Effects of dietary cation–anion difference on calcium, nitrogen metabolism and relative blood traits of dry Holstein cows

Three multiparous nonpregnant dry Holstein cows were designated in a 3×3 Latin square experiment to investigate the effects of dietary DCAD level on Ca, N metabolism, and relative blood traits. DCAD levels of the three experimental diets were 224 (HDCAD), 151 (MDCAD), and −265 (LDCAD) mequiv./kg DM respectively. The results indicated that deposition efficiencies of absorbed Ca and digestible N decreased with the decrease of dietary DCAD level (P<0.05). There was no difference of plasma Ca among treatments, but the daily amount of Ca excreted from urine increased with the decrease of dietary DCAD (P<0.05). Plasma urine N of the HDCAD treatment was higher than that of the MDCAD treatment (P<0.05), but was lower than that of the LDCAD treatment (P<0.05). Plasma Mg increased with the decrease of dietary DCAD (P<0.05). pH values of urine and ruminal fluid decreased with the decrease of dietary DCAD (P<0.05). Plasma PTH and ALD increased, and plasma CT decreased with the decrease of dietary DCAD (P<0.05). Results of the present study suggested that diets with low DCAD value could decrease the deposition rate of absorbed Ca, facilitate the mobilization of Ca in bone stores, and decrease the deposition efficiency of digested N in dry Holstein cows.