Clinical studies on bovine parturition. Maternal causes of dystocia and stillbirth in an experimental herd of Hereford cattle

Occurrence of neonatal and postnatal mortality in range beef cattle. I. Calf loss incidence from birth to weaning, backward and breech presentations and effects of calf loss on subsequent pregnancy rate of dams

Data from 13,296 calvings collected over a 15-yr period indicated 893 calves died from birth to weaning for an average loss of 6.7%. Calves lost from birth through Day 3 postcalving accounted for a 4.6% loss with an additional 2.1% loss from Day 4 through weaning. Calf deaths from primiparous 2- and 3-yr-old dams accounted for 41.0% of total mortality. Losses within groups were primiparous 2-yr-olds, 10.9%; primiparous 3-yr-olds, 8.7%; second-calf 3-yr-olds, 4.1%; second-calf 4-yr-olds, 8.3%; multiparous 4-yr-olds, 4.8%; and dams 5 yr and older, 5.3%. The majority of calf deaths (57.4%) occurred within the first 24 h postpartum with 75% of the total occurring Days 0 through 7. This loss was similar among all dam age and parity groups. Calf death due to dystocia accounted for the single largest loss category through the first 96 h postpartum, resulting in 69.6, 39.6, 30.8 and 33.3% of the loss incidence for Day 0, 1, 2 and 3 postpartum, respectively. More (P < 0.01) male calves (510, 57.6%) died than females (376, 42.4%). Backward presentations occurred more frequently (P < 0.01) than breech (1.6 vs 0.6% of all births, respectively). Incidence of backward presentation was 2.3%, 5.6% and 0.9% for primiparous 2-yr-old, 3-yr-old and multiparous dams, respectively (P < 0.01); 64.2% of the backward calves were males and 35.8% females (P < 0.01). Survival of calves in backward presentation exceeded (P < 0.01) that of breech calves (70.7 vs 32.9%). Fall pregnancy rate of dams that lost calves and reentered the breeding herd that same year was 72.4% compared to 79.4% (P < 0.01) for contemporary females that did not lose calves. The depression in pregnancy rate was not specifically due to dystocia but apparently to some general effect of calf loss.

Extraction forces in bovine obstetrics: an in vitro study investigating alternate and simultaneous traction modes

Whether extraction of a calf in longitudinal anterior presentation should be carried out by simultaneous or alternate traction on the forelimbs remains controversial. Because most recommendations are based on empirical observations rather than on scientific studies, the aim of this study was to develop an in vitro model to objectively compare the forces occurring during alternate and simultaneous traction. In a biomechanical in vitro model, 12 dead Holstein-Friesian (Bos taurus) calves were pulled through the prepared pelvic specimen of a cow at a controlled speed using two electric motors. Traction was applied simultaneously (ST) to both legs or alternately (AT) to one leg at a time to advance the calf 5 cm (AT 5) or 10 cm (AT 10). Forces on each limb were measured digitally using load cells. In all cases, two peaks of maximum force occurred during the extraction of the cranial part of the body. The first peak was observed when the elbows were pulled into the pelvis, and the second peak occurred when the chest emerged from the pelvis. Up to and including entry of the elbows into the pelvis, the maximum force on a single limb (341+/-106 N) was lowest (P<0.01) using AT10. The maximum traction forces acting on a single limb using AT5 (411+/-86 N) and ST (431+/-127 N) did not differ (P>0.05). During extraction of the thorax, the maximum force acting on a single limb was lower (P<0.0001) using ST (352+/-98 N) compared with AT5 (432+/-79 N) and AT10 (547+/-115 N). Based on these findings, alternate-limb traction, 10 cm at a time, should be used until both elbows have entered the pelvis. Simultaneous traction should then be applied to both forelimbs to complete extraction of the chest.

Duration of parturition and frequency of abdominal contractions in primiparous, 2-year-old Angus heifers and the relevance of body dimensions of calves to dystocia

The predominant cause of dystocia in 2-year-old heifers is feto–maternal disproportion, and consequently, birthweight of the calf explains much variation in dystocia. This experiment was carried out to identify other factors in addition to birthweight that contribute to the probability of dystocia. Seventy-three primiparous, 2-year-old Angus heifers were observed continuously during the calving period and record was made of the time at which various events occurred during parturition. Frequency of abdominal contractions was lower 30 min after onset of parturition than at 60–180 min after onset of parturition (P < 0.05). The longest stage of parturition was the time from the first abdominal contraction until the appearance of amnion, while the time from the appearance of the head until delivery of the calf was the shortest stage. Frequency of abdominal contractions was negatively correlated with duration of parturition. Duration of parturition was less than 135 min for 75% of the non-assisted heifers. Body dimensions of calves did not explain any additional variation in dystocia beyond that explained by birthweight and sex of calf and postpartum liveweight of the heifer. Calves that had an assisted birth took longer to attempt to stand, to stand and to suckle after birth than non-assisted calves. Within the non-assisted calves, there was no impact of duration of parturition on these behaviours of the newborn calf. In conclusion, body dimensions of the calf did not contribute to the probability of dystocia, but more frequent abdominal contractions contributed to a shorter duration of parturition. Behaviour of newborn calves was adversely affected by dystocia.

Dystocia in beef heifers: a review of genetic and nutritional influences

Breeding beef heifers for the first time at 15 months of age has potential to increase the efficiency of the beef breeding-cow herd. An increased incidence of dystocia in heifers calving at 2 years of age, compared to mature cows, is a major reason many farmers in New Zealand have not adopted the practice. The predominant type of dystocia affecting 2-year-old heifers is feto-maternal disproportion, a condition in which the fetus is too large relative to the size of the heifer's pelvis. Reducing birthweight of the calf is a means of reducing the incidence of dystocia. Birthweight and length of gestation are determined by genotype of the calf, maternal genetic effects and environmental effects. Bulls with low estimated breeding values for birthweight have been selected for mating heifers; however, the positive genetic correlation between birthweight and mature weight meant that the progeny of these bulls tended to be lighter at finishing, making them less desirable in the beef industry. The genotype of the dam also plays a role in determining the risk of dystocia; the maternal ability of the dam to nurture the fetus influences birthweight, and the dam's genetic potential for growth influences the size of her pelvic area. Heavy heifers tend to produce high birthweight calves, counteracting the reduction in the incidence of dystocia resulting from the larger pelvis in larger heifers. Manipulating feeding level during pregnancy offers an alternative method for manipulating the birthweight of calves. Little is known about the effects of nutrition in early gestation on placental development or birthweight of calves. No differences in the birthweight of calves have been observed in response to variation in feeding in mid-pregnancy, and variable responses in birthweight and the incidence of dystocia to feeding in the third trimester of pregnancy have been reported. Differences in birthweight have not always resulted in differences in the incidence of dystocia, primarily due to differences in liveweight of the heifer also induced by feeding regimens. Variability in the incidence of dystocia in response to feeding level in the third trimester of pregnancy makes it difficult to make recommendations for the feeding of heifers at this stage of gestation. More research is needed into the effects of nutrition in early gestation on fetal and placental development in cattle.

Managing the dairy cow at calving time

Managing the dairy cow at calving, unlike artificial insemination or transrectal ultrasonography, is often perceived as an unskilled task, not requiring specialist training. This article presents the argument for the financial and welfare costs associated with poor periparturient management, and how to address them by veterinarian-led education and upskilling of herd personnel. Successful management of the dairy cow at calving will result in the birth of a healthy calf and a smooth transition of the cow into the milking string with minimal calving problems and their sequelae. The tenets of good calving management are predicting accurately when calving is due, moving cows to the maternity unit on time, discrete calving supervision, knowing when and how to intervene, and ensuring the calf is vigorous and fed colostrum and the cow is healthy postpartum.

Thoracic trauma in foals: post mortem findings

REASONS FOR PERFORMING STUDY

Thoracic trauma occurs in newborn foals and may cause associated clinical signs; this condition remains poorly documented.

OBJECTIVES

The purpose of this study was to describe the pathological features of thoracic trauma in newborn foals presented for necropsy examination between 1990 and 2000.

METHODS

Necropsy reports of foals with thoracic trauma from 1990-2000 were reviewed. Subject details, clinical signs, thoracic and abdominal lesions were noted and analysed statistically.

RESULTS

Sixty-seven (9%) of 760 necropsied foals had thoracic trauma. In 19 foals, fractured ribs were considered to be the cause of death (Group A). The remaining foals had fractured ribs (Group B, n = 20) or rib contusions (Group C, n = 28) that were incidental findings. Ribs 3 to 8 accounted for 86% of the traumatised bones. The most common site of injury was the costochondral junction and an area immediately above it (94%). In Group A, all but 2 foals died within the first 8 days postpartum. Haemothorax and subsequent pulmonary collapse was cited most commonly as the cause of death (53%). Diaphragmatic rupture and hernia (n = 2) also occurred.

CONCLUSIONS

The focal site, consistent location and presence of lesions during the first week post partum, all suggest that thoracic trauma in newborn foals probably occurs during parturition.

POTENTIAL RELEVANCE

The description of lesions and site of occurrence of thoracic trauma in foals will increase awareness and improve the diagnosis and treatment of this life threatening condition.

Thoracic trauma in newborn foals

In a report describing life ending fractures (255 horses) from the Livestock Disease Diagnostic Center, Kentucky (1993 and 1994), 32 foals had rib fractures. The purpose of our study was to examine the incidence of rib fractures in newborn foals on a Thoroughbred studfarm by physical and radiographic examination, to determine factors which may contribute to the problem and to document any clinical consequences. All foals (263) included were examined within 3 days of birth. The thoracic cage was palpated externally for abnormalities and all foals were placed in dorsal recumbency to evaluate thoracic cage symmetry. Radiographs were used to diagnose foals with thoracic cage asymmetry (TCA) and rib fracture (RF). A diagnosis of costochondral dislocation (CD) was made when no radiographic evidence of fracture was present but there was severe TCA. Fifty-five foals (20.1%) had TCA (9 RF). One to 5 ribs were fractured on 9 of 40 radiographic studies. No consequences of the thoracic trauma was detected clinically, radiographically or ultrasonographically in this group of foals or at a 2- and 4-week follow-up examination. The percentage of foals with a history of abnormal parturition was higher in the TCA foals (15%) compared to the normal foals (6.8%). There were more primiparous dams in the TCA group than in the normal foal group. Fillies (56.6%) had a higher incidence of birth trauma than colts (43.4%). This study demonstrates that thoracic trauma is often present in newborn foals and may not always be of clinical significance. Dystocia foals and foals from primiparous mares should be considered high risk for thoracic trauma.

Effect of calving supervision upon the calving performance of Hereford heifers

The calving performance of 268 two-year-old Hereford heifers was studied in 2 commercial herds and at a research station to compare supervision and non-supervision during calving. Supervision in the 3 herds involved twice-daily paddock inspections of calving heifers using a vehicle and the provision of obstetrical aid to those in difficulty. The unsupervised controls were inspected once weekly and were not assisted. The supervised heifers experienced a higher incidence of live-natural births and fewer dead calves compared with the unsupervised heifers. Dam survival rates were significantly (p less than 0.05) increased in all supervised treatments. Calving supervision was justified by higher survival of both heifers and calves as well as humans considerations. It was endorsed as a worthwhile management practice in commercial herds with significant levels of dystocia in calving heifers.

The effect of nutritional restriction of Hereford heifers in late pregnancy

Two experiments were conducted to examine the consequences of attempting to control dystocia in Hereford heifers by restricting nutrition during late pregnancy. Nutritional level was controlled by varying feedlot rations in experiment 1 and by varying pasture availability in experiment 2. In neither experiment was the incidence of dystocia or stillbirths significantly affected by level of nutrition during late pregnancy. Calf birthweight was reduced and dam pelvic growth was retarded when the feed intake of heifers was restricted prior to calving. Clear evidence of the dangers associated with allowing heifers to lose too much weight in late pregnancy was provided by these experiments. The loss of around 0.5 kg/day during the last trimester of pregnancy was associated with weak labour, increase dystocia rates, increased perinatal mortality, reduced calf growth rate, prolonged post partum anoestrus and a reduced pregnancy rate (not all statistically significant differences). These effects were not evident in heifers which were maintaining or gaining weight at a moderate rate during late pregnancy. On the basis of this work it is suggested that heifers should be fed to allow modest rates of bodyweight gain (0--0.5 kg/day) during late pregnancy.

Effect of birth weight on efficiency of beef production

The large 'lean beef' breeds are vulnerable to calving difficulties and losses. Dystocia is related to high birth weight. Data recorded from evaluation experiments show that the birth weight of the 'lean beef' taurus crossbreeds was high (39+/-2.1 kg). Indicus beef genotypes were selected with the birth weight (29+/-1.9 kg) significantly lower (P is less than 0.01) without a depression in the final yield of beef. To increase efficiency of beef production the lower birth weight factor needs be incorporated into genotypes for high viability and growth. Profitability depends on output per dam, in relation to inputs, on a herd basis. Hence, progress may depend on the application of such changes of genotype.

The plasma zinc concentration of nonpregnant, pregnant and parturient Hereford cattle

Studies were made on several groups of Hereford cattle to determine the plasma zinc concentration at various phases of their reproductive life. In nonpregnant heifers a major cause of variation was due to differences between individual animals. Seasonal changes were also evident but little difference was noted in the zinc levels of cattle sampled at particular stages of the oestrous cycle or over a 24-hour period. Following conception, the plasma zinc levels remained relatively constant until late in pregnancy when a decline occurred. A more marked decline occurred during the periparturient period although the trends observed differed between animals that calved normally and those that suffered from dystocia. Samples obtained from calves approximately 24 hours after delivery contained zinc at concentrations of more than double that recorded for their dams.

Prepartum serum hormone concentrations related to dystocia in Holstein heifers

Twelve Holstein heifers from a herd having a high incidence of dystocia were bled each day at 0730 h from 260 days gestation until parturition. The blood was analyzed for estradiol-17beta, estrone, 17-hydroxyprogesterone, progesterone, and corticosteroids. Six of the animals had dystocia. The concentrations of estradiol-17beta were lower and the concentration of progesterone higher in dystocial animals during the prepartum period from 23 to 12 days. The prepartum patterns of secretion of corticosteroid, estrone, and 17-hydroxyprogesterone did not change significantly in the two groups between days 23 and 12 prepartum. The prepartum difference in serum estradiol-17beta and progesterone concentration between normal and dystocial animals suggests that the timing of hormone changes in preparation for parturition is delayed and not as pronounced in dystocial animals.

A survey of dystocia in beef cattle in Southern Queensland

Data relating to dystocia were obtained for 22% of beef herds in the Roma region of southern Queensland. In 1973 dystocia incidence in 23,129 maiden heifers was 12%; 4% of heifers and 7% of calves died. Thirty-five per cent of the 444 herds surveyed had more than a 10% incidence of dystocia, and 10% had more than a 30% incidence of dystocia. Only 6% of herds had no dystocia. Among the 73% of producers considering dystocia a problem in most years, 14% regarded it as a major problem. The incidence of dystocia in heifers was significantly higher in Poll Hereford than Hereford herds, which in turn were higher than other breeds of cattle. Poll Hereford and Hereford owners were the most concerned about dystocia but did not supervise calving more frequently. Dystocia and attitude were also examined in relation to degree of supervision at calving and size of the breeding herd.