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CASE STUDY
WINTER 2011 ISSUE
LIVESTOCK MATTERS
10
Case Study
One
This summer-calving dairy herd rears all its
own heifer replacements. These are housed
in two different sheds. In the traditional
shed, pneumonia is an extremely rare event
and only isolated cases are seen. In the
new shed, however, the whole group has
been affected by pneumonia in November
or December for the past three winters.
These are healthy, well-managed calves;
colostrum provision and onward feeding
is very good, group sizes are small and
bedding is dry.
A ventilation assessment was carried out.
This involves measuring the floorspace of
the building and the pitch of the roof, and
takes into account the number of animals
housed and their average weights. From this
it is possible to calculate how big the inlets
at the eaves, and the outlets at the ridge,
need to be.
The inlet in the new shed was found to
be ample. Outlet however is inadequate;
1.61m
2
is required, the 16 ridge-vents
provide 1.09m
2
(see Figure 1). The
additional 0.52m
2
required can be
achieved by cutting slots 10cm by 33cm
into each vent. The amount of rainwater
coming through these slots is almost literally
a drop in the ocean compared with the
amount of moisture the calves themselves
produce (through urination, sweat, etc). In
addition, a solid gate is to be placed
midway along the shed perpendicular to
the feed barrier, to provide additional
shelter from any strong winds from the more
open end of the shed.
The traditional shed was also assessed.
In theory, this shed requires an outlet of
1.15m
2
and inlets of 2.3m
2
. The actual inlet
is 0.87m
2
, and there is no visible outlet.
Yet pneumonia is far from an issue in this
building. The roof has a very steep pitch,
and the slate and wood roof materials
'breathe' (as seen in Figures 2 a, b and c)
- meaning the ventilation is actually very
good. In addition, great care is taken to
ensure bedding remains dry. This illustrates
the fact that one can't just look at the
maths. It would be a bold and foolish soul
who suggested making any alterations to
this building!
Vaccination had been considered prior to
the ventilation assessment, but the farmer
has decided to make the necessary shed
alterations with the expectation that this may
prevent further pneumonia outbreaks. A
robust treatment protocol has been designed
should pneumonia occur. This entails
administering both an antibiotic and an
anti-inflammatory drug to affected calves,
and also suggests a cut-off point at which
whole-group antibiotic treatment should be
administered. It has been demonstrated that
this approach can reduce overall drug
usage and produce better weight gains.
Figure 1: The ridge in the foreground has the
maximum possible number of ridge vents - but
provides much less than the required outlet.
Figure 2a
Figure 2b
Figure 2c
Figures 2 a, b & c: This traditional shed illustrates the fact that ventilation is even less simple
than we thought - there is virtually no visible inlet or outlet, yet the ventilation is adequate.