Endometritis in Sows: Risk Factors, Diagnosis and Reproductive Impact

Endometritis in Sows: Risk Factors, Diagnosis and Reproductive Impact 

Endometritis is an important reproductive disorder in breeding sows and can occur after farrowing as well as following artificial insemination or natural mating. Within-herd prevalence has been reported to range from 1.4% to 60%, and chronic uterine inflammation is commonly encountered^1,2. For practitioners, the challenge is that affected sows may show only vague clinical abnormalities—or no obvious signs at all- while reproductive performance progressively deteriorates. 

Recognizing the Major Risk Factors 

Sow endometritis is most often associated with bacterial contamination combined with impaired uterine clearance, immune dysfunction, or management-related factors. Important risks include delayed uterine involution, unhygienic insemination, contaminated semen, obstetrical intervention, and inadequate myometrial contractility³. 

The peripartum period deserves particular attention. Prolonged farrowing, manual obstetrical intervention, increased numbers of stillborn piglets, and retained placentas are associated with intrauterine fluid accumulation and puerperal metritis¹. Duration of placental shedding, obstetrical intervention, and fever after farrowing can also increase vaginal discharge and negatively influence uterine involution^1,4,5. 

Timing of insemination is another relevant consideration. Uterine resistance to infection is greatest around oestrus, when oestrogen is high and progesterone is low. Insemination after ovulation, when progesterone is increasing, can therefore favour endometritis by reducing uterine immune activity¹. 

Diagnosis: Look Beyond Vaginal Discharge 

Clinical diagnosis can be difficult because endometritis is frequently subclinical. Possible findings include decreased feed intake, fever, vulvar discharge, anestrus, irregular oestrus, and infertility⁶. Vaginal discharge persisting more than 6 days after farrowing is indicative of puerperal endometritis, but vaginitis, cystitis, and pyelonephritis should also be excluded¹. 

Ultrasonography can provide useful complementary information. Intrauterine fluid and retained foetal or placental material may indicate endometriti¹. 

Bacteriological investigation can be performed using cervical samples in sows with vaginal discharge, although contamination may make interpretation difficult. When affected sows are slaughtered, postmortem examination of the genital tract can provide valuable herd-level information. Uterine samples collected after slaughter are also less prone to contamination during sampling¹. 

Importantly, reproductive history itself can function as a diagnostic signal. Reviewing irregular returns to oestrus, infertility, and other reproductive-performance characteristics can help identify animals requiring further investigation. 

Reproductive and Herd-Level Consequences 

Endometritis is one of the main reasons for culling breeding sows and has substantial economic consequences through impaired reproductive performance^1,7. The condition can also negatively affect sow and offspring health and welfare¹. 

The clinical picture should therefore be interpreted at both animal and herd level. A sow with discharge, fever or poor reproductive performance warrants individual evaluation, but repeated cases should prompt assessment of farrowing procedures, insemination hygiene, semen quality, housing conditions and overall herd management. 

Practical Clinical Insights 

• Do not rely on vaginal discharge alone; many cases are subclinical. 

• Investigate discharge persisting beyond the expected postpartum period while excluding urinary and vaginal causes. 

• Use ultrasound to assess intrauterine fluid and retained material where appropriate. 

• Interpret bacteriology cautiously when samples are collected through potentially contaminated routes. 

• Examine reproductive-performance patterns at herd level when individual clinical signs are nonspecific. 

• When affected sows are culled, postmortem reproductive-tract examination can help identify underlying herd problems. 

For the practicing veterinarian, endometritis should therefore be viewed not simply as a uterine infection, but as a reproductive disorder influenced by farrowing, insemination, uterine clearance and immune function. Early recognition of risk patterns and systematic herd-level investigation can help identify where reproductive losses are originating. 

References 

1. Pascottini OB, Aurich C, England G, Grahofer A. General and comparative aspects of endometritis in domestic species: A review. Reproduction in domestic animals. 2023 Sep;58:49-71. https://onlinelibrary.wiley.com/doi/pdfdirect/10.1111/rda.14390 

2. Monteiro MS, Matias DN, Poor AP, Dutra MC, Moreno LZ, Parra BM, Silva AP, Matajira CE, de Moura Gomes VT, Barbosa MR, Sato MI. Causes of sow mortality and risks to post-mortem findings in a Brazilian intensive swine production system. Animals. 2022 Jul 14;12(14):1804. https://www.mdpi.com/2076-2615/12/14/1804 

3. Miciński B, Jana B, Całka J. Uterine inflammation changes the expression of cholinergic neurotransmitters and decreases the population of AChE-positive, uterus-innervating neurons in the Paracervical ganglion of sexually mature gilts. Animals. 2022 Jun 29;12(13):1676. https://www.mdpi.com/2076-2615/12/13/1676 

4. Grahofer A, Mäder T, Nathues H. Evaluation of different point-of-care tests to characterize the vaginal discharge of sows after parturition and parameters’ correlation with subsequent reproductive performance. Porcine health management. 2021 May 20;7(1):38. https://link.springer.com/content/pdf/10.1186/s40813-021-00217-y.pdf 

5. Trachsel C, Küker S, Nathues H, Grahofer A. Influence of different sow traits on the expulsion and characteristics of the placenta in a free farrowing system. Theriogenology. 2021 Feb 1;161:74-82. https://www.sciencedirect.com/science/article/pii/S0093691X20306282 

6. Wang Y, Guo H, Bai Y, Li T, Xu R, Sun T, Lu J, Song Q. Isolation and characteristics of multi-drug resistant Streptococcus porcinus from the vaginal secretions of sow with endometritis. BMC veterinary research. 2020 May 20;16(1):146. https://link.springer.com/content/pdf/10.1186/s12917-020-02365-9.pdf 

7. Koketsu Y, Tani S, Iida R. Factors for improving reproductive performance of sows and herd productivity in commercial breeding herds. Porcine health management. 2017 Jan 9;3(1):1. https://link.springer.com/content/pdf/10.1186/s40813-016-0049-7.pdf