balance, and regulating acid-base balance. Sodium also functions in muscle contractions, nerve impulse transmission, and glucose and amino acid transport. Chlorine is necessary for the formation of hydrochloric acid in gastric juice and for the activation of amylase.
Requirements for sodium in nonlactating beef cattle do not exceed 0.06 to 0.08 percent, while lactating beef cows require approximately 0.10 percent sodium (Morris, 1980). Ruminants have an appetite for sodium, and if it is provided ad libitum, they will consume more salt than they actually require. In a 2-year study with beef cows grazing forage containing from 0.012 and 0.055 percent sodium, providing salt ad libitum did not affect calf weaning weights or cow body weights (Morris et al., 1980). Chlorine requirements are not well defined but a deficiency of chlorine does not seem likely in practical conditions (Neathery et al., 1981). Young calves fed 0.038 percent chlorine performed similar to those fed 0.5 percent chlorine (Burkhaltor et al., 1979).
Signs of deficiency of sodium are rather nonspecific and include pica and reduced feed intake, growth, and milk production (Underwood, 1981). When sodium intake is low, the body conserves sodium by increasing reabsorption of sodium from the kidney in response to aldosterone (McDowell, 1992). The sodium:potassium ratio in saliva has been used as an indicator of sodium status. This ratio is normally 20:1, and a production response to sodium supplementation is likely when the sodium:potassium ratio is less than 10:1 (Morris, 1980). Serum or plasma sodium concentration is not a reliable indicator of sodium status. Dietary sodium concentration is a good measure of sodium adequacy.
Cereal grains and oilseed meals usually provide inadequate amounts of sodium for beef cattle. Animal products are much higher in sodium and chlorine than plant products (Meyer et al., 1950). The sodium content of forages varies considerably (Minson, 1990). Sodium can be supplemented as sodium chloride or sodium bicarbonate and both forms are highly available.
High concentrations of salt have been used to regulate feed intake and cattle can tolerate high-dietary concentrations provided that an adequate supply of water is available. Growing cattle were able to tolerate 9.33 percent salt for 84 days without adverse effects (Meyer et al., 1955). However, Leibholz et al. (1980) reported that 6.5 percent salt decreased organic matter intake and growth in calves. The maximum tolerable concentration for dietary salt in cattle was estimated at 9.0 percent in Mineral Tolerance of Domestic Animals (National Research Council, 1980).
Salt is much more toxic when present in the drinking water of cattle. Growing cattle were able to tolerate 1.0 percent added salt in drinking water without adverse effects (Weeth et al., 1960; Weeth and Haverland, 1961); however, the addition of 1.25 to 2.0 percent salt resulted in anorexia, reduced weight gain or weight loss, reduced water intake and physical collapse (Weeth et al., 1960). In some areas of the western United States, soils are high in saline, resulting in groundwater that can cause saline water intoxication. Consumption of water with more than 7,000 mg Na/kg resulted in reduced feed and water intake, decreased growth, mild digestive disturbances, and diarrhea (Jenkins and Mackey, 1979).
Sulfur is a component of methionine, cysteine, and cystine, and the B-vitamins, thiamin and biotin, as well as a number of other organic compounds. Sulfate is a component of sulfated mucopolysaccharides and also functions in certain detoxification reactions in the body. All sulfur-containing compounds with the exception of biotin and thiamin can be synthesized from methionine. Ruminal microorganisms are capable of synthesizing all organic sulfur containing compounds required by mammalian tissue from inorganic sulfur (Block et al., 1951; Thomas et al., 1951). Sulfur is required also by ruminal microorganisms for their growth and normal cellular metabolism.
Requirements of beef cattle for sulfur are not well defined. The recommended concentration in beef cattle diets is 0.15 percent. Sulfur supplementation increased gain in steers fed corn silage-corn-urea based diets containing 0.10 to 0.11 percent sulfur (Hill, 1985). In steers fed high-concentrate diets containing 0.14 percent sulfur, increasing dietary sulfur tended to reduce ruminal lactic acid accumulation and improve feed efficiency (Rumsey, 1978). Other studies have indicated that 0.11 to 0.12 percent sulfur was adequate for growing cattle (Bolsen et al., 1973; Pendlum et al., 1976). In Australia, sulfur supplementation increased gain by 12 percent in steers grazing sorghum×sudangrass containing 0.08 to 0.12 percent sulfur (Archer and Wheeler, 1978). The sulfur requirement of ruminants grazing sorghum×sudangrass may be increased because of the need for sulfur in the detoxifica-