Ráðunautafundur - 15.02.1989, Side 27

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The consequences for animal production, which have so far mainly concerned dry
cattle, have yet to be fully evaluated although the evidence is of steadily improved
performance with time. Further studies are necessary with suckler cows before the
full potential of this approach can be assessed.
Problems associated with this technique, particularly in Wales include the decline
in numbers of hill cattle and the difficulty in introducing fencing control where
open access is protected for recreational purposes.
Management of grazing on in-bye land
As the proportion of in-bye to range increases, and more particularly where
improved swards have been established through complete re-seeding or overseeding
techniques, its proportional significance to the farms total economic performance
becomes greater.
One of the most successful features of grazing research in recent years has been
an understanding of the basic processes controlling the performance of such swards
and the emergence of clear guidelines for their management (Maxwell and Treacher,
1987; Alcock et al., 1986).
Of great relevance is the use of sward state rather than stocking rate to relate
to pasture production, herbage consumption by grazing animals, and animal
production. Thus, in a continuously grazed grassy sward, gross herbage production
increases with sward height up to a maximum at which a high proportion is lost to
senescence and death. At lower sward heights gross herbage production declines but
a higher proportion is consumed and Iess is lost to senescence (Figure 3).
Experiments performed at many centres confirm that maximal removal of herbage
per unit area of land occurs when sward surface heights are maintained between 4
and 6 cm. Within this range herbage intake is linearly related to sward height
(Figure 4) with maximum intake occurring at 6 cm and declining below that. This
raises the opportunity for objective control over grazing with the target sward
height being related to the target levels of individual animal production required.
The maintenance of swards under these guidelines Ieads to a dense leafy sward
with a seasonal profile of productivity which is more evenly distributed over the
growing season than that observed in rotationally cut swards.
Arising from this research have been clear guidelines for grazing management
which have been incorporated, for example, in the Agricultural Development and
Advisory Service (ADAS) grassland management calender.
The basic features are illustrated in Figure 5.
From early January, if at all possible, swards should be rested by in-wintering,
away wintering or use of sacrifice areas.