The Effect of Fertilization of a Native Lowland Pasture on Forage Intake and Nutritional Value of Diet Selected by Grazing Sheep

Abstract

Knowledge of the forage intake and nutritional value of the diet selected by grazing animals is basic to good range management. The amount and kind of forage chosen may vary with the kind of animal, its previous history, age, size, health, and physiological state as well as with the range site, range condition, season of the year, current weather, and management practices such as intensity of grazing, grazing systems, fertilization, and supplementation With protein, phosphorus, or other nutrients. A knowledge of the various factors that affect dietary intake and selection would permit the range manager to more wisely plan the grazing use of different range sites in different ra11ge condition classes at different seasons and to use more efficiently those management practices that would optimize animal production on a sustained basis. Measurement of forage intake and nutritional value of the diet of grazing animals is difficult. Grazing animals commonly have available to them a wide range of potential food in the form of different plant species, each with its particular physical and chemical characteristics and each with different densities and growth forms. From this available forage, the grazing animal exercises a high degree of selection, the mechanisms of which appear to be based on subtle chemical and physical differences affecting smell, taste, and touch (Arnold, 1964). However, the ultimate regulator controlling food intake is the central nervous system (Anand, 1961). The methods used for measuring the food intake and nutritional value of diets of grazing animals have been reviewed by Harris et al. (1967) and Van Dyne (1969). However, many of them have not been adequately tested and require further study. No information is available concerning diets of grazing animals in South Dakota other than what can be inferred from chemic al composition of clipped samples or from supplementation studies. A few intake studies have been conducted in this area at Morris, Minnesota, (Davis et al., 1967) with wethers grazing cultivated pastures, at Scottsbluff, Nebraska, (Hoehne, 1967) on sands range with yearling heifers, and at Laramie, Wyoming, (Rice, 1968) with wethers. Otherwise, no studies are known from neighboring states. Furthermore, the extensive areas of wetland ranges in eastern South Dakota are subjected to very high stocking rates; yet very little is known about their productivity, their ecology, their response to fertilization, or the nutritional value of the diet selected by animals grazing them. This study was conducted to: l. Determine the most promising technique for the measurement of forage intake and nutritive value for use in South Dakota grazing studies. 2. Determine the effect of nitrogen, phosphorus, and potassiutt1 fertilization of lowland native pasture on forage intake and nutritional value of the diet of grazing fistulated sheep. Other studies were conducted to determine the effect of fertilization on foliage yield, forage intake and nutritional value of the diet of grazing fistulated heifers, and botanical composition of the diet of grazing cattle and sheep and to compare the use of chromic oxide with total collection to estimate the total fecal production of the sheep. These related studies will be reported elsewhere