The energy metabolism of sheep walking on the level and on gradients

Abstract

Although many investigations have been made, notably by Brody and his associates (Brody, 1945), of the energy cost and energetic efficiency of muscular work in the larger farm animals, horses, mules and cattle, no systematic studies have been made with sheep and goats. It was to try to fill this gap that this investigation was begun.The net efficiency of muscular work is defined as the ratio of the work done to the energy expended in doing it. Work is defined as force x distance, and can be expressed in units of energy by use of the mechanical equivalent of heat, i.e. I kg m work = 2-34 cal. It is impossible to assess in any simple way how much external work is done by an animal walking horizontally and, therefore, it is not possible to measure the efficiency of an animal for horizontal walking. Measurements made with animals walking on gradients, however, permit an assessment of efficiency because the energy expended in raising the body can be equated with its gain in potential energy. T o estimate the energetic efficiency of muscular work thus involves measurement of energy expenditure when the animal walks on the level and on gradients. E X P E R I M E N T A LAnimals. Two Cheviot wether sheep, each weighing approximately 90 lb, were used. One of them (sheep H) was well accustomed to walking on a treadmill having been used in previous experiments and the other (sheep J) was trained to walk over a period of I week before the experiment began. Both sheep were used to living in cages and respiration chambers.Diets. Each sheep was given a ration of artificially dried grass finely ground and pelleted; it contained 1 5 . 1 yo crude protein on a dry-matter basis. Two amounts were given to each sheep. One, referred to as the high level, was computed to be sufficient to allow the animal to retain energy even when working at the highest rate; the other, referred to as the low level, was computed to result in loss of energy from the body even when the sheep was at rest. Each of the rations was offered for 14 days before the experiment began. Food was given twice daily at 5 pm and 5.30 am. No refusal of food occurred during the experiments. The experiments with the two amounts of food were duplicated with each sheep and the amounts of food given and the order in which they were offered are shown in Table I

The metabolic cost of walking on gradients with a waddling gait

“…The increase in metabolic cost when moving up an incline agrees with previous studies (Armstrong et al, 1983;Bamford and Maloiy, 1980;Bedford et al, 1979;Brooks and White, 1978;Chassin et al, 1976;Clapperton, 1964;Cohen et al, 1978;Dill, 1965;Eaton et al, 1995;Ellerby et al, 2003;Farley and Emshwiller, 1996;Margaria et al, 1963;McDonough et al, 2002;Minetti et al, 2002;Raab et al, 1976;Robbins et al, 1979;Rubenson et al, 2006;Snyder and Carello, 2008;Taylor et al, 1972;Warncke et al, 1988;White and Yousef, 1978;Wickler et al, 2000;Wickler et al, 2003;Wunder and Morrison, 1974;Yousef et al, 1972). The finding that descending a decline is not metabolically cheaper than locomoting on the level, however, is contrary to previous findings (Armstrong et al, 1983;Byrnes et al, 1985;Cohen et al, 1978;Margaria et al, 1963;Minetti et al, 2002;Raab et al, 1976;Robbins et al, 1979;Taylor et al, 1972;White and Yousef, 1978;Yousef et al, 1972).…”

“…Although there are notable exceptions -the marabou stork Leptoptilos crumeniferus (Bamford and Maloiy, 1980), cockroach Gromphadorhina portento (Herreid et al, 1981) and ant Camponotus sp. (Lipp et al, 2005) -generally, for most species, as gradient increases so does V O2 at all locomotory speeds (Bedford et al, 1979;Brooks and White, 1978;Chassin et al, 1976;Clapperton, 1964;Cohen et al, 1978;Eaton et al, 1995;Ellerby et al, 2003;Full and Tullis, 1990;Raab et al, 1976;Robbins et al, 1979;Wunder and Morrison, 1974;Yousef et al, 1972). The relative cost of ascending or descending a gradient may also be size dependent, with a lower percentage increase or decrease (compared with locomotion on the level) of locomoting uphill or downhill, respectively, for smaller animals (Taylor et al, 1972).…”

“…Additional muscle activity means that whole-animal metabolic costs (rate of O 2 consumption, V O2 ) should also increase (Ellerby et al, 2003), assuming that additional costs are met aerobically. Accordingly, increased metabolic costs were found in birds (Bamford and Maloiy, 1980;Ellerby et al, 2003;Rubenson et al, 2006;Snyder and Carello, 2008;Warncke et al, 1988), humans (Dill, 1965;Margaria et al, 1963;Minetti et al, 2002;Yousef et al, 1972), a range of quadrupeds (Armstrong et al, 1983;Bedford et al, 1979;Brooks and White, 1978;Chassin et al, 1976;Clapperton, 1964;Cohen et al, 1978;Eaton et al, 1995;Farley and Emshwiller, 1996;McDonough et al, 2002;Raab et al, 1976;Robbins et al, 1979;Snyder and Carello, 2008;Taylor et al, 1972;White and Yousef, 1978;Wickler et al, 2000;Wickler et al, 2003;Wunder and Morrison, 1974;Yousef et al, 1972) and invertebrates (Full and Tullis, 1990;Tullis and Andrus, 2011) when ascending gradients. Although there are notable exceptions -the marabou stork Leptoptilos crumeniferus (Bamford and Maloiy, 1980), cockroach Gromphadorhina portento (Herreid et al, 1981) and ant Camponotus sp.…”

Behavioural and physiological measures following treadmill exercise as potential indicators to evaluate fatigue in sheep

“…A sheep that walked for 5 h would have walked the equivalent of 9 km, which is greater than estimates of the total distance walked by a grazing sheep in a day of about 6.4 km (Clapperton, 1964a). This result was also consistent with observations on two sheep by Clapperton (1964b) where the percentage of time spent lying down during the night only increased by 1% after walking on a treadmill at about 0.4 m/s for about 4 h/day compared with that after no exercise. In the current study, the behaviour of the treatment sheep during the first 6 h after exercise was similar to that of the control sheep in that they spent about half of this time standing and about half of the time lying down.…”

Effects of Exercise and Plane of Nutrition on Nutrient Utilization by the Hind Limb of the Sheep

“…Before comparing our results with theirs, the different levels of exercise employed in this and other studies must be considered. It is convenient to do this in terms of total energy expenditure because, although whole-animal heat production was not measured in any of these experiments, the metabolic response to a given level of exercise can readily be calculated from the equations established by Clapperton (1964), based on the speed and gradient of walking. Calculations show that the level of exercise to which sheep were subjected in the present study was very similar to the less strenuous of the two levels used by both Jarrett et al (1976) and Brockman (1979), and tothe single level used by Judson et al (1976).…”