Evaluation of the basal forage diet of village cows
A A Boodoo, R Ramjee, B
Hulman, F Dolberg* and J B Rowe**
Animal Production Division, Ministry of
Agriculture, Fisheries and Natural Resources, Reduit, Mauritius
*University of Arhus, Denmark;
**Department of Agriculture, Western Australia
Summary
The forage fraction (especially cane tops which were the
dominant component) of the the diet of village cows was assessed
by chemical analysis, in situ (nylon bag) rumen degradability and
by direct observation of eating behaviour and forage selection
practices by the cowkeepers. Cowkeepers discarded cane tops that
had flowering heads and carefully removed mature and dry leaves.
Cows began eating the cane top starting at the sheath bundle
(which represented 48% by weight of the tops) and consumed only
part of the green leaf blade, on either side of the midrib. The
sheath bundle had less nitrogen (0.88% in DM) and dry matter
(19%) than the leaf blade (1.17% N and 31% DM). The mean N
content of the assorted forages was 1.6% in DM.
Dry matter degradation in the rumen was more rapid for the
sheath bundle (56% loss at 24hr) than for the leaf blade (34%)
and was the same as for the assorted forages (55%).
The cowkeepers offered each cow some 70 kg/d of whole cane
tops (mean DM = 28%)of which the cows consumed only 55%.
Comparable data for the assorted forages were 65 kg offered daily
(23% DM) of which 84% was consumed. Total DM intakes were 3.8 and
4.3 kg DM per 100 kg liveweight for cane tops and assorted
forages respectively.
Key words: Sugar cane tops, cattle, village cowkeepers,
feed intake, rumen degradability, feed selection.
Introduction
The small cattle owners (cowkeepers) in Mauritius make a major
contribution (almost 95%) to the national production of fresh
milk. A pilot project (Boodoo et al 1990) was executed in
two climatic areas of the island on cowkeepers' farms to
demonstrate the significance of two concentrate supplements to
improve milk production at the village level. In the course of
this pilot project (1985 to 1987) regular visits (3 times a week)
were made to the cowkeepers' farms and observations were made on
management practices and animal behaviour associated with the
supply and consumption of fodder. This paper summarises the data
on the types of forages used and their digestibility and nitrogen
content.
Sugar cane tops are by far the largest single forage source
used by the cowkeepers. For this reason they have been considered
in some detail in this paper.
Materials and methods
The forage fraction of the diet of the village cows was
assessed in a number of ways. Notes were made on the animals'
feeding behaviour, particularly with respect to selection amongst
the different forage fractions. The quality of the major dietary
forages was measured by chemical analysis (nitrogen, crude fibre,
ether extract, ash and the minerals Ca and P) and by the rate of
degradation of dry matter in nylon bags incubated in the rumen.
Measurements were also made of total feed intake during the crop
season when cane tops were the main component of the diet and
again during the inter-crop season when mixed grasses and
vegetable crop residues were the principal feed resources.
Chemical analysis and nylon bag degradability
Samples of forages were taken weekly for chemical analysis and
DM degradability in nylon bags. The samples of forage were
selected on the basis of the main forage species being used in
the area each week. The quality of the cane tops was analysed by
first separating them into two fractions. Twenty three samples of
cane tops were separated into sheath bundle and leaf blade and
the two fractions were analysed for dry matter, nitrogen, crude
fibre and nylon bag degradability.
Friesian steers fitted with permanent rumen cannulae were used
for the nylon bag work. They were fed a basal diet of mixed
grasses consisting mainly of Setaria sphacelata and Ischaemum
aristatum (herbe d'argent) at the rate of 20 - 25 kg/d and
1 kg/d cottonseed cake. The fodder was given in two equal
portions at 09.00h and 13.00h. The steers also received 10 g
common salt and 30 g calcium carbonate per day.
The fodder samples to be tested were first dried at 60°C for
48 hours before being ground through a 2.5 mm sieve in a Christy
and Norris mill. Four-gram samples were weighed into the nylon
bags. Duplicate bags were incubated in each steer for each forage
and each time interval (0, 16, 24, 48 and 72h).
Intake
Twenty seven cows from the two areas that hosted the pilot
project (30% of the total number) were monitored daily for a
period of 15 consecutive days and the amount of fodder offered
and consumed was recorded. Fifteen of these cows were monitored
during the crop season and twelve in the intercrop season.
Results
Observations on the intake of forages
The cane tops collected by the cowkeepers included no
flowering ones. In addition cowkeepers carefully selected the
cane tops and discarded the very mature ones. From the cane tops
selected in this way, the outer older leaves and all dry ones
were discarded.
The cane top consists of a bundle of leaf sheaths (sheath
bundle) at the base and leaf blades at the top. The sheaths of
the youngest leaves tightly enclose the youngest part of the cane
stalk; this youngest part includes the growing point (meristem)
of the stalk. It contains a much lower proportion of sucrose than
the main portion of the mature stalk, but it is comparatively
rich in monosaccharides and non-sugars (Barnes 1974).
The leaf blade and the sheath bundle are separated at the
collar. The sheath is greyish in colour; it is attached to the
cane stalk and completely surrounds it. The leaf blade is green
in colour, grows out from the stalk and tapers to the tip. A
midrib extends along the entire length of the blade.
The following features about the cows' feeding behaviour were
noted during the farm visits and these observations were
confirmed in numerous interviews with cowkeepers:
- The cows consistently started to consume the cane top at
the sheath bundle end.
- They consumed the whole of the sheath bundle portion of
the cane top first before starting on the leaf blades.
- They consumed only part of the leaf blades on both sides
of the midrib. It was estimated that only about one third
to one half of the leaf blade was consumed in this way.
A complete list of the forage species and vegetable crop
residues fed to the cows in the two areas is given in the
Appendix. It was observed in the Vacoas area that Ischaemum
aristatum (herbe d'argent) generally formed the bulk of the
fodder that was given to the cows during the sugar cane
inter-crop season whereas other assorted forages (singly or
mixed) were given in small amounts, about 5 - 10 kg per cow.
In the Mapou area, Plantago lanceolata (herbe sagne),
Digitaria didactyla (petit gazon), Stenotaphrum dimidiatum
(herbe bourik) and young cane regrowths (about 50 cm high)
generally formed the bulk of the fodder in the inter-crop season.
Other assorted forages (singly or mixed), about 5 - 10 kg, were
also given to the cows. The amounts of these assorted forages
(mixed grasses, creepers, shrubs and twigs) and crop residues fed
were about the same in both areas. Of the 525 cane tops that were
fractionated, the sheath bundle fraction represented 48.4% (SE = "0.8) and the leaf blade fraction
51.6% (SE = "0.8) by weight of
the cane top.
Chemical composition
Data on composition of the cane top fractions are given in
Table 1.
| Table 1:
Chemical composition (%) of whole cane top and its
botanical fractions (on dry matter basis). Apart from the
"left overs" the fractions were prepared from
one original big bundle of cane top. |
 |
| |
---------- Dry Matter ---------- |
---------- Crude Prot ---------- |
---------- Crude Fibre ---------- |
| |
(n) |
Mean |
SE |
(n) |
Mean |
SE |
(n) |
Mean |
SE |
|
| Whole canetop
|
(22) |
28.3 |
1.1 |
(22) |
6.3 |
0.2 |
(20) |
32.2 |
0.4 |
| Sheath bundle
|
(23) |
19.3 |
1.0 |
(24) |
5.5 |
0.3 |
(22) |
31.9 |
0.5 |
| Leaf blade |
(23) |
31.3 |
0.9 |
(25) |
7.3 |
0.4 |
(22) |
32.9 |
0.8 |
| Left-over |
(16) |
35.9 |
1.6 |
(16) |
5.9 |
0.2 |
(13) |
33.4 |
0.8 |
|
| Table 2: Chemical
composition (%) of assorted forages and crop residues (on
dry matter basis) |
|
| |
DM |
CP |
Ash |
EE |
CF |
Ca |
P |
|
| n |
49 |
49 |
50 |
13 |
15 |
49 |
50 |
| Mean |
23.1 |
9.7 |
9.2 |
2.2 |
31.0 |
0.47 |
0.21 |
| SE |
1.0 |
0.5 |
0.4 |
0.2 |
1.2 |
0.46 |
0.04 |
| Range |
|
|
|
|
|
|
|
| Min |
13.3 |
5.0 |
3.0 |
1.5 |
14.5 |
0.02 |
0.14 |
| Max |
40.9 |
14.6 |
14.2 |
4.8 |
37.2 |
2.2 |
1.7 |
|
The sheath bundle fraction has a lower dry matter and crude
protein content (19.3% and 5.5% respectively) than the leaf blade
(31.3% and 7.3% respectively).
The mean crude protein content of the assorted forages and
crop residues (9.7%) is higher than expected indicating the care
taken by the cowkeepers in selecting the forage resources. Some
of the leguminous forages contained up to 14% crude protein.
Nylon bag degradability
The dry matter degradability values of the various cane top
fractions and the other assorted forages are summarised in Table
3. The LSD (P = 0.05) values are also shown.
The results indicate that the sheath bundle fraction degraded
much faster than the leaf blade at all the time intervals
studied. On the other hand the sheath bundle fraction of cane top
and the assorted forages show similar DM degradabilities for the
16 24 48 and 72 incubation periods.
The rate and extent of degradation of the sheath bundle
fraction and the assorted forages (about 55% and 63% after 24 and
48 hours respectively) support the view that this is equivalent
to a forage of relatively high nutritive value. The sheath bundle
and the assorted forages have a potential degradability which is
approximately 26% higher than that of the leaf blade.
| Table 3: Mean
dry matter degradability (%) of whole canetop its
botanical fractions and assorted forages at various
intervals in nylon bags |
|
| |
|
----------------------- Incubation time (h)
----------------------- |
| |
n |
0 |
16 |
24 |
48 |
72 |
|
| Leaf blade |
18 |
12.0 |
27.0 |
34.3 |
47.0 |
53.4 |
| SE |
|
0.6 |
1.1 |
1.0 |
1.1 |
1.1 |
| Whole canetop
|
18 |
15.5 |
35.4 |
43.6 |
53.7 |
59.4 |
| SE |
|
0.4 |
1.1 |
1.2 |
1.0 |
1.0 |
| Sheath bundle
|
8 |
21.5 |
46.7 |
55.5 |
62.6 |
67.2 |
| SE |
|
0.7 |
1.5 |
1.3 |
1.1 |
0.8 |
| Assorted
Forages |
18* |
16.4 |
44.5 |
54.6 |
63.5 |
66.4 |
| SE |
|
0.7 |
1.6 |
5.2 |
1.3 |
1.3 |
| LSD (P =.05) |
|
2.2 |
5.2 |
4.7 |
4.2 |
3.8 |
|
* These 18 samples were randomly
selected from an original list of 49 samples. The means of these
18 samples were almost similar to those of the original 49
samples.
Intake
The amount of fresh forage offered and refused the liveweight
of the lactating cows and the total dry matter intake are
summarised in Table 4 for the two areas.
The cowkeepers offered their cows much more than the latter
could consume especially sugar cane tops which are abundant
during the harvest season. The 14 - 50% extra that the cows were
offered gave them plenty of opportunity to select the best
components and this resulted in a very high intake (about 4 kg
DM/100 kg LW) as is shown by the relationship between liveweight
and total DM intake.
Discussion
The age-old practice of cowkeepers in Mauritius as far as
forage feeding is concerned is a wise practice which is being
scientifically documented in this work. With time the cowkeepers
have developed an appreciation of forage quality. This is
illustrated in the relatively high dry matter degradability of
the sheath bundle fraction of cane top and other selected forages
that they use. This inference is further supported by the
relatively high levels of dry matter intake that have been
recorded from measurements on the village cows.
| Table 4: Quantity
of forage offered and refused liveweight of the cows and
their total DM intake for a diet consisting predominantly
of (a) cane tops with some grasses and crop residues and
(b) mixed grasses with some other forages |
|
| |
------------- Vacoas ------------- |
------------- Mapou ------------- |
| |
Cane tops |
Mixed grasses |
Cane tops |
Mixed grasses |
|
| n |
7 |
7 |
9 |
5 |
| |
|
|
|
|
| Feed
offered (kg fresh/d) |
|
|
|
| Mean |
69.3 |
68.0 |
73.1 |
62.6 |
| SE |
4.1 |
4.3 |
1.0 |
4.2 |
| |
|
|
|
|
| Feed
eaten (kg fresh/d) |
|
|
|
| Mean |
46.0 |
59.6 |
51.8 |
51.8 |
| SE |
2.5 |
2.1 |
2.0 |
2.0 |
| |
|
|
|
|
| Surplus
feed (% of amount eaten) |
|
|
|
| Mean |
50.6 |
14.1 |
41.1 |
20.8 |
| SE |
7.2 |
2.8 |
5.0 |
3.1 |
| |
|
|
|
|
| Liveweight
(kg) |
|
|
|
|
| Mean |
342 |
353 |
364 |
311 |
| SE |
21.8 |
13.3 |
11.4 |
16.0 |
| |
|
|
|
|
| Total
intake (kg DM/d)* |
|
|
|
| Mean |
12.2 |
15.3 |
14.7 |
13.6 |
| SE |
1.1 |
0.5 |
0.7 |
0.9 |
| |
|
|
|
|
| Total
intake (kg DM/100 kg Liveweight)* |
|
|
|
| Mean |
3.6 |
4.4 |
4.1 |
4.3 |
| SE |
0.3 |
0.2 |
0.3 |
0.4 |
|
* Includes concentrate
The level of intake observed in this study is perhaps higher
than commonly found in the literature. However it has been
demonstrated recently (Hovell et al 1986; Orskov et al
1985) that voluntary intake was better related to potential
degradability (and degradability at 12 24 48 and 72 hours) than
to in vivo digestibility and that even a small difference
in the rate and extent of degradation can have large effects on
intake. These results tend to be supported by the results of the
present work.
In the forage evaluation part of this experiment it is clear
that both the extent of degradability of dry matter and its rate
of degradability are relatively good with respect to other
tropical forages (Preston 1985; Hovell 1985; Orskov et al
1980). The sheath bundle fraction of cane top and the good
quality of the assorted forages are clearly the basic reasons for
the good milk production in the villages compared to other large
scale systems of production where there is less attention to
detail in selecting forages.
Acknowledgement
The authors thank the Agricultural Chemistry Division for
chemical analyses: the MSIRI (Mauritius Sugar Industry Research
Institute) for identifying the names of the various forages; and
the Agronomy Division for statistical help. Special thanks go to
the cowkeepers who cooperated with us during the visits.
References
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* Indicates how common these forages are:
1 = widely used
2 = normally used
3 = sometimes used