A 6 year old 550 kg warmblood mare in moderate work has been diagnosed with exertional rhabdomyolysis (tying up) and the vet has recommended that the owner adjusts the diet to minimise starch intake. The horse is back in work but has lost weight and condition and the owner is worried about what to feed her to fuel her work without increasing the risk of another bout of tying up. She is currently fed hay overnight and a stubbs scoop of low energy compound chaff morning and evening. The mare is stabled overnight and turned out for 6 hours on poor pasture during the day.
There are two main types of muscle dysfunction that cause tying up, and nutrition recommendations are similar for both. Firstly, the diet must be balanced carefully.Nutrient intake from forage should be maximised so that reliance on concentrate feed is minimised. For this mare, good quality hay (ideally with a WSC of under 15%) or high fibre haylage is recommended, fed ad lib (free choice). Plenty of turnout is recommended, but pasture intake may have to be limited to avoid a large intake of sugar and fructans, so the pasture being poor is useful. Hay or haylage can be fed in the pasture if it is so poor that the mare isn’t grazing much.
Starch intake should be kept to a minimum and highly digestible fibre and oil-based compound feeds are recommended. The low energy compound chaff is unlikely to provide enough energy and protein so a medium energy, highly digestible fibre and oil-rich compound is recommended (starch < 10% and fibre >10%). If the mare puts on enough condition on less than the full recommended amount of fortified compound feed, then a multi-vitamin and mineral supplement should be fed.
Vegetable oil (e.g. linseed, rapeseed, sunflower or corn) should be added to provide extra dietary energy, increasing the amount gradually to a maximum of 300 ml daily, split between meals. Electrolyte intake is important, and should be relevant to sweat losses during work. A salt block should be available, and electrolytes added daily to the feed when the mare is in work. Supplementary antioxidants are recommended via a vitamin E and selenium supplement, fed to give a total intake of around 3000 IU of vitamin E and 2-3 mg of selenium daily.