Cost of Transport as a Discriminator of Conditioning in Horses Submitted to Incremental Jumping Tests

Introduction Heart rate (HR) and blood lactate (LAC) are biomarkers whose responses to exercise are related to physical fitness. This study evaluated the cost of transport (CT) by assessing the cardiovascular and metabolic efficiency of jumping horses using an incremental jumping test. Methods Sixteen Brazilian Sport horses of two fitness levels were used: high-level jumpers (HL, n = 8) and low-level jumpers (LL, n = 8). Tests were performed in a sandy jumping arena at a mean velocity of 18 km/h; the tests were distributed into three steps of 4 laps of 74 m, each with 10 obstacles. Each stage consisted of simple obstacles that were 0.40, 0.60 and 0.80 m high. The costs of transport were determined as (HRstep-HRrest/speed) and (LACstep-LACrest/speed). During intervals between each stage, blood samples were drawn to determine LAC (mmol/L). Student's t-test was used for the unpaired samples (P<0.05). Results There was no difference in the stage 0.40 m for HR. There were differences in the HL and LL groups, respectively, in the HR related to the effort in the obstacle series 0.60 m [1.7 ± 0.2 bpm/(km/h) and 2.0 ± 0.2 bpm/(km/h) (P = 0.02)]; 0.80 m [1.5 ± 0.2 bpm/(km/h) and 1.7 ± 0.2 bpm/(km/h); (P = 0.04)], and in the LAC for the 0.40 m obstacle [0.05 ± 0.04 mmol/L/(km/h) and 0.10 ± 0.03 mmol/L/(km/h); P = 0.04]; 0.60 m [0.07 ± 0.06 mmol/L/(km/h) and 0.14 ± 0.03 mmol/L/(km/h); (P = 0.006)] and 0.80 m [0.11 ± 0.04 mmol/L/(km/h) and 0.19 ± 0.05 mmol/L/(km/h); P = 0.009]. Conclusions The CT differentiated horses of high and low level jumping fitness. The HR method (rather than LAC) is particularly useful because it is simple, inexpensive and accessible to trainers and veterinarians. Ethical Animal Research All procedures were approved by the institutional animal care and use committee of the university (CEUA, Process: 019281/13). Sources of funding: FAPESP - Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (Process 2011/11080-0). Competing interests: none.