Measurement of Endurance of Untrained Five-Year-Old and Six-Year-Old Horses Raised in Multi-age Herds on Pasture

Abstract

The objective of this study was to explore how the endurance of five-year-old horses, kept out on pasture all their life and ridden for the first time well into their fifth year of age, developed within one year and compared to that of six-year-old horses raised under the same conditions and to other horses. 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 lactate–running 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 v4 and v180 of five-year-old horses within one year through measurements in September and in the following July and September; the comparison of endurance variables (2) between five-year-olds 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 within one year (repeated measures ANOVA P > .05); (2) there were no significant differences between five-year-olds and six-year-olds (one-way ANOVA P > .05); (3) no significant differences between six-year-old groups (one-way ANOVA; P > 05); and (4) foreign horses had higher v4 and v180 values than six-year-olds (one-way ANOVA; P = .0001 and P = .003, respectively). There was no significant relationship between v4 and v180 (P > .05; r2 = 0.02). In conclusion, one additional year on pasture in multiage herds did not increase the 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.