EQUINE VETERINARY EDUCATION Equine vet. Educ. (2020) 32 (1) 49-51 doi: 10.1111/eve.13046
Critically Appraised Topic
In the mare, does manual removal of fetal membranes negatively affect fertility? M. K. Platt*†
, A. J. Walker† and A. Gunn†‡
†School of Animal and Veterinary Science, Charles Sturt University; and ‡Graham Centre for Agricultural Innovation, Wagga Wagga, New South Wales, Australia *Corresponding author email:
mplatt@csu.edu.au
Background
Retained fetal membranes (RFM) are the most frequently occurring post-partum condition of the mare encountered in clinical practise (Threlfall 2011). The condition is defined as the retention, complete or partial, of the allantochorionic membrane for an extended period of time following expulsion of the foal. The vast majority of publications agree that fetal membranes (FM) should be considered pathologically retained if they have not been expelled within 3 h post-partum, at which time it is considered appropriate to implement therapeutic intervention (Brinsko 2007). Despite the high incidence of RFM, a lack of consensus
exists regarding the optimal treatment regimen. Due to the higher risk of fatal sequelae, the approach to treatment of RFM in the mare is very different to that taken when managing this condition in other domestic species. Manual removal as an intervention for the treatment of RFM remains controversial due to the perceived risks and potential negative effects on future fertility. The commonly cited immediate risks of manual removal include severe haemorrhage, pulmonary embolism, intussusception of the uterine horn and uterine prolapse (Threlfall 2011). It is reported that manual removal of FM may also have a negative impact on fertility by causing delayed uterine involution, the cervix to remain open longer post foaling (Vandeplassche et al. 1971), retention of microvilli that serve as foci of infection, fibrosis and permanent endometrial damage (Threlfall 2011). Methods of manual removal vary between reports and there is no well- described, universally-accepted technique for manual FM removal.
Search strategy
A population, intervention, comparison, outcome (PICO) question was constructed: In the mare, does manual removal of fetal membranes negatively affect future fertility? The keywords (mare OR mares) AND ((retained
membrane) OR (retained placenta)) AND manual were used to search CAB abstracts (1910 – present) and Scopus.
Quantity of evidence
The search yielded 14 results from CAB abstracts and no additional sources were retrieved through Scopus. Papers in a language other than English were excluded; the remaining papers were screened based on title and abstract and three experimental studies that suitably addressed the PICO
question were identified. These papers comprised of two clinical trials (Sevinga et al. 2002; Cuervo-Arango and Newcombe 2009) and a single cohort study (Ishii et al. 1999).
Quality of evidence
All studies included primarily (Cuervo-Arango and Newcombe 2009) or exclusively (Ishii et al. 1999; Sevinga et al. 2002) heavy draught breed mares. The study by Ishii et al. (1999) lacked power (n = 10) and did not include any relevant calculations of significance. Similarly, Cuervo-Arango and Newcombe (2009) included 12 manual removals, whilst Sevinga et al. (2002) had the largest sample size (n = 30). Ishii et al. (1999) performed manual removal of FM in 10
mares; however, the technique they used to perform this procedure was not described in the paper. These authors found that mares, which underwent manual removal of FM, tended to have an increased non-pregnant term, defined as the number of days from parturition to last mating prior to a positive pregnancy diagnosis (58.5 days), in comparison to mares that did not undergo manual removal of FM (33.8 days). The timing of manual removal of FM relative to parturition was not recorded, making it difficult to identify other factors, such as retention time, that may have contributed to decreased fertility rates. They stated that a number of mares with positive bacterial swabs were treated with an intrauterine infusion of antibiotics with or without uterine irrigation; however, it was not specified whether these mares were those that had undergone manual removal of FM. Cuervo-Arango and Newcombe (2009) described
successful prophylactic removal of FM immediately post foaling. Whilst this study did not address RFM ‘per se’ it does provide clinically relevant information. Attempts at removal were ceased if the mare stood prior to completion of the procedure, and these mares were allowed to expel membranes naturally. In this study, mares that retained FM or experienced dystocia were excluded from the results, reducing the relevance of these findings to a clinical scenario. However, exclusion of mares that retained FM does remove the influence of placental retention time on the measured fertility outcomes. Sevinga et al. (2002), did not describe the technique used
for manual removal of FM; however, the uterus of each mare was flushed with 50–100 L of water once manual removal was complete. They performed manual removal of RFM approximately 7 h post parturition to first allow for repeated oxytocin administration. Mares that retained FM and underwent manual removal received significantly (P = 0.005) more subsequent intrauterine treatments than those mares
© 2019 EVJ Ltd
49
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76
