Effects of Manipulating Dietary Cation-Anion Balance on Macromineral Balance in Sheep

¹ Department of Animal Science, Macdonald Campus of McGill University, Ste. Anne de Bellevue, PQ, Canada H9X 1C0

Effect on macromineral balance in sheep of dietary excess of inorganic anions (Cl and S) or inorganic cations (Na and K) was studied. Dietary cation-anion balance was calculated as milliequivalents [(Na + K) - (Cl+ S)] kg^-1 of DM. Eight crossbred wethers were fed two levels of Ca, designated high Ca (.82%) or normal Ca (.48%), with four treatments each, three of which differed in dietary cation-anion balance. Control and two treatments had +284, +61, and –27 meq kg^-1 of DM for high Ca and +343, +218, and +63 meq kg^-1 of DM for normal Ca, respectively. A fourth treatment was control plus injection of vitamin D₃ (16,670 IU kg^-1 of BW). Reducing dietary cation-anion balance reduced Ca retention by increasing excretion of urinary Ca. Apparent absorption of Ca was similar across cation-anion balances. There was no correlation observed between dietary cation-anion balance and concentration of plasma Ca. No difference was observed in apparent absorption of Ca between high and normal Ca. This result may be related to an oversupply of dietary Ca Magnesium retention as a proportion of that absorbed for lowest cation-anion balance was smaller than that for the intermediate balance and control plus vitamin D₃, although not different from control. Results showed that reduced dietary cation-anion balance resulted in a reduction of Ca retention.

Key Words: cation-anion balance • mineral metabolism • calcium • sheep

Submitted on April 30, 1990
Accepted on July 15, 1991