NOVEMBER 2022
603
a)
b)
Fig 1: (a) A normal abdominal radiograph of an adult horse. (b) An abdominal radiograph of an adult horse with a large accumulation of sand in the ventral colon (highlighted).
colon impactions, and it has been shown that a dose of 1 g/ kg bwt of MgSO4 results in a greater total weight of faeces excreted and faecal water excretion than either a lower dose (0.5 g/kg bwt), dioctyl sodium sulfosuccinate or water alone (Freeman et al., 1992). The combination of psyllium and MgSO4 (both at 1 g/kg bwt s.i.d.) has been compared with the use of each ingredient alone (each at 1 g/kg bwt s.i.d.) with all treatments administered by nasogastric tube (Niinist€
75% of horses resolved to a radiographically measured sand area of <25 cm2 by Day 4 compared with ≤25% in the monotherapy treatment groups (Niinist€
o et al., 2014). A further
study compared the use of the combination therapy via nasogastric tube, as described above, against an untreated control group which was removed from access to sand (Niinist€
o et al., 2018). Comparable with the results from the
previous study, 75% of treated horses were considered resolved by Day 4 (Niinist€
o et al., 2018). The lack of a meaningful o et al., 2018) supporting the use of
this approach. Further, in that study 20% of placebo horses self-resolved (Niinist€
difference between monotherapy with either psyllium or MgSO4 via nasogastric tube in the earlier study and untreated controls in the later study suggests that there is no benefit to monotherapy over removal from access to sand alone. These findings are consistent with a further study that compared the feeding of psyllium at home over a 10-day period (25% resolution) against 3–7 days of combination therapy via nasogastric tube (54% resolution) (Kaikkonen et al., 2016). Given that daily nasogastric intubation is an invasive and
time-consuming approach, the practice of feeding psyllium at home is a commonly used alterative. However, data to support this approach are lacking with a recent study demonstrating no benefit of daily feeding of a combination of psyllium and prebiotics and pro-biotics over a 35-day period when compared with a placebo controlled group (Hassel et al., 2020). Collectively, the findings support the use of combination
therapy of psyllium and MgSO4 (both at 1 g/kg bwt) via nasogastric tube once daily as the preferred method of treatment. Further, the collective findings of the research suggest that administering psylliumin feed has no advantage over simply removing access to sand. Carboxymethylcellulose has been suggested as an alternative to psyllium but a recent study demonstrated no difference between the two when administered via nasogastric tube for 7 days (Alonso et al., 2020).
In the authors’ experience, administration of psyllium and o et al., 2014). In the combination treatment group,
MgSO4 by nasogastric tube can result in mild abdominal discomfort. Consequently, the authors routinely premedicate patients with flunixin at 1.1 mg/kg i.v. or per os at the time of nasogastric intubation. Although rare, gastric rupture following administration of psyllium can occur associated with swelling of the psyllium within the stomach or the formation of a bezoar (Bergstrom et al., 2018). Accordingly, the authors routinely starve horses for ≥4 h to reduce the gastric volume prior to the administration of the combination treatment. Care should be taken with dosing of MgSO4 or administering it to a horse with renal failure, and abnormal magnesium excretion can result in high serum magnesium levels that can be toxic, or even fatal (Henninger & Horst, 1997). Magnesium toxicity is treated by increasing renal flow to enhance excretion and using calcium salts to replace magnesium (Henninger & Horst, 1997). Surgical treatment is required in severe acute cases or in
those refractory to medical management, which may occur in as many as 14–31% of acute presentations (Graubner et al., 2017; Hart et al., 2013; Kilcoyne et al., 2017). The amount of sand should not be considered as a determinant of the need for surgery; instead, it is the overall assessment of the patient that dictates the surgical need (Kilcoyne et al., 2017; Rakestraw & Hardy, 2012). Removal of the sand accumulation through a pelvic flexure enterotomy via a ventral midline approach is recommended (Rakestraw & Hardy, 2012). Caution should be exercised during surgical manipulation of the large colon as the distended bowel is often friable, especially in chronic cases. Surgical exteriorisation of the large colon can be further complicated by the weight of the sand. Reported complications during surgery include tears and ruptures of the heavy sand-filled colon, especially when operating on chronic cases (Specht & Colahan, 1988; Granot et al., 2008; Rakestraw & Hardy, 2012; Hardy, 2017; Kilcoyne et al., 2017). Complications after surgery include endotoxaemia (Specht & Colahan, 1988), diarrhoea (Granot et al., 2008; Rakestraw & Hardy, 2012; Specht & Colahan, 1988), fever (Kilcoyne et al., 2017), septic peritonitis (Ragle et al., 1989a; Rakestraw & Hardy, 2012; Specht & Colahan, 1988), incisional hernia (Granot et al., 2008; Kilcoyne et al., 2017; Specht & Colahan, 1988), laminitis (Granot et al., 2008; Ragle et al., 1989a), internal bleeding (Granot et al., 2008) and adhesions (Ragle et al., 1992). The results of short-term medical treatment of large colon sand accumulations are presented above. The overall
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