese Black cows, that had been kept under a stable in private farm conditions, was examined. The cows were monitored every 20 days from Day 25 to Day 65 of gestation for pregnancy and fetus survival (estrus is Day 0). Seventy-five per cent (15 of 20), 65.0% (13 of 20) or 60.0% (12 of 20) and 61.5% (16 of 26), 53.8% (14 of 26) or 50.0% (13 of 26) of Japanese Black cows were diagnosed pregnant at 25, 45 and 65 days after transfer by ultrasonic echography. Embryonic losses were observed between Days 25 and 65 in 29.2% (7) Holstein and 31.8% (7) Japanese Black cows. The twin pregnancy rate in Holstein and Japanese Black cows decreased with time; 60.0% (9 of 15) vs. 37.5% (6 of 16) at Day 25; 53.8% (7 of 13) vs. 28.6% (4 of 14) at Day 45 and 41.7% (5 of 12) vs. 15.4% (2 of 13) at Day 65. At calving, Holstein cows produced five sets of twins and seven single calves, and Japanese Black cows two sets of twins and 11 single calves. The twinning rate in Holstein cows was higher (P < 0.05) than that in Japanese Black cows, 41.7% (5 of 12) vs. 15.4% (2 of 13). The calf birth weight in Holsteins was heavier (P < 0.05) than that in Japanese Black dams (24.5 kg, 33.6 kg vs. 19.3 kg, 25.5 kg for twin and single calves). The placental weight in Holstein dams calving twins was heavier than that in Holstein dams calving a single calf or in Japanese Black dams calving either twins or a single calf (6.6 kg vs. 3.5 kg, 4.6 kg or 2.8 kg). The number of placentome in Holstein dams calving twins was also higher (P < 0.05) than that in Holstein dams calving a single calf or Japanese Black dams (103.5 vs. 41.8, 67.9, 33.0). The number of placentome was approximately double in dams calving twins than that of dams calving a single calf.     

Induction of twinning in crossbred heifers by ipsilateral frozen embryo transfer

Induction of twinning by means of nonsurgical ipsilateral transfer of two frozen embryos or of demi-embryos was attempted in 297 virgin crossbred dairy heifers that were kept at the following locations: in stables at our breeding station (Group 1), in a mountain field (Group 2) and at a private farm (Group 3). Of these, 187 heifers (63%) were diagnosed pregnant at 25 d after embryo transfer and 134 heifers (45%) were diagnosed pregnant at 60 d after transfer by ultrasonic echography or by palpation per rectum. At calving, 118 heifers produced 46 sets of twins and 72 single calves, for a total of 164 calves sixteen pregnant heifers aborted fetuses between 2 and 7 mo. The pregnancy rate of Group 1 (39%) was lower than that of Group 2 (48%) or Group 3 (50%). Abortion and mortality rates for Group 3 (8% and 8%, respectively) were significantly lower (P<0.05) than for Group 1 (16% and 12%) or Group 2 (13% and 18%). Twin calves had lower birth weights (P<0.05) than singles, but at 270 to 330 d of age, there was no significant difference between the weights of single and twin calves. Dystocia or difficult delivery was not observed heifers producing twins. Retention of the placenta was observed in twin calving heifers, with placenta retention levels the highest in Group 2 (33%) than followed by Group 1 (14%) and Group 3 (10%). When gestation periods were compared between single and twin calves in Groups 1 and 2, the gestation period of single calves was 5.0 to 7.0 d shorter than that of twin calves. No significant difference was observed between the gestation periods of single and twin births in Group 3.     

Postpartum fertility in beef cattle producing twins

Postpartum fertility was measured in 42 plur iparous Hereford cows and first calf Hereford heifers that calved after embryo transfer to induce twins. Dams were exposed to a Hereford bull from 4: 00 P.M. to 8:00 A.M. each day from 60 days postpartum until pregnancy was confirmed or calves were weaned at 180 days of age. Days open ($\text{X}\text{± SE}$) for dams that produced single and twin calves were 84.1 ± 4.6 (n = 12) and 94.9 ± 6.2 (n = 30), respectively. Corresponding values for dams that nursed one calf, including six females that lost one calf of a twin set at birth, and dams that nursed twins were 89.3 ± 6.4 (n = 18) and 93.4 ± 8.5 (n = 24). No significant differences were observed due to calving or suckling twin calves. Heifers that calved twins had a shorter mean interval to conception than cows that calved twins. These results are interpreted to mean that with proper management during the prepartum and postpartum periods, reduced fertility in beef cattle that produce twins need not occur.     

Morphology and morphometry of in vivo- and in vitro-produced bovine concepti from early pregnancy to term and association with high birth weights

This study was designed to characterize conceptus development based on pre- and postnatal measurements of in vivo- and in vitro-derived bovine pregnancies. In vivo-produced embryos were obtained after superovulation, whereas in vitro-produced embryos were derived from established procedures for bovine IVM, IVF and IVC. Blastocysts were transferred to recipients to obtain pregnancies of single (in vivo/singleton or in vitro/singleton groups) or twin fetuses (in vitro/twins group). Ultrasonographic examinations were performed weekly, from Day 30 of gestation through term. Videotaped images were digitized, and still-frames were used for the measurement of conceptus traits. Calves and fetal membranes (FM) were examined and measured upon delivery. In vitro-produced fetuses were smaller than in vivo controls (P < 0.05) during early pregnancy (Day 37 to Day 58), but in vitro/singletons presented significantly higher weights at birth than in vivo/control and in vitro/twin calves (P < 0.05). From late first trimester of pregnancy (Day 72 to Day 93), placentomes surrounding in vitro-derived singleton fetuses were longer and thinner than controls (P < 0.05). At term, the presence of giant cotyledons in the fetal membranes in the in vitro group was associated with a larger cotyledonary surface area in the fetal horn (P < 0.05). The biphasic growth pattern seen in in vitro-produced pregnancies was characterized by conceptus growth retardation during early pregnancy, followed by changes in the development of the placental tissue. Resulting high birth weights may be a consequence of aberrant placental development due to the disruption of the placental restraint on fetal growth toward the end of pregnancy.     

Radioimmunoassay of a bovine pregnancy-associated glycoprotein in serum: its application for pregnancy diagnosis.

A sensitive and specific double-antibody RIA for a bovine pregnancy-associated glycoprotein (bPAG) is described. The limit of detection was 0.2 ng/ml. The assay was specific for bPAG in that pituitary and placental gonadotropic hormones and other placental or serum proteins assayed in serial dilutions did not cross-react. The RIA allowed measurement of bPAG in placental extracts, fetal serum, fetal fluids, and serum or plasma of pregnant cows. About 20% of unbred heifers and nonpregnant cows had detectable levels ranging from 0.30 +/- 0.09 to 0.50 +/- 0.17 ng/ml (mean +/- SD), and 15% of bull sera showed higher concentrations (3.01 +/- 1.73 ng/ml) of bPAG or bPAG-like protein. Variations among animals was observed in fetal serum bPAG concentrations. Bovine PAG was detected in maternal peripheral blood at Day 22 of pregnancy (mean +/- SD, 0.38 +/- 0.13 ng/ml) in some animals and at Day 30 in all pregnant cows. Peripheral serum bPAG levels increased progressively to 3.60 +/- 1.73 ng/ml (mean +/- SD) at Day 30 of pregnancy, to 24.53 +/- 8.81 ng/ml at Day 120, and to 1551.91 +/- 589.68 ng/ml at Day 270. Peak concentration of bPAG was 2462.42 +/- 1017.88 ng/ml and it occurred 1-5 days prior to parturition. After delivery, bPAG concentrations decreased steadily to 499.63 +/- 267.20 ng/ml at Day 14 postpartum (pp), 10.12 +/- 7.84 ng/ml at Day 60 pp, and 1.44 +/- 1.08 ng/ml at Day 90 pp. The undetectable concentration (less than 0.20 ng/ml) was reached by Day 100 +/- 20 pp. An investigation undertaken in Holstein heifers, Holstein cows, and Hereford cows used as recipients for purebred Holstein embryos supplied evidence of the influence of breed of recipient and sex of fetuses on peripheral concentrations of bPAG. A herd of 430 Holstein-Friesian heifers that had received transferred embryos were bled at Day 35 postestrus (pe) for measurement of bPAG. The bPAG was detected in 287 of 430 serum samples analyzed. By rectal palpation performed at Day 45 pe, 267 heifers with detectable levels of bPAG at Day 35 pe were confirmed to be pregnant as were 3 of 143 heifers previously diagnosed as not pregnant by RIA. These results suggest that detection of this placental-specific antigen in the serum could be used as a specific serological method for early pregnancy diagnosis in cattle from 28 days after breeding.     

Production efficiency of Japanese black calves by transfer of bovine embryos produced in vitro

The objective of this study was to examine the production efficiency of Japanese Black beef calves after transfer of bovine embryos derived from an in vitro procedure. In vitro-produced (IVP) embryos were obtained from in vitro maturation and fertilization and in vitro development by co-culture with cumulus cells until 7 or 8 days after insemination. In vivo-developed (IVD) embryos from superovulated Japanese Black heifers and cows 7 days after artificial insemination were used as a control group. Bovine embryos were transferred nonsurgically to recipient cows on Day 7 +/- 1 of the estrous cycle. Pregnancy was diagnosed by palpation per rectum at Day 60 to 70 after estrus. Pregnancy, abortion, perinatal accident and birth rates were examined according to the origin of embryos (IVP or IVD), the number of transferred embryos (single or twin) and the storage status (fresh or frozen-thawed). In Experiment 1, production efficiency by twin transfer of fresh IVP embryos was examined. Higher pregnancy rates (52 1% vs 42 9%, P < 0.05) and birth rates (47.0% vs. 33.0%, P < 0.05) were obtained by twin transfer than by single transfer of fresh IVP embryos. Thus, the twin transfer of fresh IVP embryos was effective for production of calves, although the birth rates for single and twin transfers of fresh IVD embryos were still higher (55.5% and 76.1%, P < 0.05). But the abortion and perinatal accident rates for twin transfer of fresh IVP embryos were also significantly greater than those for single and twin transfer of fresh IVD embryos (P < 0.05). In Experiment 2, production efficiency by twin transfer of frozen-thawed IVP embryos was examined. Either single or twin transfer of frozen-thawed IVP embryos resulted in a similar pregnancy rate (41.3% vs. 46.7%, P > 0.05) and birth rate (34.1% vs. 41.1%, P>0.05). Thus, in combination with frozen-thawed IVP embryos, the twin transfer did not enhance production efficiency. In conclusion, Japanese Black beef calves could effectively produce calves by twin transfer to Holstein recipients when using fresh IVP embryos, and by single transfer when using frozen-thawed IVP embryos.     

Normal calves from transfer of biopsied, sexed and vitrified IVP bovine embryos

Data on biopsied, sexed and cryopreserved in vitro produced (IVP) bovine embryos, and their in vivo developmental competence are very limited. Two preliminary studies were conducted before the primary study. In Experiment 1, post-thaw in vitro developmental competence of biopsied and vitrified IVP embryos was evaluated using re-expansion as an endpoint. In Experiment 2, the pregnancy rates of biopsied fresh, frozen or vitrified embryos following single embryo transfer were compared. Since vitrified embryos resulted in a higher pregnancy rate than frozen-thawed embryos, in the primary study (Experiment 3), all IVP embryos were vitrified following biopsy and sexing (by DNA fingerprinting). In Experiment 3, we compared pregnancy initiation and calving results of heifers in the following treatments: 1) artificial insemination (AI); 2) AI plus contralateral transfer of a single embryo (AI + SET); 3) ipsilateral transfer of single embryo (SET); or 4) bilateral transfer of two embryos (DET). Birth weights, gestation lengths and dystocia scores were recorded. In Experiment 1, post-thaw re-expansion rate of biopsied and vitrified embryos was 85% (70/82). In Experiment 2, pregnancy rates (90 d) were 44% (7/16), 23% (3/13), and 50% (7/14) for vitrified, frozen and fresh embryos, respectively (P < 0.10). In Experiment 3, pregnancy rates of AI and SET were 65% (20/31) and 40% (16/40), respectively (P < 0.05). The pregnancy rate of AI + SET was 75% (27/36) with 11 carrying twins, and the pregnancy rate of DET was 72% (26/36) with 10 carrying twins. All AI fetuses were carried to term, but only half the SET fetuses were carried to term. Similar calving rates were observed in the AI + SET and DET groups, 76 and 70%, respectively, of those pregnant at Day 40. Mean birth weight, dystocia score and gestation length of AI calves were not different from those of SET calves. Mean birth weight and dystocia score of single-born calves were greater than those of twin born calves (P < 0.05). These data demonstrate that biopsied IVP bovine embryos can be successfully cryopreserved by vitrification and following post-thaw embryo transfer, acceptable rates of offspring with normal birth weights can be obtained without major calving difficulties.     

Perinatal mortality in term and preterm twin and singleton births.

Although, in general, twins have higher perinatal mortality rates than singletons, preterm twins have lower perinatal mortality rates than singletons of the same birth weight or gestational age. This study investigated the hypotheses that this paradoxical twin advantage: 1) is due to gestational age distribution differences between the singleton and twin populations, and 2) is due to increased likelihood of birth having occurred in a tertiary perinatal center. A pre-existing, time-limited data set of all births in the province of Ontario in odd years between 1979 and 1985 was chosen for this study because of the large sample size (n = 618,579). Multivariable logistic regression of the relationship between perinatal mortality and twin status was controlled for mother's age, hospital level and gestational age. Findings confirm the lower mortality of preterm twins. After controlling for level of hospital of birth this difference remained, suggesting that level of hospital of birth was not a major factor responsible for the twin advantage. Analyses in which gestational age was standardized indicate that, for those whose gestational age was less than 2 SD below the mean for their particular group (twin or singleton), twins were actually at higher risk than singletons. These results support hypothesis 1 and do not strongly support hypothesis 2. The results also support earlier authors' suggestions that the definition of term birth should be different for twins and singletons     

Freemartins in beef cattle twins induced by embryo transfer

The incidence of freemartinism in heterosexual twins (male-female) resulting from embryo transfer was studied by determining sex chromosome chimerism in lymphocytes and masculinization of female reproductive tracts at slaughter. In one group of calves, ten of 11 heifers born co-twin to full sib, paternal half sib, or unrelated bull calves exhibited sex chromosome chimerism, a proportion in close agreement with that observed in naturally occurring twins. The ten calves with sex chromosome chimerism also had masculinized tracts whereas the other had an apparently normal female tract. Bull calves had a percentage of XY cells similar to their female co-twins, except for the twin set from which the “normal” female was obtained. The bull calf from this set had 5.6% XX cells although no XY cells were observed in the heifer in 66 metaphase spreads. No association was observed between the degree of sex chromosome chimerism and abnormalities of the female tract. Reproductive tracts from all female-female twin sets were normal. In another group of calves, all 20 heifers from heterosexual twin sets had masculinized reproductive tracts. It is concluded that the induction of twins by embryo transfer results in normal expression of freemartinism even though calves may be unrelated and are known to develop in separate uterine horns.     

Effects of experimental Trypanosoma vivax infection on first-, second-, and third-trimester pregnancy in heifers

The effects of Trypanosoma vivax on pregnancy were studied in 18 heifers. The heifers were bred by a proven bull and divided into three groups of six heifers each. In the first group, four heifers were infected with T . vivax on Day 60 (first trimester) of pregnancy; two other pregnant heifers were uninfected controls. The second and third groups were similarly infected in the fourth (second trimester) and seventh (third trimester) month of pregnancy. One infected heifer in the first-trimester group aborted 39 days postinfection (p.i.); the remaining three had relatively normal gestation and parturition. In the second-trimester group, the pregnancies were carried to term with normal deliveries. In the third-trimester group, three infected heifers (75%) had premature deliveries while the fourth died about three hours after the full-term calf was pulled out. All of the control heifers had normal gestation and parturition. No gross abnormalities were seen in the placentae of the infected heifers, but histological sections of the heifers infected in the third trimester of pregnancy revealed more mononuclear cells than in those of the uninfected controls. Postmortem examination of the dead premature calves showed lymphadenopathy, splenomegaly, serous atrophy of perirenal and pelvic fat, epicardial petechiae, and blood-tinged peritoneal and pericardial fluids. Histologically, there were slight myocardial haemorrhages and edema. T. vivax was recovered from the blood of one of the premature calves. Both birth weights and PCV were affected by the experimental maternal infection in the first- and third-trimester calves. The birth weights and PCV of calves of infected dams were lower than those for the calves of the control heifers. This work therefore demonstrates transplacental transmission of T. vivax in heifers.     

Production of identical twins by bisection of blastocysts in the cow

Day-8 embryos were recovered by a non-surgical method from superovulated crossbred heifers. Normal expanded blastocysts with a distinct inner cell mass and a trophoblast were released from the zona pellucida and bisected along a sagittal plane into two 'half' blastocysts. Each 'half' blastocyst was replaced in an empty zona pellucida and cultured for 2 h in B2 medium. After culture the 'half' blastocysts were directly transferred to recipient heifers via the cervix. From 11 blastocysts, 11 monozygotic 'half' blastocyst pairs were transferred to 11 recipients: 8 recipients became pregnant, 4 carried twins and one delivered a normal calf and an acardiacus amorphus monster consisting of disorganized embryonic tissues. A further 11 'half' blastocysts were transferred as singletons to 11 recipients. Five recipients were apparently pregnant at Day 42. One returned to oestrus at Day 45, 3 were carrying normal fetuses and 1 a pair of normal twin fetuses when slaughtered at Day 128. It is concluded that even after the first irreversible cellular differentiation which occurs at the blastocyst stage it is still possible to produce identical cattle twins by bisection of the Day-8 blastocyst.     

Abnormal offspring following in vitro production of bovine preimplantation embryos: a field study

Data on 944 calves from 2228 in vitro-produced (IVP) bovine preimplantation embryos were compared with data on 2787 AI calves born in the same herds in 1995. Bovine preimplantation embryos were produced in vitro following ovum pick up (OPU) from donor cows and pregnant heifers in an open nucleus breeding program. After 7 d of in vitro culture on a BRL cell monolayer in the presence of 10% FCS, frozen-thawed expanded blastocysts and fresh morulae to expanded blastocysts were transferred into recipient heifers and cows at 119 contracted farms throughout the Netherlands. The pregnancy rate, as confirmed by palpation per rectum between 90 and 150 d after transfer was 43.5% for both fresh and frozen embryos. Data on IVP and AI calves were registered by the farmers. The percentage of calves with a congenital malformation and the percentage of male calves were related to the total number of calves born. Gestation length, birth weight (measured by a balance), perinatal mortality and ease of calving were analyzed in a subdataset (699 IVP and 2543 AI calves, respectively) by a comparative analysis of variance (ANOVA). The ANOVA model included herd, month of calving, sire nested within AI or IVP, parity and breed of the inseminated cow/embryo recipient, sex of calf, type of calf (AI or IVP) and two-way interactions between type of calf and sex, parity and breed. The percentage of calves with congenital malformations was 3.2% and 0.7% for IVP and AI calves, respectively. An increased incidence of hydro-allantois and abnormal spinal cords and limbs was observed in IVP calves. The percentage of male calves was significantly different between IVP and AI, 55.5% and 48.9%, respectively (Chi-square, 1 degree of freedom, P < 0.05). On the average, IVP calves showed a significant increase of birth weight by 10% (4-5 kg), a 3-d longer gestation period, 2.4% more perinatal mortality and a more difficult calving process compared to AI calves (P < 0.05). From these results it is concluded that calves produced by IVP deviate significantly from calves produced by AI.     

The production of mixed-species Bos taurus-Bos indicus twin calves

Bos taurus-Bos indicus twin calves were produced by transferring Day 6–8 Bos indicus or Bos taurus embryos to previously inseminated Bos taurus or Bos indicus cows. Embryos were transferred to 112 recipients of which 64 (57.1%) were diagnosed as pregnant by rectal palpation at 7–8 weeks gestation. Twin foetuses were diagnosed in 38 (65.5%) of 58 cows in which the location and number of foetuses was recorded. Substantial foetal losses occurred after 7–8 weeks and only 44 cows calved giving 21 sets of twins and 23 singletons. Six of the single calves were from transferred embryos. The duration of gestation of the twin pregnancies (282 days) was similar to that of single Bos taurus pregnancies (282 days for Jerseys and 286 days for Friesians) and 14 days shorter than single Bos indicus pregnancies (296 days). Consequently Bos indicus members of mixed-species twins were premature at birth and required intensive care to ensure their survival.     

Evaluation of productivity of sexually precocious Nelore heifers

The objectives of the present study were to investigate the influence of yearling weight on the occurrence of early pregnancy and to determine differences between precocious and non-precocious heifers in terms of pre- and postnatal calf mortality, calf weight and height, mature cow weight, and stayability of the cow in the herd. Data from 26 977 females of a Nelore herd that participated in the breeding season between 1986 and 2004 were analyzed. The influence of yearling weight on sexual precocity and differences between precocious and non-precocious heifers in pre- and postnatal calf mortality and stayability were analyzed using the GENMOD procedure of the SAS program. Differences in the growth traits between precocious and non-precocious animals were estimated by contrast analysis. Three groups were analyzed for postnatal mortality: first calving of the heifers, calves born from the third calving and all offspring of the cow. In order to have a standardized calving to conception period for all females (precocious and non-precocious), calves born from the second calving were not included in the analysis. This was necessary because the first calving to conception period (days open) of precocious heifers was longer than for non-precocious due to farm reproductive management. No differences in postnatal mortality rates, from the third calving, were observed between the two groups of heifers studied. Analysis of all offspring of the dams showed a 9% higher probability of death of calves born to precocious heifers compared with calves born to non-precocious heifers. With respect to stayability, precocious heifers presented 33% greater odds to remain in the herd until 5 and 6 years of age and 28% greater odds to remain in the herd until 7 years when compared with non-precocious heifers. Precocious heifers weaned calves (205 days) significantly heavier than non-precocious ones, 1.410 and 0.797 kg considering the weaning weights of all offspring and of the third calving, respectively. With respect to sexual precocity, the results suggest that the probability of heifers to become pregnant at 16 months of age increases with increasing weight. However, heifers weighing more than 240 kg present practically the same pregnancy probability. Nevertheless, exposure of heifers during the early breeding season is recommended for beef cattle herds raised in tropical regions in view of the numerous benefits demonstrated here.     

Endocrine Measurements and Calving Performance of Swedish Red and White and Swedish Holstein Dairy Cattle with Special Respect to Stillbirth

During 3 consecutive calving seasons, calving performance, placental characteristics and endocrine profiles of total 98 pregnancies of late pregnant Swedish Red and White (SRB) and Swedish Holstein (SLB) dairy heifers and cows, were investigated. Ninety-four singleton pregnancies and 4 sets of twins were recorded. In animals with singleton pregnancy, 8 stillbirths, 7 weak calves, 3 premature parturitions and 1 abortion were registered. In the SLB heifers, 19% of stillbirth (5/26) were observed, while 5% (2/42) were noted for the SRB heifers. One stillborn calf derived from the SRB cows and none was found from the SLB cows. In the heifers and cows delivering a normal living calf with unassisted parturition, the placentome thickness monitored by ultrasonography was constant towards the end of pregnancy. The numbers of foetal cotyledons varied individually between animals but in total, fewer cotyledons were found in the foetal membranes of the SRB animals than in the SLB animals (69 ± 19) vs. (88 ± 29) (p < 0.05). No morphological and numerical differences of the placentome thickness in animals delivering a stillborn or weak calf, compared to animals delivering a normal living calf, could be observed. In animals with unassisted parturition and without birth complications, the levels of progesterone (P4), PGF_2α metabolite (PG-metabolite), cortisol, oestrone sulphate (E1SO4) and pregnancy associated glycoproteins (PAGs) were not different by breeds and parities. In animals carrying stillbirth, higher levels of E1SO4 were found in 3 SRB animals and 1 SLB heifer, whereas lower levels of E1SO4 were recorded in 3 SLB heifers during the last week of pregnancy, compared to the profiles found in animals with unassisted parturition. Additionally, the levels of PAGs remained low and constant in 1 SRB cow (delivering a stillborn calf), 1 SRB heifer (giving birth prematurely), 4 animals (carrying twins) and 1 aborting SRB cow. Our results show a very high rate of stillbirth in especially SLB heifers and deviating profiles of E1SO4 and PAGs in animals with impaired parturition were recorded.     

Mortality in Holstein-Friesian calves and replacement heifers, in relation to body weight and IGF-I concentration, on 19 farms in England

The incidence of mortality and culling in Holstein-Friesian heifers from birth through first calving was determined on 19 dairy farms selected from across southern England. The outcome of 1097 calvings was determined. Size (BW, heart girth, crown-rump length and height at withers) and insulin-like growth factor-I concentration of live heifer calves were measured at a mean age of 26 ± 0.7 days (n = 506). Associations between the heifer-level variables and mortality were determined using clustered binary logistic regression. Perinatal mortality (stillbirths and mortality within the first 24 h of birth) of male and female calves was 7.9%. This figure was significantly higher in cases where calving assistance was required (19.1% v. 5.6%, P < 0.001) and in twin births (18.5% v. 7.0%, P < 0.05), and was lower in pluriparous v. primiparous dams (5.6% v. 12.1%, P < 0.01). On average, 6.8% of heifers died or were culled between 1 day and 6 months of age. Low BW at 1 month was associated with reduced subsequent survival up to 6 months. Between 6 months and first calving, a further 7.7% of heifers either died (42%) or were culled (58%); accidents and infectious disease accounted for the majority of calf deaths between 6 and 15 months, whereas infertility (16/450 animals served, 3.5%) was the main reason for culling following the start of the first breeding period. In total, 11 heifers (2.2%) were culled as freemartins; eight at birth and three around service. Overall, 14.5% of liveborn potential replacement heifers died or were culled before first calving.     

The effect of Trypanosoma vivax infection on late pregnancy and postpartum return to cyclicity in Boran cattle

A study was designed to examine the effect of infection with Trypanosoma vivax KETRI 2501 on the maintenance of pregnancy and postpartum return to reproductive function in susceptible Galana (n = 6) and trypano-tolerant Orma Boran (n = 6) heifers during the third trimester of pregnancy. Of the 12 study animals, 3 Galana and 3 Orma Boran heifers served as controls. One of 3 Galana heifers calved prematurely with subsequent perinatal loss. Of the 2 heifers that produced live calves, 1 calf died shortly after birth, while the other survived. Two of 3 Orma heifers calved prematurely and all 3 calves died shortly after birth. The 6 control heifers produced live calves at term, all of which survived. Infection with T. vivax during the third trimester of pregnancy delayed the resumption of ovarian activity after calving, with the Ormas taking a significantly (P < 0.05) shorter time from calving to ovulation. There was no clear evidence that premature birth was associated with pathological changes in reproductive organs. Results from this study demonstrated that infection with pathogenic T. vivax during late pregnancy influenced the outcome of pregnancy in both susceptible Galana and trypano-tolerant Orma Boran heifers, resulting in premature births, perinatal loss, retained placentae, low birth weights and a prolonged period to the onset of postpartum ovarian activity.     

Transuterine embryo migration in recipient cattle

Transuterine migration of bovine embryos following fertilization in vivo is apparently rare, but little is known about migration following embryo transfer. We studied heifers receiving either 1 or 2 in vitro produced embryos to determine 1) the incidence of transuterine migration, 2) the timing of migration and 3) the random or systematic occurrence of the event. In 4 experiments, 436 heifers received embryos and 218 of these were pregnant at necroscopy on either Day 14, Day 18, Day 26 or Day 60 of pregnancy. Overall, 43/218 (20%) of the heifers had embryos that had migrated. The frequency of migration was higher in twin (30/68) than in single (13/150) embryo transfers of pregnant recipients (44 vs 9%; P<0.001), and in contralateral (9/15) than in ipsilateral (33/170) transfers (60 vs 19%; P<0.001). Among the heifers that received embryos by ipsilateral transfer, the migration rate was similar to that in heifers pregnant with a singleton after the transfer of either 1 (2/48) or 2 (4/60) embryos (4 vs 7%, NS). The migration rate was highest at Day 26 (12/37) in heifers receiving twin embryos by ipsilateral transfer but was similar at all other stages of pregnancy (15/111, 32 vs 14%; P<0.01). Migration was first observed by Day 14, and it appears that either further migration occurred over the next 12 d or that migration was associated with a higher survival rate from Day 14 to Day 26. The low migration rate evident at Day 60 suggests that migration by Day 26 was associated with increased embryo or fetal death by Day 60. The data suggest that embryo migration is probably independent for each of a pair of surviving embryos. We conclude that in cattle embryo migration is embryo-dependent, but this capability is dormant unless more than 1 embryo is present in a uterine horn or the embryos are transferred to the contralateral uterine horn. The relationship between migration and embryo survival remains unclear.     

Birth of large calves that developed from in vitro-derived bovine embryos

High birth weights were observed in calves that developed from bovine embryos produced by in vitro maturation (IVM) and in vitro fertilization (IVF) procedures. After IVM and IVF, embryos were either co-cultured in vitro with oviductal epithelial cells or transferred into the sheep oviduct for development to the blastocyst stage. Blastocysts were transferred to the reproductive tracts of recipient heifers and cows for development to term. Birth weights and gestation periods were compared between calves that developed from in vitro-derived embryos and calves born after artificial insemination (AI) of cows in the herd from which recipient females were selected. Gestation periods were not different among the groups (P > 0.05), but calves that developed from IVM/IVF-derived embryos co-cultured in vitro were larger at birth than calves born from IVM/IVF-derived embryos that developed into blastocysts in the sheep oviduct and calves born from AI (P < 0.001). Dystocia and calf mortality were associated with large calf size at birth. These data were collected from an experiment designed for other purposes, and confounding variables and small sample size could have influenced the observed differences in birth weights. Nevertheless, the extreme birth weights of some calves suggest that abnormal prenatal growth occurs in some IVM/IVF-derived bovine embryos and that conditions for co-culture to the blastocyst stage may exacerbate the problem.     

The East Flanders Prospective Twin Survey (Belgium): a population-based register.

The East Flanders Prospective Twin Survey (EFPTS), started in 1964, is unique among the 17 major European twin registers because it is population based, the twins (and higher order births) are ascertained at birth, basic perinatal data are collected, chorion type is established and, when appropriate, genetic markers including DNA fingerprints, are determined. The total number of sets is 5089 twin, 158 triplet and 14 of higher order. Zygosity has been diagnosed on the basis of sex, placental structure and genetic markers in more than 95% of pairs. The EFPTS is the only large register that includes placental data and allows differentiation of three subtypes of monozygotic twins based on the time of the initial zygotic division: the dichorionic-diamnionic pairs (early), the monochorionic-diamnionic pairs (intermediate), and the monochorionic-monoamnionic pairs (late). Methodology and basic results in twins are considered in this article; detailed studies will be reported later. The sex proportion in dizygotic (DZ) twins is the same as in singletons, whereas monozygotic (MZ) twins number more girls than boys. The difference in perinatal mortality between DZ and MZ twins is limited to the monochorionic MZ subgroup. Birth weight is highest in DZ twins and diminishes stepwise in MZ dichorionic and MZ monochorionic twins. Duration of pregnancy follows the same trend but is limited to a few days. Iatrogenic pregnancies are increasing to the point of representing almost 50% of the twin births in 1997.