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Increasing intake by the development of optimal grazing management in relation to animal behaviour at pasture.
Linnane, M. Brereton, A. J. Giller, P.S.
Linnane, M.
Brereton, A. J.
Giller, P.S.
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1999-12-01
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Linnane, M., Brereton, A.J., Giller, P.S., Increasing intake by the development of optimal grazing management in relation to animal behaviour at pasture, End of Project Reports, Teagasc, 1999.
Abstract
In each month from July to December, grazing activity for each of 12
animals was recorded over a number of days continuously using
vibrarecorders. The work was done at Killarney National Park and the
animals were heifers of the Kerry breed living under semi-natural
conditions with abundant pasture available.
In July (16 hour day-length) - all animals began grazing at dawn and
grazed for about 2.5 hours. This first bout was followed at intervals
of about 2 hours by shorter bouts each about one hour in duration. In
late afternoon another bout commenced which continued for 4 to 5
hours through until after dusk. During darkness, about midnight,
there was a short bout of grazing. All of the animals behaved thus
and the pattern was repeated each day. Total grazing time was near
11 hours each day.
By October day-length had decreased. There was still a bout at dawn and
a bout at sunset. As in July there were three smaller bouts but all
occurred during darkness. The total grazing time was close to 11 hours
as before. The pattern of grazing was consistent between animals and
days. In August-September-October and November there were always two
major bouts of grazing related to dawn and dusk. Grazing total time was
always near 11 hours. As day-length decreased the smaller daylight
bouts were progressively replaced by bouts during darkness. Similar
patterns were also found in studies of grazing Holstein/Friesian heifers
and of housed non-lactating cows at Moorepark.
The primary feature of the grazing pattern is the bout. The bout implies
that there is a control that determines when grazing commences and
ends. Rumen capacity plays a part but does not explain why minor bouts
are only one hour and major bouts are more than 4 hours. The rigid
association of the two major bouts with dawn and dusk implies that light
also plays a part. That the total grazing time is constant suggests that yet
another control is operating that is related to the state of the animal
relative to a target state. And this control relates to a 24-hour period.
Domestic bovines do not display any patterns of behaviour related to
seasonal or lunar cycles. The patterns appear to be circadian and in that
case it would not be surprising to find that the suggested light cue was
present as a means of measuring the day.