Retrospective study of dystocia in mares at a referral hospital

Recumbency decreases mare and foal survival following in-hospital dystocia management

BACKGROUND

Mare and foal survival are increased with prompt dystocia management. Data regarding mortality outcomes in mares and foals, when mares are recumbent at admission for dystocia resolution, are scarce.

OBJECTIVES

To evaluate recumbency at hospital admission as a risk factor for survival of mares and foals following dystocia management. Subsequent mare fertility was also evaluated.

STUDY DESIGN

Retrospective cohort.

METHODS

Data were obtained from medical records at Rood and Riddle Equine Hospital of mares with dystocia between 1995 and 2018. Mare signalment, ambulation status, survival data and foaling records were collected. The proportion of mare survival and mare fertility were analysed using chi-squared tests. Foal survival was analysed using Fisher's exact test. Odds ratios were calculated using multivariable logistic regression.

RESULTS

There were 1038 ambulatory mares and 41 recumbent mares included in the analysis. Survival rates after dystocia resolution were 90.5% (977/1079) in mares and 37.3% (402/1079) in foals. Ambulatory mares had higher odds of survival (OR 6.93, 95% CI: 3.25-14.78, p < 0.001) than recumbent mares. Foals delivered from ambulatory mares had higher odds of survival (OR 22.7, 95% CI: 3.11-165.44, p = 0.002) compared with foals delivered from recumbent mares. Fertility was not statistically different for surviving Thoroughbred mares within 3 years following dystocia resolution between ambulatory and recumbent mares.

MAIN LIMITATIONS

Retrospective study design and small case number of recumbent mares.

CONCLUSIONS

Mare and foal survival was significantly decreased when mares with dystocia were recumbent at hospital admission. Subsequent fertility, as defined for this study, of surviving mares was not affected by ambulation status at the time of dystocia resolution.

A Case Report of Uterine Body Constriction Precluding Normal Parturition Leading to Dystocia in a Mare

A 13-year-old multiparous Quarter Horse mare was presented to the Michigan State University's, Large Animal Emergency service for dystocia. Clinical evaluation revealed a minimally dilated cervix on vaginal examination, with a palpable deceased fetus. Postmortem evaluation following owner-elected humane euthanasia revealed a circumferential, tan, fibrous band at the base of the uterine body that constricted the uterus and was adhered to the left and right ovaries. A routine histologic section of the incarcerating cord attached to the ovary consisted predominately of dense fibrous connective tissue, large blood vessels, and a central oviduct suggestive of a rent in the broad ligament. To the authors' knowledge, this is the first case report to describe uterine body constriction that precluded vaginal delivery of a fetus in a late gestation mare.

[Definition, incidence and causes of dystocia in horses - a review of the literature]

In horses, birth is classified as dystocia when the process of parturition threatens to inflict damage onto the mare or the foal, when assistance is required to complete the process of parturition, or when there are temporal deviations in the physiological duration of the first and/or second parturition stages. In this, the duration of the second stage is an important indicator in identifying dystocia, as this phase is easily discernible by the mare's behavior. Equine dystocia is classified as an emergency with life-threatening consequences for mare and foal. A large degree of variation has been found in the reported incidence of dystocia. Stud farm surveys reported dystocia in 2-13% of all births, regardless of breed. Fetal malpositioning of the limbs and neck during parturition is described as the most common cause of dystocia in horses. The species-specific length of limbs and neck is considered to be the reason for this finding.

Autonomic nervous system balance in parturient mares: Spontaneous vs induced delivery

Delivery is not easily predictable in horses and the consequences of dystocia can be serious for both the mare and foal. An induction protocol with low doses of oxytocin has been reported as a safe procedure. This study investigates the effect of induced delivery on at-term mares' sympathetic-vagal balance. Fourteen mares were included and divided into two groups, one subjected to spontaneous delivery (SD), and one to induced delivery (ID). In both groups, an ECG was recorded using an elastic belt with integrated smart textile electrodes. The recording started before the delivery (Basal), continued close to delivery (Pre-delivery) and during delivery (Delivery), and ended after parturition (Placental expulsion). From the ECGs, Heart Rate Variability (HRV) parameters relating to time and frequency domains and non-linear analysis were extrapolated. The HRV analysis was performed both within the same group (IntraGA) and between the two groups (InterGA). In the present study, spontaneous and induced delivery did not appear to differ in autonomic nervous system functioning. In IntraGA analysis, both for SD and ID mares, delivery and placental expulsion periods were parasympathetic dominated since vagal-related HRV parameters increased. Moreover, no differences were found in InterGA comparison between SD and ID mares, except for the pre-delivery period of ID mares, during which both branches of the autonomic nervous system were activated. These results are in line with the literature on parasympathetic dominance during parturition and no change in Heart Rate Variability following exogenous oxytocin administration in parturient mares.

Dystocia in the Standardbred Mare: A Retrospective Study from 2004 to 2020

Dystocia as a prolonged stage II parturition (>30 min) was associated with a higher risk of complications. The hypothesis of the study was that any type of dystocia could affect the foal’s health, even when the stage II was <30 min. Clinical reports on 222 Standardbred mares and their foals hospitalized at the Veterinary Teaching Hospital of the University of Bologna from 2004 to 2020 were reviewed. Mares were divided into the Eutocia Group (165, eutocic delivery) and the Dystocia Group (57, dystocic delivery). The incidence of dystocia was 4.9%. Stage II was longer in the Dystocia Group (median 20 min) than in the Eutocia Group (median 12 min). All occurrences of dystocia were retrospectively classified into three categories of severity: mild, moderate and severe dystocia. The occurrence of postpartum complications in mares and neonatal diseases and failure of passive transfer of immunity in foals was higher in the Dystocia Group. Foal venous lactatemia and serum creatine kinase were significantly higher in the Dystocia Group (median 3.9 mmol/L; 262 UI/L respectively) than in the Eutocia Group (median 3.1 mmol/L; 187 UI/L respectively). The APGAR score was lower in the Dystocia Group (median 8) than in the Eutocia Group (median 10) and significantly lower in severe dystocia (median 3). The duration of stage II should not be considered the only parameter of dystocia in mares: even a rapid resolution of dystocia could pose health risks to the foal and the mare.

Managing Reproduction Emergencies in the Field: Part 2: Parturient and Periparturient Conditions

Selected conditions affecting broodmares are discussed, including arterial rupture, dystocia, foal support with ex utero intrapartum treatment, uterine prolapse, postpartum colic, the metritis/sepsis/systemic inflammatory response syndrome complex, and retained fetal membranes. Postpartum colic beyond third-stage labor contractions should prompt comprehensive evaluation for direct injuries to the reproductive tract or indirect injury of the intestinal tract. Mares with perforation or rupture of the uterus are typically recognized 1 to 3 days after foaling, with depression, fever, and leukopenia; laminitis and progression to founder can be fulminant. The same concerns are relevant in mares with retention of fetal membranes.

Causes of equine perinatal mortality

The peripartum period is critical in equine medicine for maintaining healthy mares, and ensuring the delivery of healthy neonatal foals. The field of perinatal mortality in horses is continuously evolving, with several advances being recently made in causes of perinatal fetal and foal loss. This review details the main causes of perinatal loss in horses, through late pregnancy, parturition and the neonatal period. Recent advances in identification of infectious organisms and indicators of survival in neonatal foals will be discussed. Continued advances in reproductive and neonatal medicine will aid improved survival of foals through fewer pregnancy losses, and improved management of high-risk pregnancies and critically ill neonatal foals.

Peripartum findings and blood gas analysis in newborn foals born after spontaneous or induced parturition

Induction of parturition in horses is still not well accepted due to the potential peripartum complications for mares and newborn foals. We assessed differences after spontaneous and induced parturition with low doses of oxytocin (OX) in 1) incidence of peripartum complications in mares; 2) viability, behavioral, physical, and venous blood gas analyses in foals. In this study 61 mares were included; 45/61 were enrolled in the spontaneous foaling group (SF) and 16/61 in the induced foaling group (IF). In the IF group, when the calcium in mammary secretion reached concentrations of ≥250 ppm, mares received a single injection of 2.5 IU of oxytocin IV once a day until foaling. Mares' breed, age, parity, gestational and stage II length, and peripartum complications were recorded. Foal maturity, vital (Apgar score), behavioral and physical parameters were assessed at birth, and the foal clinical condition was monitored for one week. A jugular venous blood sample was collected at birth for blood gas analysis, acid-base status, and lactate assessment. The median gestational length was within the reference interval in all the mares included and did not differ between the two groups. No statistical differences in the II stage length nor in incidence of peripartum complications were observed between the two groups. All the foals were born alive and showed no signs of prematurity/dysmaturity. No statistical differences were found in foal viability between the two groups. Time to stand and nurse from the mare, and body temperature were significantly higher in the IF compared to the SF group. Venous blood pH, SO₂% and BE were lower, while pCO₂ and lactate were higher in the IF than in the SF group. All the foals in both groups remained clinically healthy during the observation period. In conclusion, at term induction of parturition with a low dose of oxytocin does not have adverse effects on peripartum in mares. Our findings suggest that at term induced foals suffer slightly greater, but not clinically significant, hypoxia, hypercapnia and acidosis than spontaneously delivered foals.

Clinical and pathological findings for rabbits with dystocia: 10 cases (1996-2016)

OBJECTIVE

To characterize clinical and pathological findings of rabbits evaluated at a veterinary teaching hospital because of dystocia.

DESIGN

Retrospective case series.

ANIMALS

9 client-owned rabbits and 1 wild rabbit with signs of dystocia evaluated at a veterinary teaching hospital from 1996 through 2016.

PROCEDURES

Medical records of rabbits were reviewed to collect data on signalment; medical history; physical examination, laboratory, diagnostic imaging, and procedural findings; treatment; final diagnosis; and outcome. Data were summarized.

RESULTS

Dystocia in 7 rabbits was successfully managed through medical treatment, assisted vaginal delivery, or both (n = 6) or surgery alone (1); 3 rabbits were euthanized. Primiparous does, does ≤ 4 years old, and does of small breeds (< 2 kg [4.4 lb]) were most common. All client-owned rabbits had clinical signs of abnormal second-stage parturition, whereas the wild rabbit had only hemorrhagic vulvar discharge. Imaging was used to identify the number, size, and state of fetuses in most rabbits. Overall, 35 fetuses were accounted for, 25 of which were dead or later died. The cause of dystocia was determined for 8 rabbits and included fetal-maternal mismatch (n = 4), uterine inertia (2), fetal death or mummification (1), and stress-induced abortion (1).

CONCLUSIONS AND CLINICAL RELEVANCE

Obstructive dystocia from fetal macrosomia with or without secondary uterine inertia was the most common cause of dystocia in the evaluated rabbits. Although medical management was successful for many rabbits with dystocia in this study, surgery could still be required in other affected rabbits, particularly when fetal-maternal mismatch is involved.

Controlled delay of the expulsive phase of foaling affects sympathoadrenal activity and acid base balance of foals in the immediate postnatal phase

Stress at foaling has been demonstrated to delay birth. In this study, we followed the hypothesis that even a short delay of foaling increases catecholamine and cortisol release in foals, induces acidosis and impairs neonatal adaptation. Foaling was prolonged for 5 min by transferring mares to an unfamiliar environment at rupture of the allantochorion (group delay, n = 6) while control mares (n = 5) were left undisturbed. In their foals, times from birth to first standing and first suckling, heart rate, heart rate variability (HRV) and salivary cortisol concentration were analysed. Blood for analysis of epinephrine, norepinephrine, hematology and blood gases was collected directly and 30 min after birth. Statistical comparisons were made by repeated measures ANOVA. Times to first standing and suckling did not differ between groups. Fetal heart rate remained unchanged during birth and increased within 15 min postnatum (p < 0.001) while HRV decreased during the first hour of life in foals of both groups (p < 0.05). Immediately after birth, actual base excess was lower in foals with delayed birth than in control foals (p < 0.05). Epinephrine concentration immediately after birth was higher in group delay foals and increased from 0 to 30 min after birth in control foals (time p < 0.001, time x group p = 0.001). Cortisol concentration peaked at 1 h after birth in both groups (p < 0.001). Leukocyte and PMN count decreased from 0 to 30 min after birth (p < 0.001). In conclusion, a 5-min delay at foaling affected epinephrine release and acid base balance, but was without further effect on neonatal adaptation.

Effects of dystocia on blood gas parameters, acid-base balance and serum lactate concentration in heavy draft newborn foals

Dystocia is often lethal for neonatal foals; however, its clinicopathological features remain largely unknown. We investigated the effect of dystocia on the foal blood profile. Venous blood samples were collected from 35 foals (5 Percheron and 30 crossbreds between Percheron, Belgian, and Breton heavy draft horses) at 0 hr, 1 hr, 12 hr and 1 day after birth. Dystocia was defined as prolonged labor >30 min with strong fetal traction with or without fetal displacement. The dystocia group (n=13) showed lower mean values for pH (P<0.01), bicarbonate (P<0.01), total carbon dioxide (P<0.05), and base excess (P<0.01) and higher mean values for anion gap (P<0.05) and lactate (P<0.01) immediately after birth than the normal group (n=22). Remarkably high pCO₂ values (>90 mmHg) were observed in three foals in the dystocia group but in none of the foals in the normal birth group immediately after birth. These results suggest that dystocia results in lactic acidosis and may be related to respiratory distress.

Prognostic Indicators for Survival and Athletic Outcome in Critically Ill Neonatal Foals

Equine neonatal intensive care units have expanded knowledge and understanding of the normal and abnormal physiology of the equine neonate, resulting in successful treatment of critically ill equine neonates. The overall survival rate has increased tremendously since the early 1980s, from a little more than 50% to 80% or more for most facilities. The severely septic foal and the very premature foal still remain large treatment challenges, but less severely septic foals and foals challenged by adverse peripartum events such as dystocia and placentitis are surviving to hospital discharge and performing to the owners' expectation in larger numbers.

Dystocia in dromedary camels: Prevalence, forms, risks and hematobiochemical changes

The objectives of this study were to investigate the prevalence of dystocia in camel herds, its forms in primi- and multipara, the risks to fetus and dam, and the associated hematobiochemical changes. A total of 1890 calvings were surveyed for the prevalence of dystocia. Cases with dystocia (n=107) were examined for causes and treated with traction, fetotomy or Cesarean section. Logistic regression was performed to identify risk factors. The dependent variables were the fetal and maternal mortality, while the independent variables were parity, duration of dystocia, causes of dystocia, and method of treatment. Blood samples were collected from all dystocia camels and six controls for hematology and concentrations of serum amyloid A (SAA), haptoglobin (Hp), estradiol-17β (E2), progesterone (P4), total protein, albumin, calcium, phosphorus, magnesium, blood urea nitrogen (BUN), creatinine and aspartate aminotransferase (AST). The overall prevalence of dystocia was 8.6%. Risk of dystocia was higher in camels managed in an intensive system than in those in a free system (Odds ratio=1.9, P=0.0003) and higher in primipara than in multipara (Odds ratio 1.7, P=0.005). Abnormal posture was the most important cause of dystocia (51.4%). Uterine torsion was the second most important cause (23.4%) and was mainly observed in multipara (P=0.0006). Dystocia was linked to high fetal mortality (87.9%). A significant relationship was found between fetal death and duration of dystocia (Odds ratio=8.04, P=0.005). The percentage of dam mortality was 17.8%. Significant associations were detected between dam mortality rate and the duration of dystocia (Odds ratio=4.74, P=0.03) and fetal viability (Odds ratio=5.82, P=0.02). Increasing duration of dystocia was associated with significant increases in SAA, Hp, BUN and AST, but with decreases in E2 (P<0.05). After a transient period of elevation, the white blood cell and neutrophil counts decreased (P<0.05). In conclusion, abnormal posture and uterine torsion were found to be the common causes of dystocia in dromedary camels, and fetal and maternal deaths were mainly associated with the duration of dystocia.

Fertility after fetotomy: a clinical study focusing on heavy draft mares

Although fetotomy is recommended for all mares when the fetus is dead and difficult to extract, little has been written about fetotomy and heavy draft mares. This lack includes indications for fetotomy in heavy draft mares, differences in treatment and prognosis of heavy mares kept by farmers of low socioeconomic status, and how this procedure affects the mare's further fertility. The literature on mares, in general, also differs on the survival rate of mares that undergo fetotomy, the prevalence of postpartum complications, and further fertility. To answer these questions, we reviewed the medical records of 102 mares that underwent fetotomy, mostly heavy draft mares (n=93). Head malposture (62.7 per cent) was the most common fetal maldisposition, which required fetotomy in all cases. The survival rate was 84.3 per cent (n=86). The most common postpartum complications were endometritis puerperalis (32.5 per cent) and retained placenta (27.9 per cent). 61 mares (70.9 per cent) both showed foal heat and cycled regularly in the first season after fetotomy. Out of 45 mares that were bred in the first season, 14 became pregnant (31.1 per cent). Survival rate and further fertility were reduced by delayed requests for veterinary assistance due to the difficult economic situation of the owners. Fetotomy is the method of choice for serious maldispositions, especially head malpostures, because in contrast with cesarean sections, it has a higher survival rate and allows the mare to return to breeding in the same season.