Abstract:
Animal Production in Australia Vol. 15 EFFECTS OF NaOH TREATMENT OF WHEAT STRAW ON ACID-BASE BALANCE IN SHEEP P.J. TREVOR-JONES* and JANE LEIBHOLZ* Low quality roughages contain relatively high amounts of lignified structural carbohydrates that are low in digestibility. NaOH treatment of roughages breaks bonds in lignified matrices freeing potentially digestible carbohydrates for microbial attack, however, a problem of excess sodium load may arise. Voigt and Piatkowski (1974) found that in cows eating a ration comprising one-third NaOH-treated (60 g/kg) wheat straw which represented an intake of an additional 103 g sodium/d, the excretory capacity of the kidneys for sodium was exceeded as indicated by the increased protein excretion in the urine. The acid-base balance of the animal may also be affected by the intake of NaOH-treated straw, and this was studied in the present experiment. Sheep were fed ad lib. at three-hourly intervals. Five sheep were offered a diet of NaOH-sprayed straw ((g/kg) 50 NaOH, 2 KCl, 26 urea and supplemented with S, Ca, P, Co, Cu, Mn, Zn, Fe and Se); another four sheep were offered lucerne chaff. The sheep were fitted with carotid loops and samples of blood were withdrawn at three-weekly intervals. The changes in blood gases and acid-base balance are shown in Table 1. TABLE 1 Blood pH, blood gases (pCO$, actual bicarbonate (HCOs-) and base excess (BE) in sheep fed NaOH-treated wheat straw or lucerne * P < 0.05. Feeding NaOH-treated straw resulted in a primary metabolic alkalosis as exhibited by increased blood pH, bicarbonate and base excess (P < 0.05). Over the 15 weeks of the experiment there was a linear increase (P < 0.05) in base excess and plasma bicarbonate in the sheep given NaOH-treated wheat straw. The acidbase balance in the blood is controlled by three mechanisms, the bicarbonate buffer system, the respiratory response to retain or excrete acid in the form of carbonic acid, and renal excretion or absorption of bicarbonate (Smith and Brain 1980). The above results indicate adjustments in the first two control mechanisms. It may be concluded that the sheep were unable to adjust to the high alkali intakes over a 15-week period, which may cause production problems in certain environmental situations. 'Fluids and Electrolytes- A Conceptual (1980). SMITH, K. and BRAIN, E. Approach'. Churchill Livingstone Inc.: New York, Edinburgh and London. (1974). Arch. Tierernzhrung 24: 589. VOIGT, J. and PIATKOWSKI, B. C * Dept of Animal Husbandry, University of Sydney, Camden, N.S.W. 2570.
