# Uterine Atony: Causes and Management in Animals Uterine atony (atony of uterus) is the failure of the myometrium, the muscular wall of the uterus, to generate the strong coordinated contractions that expel a fetus. When the uterus will not contract, labor stalls even though the birth canal is open and the fetus is correctly positioned. The single most important clinical decision is to distinguish a uterus that is not contracting from a fetus that physically cannot pass. Oxytocin, the drug most owners and many clinicians reach for first, is contraindicated when an obstruction is present because it can drive a uterus into rupture against a blocked outlet. A published case report describes exactly this outcome in a Great Dane bitch treated with repeated oxytocin doses and manual assistance, which resulted in uterine rupture and septic peritonitis [1]. This article is educational and is not a substitute for veterinary diagnosis or treatment. ## Owner Triage: What to Do Right Now If your dog, cat, cow, ewe, mare, or sow has been in active labor and no offspring has been delivered within the expected interval, treat it as an emergency. Call a veterinarian before giving any medication. Key triage points: - **Do not give oxytocin at home.** Oxytocin is a prescription hormone with species-specific and label-specific dosing, and it is dangerous if the fetus is obstructed. - **Do not pull on a fetus** unless a veterinarian has confirmed the fetus is in the canal and instructed you how to assist. - **Note the timeline.** Record when hard straining started, when the last offspring was born, and whether any fluid or fetal membranes have passed. - **Check the mother's gums and mentation.** Pale gums, collapse, tremors, or a distended painful abdomen are red flags for rupture, hemorrhage, or sepsis. - **Keep neonates warm and dry** while you arrange transport. Newborns lose body temperature quickly after birth. ## At a Glance: Causes, Signs, and First-Line Actions by Species | Species | Most common atony pattern | Typical clinical signs | First-line veterinary action | |--|--|--|--| | Dog (bitch) | Primary uterine inertia, often with low ionized calcium or low oxytocin | Weak or absent straining, long intervals between pups, green-black discharge without a pup | Assess for obstruction, check ionized calcium, consider calcium and oxytocin only if the canal is clear, proceed to cesarean if medical therapy fails | | Cat (queen) | Primary inertia, often with small litters | Prolonged resting stage, no kitten after strong contractions, vocalizing | Similar to the bitch, but cesarean is often preferred over repeated oxytocin | | Cow | Hypocalcemia-associated atony, especially in older high-producing dams | No abdominal effort, retained fetus, recumbency, cold extremities | Calcium borogluconate intravenously, then reassess, assisted delivery or cesarean if needed | | Ewe | Hypocalcemia and twin pregnancy | Dull, no straining, weak or absent reflexes | Calcium borogluconate, then assisted delivery | | Mare | Rare, often secondary to obstruction or exhaustion | Rapid deterioration, signs of shock | Emergency referral, cesarean is the usual path | | Sow | Secondary inertia after prolonged farrowing | Long interval between piglets, weak contractions | Manual exam, calcium if indicated, oxytocin only after obstruction is ruled out | ## Anatomy and Physiology of Uterine Contraction The uterus has two muscle layers, an outer longitudinal layer and an inner circular layer. During labor these layers contract in a coordinated wave that pushes the fetus toward the cervix while the cervix relaxes. Two systems drive this wave. **Hormonal drive.** Oxytocin from the posterior pituitary binds to oxytocin receptors (OXTR) on myometrial cells. Receptor density rises sharply near term. In the dog, uterine and placental oxytocin receptor expression is constant from before implantation through mid-gestation, then increases significantly at prepartum luteolysis, the point when the corpus luteum stops producing progesterone [2]. Progesterone withdrawal is what allows the uterus to become responsive. Prostaglandin F2 alpha (PGF2 alpha) also drives contraction and helps complete luteolysis. **Calcium drive.** Myometrial contraction depends on calcium entering the muscle cell. Ionized calcium is the physiologically active fraction. When ionized calcium falls, the muscle cannot generate force even if oxytocin and its receptor are present. This is why hypocalcemia is a leading cause of atony in cattle and ewes, and a contributing factor in dogs. **Energy and acid-base drive.** Prolonged labor depletes glucose and creates lactic acidosis in the muscle. A tired, acidotic uterus contracts poorly. This is the basis of secondary inertia. ## Primary Uterine Inertia Primary uterine inertia (PUI) means the uterus fails to contract from the start. There is no preceding period of normal effective labor. The fetus is usually in the correct position, the cervix is open or opening, and yet the myometrium does not generate adequate force. ### Causes of Primary Inertia - **Low circulating oxytocin.** In a study of 27 bitches with primary inertia, plasma oxytocin concentrations were low (35 ± 15 pmol/L in one treatment group and 30 ± 15 pmol/L in the other), and the authors concluded that low plasma oxytocin is a cause of primary inertia in bitches with normal serum calcium, and worsens the condition when calcium is also low [3]. - **Low ionized calcium.** Bitches from a population with a history of increased uterine inertia and stillbirths had lower ionized calcium (1.31 ± 0.08 mmol/L) and higher parathyroid hormone than a comparison group during the periparturient period [4]. A 2026 review of canine pregnancy complications lists lower than normal maternal peripheral oxytocin and blood ionized calcium concentrations as factors in PUI, along with placental dysfunction that reduces PGF2 alpha production [5]. - **Receptor abnormalities.** A study comparing uterine tissue from bitches with PUI and bitches with obstructive dystocia found that OXTR and progesterone receptor (PGR) expression ratios were significantly higher in PUI (OXTR p = 0.0019, PGR p = 0.0339) [6]. The authors proposed that OXTR may be upregulated in PUI as a counterregulatory attempt to overcome myometrial quiescence, or downregulated in obstructive dystocia due to receptor desensitization after prolonged labor [6]. - **Hormonal imbalance.** Bitches with primary inertia had a higher progesterone to PGFM ratio than controls, and lower oxytocin and vasopressin concentrations when the last puppy was delivered [7]. Progesterone concentrations were highest in bitches having elective cesarean and significantly higher than in obstructive dystocia and combined dystocia groups in a separate study [8]. - **Litter size effects.** The same receptor study found the lowest PGR myometrial score in PUI bitches with large litters (p = 0.0391), suggesting litter size interacts with receptor expression [6]. - **Breed and age.** In a study of 530 dogs, miniature and small breeds made up 59.4% of dystocia cases, and older primiparous bitches over 6 years of age had a significantly higher risk of obstetric complications and stillbirths [9]. ### What Primary Inertia Looks Like The classic picture is a bitch or queen that goes through the nesting and nesting behaviors of stage one labor, may pass a small amount of green-black discharge (uteroverdin, the placental pigment that signals placental separation), and then simply stops. There may be weak, ineffective abdominal contractions or none at all. The interval between offspring stretches well beyond normal. The mother is often bright and not in distress early on, which can falsely reassure owners. ## Secondary Uterine Inertia Secondary inertia is exhaustion of a uterus that was contracting normally. The muscle has been working, often for hours, and has run out of energy or become acidotic. Secondary inertia is a consequence, not a primary disease. ### Causes of Secondary Inertia - **Prolonged labor** from any cause, including large fetal size, malpresentation, or a narrow birth canal. - **Obstructive dystocia that has been ongoing.** The uterus contracts against a fetus that cannot pass, then fatigues. - **Metabolic exhaustion.** Low glucose, dehydration, and acid-base derangement. - **Hypocalcemia that develops during labor**, especially in cattle and ewes. The distinction matters because secondary inertia often coexists with obstruction. Treating it as simple atony and giving oxytocin can rupture the uterus [1]. ## Obstructive Dystocia: The Critical Differential Obstructive dystocia means the fetus cannot pass because of a physical barrier. Causes include fetal malposition (for example, a head or limb back), fetal oversize, a narrow pelvis, or a uterine torsion. In obstructive dystocia the uterus may contract vigorously at first and then fatigue, producing a picture that looks like secondary inertia. The rule is simple. **Rule out obstruction before giving oxytocin.** If a fetus is stuck, oxytocin increases pressure against the blockage and risks uterine rupture. A case report documents rupture and septic peritonitis in a bitch after repeated oxytocin and manual assistance [1]. In the receptor study, obstructive dystocia was associated with a different receptor profile than primary inertia, supporting the view that these are distinct entities [6]. ## Species Differences in Presentation and Management ### Dogs Dystocia affects 5% to 37% of all canine whelpings and is a significant risk to both newborns and the mother [5]. Primary uterine inertia is the most frequently diagnosed type of dystocia in the bitch [5]. In a study of 530 dogs, uterine forces (inertia and spasm), fetal malpresentation, and litter size were the most common causes, and the duration of the expulsion stage had the highest influence on puppy survival (p < 0.001) [9]. Medication with oxytocin led to higher puppy losses than other medicaments in that study [9]. Calcium status in dogs is not a simple story. A guide dog population study found no significant difference in ionized calcium between bitches that did or did not develop mastitis, metritis, or dystocia at any time point [10]. However, bitches from a population with a history of increased uterine inertia and stillbirths had lower ionized calcium and higher parathyroid hormone than a comparison group [4]. The practical takeaway is that ionized calcium should be measured, and hypocalcemia corrected when present, but calcium is not universally low in every atonic bitch. A study of 27 bitches with primary inertia found that combining intravenous calcium with oxytocin did not improve outcomes over oxytocin alone. The number of bitches needing cesarean and the number of puppies born did not differ between groups [3]. This does not mean calcium is useless. It means calcium helps when calcium is actually low, and the study population had normal serum calcium (2.1 ± 0.2 mmol/L in both groups) [3]. ### Cats Uterine dysfunctions in pregnant dogs and cats include uterine inertia, and the clinical approach in queens parallels the bitch [11]. Queens often have small litters, and a single kitten may fail to provide enough stretch stimulus to drive labor. Cesarean section is frequently the more reliable path than repeated oxytocin, because the queen's small size and the risk of uterine rupture make aggressive medical management less forgiving. ### Cattle Hypocalcemia is the dominant cause of atony in cattle, especially in older, high-producing dairy cows around calving. The classic presentation is a cow that is recumbent, cold to the touch, with no abdominal effort and a fetus still in the uterus. Calcium borogluconate given intravenously is the first-line treatment. Oxytocin is used only after the cervix is confirmed open and no obstruction is present. Dystocia and oxytocin both affect the calf. In a study of 30 Holstein calves, calves from dystocic births had lower Apgar scores and respiratory and metabolic acidosis compared with calves from normal calvings [12]. Calves whose dams were treated with oxytocin had lower partial pressure of oxygen than calves from normal calvings [12]. This is a reminder that the decision to intervene affects the neonate, not just the mother. ### Ewes Ewes with hypocalcemia-associated atony, especially those carrying twins or triplets, present dull and unresponsive with no straining. Calcium borogluconate is the first-line treatment, followed by assisted delivery. The metabolic demand of multiple fetuses makes hypocalcemia more likely. ### Mares Atony in mares is uncommon and usually secondary to obstruction or exhaustion. Mares deteriorate rapidly. Emergency referral and cesarean section are the usual path rather than prolonged medical management. ### Sows Sows commonly show secondary inertia after a prolonged farrowing. The interval between piglets lengthens and contractions weaken. Manual examination to rule out obstruction comes first, followed by calcium if indicated and oxytocin only after obstruction is excluded. ## Risk Factors - **Breed size.** Miniature and small breeds accounted for 59.4% of dystocia cases in a large canine study [9]. - **Age and parity.** Older primiparous bitches over 6 years of age had a significantly higher risk of obstetric complications and stillbirths [9]. - **Litter size.** Both single-pup pregnancies and hyperfoetation (large litters) are risk factors for dystocia [9]. Receptor expression also varies with litter size [6]. - **Hypocalcemia.** Low ionized calcium is associated with increased uterine inertia in at-risk bitch populations [4] and is a primary cause in cattle and ewes. - **Low oxytocin.** Low plasma oxytocin is a documented cause of primary inertia in bitches [3]. - **Prolonged labor.** Duration of the expulsion stage had the highest influence on puppy survival [9], and prolonged labor is the mechanism of secondary inertia. - **Prior history.** A bitch with a previous uterine inertia is at higher risk in subsequent pregnancies. ## Veterinary Examination and Diagnostics A systematic examination separates the three main scenarios: primary inertia, secondary inertia, and obstructive dystocia. ### History Establish when labor started, the interval between offspring, whether membranes have passed, whether the mother is straining, and whether any discharge is present. Green-black discharge without a fetus suggests placental separation and warrants urgent intervention. ### Physical Examination Assess mentation, mucous membrane color, capillary refill time, heart rate, and temperature. Palpate the abdomen for fetal size and position. In cattle and ewes, assess for hypocalcemia signs such as cold extremities, muscle fasciculation, and recumbency. ### Vaginal Examination A sterile vaginal examination determines whether the cervix is open, whether a fetus is in the canal, and whether the fetus is correctly positioned. This is the single most important step for ruling out obstruction. If a fetus is palpable in the canal and is malpositioned, manual correction or cesarean is needed, not oxytocin. ### Bloodwork - **Ionized calcium.** The active fraction. Low values support calcium therapy [4][10]. - **Total calcium.** Easier to run but less physiologically precise. In the bitch study, total serum calcium was 2.1 ± 0.2 mmol/L in both treatment groups [3]. - **Glucose.** Hypoglycemia was not observed in the bitch inertia study [3], but it remains a reasonable check in any exhausted animal. - **Progesterone and PGFM.** A higher progesterone to PGFM ratio was found in bitches with primary inertia compared with controls [7], and progesterone was highest in elective cesarean bitches [8]. These are research tools more than routine clinical tests. - **Blood gas and acid-base.** Metabolic acidosis in the dam depresses myometrial function. ### Imaging Radiography or ultrasound confirms fetal number, position, and viability, and can identify a fetus that is too large or malpositioned for vaginal delivery. ## Evidence-Based Management ### Step 1: Rule Out Obstruction Vaginal examination and imaging. If a fetus is obstructed, the path is manual correction if feasible or cesarean section. Oxytocin is withheld. ### Step 2: Correct Metabolic Derangements - **Calcium.** In cattle and ewes, calcium borogluconate intravenously is first-line. In dogs, calcium is indicated when ionized calcium is low. The combination of calcium and oxytocin did not outperform oxytocin alone in a bitch study where calcium was normal [3], so calcium is a targeted therapy, not a universal one. - **Fluids.** Correct dehydration and support perfusion. - **Glucose.** Supplement if hypoglycemia is present. ### Step 3: Oxytocin, Only When Appropriate Oxytocin is indicated for confirmed uterine atony with a patent, unobstructed birth canal. Dose and route are label-specific and species-specific. Follow the product label for the species being treated. Do not extrapolate doses between species. Important cautions: - Oxytocin caused higher puppy losses than other medicaments in a large dystocia study [9]. - Pups delivered after oxytocin administration had the lowest base excess in a neonatal blood gas study [13]. - Calves from oxytocin-treated dams had lower partial pressure of oxygen than calves from normal calvings [12]. - Repeated oxytocin with manual assistance has been associated with uterine rupture [1]. ### Step 4: Cesarean Section Cesarean is indicated when medical management fails, when obstruction cannot be corrected, when the fetus is too large, or when the mother is deteriorating. In dogs and cats, cesarean is often the preferred path rather than repeated oxytocin, because the risk of rupture and the poor neonatal outcomes with repeated oxytocin outweigh the chance of a successful medical delivery. ### Step 5: Postpartum Monitoring After delivery, monitor the mother for retained fetal membranes, hemorrhage, uterine rupture, and infection. Monitor neonates for warmth, nursing, and acid-base status. Pups born after dystocia or oxytocin have measurable acid-base abnormalities that improve over the first hour but may persist as metabolic acidosis [13]. ## Stepwise Postpartum Decision Flowchart The following flowchart summarizes the decision path from suspected atony through delivery and postpartum monitoring. ```mermaid flowchart TD A[Labor stalls or no progress] --> B[Vaginal exam and imaging] B --> C{Fetus obstructed} C -->|Yes| D[Manual correction or cesarean] C -->|No| E[Check ionized calcium and glucose] E --> F{Calcium low} F -->|Yes| G[Correct calcium] F -->|No| H[Consider oxytocin per label] G --> H H --> I{Progress within expected interval} I -->|Yes| J[Deliver and monitor mother and neonates] I -->|No| K[Cesarean section] D --> J K --> J J --> L[Monitor for retained membranes hemorrhage and infection] ``` ## Unsafe Home Remedies and Common Mistakes - **Giving oxytocin without ruling out obstruction.** This is the most dangerous mistake. It can rupture the uterus [1]. - **Repeated oxytocin doses.** Higher puppy losses are associated with oxytocin compared with other medicaments [9], and neonatal acid-base status is worse after oxytocin [13]. - **Pulling on a fetus that is not in the canal.** Manual intervention has been linked to uterine rupture [1]. - **Assuming a bright, comfortable mother is fine.** Early primary inertia often presents with a mother that is not distressed. - **Waiting too long.** Duration of the expulsion stage had the highest influence on puppy survival [9]. - **Giving calcium without measuring it.** Calcium helps when calcium is low. In bitches with normal calcium, adding calcium to oxytocin did not improve outcomes [3]. - **Extrapolating doses between species.** Oxytocin dose and route are label-specific and species-specific. Follow the label for the species being treated. ## Prevention - **Monitor at-risk dams closely.** Small breeds, older primiparous bitches, and dams with a prior history of inertia need early veterinary involvement [9]. - **Check calcium in at-risk populations.** Bitches from lines with a history of inertia and stillbirths may have lower ionized calcium [4]. - **Plan for a controlled setting.** For dams with a prior cesarean or prior inertia, having a veterinarian available at the expected due date reduces delay. - **Manage body condition and nutrition.** Adequate calcium and energy balance before calving reduces hypocalcemia risk in cattle and ewes. - **Know the normal timeline.** Owners who know the expected interval between offspring recognize a stall earlier. ## Prognosis Prognosis depends on the cause and the speed of intervention. Primary inertia with a patent canal and a responsive uterus can resolve with appropriate medical therapy. Obstructive dystocia requires mechanical or surgical resolution. Duration of the expulsion stage has the highest influence on puppy survival [9], so time is the dominant prognostic factor. Maternal prognosis is good when rupture and sepsis are prevented. Uterine rupture with septic peritonitis is survivable with surgery and peritoneal drainage, as documented in one case that recovered and was discharged five days later [1], but it is a serious complication that is better prevented. ## Clinical Relevance, Limitations and Common Mistakes Uterine atony is a diagnosis of exclusion. The clinician must first rule out obstruction, then assess calcium and metabolic status, then decide between medical therapy and surgery. The most common clinical mistake is treating every stalled labor as atony and reaching for oxytocin. The second most common mistake is repeating oxytocin when the first dose fails, which increases fetal risk and maternal risk without improving the chance of vaginal delivery. The third is failing to measure ionized calcium and missing a correctable hypocalcemia. Limitations exist in the evidence base. Much of the canine data comes from specific populations and may not generalize to every breed or practice setting. The relationship between ionized calcium and dystocia in dogs is inconsistent across studies, with one population showing lower calcium in at-risk bitches [4] and another showing no difference between bitches with and without dystocia [10]. Receptor expression findings are research observations and are not yet routine clinical tests [6][2]. Oxytocin doses must come from the product label for the species being treated, and this article does not provide doses because they are label-specific. Individual cases require a veterinarian. The decision to use oxytocin, calcium, or surgery depends on the examination findings, the species, the stage of labor, and the condition of the mother and offspring. ## Frequently Asked Questions ### What is uterine atony? Uterine atony is the failure of the uterine muscle to contract strongly enough to deliver a fetus. It is also called uterine inertia. ### What is the difference between primary and secondary uterine inertia? Primary inertia means the uterus never contracted effectively. Secondary inertia means the uterus contracted normally and then became exhausted. ### Why is oxytocin dangerous in some cases? Oxytocin increases uterine pressure. If a fetus is obstructed, that pressure can rupture the uterus. A case report documents rupture and septic peritonitis after repeated oxytocin and manual assistance [1]. ### Do dogs with uterine inertia always have low calcium? No. One study found low ionized calcium in a population of bitches with a history of inertia and stillbirths [4], but another found no difference in ionized calcium between bitches with and without dystocia [10]. Measure calcium rather than assuming. ### Why do cattle and sheep often need calcium? Hypocalcemia is a leading cause of atony in cattle and ewes. Calcium borogluconate given intravenously is the first-line treatment. ### Why is cesarean often preferred over repeated oxytocin in dogs and cats? Repeated oxytocin is associated with higher puppy losses [9], worse neonatal acid-base status [13], and risk of uterine rupture [1]. Cesarean is often the safer path when medical therapy fails. ### How long is too long in labor? Duration of the expulsion stage has the highest influence on puppy survival [9]. Any stall beyond the expected interval for the species warrants immediate veterinary contact. ### Can uterine atony be prevented? Some risk factors cannot be changed, such as breed size and age. Close monitoring of at-risk dams, early veterinary involvement, and correcting hypocalcemia in cattle and ewes reduce the risk of a poor outcome. ## Related Articles - [Uterine Infections in the Bitch: Diagnosis and Management](/knowledge/veterinary-medicine/theriogenology/uterine-infections-in-the-bitch-diagnosis-and-management) - [Rabbit Care: Uterine adenocarcinoma prevention and spay timing](/knowledge/veterinary-medicine/exotic-small-animals/rabbit-care-uterine-adenocarcinoma-prevention-and-spay-timing) - [Equine Uterine Therapy: Decision-Making for Endometritis](/knowledge/veterinary-medicine/theriogenology/equine-uterine-therapy-decision-making-endometritis) - [Differential Diagnosis of Infertility in Dairy Cows: Uterine, Ovarian, and Management Factors](/knowledge/veterinary-medicine/food-animal-medicine/differential-diagnosis-infertility-dairy-cows-uterine-ovarian-management) - [Animal Model Selection for Neurological Research](/knowledge/veterinary-medicine/laboratory-animal-science/animal-model-selection-for-neurological-research) - [Anesthesia Monitoring Parameters for Laboratory Animals](/knowledge/veterinary-medicine/laboratory-animal-science/anesthesia-monitoring-parameters-for-laboratory-animals) - [Megacolon in Cats: Causes, Symptoms and Management](/knowledge/veterinary-medicine/digestive-and-urinary-care/megacolon-in-cats-causes-symptoms-and-management) - [Paralytic Ileus: Causes and Management in Pets](/knowledge/veterinary-medicine/digestive-and-urinary-care/paralytic-ileus-causes-and-management-in-pets) ## Sources 1. 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