Heat energy for growing goats and sheep grazing different pastures in the summer
M. J. Herselman, S. P. Hart, T. Sahlu, S. W. Coleman, and A. L. GoetschJournal of Animal Science 77:1258-1265. 1999.
Energy used by ruminants to graze is thought affected by environmental conditions, such as land area and topography and types of herbage available. Currently, the National Research Council (NRC) 1981 publication on the nutrient requirements of goats recommends that activity energy costs be estimated as 25% of the maintenance cost for light activity, 50% with semiarid rangeland and slightly hilly conditions, and 75% with sparsely vegetated rangeland or mountainous transhumace pasture. However, differences among forage systems typical of goat production conditions in the US or among ruminant species or breeds of a particular species are largely unknown. Thus, this experiment was conducted to investigate influences of animal type (Angora goat, Spanish goat, and Suffolk × Rambouillet sheep wethers) on energy used for activity during summer grazing of two types of grass-based pastures. An improved pasture treatment consisted of 0.7-hectare pastures primarily of Old World bluestem and johnsongrass, and a native pasture treatment entailed 10.8-ha paddocks dominated by big and little bluestems and indiangrass. The NRC (1981) publication suggests that activity energy costs may be greater for goats than for other ruminants such as sheep. However, in this experiment total energy expenditure was greater for sheep, which related to a longer period of time spent grazing and greater energy intake, with the endresult of a similar quantity of stored energy by the sheep and goats. Energy intake was similar between native and improved pastures, although grazing time and the activity energy cost were greater for native pastures. Animals on native pasture also took more steps per unit of time spent grazing, implying that increases in energy intake for native pasture that could be achieved through increased grazing time would occur at a relatively greater energy cost than for improved pasture. Consequently, forage availability may be relatively more important for achieving energy intake adequate for body weight maintenance or greater with pasture conditions similar to those of the native pasture treatment than with the improved pasture treatment. Furthermore, grazing conditions of improved and native pasture treatments may similarly influence productivity by goats and sheep and by different goat breeds.
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