Furosemide Administration Affects Mineral Excretion and Balance in Non-Exercised and Exercised Thoroughbreds

Two studies were conducted to measure the effect of furosemide on 72-hour digestibility and urinary excretion of calcium (Ca), phosphorus (P), magnesium (Mg), sodium (Na), potassium (K), and chloride (Cl) in nonexercised and exercised mature Thoroughbred geldings.

In study 1, total fecal and urinary mineral excretion was measured in three unexercised Thoroughbred geldings for 72 hours before and 24 hours, 48 hours, and 72 hours after a single dose (.5 mg/kg IV) of furosemide. The horses were fed 8.3 ± 0.98 kg orchard grass hay, 1 kg of grain mix, and 120 g of a vitamin/mineral supplement daily for 15 days before and during the 6- day collection period. Urinary sodium excretion increased 24 hours post furosemide administration but returned to pretreatment levels 48-72 hours post treatment. Urinary Ca, K, and Cl excretion increased post treatment and remained elevated 72 hours post treatment. 72-hours Ca, K, and Cl balances were lower post treatment than pretreatment (p<.05). Urinary P and Mg excretion was unaffected by treatment. Digestibility of all minerals was unaffected by treatment.

In study 2, six fit Thoroughbred geldings (age: 6.8 ± 1.2 y, BW: 585 ± 19 kg) were used in a 3 X 3 Latin square trial to measure the effect of furosemide on urinary and fecal mineral excretion for 24 hours before (-24 hours) and 24 hours, 48 hours, and 72 hours after a standardized exercise test (SET) on an inclined (3º) high-speed treadmill. The SET was performed at 1.7 m/s for 5 min; 4 m/s, 6 m/s, and 8 m/s for 2 min per step; and 9 m/s, 10 m/s, 11 m/s, 12 m/s, and 13 m/s for 1 min per step. The horses were not allowed access to water, hay, or feed for 4 hours before the SET. The treatment groups consisted of an untreated control (C) and two groups (F and FE), which received furosemide (0.5 mg/kg, IV) 4 hours before the SET. C and F were fed 60 g/d NaCl, and (FE) was fed 200 g/d of an electrolyte mix (14 g K+, 37.7 g Na+, and 43.3 g/d Cl-) for 21 days before the SET along with 5.85 kg hay, 4 kg grain, and .12 kg of a vitamin/mineral supplement. Following the SET, the FE group was supplemented with an additional 10 g/d Ca and 10 g/d Mg. Urinary Ca, P, Na, and Cl excretion increased 24 hours post treatment in the F and FE groups (p<.05) compared to -24 hours and were higher than C 24 hours levels (p<.05).

J.D. Pagan, B.M. Waldridge, C. Whitehouse, L. Dalglish, S. Fuchs, M. Goff, Furosemide administration affects mineral excretion and balance in non-exercised and exercised Thoroughbreds. Journal of Equine Veterinary Science. Volume 33, Issue 5, Page 329. (Proceedings of the 2013 Equine Science Society Symposium)

This research was also presented at the 2014 Australian Equine Science Symposium 5:23.