Effects of dietary cation–anion concentrations on performance and acid–base balance in growing lambs

Abstract

Twenty-four castrated lambs (32.4 ± 4.1 kg BW) were used to study the effect of varying dietary cation–anion concentration [C–A] on performance and acid–base balance. The diets contained approximately 100, 300, 500 and 700 mequiv Na + K − Cl kg−1 of feed. Each group of six lambs was fed one of the diets ad libitum during a 6-wk test. Increasing the [C–A] of the diets resulted in higher feed intake and higher daily gains (P < 0.01) without affecting feed efficiency. Apparent digestibility of nutrients was not affected by the dietary treatments but a negative relationship was found between intake and energy digestibility (P < 0.01). Blood pH was lower in lambs receiving the 100 [C–A] diet (P < 0.05). Blood bicarbonate and base excess increased as [C–A] in the diet increased from 300 to 700 mequiv (P < 0.05). Plasma Mg concentration decreased with increasing dietary [C–A] (P < 0.01). Urinary pH and urine volume increased as [C–A] in the diet increased (P < 0.01). The results indicate that diets containing between 500 and 700 mequiv Na + K − Cl kg−1 stimulated growth by allowing greater feed intake and greater daily gains with little effect on nutrient digestibility. Blood profile showed a systemic response to dietary changes in [C–A], but indicated that lambs were able to adapt to cation loads since the values obtained for acid–base balance were within physiological range for lambs. Key words: Cation–anion, acid–base, lambs