Lambs were given a diet of oaten chaff-sucrose-fishmeal (48:48:4, w/w) and either 60 (diet A) or 120 (diet B) g urea/kg sucrose in the diet. All animals were defaunated and half were refaunated. Each group of lambs (faunated and defaunated) was then divided into two groups and given diet A or diet B. Feed intake, wool growth and live-weight change were monitored over a 182 d period. The level of urea supplementation had no effect on wool growth or live-weight gain. Defaunated lambs gained live weight at a higher rate (9%, P less than 0.06) and grew 37% more wool (P less than 0.01) than the lambs with large populations of protozoa in their rumens.
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Bird et al. (1984) studied this question.