An investigation of factors influencing the grazing of ragwort (Senecio jacobaea L.) by sheep (Ovis aries L.) on a hill country farm : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Ecology at Massey University
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Date
1997
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Massey University
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Abstract
Grazing by sheep (Ovis aries) can control ragwort (Senecio jacobaea), but some
flock members seldom eat it. For mature ewes, 11% appeared to avoid eating
ragwort, compared with 16% of hoggets and 25% of lambs. Reluctant and avid
ragwort feeders from each age group were fed ragwort indoors. During 5-min
feeding sessions on three consecutive days, sheep classed as ragwort-averse,
regardless of age, consumed less ragwort than avid ragwort eaters. Half of the
ragwort-averse and avid ragwort eaters were confined on ragwort containing
pasture for 10 days. Avid eaters consumed 45% of the volume of tagged ragwort
plants within two days compared with no ragwort grazing by averse sheep. After
10 days, the ragwort-averse sheep consumed a similar rosette volume as the avid
eaters, but lower volumes of elongated plants. Scan-sampling before and after
confinement detected n()_change in the ragwort grazing of avid and averse sheep.
Two further days of indoor ragwort grazing detected no differences in the
behaviour of sheep that experienced restricted grazing compared with those that
did not. The ragwort grazing of ragwort-averse and avid ragwort eaters may not
be modified easily. The effects of pre-weaning ragwort exposure and postweaning
grazing with ewes on ragwort grazing by lambs were studied. Sampling
periods were Weeks 1, 3, and 12 following weaning. Grazing behaviour was
observed for 1-hour daily and the 24-hour reduction in ragwort volume measured
on each of 4 or 5 consecutive days. Lambs exposed to ragwort before weaning
consumed more ragwort than non-exposed lambs during the first two sampling
periods. Lambs from ragwort-free pasture that grazed with ewes spent more time
grazing ragwort than lambs grazing alone from the same background during
Weeks 1 and 3. These effects did not persist into the 12th week following
weaning. Lambs in all groups increased their ragwort eating markedly between
·weeks 3 and 12. This may indicate an increased ability of lambs to consume
ragwort with increasing age or an acclimation period in which all lambs come to
accept ragwort. Grazing management techniques employed before, and
immediately after weaning, appear not to effect the long-term ragwort eating of
lambs.
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Keywords
Tansy ragwort, Sheep, New Zealand, Feeding and feeds