Thoroughbred racehorses are at increased risk of bone injury. Intense exercise, Furosemide (F) and clodronate (C) lower ionized calcium (iCa), vital for bone turnover, and increase parathyroid hormone (PTH). Osteocalcin (OSC), and C-terminal telopeptide of type I collagen (CTX-I) are biomarkers of bone turnover. This study examined how F and C affect serum iCa, PTH, OSC, and CTX-I in young, exercising thoroughbreds.
16 Thoroughbred horses, 2.83 (±0.38) years received a single, 1.8 mg/kg IM dose of C and received F, 1.1mg/kg IV, q7d for 12 weeks, or equivalent volumes of saline (S). Four horses were assigned to each treatment group (C/F, C/S, S/F or S/S) and exercised for 3 months. Serum PTH and iCa were measured at acute (0, 1, 2, 4, 8hrs) and chronic (24h, 96h, 2, 6, 9 and 12 week) timepoints. Serum CTX-I and OSC were measured at 0, 1, 7, 14, 48 and 84 days. Data was evaluated using multilevel mixed-effects linear regression.
Serum iCa (mean; 95%CI) was significantly lower (P=0.031 and P=0.008) in C/F treated horses from 0-8hrs (1.51; 1.47-1.56) and 24h-12weeks (1.52; 1.51-1.53) compared to S/S treated horses (1.55; 1.53-1.57 and 1.58; 1.54-1.61). PTH was significantly higher in C/F (21.04; 6.02-31.69) compared to S/S (5.70; 3.39-8.01) treated horses from 0-8hrs (P=0.045). CTX-I was significantly lower in S/C treated horses at 1 (5.01; 4.45-5.56), 7 (4.65;3.87-5.42) and 48 (4.00; 3.06-4.92) days (P=0.006, 0.005 and 0.019, respectively) compared to S/S (6.58; 5.62-7.54, 6.19; 5.43-6.94 and 5.52; 4.65-6.39, respectively). OSC levels were significantly higher in F/S treated horses on day 0 (40.8; 36.5-45.1) and significantly lower on day 84 (14.4; 7.4-21.4) (P < 0.01 and P=0.022) compared S/S (30.6; 29.8-31.4 and 25.6; 19.1-32.2, respectively).
Furosemide and clodronate disrupt calcium balance and alter CTX-I and OSC levels in young, exercising Thoroughbreds.