Factors limiting the intake of feed by sheep. IX.* Further studies of the roughage requirement of the ruminant lamb fed on concentrate diets based on wheat

Abstract

The voluntary feed consumption (VFC) and body weight gain of lambs initially weighing 22 kg were measured when pelleted diets based on ground wheat grain and varying in content of ground straw were offered. VFC increased progressively as the straw content of the diet was increased from 2% through 8% to 14%. Lambs fed on the diets with 8 and 14% straw performed similarly, whereas those with 2% straw had lower rates of body weight gain (– 11%) and intakes of digestible organic matter (– 4%). Increase in straw content from 2 to 14% was accompanied by a decrease in diet digestibility and increases in (i) the rates of flow from the rumen of digesta, sodium and potassium, (ii) the pH of ruminal contents, and (iii) the time spent ruminating.

Lambs initially weighing 37 kg were offered 'roughage-free' concentrate diets based on wheat in which the wheat was presented either as whole grain or in ground and pelleted form. With whole grain, values for VFC, digestible organic matter intake and body weight gain were respectively 17, 17 and 29% higher than with ground grain. The feeding of whole grain instead of ground grain increased the time spent daily in ruminating from 0.3 to 2.2 h.

It was concluded that the roughage requirement of the ruminant lamb fed on concentrate diets based on wheat was higher when the wheat was in ground form than when whole grain was used. The requirement with ground wheat diets was tentatively assessed as in the range of 2–8 g ground straw per 100 g diet.

Lambs were slow in adapting to a chopped roughage diet following prolonged feeding with wheat-based diets. VFC data suggested that the slow adaptation was associated with changes in rumen function.

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*Part VIII, Aust. J. Agric. Res., 25, 349 (1974).