No abstract

The objective of this study was to examine the endurance of five-and six-year-old horses raised and kept close to natural living conditions and ridden for the first time well into their fifth year of age. Horses were submitted to a standardized exercise test (SET) to calculate their v4 (velocity run under defined conditions inducing 4 mmol/L of blood lactate concentration (LA)) and v180 (velocity run under defined conditions inducing a heart rate of 180 beats/min). The test consisted of up to five consecutive intervals at increasing speed until the blood LA of a horse increased above 4 mmol/L. The blood LA measured after each interval was plotted exponentially against running speed to derive v4 from the blood lactaterunning speed relationship, and the mean heart rate during the intervals was plotted linearly against running speed to derive v180 from the heart rate-running speed relationship. The following were examined: 1) the development of the endurance variables of five-year-old horses during one year through measurements in September and in the following July and September; the comparison of endurance variables 2) between five-and six-year-olds; 3) between six-year-olds on consecutive years; and 4) between six-year-olds and foreign horses. The results showed that: 1) there were no changes of either variable during one year (P > 0.05); 2) there were no significant differences between five-and six-year-olds (P > 0.05); 3) no significant differences between six-year-old groups (P > 005); and 4) foreign horses had higher v4 and v180 values than six-year-olds (P = 0.0001 and P = 0.003, respectively). There was no significant relationship between v4 and v180 (n = 42; P > 0.05; r 2 = 0.02). In conclusion, one additional year on pasture in multi-age herds did not increase endurance variables of five-year-old horses. Thus, the endurance appeared to be consolidated in these horses at the age of five years and additional training seems to be necessary to increase it.