170


EQUINE VETERINARY EDUCATION / AE / MARCH 2016


certain geographic regions such as California have a higher prevalence (Lloyd et al. 1987; Hassel et al. 1999). Many causes for the pathophysiology of enterolith formation have been hypothesised, but a definitive pathogenesis remains uncertain. Previous studies evaluating dietary and environmental management practices in horses with enteroliths have identified associations with feeding of alfalfa hay, breed predispositions (Arabian descent), spending ≤50% of time outdoors and lack of daily access to pasture grazing (Hassel et al. 1999, 2004, 2008; Cohen et al. 2000). Additionally, excessive dietary levels of magnesium, nitrogen and phosphorous, combined with an alkaline colonic pH, are thought to contribute to enterolith formation (Hassel et al. 2004). Foreign objects, collectively referred to as nidi, are typically required for their development. Small stones, nails, pins, needles, coins, metal fragments, horse hair, cloth and rubber may act as nidi within the equine intestinal tract (Bray 1995).


Alfalfa hay contributes to alkalinisation of the colon and


provides an abundant source of magnesium, nitrogen and calcium to the diet (Bray 1995; Hassel et al. 2008). Alkaline conditions within the colon enable magnesium, ammonia and phosphorous to crystallise on a nidus, gradually allowing an intestinal stone to form rings, layer by layer (Lloyd et al. 1987; Bray 1995). A small stone(s) may be eliminated with normal passage of manure (Figs 1 and 2). Large enteroliths are typically discovered when they cause complete or partial obstruction, and subsequent signs of colic; these cases will require exploratory celiotomy for removal of the stone. Dietary considerations relative to enterolith formation should include: eliminate excess magnesium; eliminate excess nitrogen by not feeding excessive protein; balancing the calcium and phosphorus ratio; and potentially reducing the pH in the gastrointestinal tract (Bray 1995). A more recent study by Hassel et al. (2008), found that feeding >50%


IMG_T:2:12 PM


59.6 mm det. 48.7 mm det.


R 1 of 1 LOSSY COMPRESSION 20:1 R


58.6 mm det.


16.8 mm det. 8.9 mm det.


Fig 2: Abdominal radiographs of draught horse with the stones shown in Fig 1. © 2016 EVJ Ltd


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