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14. Feeding Grass to Nonlactating Dairy Cows

Hypocalcemia results from a deficiency in plasma Ca at the onset of lactation in dairy cows, and is the main cause of several severe metabolic disorders. Milk fever is a metabolic disorder due to high Ca demand at the start of lactation. Animal nutritionists tend to be concerned with the dietary cation-anion difference (DCAD, expressed as milliequivalents per 100 grams dietary DM) in the total ration of a dairy cow. DCAD = [(K + Na) - (Cl + S)], although more complex forms of this relationship are sometimes used. During the transition period 3 to 4 weeks prior to calving, it is desirable to have a moderately anionic diet, to avoid milk fever and hypocalcemia. The effect can be minimized by reducing the level of cations (K and Na) and/or increasing the level of anions (Cl and S) in the diet. Anionic salts can be fed to lower DCAD, but a more effective strategy is to reduce K content of the forage for dry cows. Immediately after calving, however, a cationic diet is essential.

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Timothy will generally be lowest in K content among cool-season grasses.