The effect of varying leafy sward height and bulk density on the
ingestive behaviour of young deer and sheep
R.J. Mitchell, J. Hodgson, D.A. Clark
DSIR Grassland, Private Bag, Palmerston, New Zealand
Proceedings of the New Zealand Society of Animal Production.
1991, 51: 159-166
The effect of varying the height and bulk density of the leafy
zone of the sward on the ingestive behaviour of six 11 month old Red
deer hinds and seven 14 month old Romney ewe hoggets was examined. Deer
and sheep, confined to metabolism crates were randomly allocated 21
sward height x density combinations consisting of 7 heights (3-21 cm) x
3 bulk densities (0.19-0.75 mg DM/cm3). The Sorghum bicolor
swards were grown in 42 x 30 cm trays and had a deep, stem free leafy
zone. The required height of leaf was made accessible to animals by
raising or lowering each sward relative to a horizontal grid of fine
rods forming 3 cm x 3 cm squares below which animals could not graze.
The two lower bulk densities were engineered by snipping out alternate
rows, or rows and columns of plants. After grazing for at least 20
bites, bite depth, bite weight, grazed stratum bulk density, bite volume
and bite area were calculated.
The ingestive behaviour of deer and sheep was very similar in relation
to height and bulk density. The positive effect of height on bite depth
was on average 11 times as large as the negative effect of bulk density.
Height had little or no effect upon bite area, while bulk density had a
moderate, negative effect. On average a 100% increase in height or bulk
density respectively resulted in a 64% vs only 21% increase in bite
weight; reflecting the fact that bite volume increased in relation to H
(39%) but decreased in relation to bulk density (18%). Thus height was
the major determinant of bite volume and bite weight via its influence
on bite depth.
Keywords: NZSAPAB;
Ingestive behaviour; bite dimensions; sward height; bulk
density; Red deer; Romney sheep
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Last Updated 25-01-1997
