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Nutrient Requirements of Beef Cattle: Seventh Revised Edition, 1996
dence of disease was 57 percent compared with 47 percent when a 25 percent concentrate diet was used (Preston and Kunkle, 1974; Preston and Smith, 1974). Supplementing high-energy diets with hay for 3 to 7 days can overcome the adverse health effects of the high-energy diet (Lofgreen et al., 1981; Lofgreen, 1983, 1988). The source of grain type—corn, grain sorghum, barley or wheat—used in starter and receiving diets did not affect calf health or performance (Smith et al., 1988).
Grain type used in receiving diets did not affect calf health or performance. In fact, a better rate of gain was obtained with a mixture of grains (Brethour and Duitsman, 1972; Addis et al., 1975, 1978); however, highly stressed calves seem to have low tolerance for added fat, thus fat should probably not exceed 4 percent of dietary dry matter in receiving diets (Cole and Hutcheson, 1987b). Stressed calves prefer a dry diet compared to a diet high in corn silage, but they adapt to high amounts of corn silage in the diet after 7 to 14 days (Preston and Smith, 1973, 1974; Preston and Kunkle, 1974; Koers et al., 1975; Davis and Caley, 1977).
Protein requirements of stressed calves do not seem to be different than those of nonstressed calves. Stressed calves, however, generally decrease their feed intake; therefore the concentration of protein in the diet should be increased for stressed or diseased calves (Cole and Hutcheson, 1990; Hutcheson et al., 1993). Protein concentrations of 13.5 to 14.5 percent on a dry matter basis in receiving diets meet the protein requirements of stressed calves (Embry, 1977; Bartle et al., 1988; Cole and Hutcheson, 1988; Eck et al., 1988; Cole and Hutcheson, 1990). Diseased calves exhibit a hypermetabolic response with increased excretion of nitrogen (Cole et al., 1986). The nitrogen kinetics of virus-infected calves are affected by shifts in the rates of protein metabolism (Orr et al., 1989). Figure 8–1 represents the differences in nitrogen (N) rate constants for infectious bovine rhinotracheitis virus calves. When fed increased protein, hyperurinary excretion of nitrogen during disease is partially alleviated (Boyles et al., 1989).
Stressed calves have a lower tolerance for nonprotein nitrogen (urea) than do nonstressed calves. Urea intakes of 30 gm/day or less seem to be tolerated by newly arrived or stressed calves during the first 2 weeks of feeding (Preston and Kunkle, 1974; Gates and Embry, 1975; Cole et al., 1984).
Feeding undigestible intake protein (UIP) to stressed calves resulted in increased performance (Preston and Kunkle, 1974; Preston and Smith, 1974; Grigsby, 1981; Phillips, 1984). UIP as 5.4 percent of dietary dry matter,
FIGURE 8–1 Changes in nitrogen (N) rate constants for calves with infectious bovine rhinotracheitis virus (IBRV). Infected calves fed an increased amount of protein experienced partial alleviation of hyperurinary excretion of nitrogen (Boyles et al., 1989).
at 45 percent of total protein, resulted in increased daily gains and dry matter intake (Preston and Bartle, 1990; Gunter et al., 1993; Hutcheson et al., 1993; Fluharty and Loerch, 1995).
Research indicates that, in general, mineral requirements for stressed cattle are not different than those for nonstressed cattle (Orr et al., 1990); however, decreased feed intake of stressed cattle suggests that higher concentrations of minerals should be formulated into their diets (Hutcheson, 1987, 1990). Cattle subjected to the stresses of marketing and shipping lose weight—primarily from loss of water from the digestive tract and, subsequently, from body cells. When intracellular water is lost, cellular deficiencies of potassium (K) and sodium (Na) can occur (Hutcheson, 1980). The potassium requirement of stressed calves is 20 percent more than that of nonstressed calves (Hutcheson et al., 1984). Data suggest that 1.2 to 1.4 percent potassium in the diet for 2 weeks is the optimum concentration for newly arrived, stressed calves. Additional potassium may not increase gain response if cattle shrink 2 to 4 percent; but with shrinkage of 7 or more percent, a significant effect may be observed with added potassium. Increasing dietary potassium allows the electrolyte and water balance to return to normal. When potassium is added as potassium chloride (KCl), however, care should be taken to limit salt (NaCl) to 0.25 percent of dietary dry matter so as not to increase chloride intake.