Behavioural and physiological methods to evaluate fatigue in sheep following treadmill exercise

Previous observational studies suggested either that sheep do not become markedly fatigued by long journeys or that previous methods did not identify fatigue. A range of methods was used to identify fatigue in 7 pairs of 13-month-old, female and castrated male, non-breeding sheep walked on a treadmill at 0.5m/s for up to 5h (treatment) or for two 10-minute periods (control). Median ambient temperature 14°C (range 10-17°C). One sheep only walked for 4.5h, but all other treatment sheep walked for 5h without apparent difficulty. A repeated measures mixed model (treatment,time, treatment×time) analysis was undertaken. In treatment sheep, there was a proportionate decrease in the median frequency of the electromyogram (-0.004±0.0988) that was significantly different from control sheep (0.109±0.0988) (P<0.05). Treatment sheep did not lie down sooner (median latency 1.3h, Q₁ 1.1, Q₃ 1.8) of for longer after exercise (49% of 24h post-exercise period ± 5.7) than controls (1.7 h, Q₁ 1.0, Q₃ 2.4 and 61% ± 5.7, respectively) (P>0.05). After exercise, there was no significant difference between the times taken by treatment (7.0 s) and control (6.7 s) sheep to obtain a food reward in a maze (P>0.05). Observers (näive to the treatments), using free choice profiling, could not identify qualitative behavioural differences between treatments and controls. Two groups of terms were identified: agitated/active to still/calm, and tense to relaxed/calm, the term weary was used once. Although previous studies showed that vigorous exercise can fatigue sheep, there was little evidence that prolonged gentle walking fatigues sheep. In this study, the speed and gradient of the treadmill was not sufficient to consistently cause fatigue.