72146 KONDININ 58-73 FINAL - CSIRO

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Nutrition
Fallen leaves offer northern grazing option
CSIRO Livestock Industries researcher Brian Lowry suggests fallen leaves from native deciduous trees has the potential to
supplement dry season diets of sheep and cattle in northern Australia.
Fallen tree leaves have the potential to
contribute to the grass diets of sheep and
cattle grazing northern rangelands during the
dry season, according to new CSIRO research.
Compared with the poor feed quality of dry
pasture grass, fallen leaves have more protein,
break up more readily after chewing and the
digestion — although less than for grasses —
happens quickly.
Although fallen leaves are recycled in
various ecosystems, few people recognise their
value as a nutritious feed source.
But scientists are evaluating new evidence
which may cause a rethink of what grazing
animals in the northern rangelands actually
eat.
Using new methods, Queensland-based
CSIRO researchers Andrew Ash and David
Coates have found high proportions of
non-grass materials, up to 30–40 per cent,
in northern sheep and cattle diets. This lack
of accessible green leaf in their diets suggests
much of it is fallen leaves from dry season
deciduous trees, woody vines and even
eucalypts.
Fallen leaves availability
All trees drop their leaves. Even for large
trees most of the leaf will eventually fall to
the ground becoming accessible to grazing
animals.
inbrief
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• Fallen leaves from native
deciduous trees have the
potential to supplement the dry
season diets of sheep and cattle
in northern Australia.
• CSIRO studies have found high
proportions, up to 30–40
per cent, of non-grass materials
such as fallen leaves in the diets
of sheep and cattle.
• In voluntary intake experiments
with sheep it was found the
fallen leaves of many Australian
trees were readily eaten when
added to a basic diet of mature
grass.
• Compared with the poor feed
quality of dry grass, fallen
leaves have more protein, break
up more readily on chewing
and the digestion which occurs,
although less than for grasses,
happens more quickly.
CSIRO Livestock Industries
The fallen leaves from crows ash (Flindersia australis) have been readily eaten by sheep in CSIRO feed
trials. The yellow colour of the leaves shows it has fallen freshly.
There are different patterns of leaf fall at
different times, including an annual leaf
change during the dry season.
This may happen with trees not normally
thought of as being ‘deciduous’ (totally
leafless for a prolonged period). But the
leafless period can be short, a few days or
weeks, and this is often seen at the end of the
dry season in the wet-dry tropics.
Sometimes, as with many native figs, and
the Belmont siris (Albizia canescens), leaf
drop occurs together with, or just after,
production of new leaf, so there is no visibly
leafless period.
Leucaena and many other warm-climate
trees may be normally evergreen but drop
their leaves under frosting or drought stress,
or dry season. Some species such as white
cedar (Melia azedarach) shed their leaf
completely more than once a year. In white
cedar this happens irrespective of rainfall and
may be a strategy to minimise insect attack.
Some eucalypts also have an annual leaf
change.
The value of fallen leaves
Evidence shows large amounts of fallen
leaves of yellow-wood (Terminalia oblongata)
are occasionally eaten by sheep or cattle. This
has been noted in the context of a sporadic
toxicity problem with yellow-wood, which
overall is regarded as a useful browse tree.
Livestock will also eat the fallen leaves from
fodder trees including siris (Albizia lebbeck),
Kylie Wright
velvet leaf (Planchonella pohlmania), Chinese
elm (Celtis sinensis) and even the Moreton Bay
fig (Ficus macrophylla).
Various field observations from inland
Australia refer to sheep eating the fallen
leaflets from prickly acacia (Acacia nilotica)
and cattle eating the fallen leaves of native
Bauhinia spp.
Sheep are also sometimes moved from
Mitchell grass paddocks into gidgee (Acacia
cambagei) woodland to graze leaf fall.
Indirect evidence comes from some recent
CSIRO studies on stocking rates and land
condition in northern Australia.
Fallen leaves from native deciduous trees have the
potential to supplement the diets of sheep and
cattle in northern Australia.
FARMING AHEAD No. 112 - April 2001

Nutrition...
Faecal measurements were used to
determine the proportion of C4 plants
(grasses) and C3 plants (non-grasses) in the
diets of grazing cattle.
The research found on degraded lands
during the dry season, cattle had up to 30% C3
plants in the diet. This was under conditions
where no green legumes or green browse
could be found. It seems inescapable that a
high proportion of the diet was fallen tree leaf,
even of eucalypts.
Another method using near infrared
technology also showed animals obtaining
more non-grass material than expected and
fallen tree leaf would be the most obvious
source.
Feed trials
As part of an agroforestry project supported
by the Joint Venture Agroforestry Programme,
a series of voluntary intake experiments with
penned sheep was carried out, in which fallen
leaves were provided as a supplement to a
basic diet of mature rhodes grass.
The results show the sheep readily ate more
than 100 grams per day of Leichhardt bean
(Cassia brewsteri), exotic bauhinia ( Bauhinia
variegata), Chinese elm, white cedar, crows ash
(Flindersia australis) and white kurrajong
(Brachychiton discolor) in addition to the basic
grass diet (see Table 1).
An unexpected finding was the preference
for freshly fallen leaves (offered within 24
hours of falling) for all species.
In some cases sheep were able to distinguish
between the fresh material and a batch only
24 hours older.
This rapid loss of palatability compared with
the slow loss of quality of mature grasses may
be due to an oxidation process.
But this loss of quality is unlikely to be a
problem — if animals eat fallen leaves in the
field they would be able to do so as they fall.
Feed quality
Biology indicates freshly fallen senescent
(older or dry) leaf would be of much lower
feed value than green leaf. It should therefore
have lower protein and higher cell wall or
fibre content.
Reviews show that on average, woody
perennials reabsorb 50% of nitrogen and 52%
CSIRO Livestock Industries
The white cedar tree (Melia azedarach) dropping
its leaves during late June. Evidence shows the
fallen leaves from this tree will be eaten by
livestock.
of phosphorus, and because of higher initial
concentrations, nutrient levels in fallen leaves
of deciduous species are much higher than
evergreens.
For nitrogen-fixing trees, there is less
nitrogen reabsorbed leaving higher levels of
protein in the fallen leaves.
Protein contents of fallen tree leaf of
potential agroforestry species evaluated, while
about half that of the green leaf, were
generally higher than for mature herbage of
dry season grasses.
Fallen tree leaf also had fibre content of
25–55%, much less than mature grass forage
(70–80%). But fallen leaves should still be
regarded as a low-quality fibrous feed.
In temperate areas, autumn leaf fall occurs
when pasture feed supply is not too low and
most temperate pastures would be expected
to be of higher quality than the fallen leaves.
Therefore, there is little reason to expect
animals to eat it.
A different situation applies in the wet-dry
tropics, where the dry season loss of feed
quality in the grasses makes the comparative
feed value of fallen leaves much higher.
TABLE 1 Voluntary intake for sheep offered mature grass and fallen leaves
Tree species Grass species Days Grass Intake Leaf intake
(grams/head/day)
Celtis sinensis Carpet and Rhodes 9 422 321
Melia azedarach Carpet and Rhodes 4 602 102
Cassia brewsteri Carpet and Rhodes 7 557 102
Flindersia australis Carpet and Rhodes 4 Not determined 183
Bauhinia variegata Angleton 3 Not determined 302
Tipuana tipu Carpet and Rhodes 4 570 Nil
Ficus benjamina Carpet and Rhodes 4 670 64
Source: CSIRO Livestock Industries
fallen leaves would be available in the
presence of grass that had been dead for
months.
The grass would have been subject to
photochemical bleaching, oxidation, possible
leaching and have extremely low protein and
digestibility.
With fallen tree leaf the transition from
living tissue to being available on the ground
would occur within days.
Experiments on the feed value of fallen
leaf have indicated it behaves differently
from dry season grasses. It breaks up more
readily so the animal can process it faster and
eat more.
The total amount which can be fermented in
the rumen may be less than for grasses but it
ferments more rapidly. This means the animal
may get more than expected digestible energy
from it.
Improved digestibility
Apart from the value of leaf by itself,
CSIRO trials have also found there can be
positive interactions when fallen leaves and
grass are fed together — the leaf may improve
the utilisation of the grass.
A CSIRO trial in Townsville, Queensland,
found cattle increased their intake of
digestible dry matter by 60% when a poor
native pasture hay was supplemented with
only 15% siris leaf.
Laboratory experiments have found that
even in a situation where nutrients were
supplied the digestion of grass was enhanced
when fallen tree leaf was added.
But the effect of fallen leaves on the
digestibility of the dry-season pasture will
depend on the tree species.
Some tree species had a negative effect
but these were not common forages, while
positive effects (synergies) were found with
inter alia, white cedar, tipuana (Tipuana tipu)
and siris.
Future potential
The results of this research have
implications for developing new agroforestry
systems in northern Australia.
It suggests the feed value of fallen leaves
should be one of the factors when choosing
tree species.
But of more significance, it suggests that in
the sustainable management of native
rangelands, the native deciduous trees and
vines should be valued more highly, and the
‘dry rain forest’ elements, already regarded as
important for preserving biodiversity, have
real production value.
Acknowledgements: This project was funded
by the Rural Industries Research and
Development Corporation’s Joint Venture
Agroforestry Programme.
For more information contact Brian Lowry,
CSIRO Livestock Industries, by email
on brian.lowry@tag.csiro.au, phone
(07) 3214 2840 or fax (07) 3214 2882.
This article appeared in the April 2001 edition of the Kondinin Group’s monthly magazine Farming Ahead. The Kondinin Group holds the
copyright on the article but CSIRO has the unlimited right to reproduce the text royalty free in its own publications. Reproduction of this
text in whole or part by any other publication or for any other purpose is not permitted without permission of the Farming Ahead editor.
For more information contact the Kondinin Group on (08) 9478 3343.
FARMING AHEAD No. 112 - April 2001 71
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