The effects of additions of sodium hydroxide and a concentrated solution containing urea, calcium, phosphorus, sodium, trace elements and vitamins on the intake and digestibility of oat straw by beef cows

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Abstract
Eight pregnant beef cows and four rumen-fistulated cows were given 1·67 kg barley dry matter per day and 5·1 kg chopped oat straw dry matter treated by one of four different methods. The straw treatments (given in a 4 × 4 Latin square design) were (A) nil, (B) sodium hydroxide (25 g/kg straw, dry matter basis), (C) a fully soluble liquid supplement containing urea, calcium, phosphorus, sodium, trace elements and vitamins (40 g/kg straw, dry matter basis), and (D) sodium hydroxide plus liquid supplement. In the absence of liquid supplement 0·3 kg per day of the straw dry matter was not consumed, and with the sodium hydroxide plus liquid supplement treatment the cows would have consumed more straw than was offered. Sodium hydroxide increased the digestibility of the straw organic matter from 0·46 to 0·50 (P <0·05), and this was further increased to 0·53 (P <0·01) for the combined sodium hydroxide plus liquid supplement treatment. The calculated metabolizable energy intakes from straw were increased from 31 (nil) t o 36 by either the sodium hydroxide or liquid supplement treatments (P <0·05) and to 41 by the combined treatments (P <0·001). Sodium hydroxide tended to increase the concentrations of n- and iso-butyric acids in the rumen liquor.