Calcium and cation-anion balance effects on feed intake, body weight gain, and humoral response of dairy calves.

Our objective was to examine whether feeding low cation-anion diets altered the Ca status of the growing calf. Holstein calves (n = 32; 16 males) were blocked at 56 to 70 d after birth according to sex and birth date and assigned randomly to dietary treatments containing Ca content and cation-anion balances as milliequivalents of (Na+K)-(Cl+S)/100 g of dietary DM of .42% and -18, .52% and -18, .42% and 13, and .52% and 13. Feed intake did not differ among treatments. Calves fed the diet with cation-anion balance of 13 had higher gain (.85 vs. .71 kg/d) than those fed the diet with balance of -18. Venous blood pH (7.374 vs. 7.323), partial pressure of CO2 (47.9 vs. 45.6 mm Hg), and bicarbonate (28.3 vs. 23.3 mmol/L) were higher for calves fed the 13 versus -18 balances. Plasma Ca and P were unaffected by Ca or cation-anion balance. Urinary pH was higher for calves fed the high than the low balance (7.442 vs. 6.047). Urinary Cl and Ca excretion was higher for calves fed the low than the high balance. Breaking strengths for 7th and 9th ribs were higher for calves fed the high balance and higher for the 7th rib only for calves fed the high Ca diet. Cation-anion balance altered Ca metabolism, but it is unclear whether Ca requirements were also altered.