Abstract:
MAINTENANCE REQUIREMENTS OF SHEEP INDOORS AND AT PASTURE N. McC. GRAHAM* I. INTRODUCTION The generally The aim costs of of these activities of sheep at pasture vary with pastoral conditions and are more extensive than those of sheep confined in calorimetric apparatus. of this paper is to use previously published data on the extent and energy walking, feeding, ruminating and standing to determine the relative effects activities on the maintenance requirements of sheep indoors and at pasture. II. CALCULATIONS AND DISCUSSION The data of Clapperton (1961) and Graham (1964) on the energy costs of various activities of sheep, summarized in Table 1, require some qualification. First, walking means forced walking on a treadmill; whether free walking has a smaller cost has yet to be determined. Secondly, the costs of feeding, ruminating and standing were derived from comparisons between short (<1 hr) periods of activity and contiguous periods of inaction and may not apply to long periods of activity. However, measurements made by Brockway (1964) indicate that the cost of standing, at least, is independent of its duration. Thirdly, since the cost of ingesting food very slowly is small (Graham 1964), expenditure in grazing sparse pasture may be overestimated. Thus the following calculations are approximate and for comparative purposes only. In Table 2, a possible schedule of activities is given for sheep in several situations and, in Table 3, daily energy expenditures are calculated for a 50 kg adult sheep, based on the data in Tables 1 and 2. The calculations indicate that a 50 kg sheep kept on sparse pasture 5 km from drinking water could expend more than eight times as much energy per day in various activities as a sheep confined in a calorimeter and almost twice as much as a sheep on good pasture. If maintenance costs other than of work were constant, total energy expenditure at *Division of Animal Physiology, C.S.I.R.O., Ian Clunies Ross Animal Research Laboratory, Prospect, N.S.W., Australia. 272 TABLE 2 A possible schedule of daily activiti' of adult sheep in several locations, es maintenance of zero energy balance would range from 1200 to over 2000 kcal/day; by definition this is the metabolizable energy required for maintenance. Even if the costs of work were half of the values given in Table 1, the cost per day would still be quite large when the various activities occupy a large part of the day. Relative food requirements may be calculated approximately by taking account of herbage digestibility. For example, if digestibility of the sparse pasture were 50% and digestibility of the good pasture were 80% (1: 1.6), then the ratio of expenditures on these pastures (Table 3) multiplied by 1.6 would give 2.2:1 as the ratio of food requirements for zero energy balance. A partial explanation of the results of many grazing trials could be provided thus (see review by Lambourne and Reardon 1963), but reliable comparisons cannot be made in the absence of actual timetables. These calculations emphasize the importance of behavioural studies on sheep used in comparative feeding and grazing trials. TABLE 3 273 A B RNOLD , G. (1962). Grazing behaviour of sheep. Journal III. REFERENCES of the British Grassland Society 41. ROCKWAY 17: , J. M. (1964). Posturally associated changes in heat content of sheep. Proceedings of 3rd Symposium on Energy Metabolism of Farm Animals. European Association for Animal Production (in press). C LAPPERTON , J. L. ( 1961). Energy expenditure of sheep in walking. Proceedings of Nutrition Society 20: xxxi. C RESSWELL , E. ( 1960). Ranging behaviour studies with sheep. Animal Behaviour 8: 32. G RAHA M, N. McC. ( 1964). Energy costs of feeding activities and energy expenditure of grazing sheep. Australian Journal of Agricultural Research 15 (in press). H UNTER , R. F., and M ILNER , C. (1963). Behaviour of hill sheep. Animal Behaviour 11: 507. L AMBOURNE , L. J., and REARDON, T. F. (1963). Effect of environment on maintenance requirements of Merino wethers. Australian Journal of Agricultural Research 14: 272. , 274