EQUINE VETERINARY EDUCATION / AE / JANUARY 2020


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as a single pH measurement undertaken each evening is simple, practical and cost effective. The procedure can be performed with pH strip papers or a simple, pH meter (Ellerbrock and Canisso 2016). The majority of mares with a pH <7 have been shown to foal within 24 h (Canisso et al. 2013). Other clinicians have confirmed this; in addition it is possible that the pattern of pH change may reflect fetal maturation (Ellerbrock and Canisso 2016), which is an exciting prospect for the future. In cases in which the mare deteriorates during treatment


and suspected intervention is likely, clinicians should consider starting the mare on dexamethasone in a bid to hasten fetal maturity. Ousey et al. (2011) have shown that 100 mg of i.m. dexamethasone given daily for 3 days at 315–317 days of gestation can result in a shorter gestational length and advanced fetal maturity. In their initial studies, treated mares had a shortened gestation length, on average, by nearly 2 weeks compared with control mares. The foals appeared mature and healthy, and though smaller, they had similar bodyweights compared with control mares. It is important to note that clinicians should take care in


extrapolating this work to clinical cases for several reasons; as outlined in this article, similar regimes of glucocorticoid administration to pony mares later in pregnancy (Days 331– 347) caused dystocia and fetal death (Jeffcott and Rossdale 1977). Ousey et al. (2011) suggest that the difference in these results are likely linked to the level of fetal cortisol at the time of treatment; perhaps glucocorticoid treatment when fetal cortisol levels are low simulate endogenous production and the ensuing tissue maturation whereas administration closer to parturition when fetal cortisol levels are higher may suppress endogenous adrenocortical activity and maturation. In addition, treatment is not without disadvantages; as well as potentially suppressing the fetal adrenal activity (via the negative feedback on the hypothalamus-pituitary-adrenal axis), dexamethasone has potential effects on prostaglandin synthesis in the mare with the potential to contribute to dystocia and/or premature placental separation (Ousey et al. 2011). Ousey et al. also make the comment that many sick mares will already have raised cortisol levels and activation of the fetal hypothalamic-pituitary-adrenal axis; in these instants glucocorticoids may disrupt the maturation process, further evaluation of the regime in the compromised mare is required. Currently the use of steroids to hasten fetal maturation in a sick mare is still in the experimental stages; however, favourable results have occurred in a small number of mares (Ousey 2008). The regime does however give the clinician a management option to attempt precocious fetal maturation in the situation in which a mare starts to deteriorate whilst carrying a likely premature foal.


Parturition


If the mare can reach full term, attendance and assistance of parturition is essential, as mares have little to no ability to contract their abdominal wall. To plan for adequate personnel to assist foaling, induction of these mares can be desirable.


Induction of parturition may be performed in cases in


which one is confident of fetal readiness for extra-uterine life. It should be remembered that success of elective parturition is very much dependant on readiness for birth. Criteria for successful parturition include a gestational length of


>330 days, colostrum in the udder (though this may be hard to ascertain with blood), relaxed sacrosciatic ligaments around the tailhead, a relaxed cervix and the appropriate changes in the mammary secretions (Jeffcott and Rossdale 1977). In cases in which one is not confident of this, induction should be restricted to cases in which the mare is uncontrollably painful, or terminally compromised. If induction is performed, oxytocin is generally the clinician’s drug of choice. Glucocorticoids are inappropriate, as multiple doses over multiple days are needed. Their use is more appropriate in attempting to increase fetal maturation as previously outlined. Prostaglandins are discouraged, as there is a relatively long and variable time to foaling. There is also an increased risk of premature placental separation (Macpherson and Paccamonti 2011). There are many different dosage regimes for oxytocin


and in general, the method of oxytocin administration has not been shown to affect foal viability (Macpherson et al. 1997). A slow approach to induction with lower doses such as 2.5–5 IU is preferable as 10–20 IU can be quite painful and rapid with poor fetal positioning. Our preferred regime is a simple 5–10 IU i.v., repeated if necessary in 20–30 min (LeBlanc 2007). Prostaglandin E2 may be used to increase cervical


dilation in mares undergoing induction, but is not mandatory. Following successful parturition, the mare should be


carefully monitored for complete expulsion of the fetal membranes. The foal should be initially classed as a neonate at high risk of developing neonatal maladjustment syndrome, and neonatal sepsis. If the foal does appear normal, consider colostrum supplementation as severe oedema may hinder normal nursing. Reduced colostrum quantities and running milk are reported in mares with pregnancies matured with corticosteroids (Ousey et al. 2011). As the oedema resolves post foaling, the extent of the


defect can be re-evaluated. Surgery is indicated in a small number of cases of true abdominal wall tears and these are repaired with direct suturing or insertion of a prosthetic mesh. If surgery is considered to be viable, the ideal timing will be 3–4 months post foaling (Freeman 2005). This delayed surgical repair reduces the risk of infection present when inflammation and oedema still persist. In addition, fibrosis and scarring of the edges of the defect will have greater strength for suture holding (Meek et al. 1977). There are many publications in the literature discussing variations in repair of acquired hernias (albeit mostly focused on incisional hernias, rather than abdominal wall defects in pregnant mares) and from these it appears that the choice between direct suture repair and mesh placement can largely be dictated by surgeon preference, as the overall success rate (in incisional hernias) is similar between the two techniques (Davis and Rakestraw 2002; Whitfield-Cargile et al. 2011). If using mesh, it may be placed within the abdominal cavity (Caron and Mehler 2009), inside the defect but in a retroperitoneal location (Elce et al. 2005), or subcutaneously, outside the hernia ring (Van Der Velden and Klein 1994). A variety of materials have been described for incisional hernias and traumatic abdominal wall hernias; polypropylene (Van Der Velden and Klein 1994), plastic (Elce et al. 2005), composite materials (combining polypropylene and expanded polytetrafluoroethylene [Caron and Mehler 2009]) and silk (Haupt et al. 2015). Again the choice is dictated by surgeon preference.


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