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The value of ‘worm-free’ sheep in the assessment of pasture is illustrated by an experiment in which the effect of internal parasites could only be distinguished by the use of ‘worm-free’ controls. 2. The effect of augmenting the initial pasture infestation (with nematodes parasitic in the sheep) was slight. 3. In an experiment with ewes and lambs at three lambing percentages and over a range of stocking rates:
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Spedding et al. (1964) studied this question.
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