• TABLE OF CONTENTS
HIDE
 Copyright
 Front Cover
 Introduction
 Shade
 Air movement
 Cooling
 Summary
 Back Cover






Group Title: Florida Cooperative Extension Service circular 782
Title: Methods to relieve heat stress for Florida dairies R.A. Bucklin, D.R. Bray and D.K. Beede
CITATION PAGE IMAGE ZOOMABLE PAGE TEXT
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00049212/00001
 Material Information
Title: Methods to relieve heat stress for Florida dairies R.A. Bucklin, D.R. Bray and D.K. Beede
Series Title: Circular
Physical Description: 3 p. : ill. ; 28 cm.
Language: English
Creator: Bucklin, R. A
Bray, D. R ( David Russell ), 1940-
Beede, David Kent, 1950-
Florida Cooperative Extension Service
Publisher: Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida
Place of Publication: Gainesville
Publication Date: 1991
 Subjects
Subject: Dairy cattle -- Climatic factors -- Florida   ( lcsh )
Dairy barns -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
 Notes
General Note: Title from cover.
General Note: "December 1991."
Funding: Florida Historical Agriculture and Rural Life
 Record Information
Bibliographic ID: UF00049212
Volume ID: VID00001
Source Institution: Marston Science Library, George A. Smathers Libraries, University of Florida
Holding Location: Florida Agricultural Experiment Station, Florida Cooperative Extension Service, Florida Department of Agriculture and Consumer Services, and the Engineering and Industrial Experiment Station; Institute for Food and Agricultural Services (IFAS), University of Florida
Rights Management: All rights reserved, Board of Trustees of the University of Florida
Resource Identifier: oclc - 26812838

Table of Contents
    Copyright
        Copyright
    Front Cover
        Page i
        Page ii
    Introduction
        Page 1
    Shade
        Page 1
    Air movement
        Page 2
    Cooling
        Page 2
    Summary
        Page 3
    Back Cover
        Page 4
Full Text





HISTORIC NOTE


The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
Electronic Data Information Source
(EDIS)

site maintained by the Florida
Cooperative Extension Service.






Copyright 2005, Board of Trustees, University
of Florida






December 1991


Circular 782


Methods to Relieve
Heat Stress
for
Florida Dairies

R.A. Bucklin, D.R. Bray and D.K. Beede


Florida Cooperative Extension Service
Institute of Food and Agricultural Sciences
University of Florida
John T. Woeste, Dean


...*;.; &F FL8R12A U3,UR'iES
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3C1EWI1


R.A. Bucklln Is Assistant Professor of Agricultural Engineering, D.R. Bray is Extension Agent II, Dairy Science Department and D.K.
Beede Is Associate Professor, Dairy Science Department, IFAS, University of Florida, Gainesville.








Introduction
Hot, humid weather causes declines in Florida's
milk production each summer. Reducing heat
stress for the cows can reduce or eliminate these
production losses. The most practical methods to
reduce heat stress can be grouped into three main
areas; shade, ventilation, and cooling. These
methods can be used alone or in any combination.
They are most effective when located in areas of
high heat stress. Common areas that will benefit
are feed barns, loafing areas, and holding areas.

Shade
Shade can be either natural or artificial. In most
cases, the best method for relieving heat stress is
natural shade in the form of shade trees. When not
enough natural shade is available, artificial shades
can provide needed shelter from the effects of solar
radiation. Several factors should be considered
when constructing shades. The orientation of
shade structures is very important. During the
summer, a higher percentage of shadow lies under
a shade structure with an east-west orientation
than with a north-south orientation. During the
winter, the amount of floor that is sunlit for drying
is about the same. If you want the driest possible
conditions for nonconfined situations, a north-south
orientation with a large fenced-in area is best.

If the cows are to be confined under a shade
structure, it should be oriented east-west. Each
cow should be provided with 40 to 60 square feet of
shade. The floor should be four-inch concrete
grooved to provide firm footing. It should be sloped
about 1.5 to 2% for proper operation of flush sys-
tems. Earthen floors under shades quickly can be-
come mud holes in Florida, and so are not generally
recommended. If earth floors are used, the struc-
ture should be located on a well-drained location,
such as a mound. The concrete slab needs to be
larger than the area of the shade roof. This is be-
cause the orientation of the sun varies with the sea-
son and even with an east-west orientation, the
shadow will not always be entirely under the struc-
ture. The slab should extend 8 feet on the north
side, and 20 feet on the east and west sides if the
eave height is 12 feet. Higher eaves will require
that the slab be extended further. In Florida, the
shade pattern will fall on the south side only in the
early morning and late afternoon, so the slab does
not need to be extended to the south.

Several factors influence the selection of shade
structure height. Air movement under the shade is


increased as eave height is increased, but the cost
of the structure also increases with height, and the
shade pattern moves more with tall structures.
The recommended eave height in Florida is 12 feet
as illustrated by Figure 1. Shade structures wider
than forty feet result in reduced air movement in
the center of the shade. If a structure wider than
this is needed, several continuous openings in the
roof should be provided to promote air circulation.
The site of the shade structure should provide at
least 50 feet of clearance on each side between adja-
cent buildings, trees, or other obstructions. Gable
roofs should have a continuous open ridge to pro-
mote natural ventilation.


Figure 1. Shade structure.

The most effective shade roof is an aluminum or
white colored galvanized metal roof with about one
inch of insulation directly beneath the metal roof-
ing. The insulation reduces the radiation heat load
on the cows but can cause problems if birds or other
pests establish themselves in the insulation and
damage the material. Painting the lower surface of
the roofing material with a low-emittance paint
also will reduce the radiation load. The top surface
always should be painted white or silver to reflect
solar radiation.

Shade cloth can be used as the material for
shade roofs. These cloths are available in patterns
providing 30 to 90% shade and fabricated from a
variety of yarn materials. The most common mate-
rial used for animal shades is woven polypropylene
fabric providing 80% shade. Knitted and non-wo-
ven materials are entering the market and some
show promise for use as shade cloth. Shade cloth is
considerably less expensive than solid roofing mate-
rial but does not provide as much protection from
solar radiation as a solid roof. The fabric tension
must be tightened whenever slack in the shade
cloth is noticed or it will quickly be torn apart by
the wind.

To achieve the most benefit from the shade
structure, feed and water must be available to the








Introduction
Hot, humid weather causes declines in Florida's
milk production each summer. Reducing heat
stress for the cows can reduce or eliminate these
production losses. The most practical methods to
reduce heat stress can be grouped into three main
areas; shade, ventilation, and cooling. These
methods can be used alone or in any combination.
They are most effective when located in areas of
high heat stress. Common areas that will benefit
are feed barns, loafing areas, and holding areas.

Shade
Shade can be either natural or artificial. In most
cases, the best method for relieving heat stress is
natural shade in the form of shade trees. When not
enough natural shade is available, artificial shades
can provide needed shelter from the effects of solar
radiation. Several factors should be considered
when constructing shades. The orientation of
shade structures is very important. During the
summer, a higher percentage of shadow lies under
a shade structure with an east-west orientation
than with a north-south orientation. During the
winter, the amount of floor that is sunlit for drying
is about the same. If you want the driest possible
conditions for nonconfined situations, a north-south
orientation with a large fenced-in area is best.

If the cows are to be confined under a shade
structure, it should be oriented east-west. Each
cow should be provided with 40 to 60 square feet of
shade. The floor should be four-inch concrete
grooved to provide firm footing. It should be sloped
about 1.5 to 2% for proper operation of flush sys-
tems. Earthen floors under shades quickly can be-
come mud holes in Florida, and so are not generally
recommended. If earth floors are used, the struc-
ture should be located on a well-drained location,
such as a mound. The concrete slab needs to be
larger than the area of the shade roof. This is be-
cause the orientation of the sun varies with the sea-
son and even with an east-west orientation, the
shadow will not always be entirely under the struc-
ture. The slab should extend 8 feet on the north
side, and 20 feet on the east and west sides if the
eave height is 12 feet. Higher eaves will require
that the slab be extended further. In Florida, the
shade pattern will fall on the south side only in the
early morning and late afternoon, so the slab does
not need to be extended to the south.

Several factors influence the selection of shade
structure height. Air movement under the shade is


increased as eave height is increased, but the cost
of the structure also increases with height, and the
shade pattern moves more with tall structures.
The recommended eave height in Florida is 12 feet
as illustrated by Figure 1. Shade structures wider
than forty feet result in reduced air movement in
the center of the shade. If a structure wider than
this is needed, several continuous openings in the
roof should be provided to promote air circulation.
The site of the shade structure should provide at
least 50 feet of clearance on each side between adja-
cent buildings, trees, or other obstructions. Gable
roofs should have a continuous open ridge to pro-
mote natural ventilation.


Figure 1. Shade structure.

The most effective shade roof is an aluminum or
white colored galvanized metal roof with about one
inch of insulation directly beneath the metal roof-
ing. The insulation reduces the radiation heat load
on the cows but can cause problems if birds or other
pests establish themselves in the insulation and
damage the material. Painting the lower surface of
the roofing material with a low-emittance paint
also will reduce the radiation load. The top surface
always should be painted white or silver to reflect
solar radiation.

Shade cloth can be used as the material for
shade roofs. These cloths are available in patterns
providing 30 to 90% shade and fabricated from a
variety of yarn materials. The most common mate-
rial used for animal shades is woven polypropylene
fabric providing 80% shade. Knitted and non-wo-
ven materials are entering the market and some
show promise for use as shade cloth. Shade cloth is
considerably less expensive than solid roofing mate-
rial but does not provide as much protection from
solar radiation as a solid roof. The fabric tension
must be tightened whenever slack in the shade
cloth is noticed or it will quickly be torn apart by
the wind.

To achieve the most benefit from the shade
structure, feed and water must be available to the







cows under the shade. A waste management sys-
tem must be planned as an integral part of any
shade structure. Waste can be removed by scrap-
ing or flushing. Even if flushing is not desired
originally it is still a good idea to design the slab for
flushing so that a flush system can be added easily
at some later time.

Air Movement
An important factor in the relief of heat stress is
air movement. Air movement can be natural or
forced. Air movement can reduce the temperature
in a building or under a shade structure to that of
the outside air. A ventilation system that provides
at least one air change per minute is recommended.

Mechanical ventilation, or forced ventilation, is
that provided by fans. If the system is properly
designed, this method is very effective. However, it
also can be expensive. Fans are often necessary in
the milking parlor to reduce heat build-up.

Many agricultural buildings can be ventilated
adequately by natural means. Natural ventilation
is caused by two effects. The first is air movement
caused by breezes moving through open sides of
sidewall vents. The second is air movement caused
by thermal buoyancy. This also is referred to as
the stack or chimney effect. Air enters the struc-
ture through side or eave vents, is heated and then
rises and exits through a ridge vent. This method
is effective even on a totally still day. It is most ef-
fective in a building with sidewalls. The air move-
ment caused by thermal buoyancy in a building
without sidewalls will occur at the eave height, not
at animal level. Air movement at eave height will
reduce the roof temperature and thus the radiation
load on the cows, so it is still beneficial. The stack
effect is most effective in structures with steep
roofs and large ridge vents. Roof slopes between
4:12 and 6:12 are the most effective. Roofs with
slopes of less than 4:12 often leak and don't have
enough slope to generate a good stack effect. Roofs
steeper than 6:12 will still have a good stack effect
but are expensive to construct and difficult to work
on.

Ridge vents in Florida should be at least one foot
wide plus two inches for each ten feet of structure
width over twenty feet. A vent functions best when
it is totally open without a cap. If a cap is neces-
sary, the eave of the cap should have at least one
foot of clearance between it and the roof peak.
Most commercially available ridge vents are under-
sized for Florida conditions. Several ridge vent


types are illustrated in Figure 2. Overshot and
baffled designs are not recommended. Under most
conditions they reduce rather than promote air flow
through a structure. If a flat or nearly flat roof is
desired, a ridge vent will be of little benefit if the
structure is less than 40 feet wide. Buildings with
flat roofs with widths greater than forty feet may
benefit from ridge vents or openings in the roof, but
will probably require mechanical ventilation to be
satisfactory.


BEST TOTALLY OPEN



OK WITH RIDGE CAP
Figure 2. Ridge vent types.


NOT RECOMMENDED OVER SHOT



NOT RECOMMENDED BAFFLED


Cooling
Summer conditions in Florida may require cool-
ing below ambient temperatures for optimum pro-
duction. A cow loses heat through its skin surface
and respiratory tract. A cow does not have a large
number of sweat glands, so if supplemental cooling
methods are not used it must lose a large amount of
heat through its respiratory tract.

There are several methods available that can re-
duce air temperatures below outside ambient tem-
peratures. The most familiar is mechanical air con-
ditioning or refrigeration. This method generally is
too expensive to use with livestock operations.

A more economical method is evaporative cool-
ing. Evaporative cooling works by using energy
from the air to evaporate water. This lowers the
temperature of the air and raises its relative hu-
midity. Evaporative cooling is most effective in ar-
eas of low humidity. However, even in muggy
Florida, daytime humidities are low enough to al-
low for beneficial cooling to occur when the air tem-
peratures are the highest.

Several evaporative cooling methods are avail-
able. The most common method is the fan and pad
system used in many greenhouse. This is a fairly
expensive system but it may be economically practi-
cal to use with high yielding animals. This system
requires fans, evaporative cooling pads, and pumps
to circulate water to the pads. A disadvantage of







cows under the shade. A waste management sys-
tem must be planned as an integral part of any
shade structure. Waste can be removed by scrap-
ing or flushing. Even if flushing is not desired
originally it is still a good idea to design the slab for
flushing so that a flush system can be added easily
at some later time.

Air Movement
An important factor in the relief of heat stress is
air movement. Air movement can be natural or
forced. Air movement can reduce the temperature
in a building or under a shade structure to that of
the outside air. A ventilation system that provides
at least one air change per minute is recommended.

Mechanical ventilation, or forced ventilation, is
that provided by fans. If the system is properly
designed, this method is very effective. However, it
also can be expensive. Fans are often necessary in
the milking parlor to reduce heat build-up.

Many agricultural buildings can be ventilated
adequately by natural means. Natural ventilation
is caused by two effects. The first is air movement
caused by breezes moving through open sides of
sidewall vents. The second is air movement caused
by thermal buoyancy. This also is referred to as
the stack or chimney effect. Air enters the struc-
ture through side or eave vents, is heated and then
rises and exits through a ridge vent. This method
is effective even on a totally still day. It is most ef-
fective in a building with sidewalls. The air move-
ment caused by thermal buoyancy in a building
without sidewalls will occur at the eave height, not
at animal level. Air movement at eave height will
reduce the roof temperature and thus the radiation
load on the cows, so it is still beneficial. The stack
effect is most effective in structures with steep
roofs and large ridge vents. Roof slopes between
4:12 and 6:12 are the most effective. Roofs with
slopes of less than 4:12 often leak and don't have
enough slope to generate a good stack effect. Roofs
steeper than 6:12 will still have a good stack effect
but are expensive to construct and difficult to work
on.

Ridge vents in Florida should be at least one foot
wide plus two inches for each ten feet of structure
width over twenty feet. A vent functions best when
it is totally open without a cap. If a cap is neces-
sary, the eave of the cap should have at least one
foot of clearance between it and the roof peak.
Most commercially available ridge vents are under-
sized for Florida conditions. Several ridge vent


types are illustrated in Figure 2. Overshot and
baffled designs are not recommended. Under most
conditions they reduce rather than promote air flow
through a structure. If a flat or nearly flat roof is
desired, a ridge vent will be of little benefit if the
structure is less than 40 feet wide. Buildings with
flat roofs with widths greater than forty feet may
benefit from ridge vents or openings in the roof, but
will probably require mechanical ventilation to be
satisfactory.


BEST TOTALLY OPEN



OK WITH RIDGE CAP
Figure 2. Ridge vent types.


NOT RECOMMENDED OVER SHOT



NOT RECOMMENDED BAFFLED


Cooling
Summer conditions in Florida may require cool-
ing below ambient temperatures for optimum pro-
duction. A cow loses heat through its skin surface
and respiratory tract. A cow does not have a large
number of sweat glands, so if supplemental cooling
methods are not used it must lose a large amount of
heat through its respiratory tract.

There are several methods available that can re-
duce air temperatures below outside ambient tem-
peratures. The most familiar is mechanical air con-
ditioning or refrigeration. This method generally is
too expensive to use with livestock operations.

A more economical method is evaporative cool-
ing. Evaporative cooling works by using energy
from the air to evaporate water. This lowers the
temperature of the air and raises its relative hu-
midity. Evaporative cooling is most effective in ar-
eas of low humidity. However, even in muggy
Florida, daytime humidities are low enough to al-
low for beneficial cooling to occur when the air tem-
peratures are the highest.

Several evaporative cooling methods are avail-
able. The most common method is the fan and pad
system used in many greenhouse. This is a fairly
expensive system but it may be economically practi-
cal to use with high yielding animals. This system
requires fans, evaporative cooling pads, and pumps
to circulate water to the pads. A disadvantage of







these systems is that the pads require maintenance
and have a limited lifetime.

Other evaporative cooling methods can be
grouped into mist, fog, and sprinkling systems.
The difference between a mist and a fog system is
in droplet size. A mist droplet is larger than a fog
droplet and will drop slowly to the floor, evaporat-
ing as it falls. A fog particle stays suspended in the
air and evaporates before it touches the ground.
Fog systems are very efficient methods of cooling
air but also are more expensive than mist systems
and require more maintenance. A mist or fog sys-
tem that sprays small water droplets into the air,
cools the air as the droplets evaporate. When an
animal inhales the cooled air it can exchange heat
with the air and remove heat from its body. This
type system can be effective, but is difficult to use
under windy conditions or in combination with
fans. If a misting system does not wet the cows'
hair coat to the skin, an insulating layer of air can
be trapped between the skin and the layer of water.
This effect can cause a harmful heat buildup. Cool-
ing studies involving mist systems also have re-
ported respiratory and pneumonia problems when
cows were exposed to mist or fog particles for long
times. Systems in which the cow inhales cool air
from an air duct have been tested with some suc-
cess but are expensive.

An alternative to mist and fog systems is the
sprinkling system. This method does not attempt
to cool the air, but instead uses a large droplet size
to wet the hair coat and skin of the cow, and then
water evaporates from the hair and skin. This al-
lows the cow to lose heat more effectively through
its skin.

Sprinkling is most effective when combined with
air movement. This promotes evaporation of water
from the skin and hair coat. An air velocity of 400
to 600 feet per minute over the cow is recom-
mended. At least one 36 inch fan for each forty ani-
mals is needed to provide this velocity. Each fan
should provide an airflow of about 11,000 cfm. A
fan of this size will move air effectively for about 10
diameters or 30 feet. Other fan sizes also can be
used. Dairy production trials with a system of this
type at the University of Florida's Diary Research
Unit at Hague compared a sprinkling and fan sys-
tem under a freestall shade structure and in the
holding area to no cooling system under the same


structure during summer conditions. The treated
cows consumed 2.8 lb/day more feed than the un-
cooled controls and produced 4.6 lb/day more milk.
This was an 11.6% increase in milk production.
This system combines fans and sprinkling, with the
animals being sprinkled for one and one-half min-
utes at fifteen-minute intervals when the ambient
temperatures were above 780F. A typical cooling
system is shown in Figure 3. The fans should be
located as low as possible above the height neces-
sary for cow and equipment clearance. Sprinklers
should be located immediately below the fans so
that the water is thrown just under the bottom of
the fans. If the fans blow water onto areas that
must be kept dry, they should be shut off when the
sprinklers are activated. This can be done by using
a double-pole switch to control both the fans and
water pump. The nozzles selected to sprinkle the
desired flow rate should operate at a low pressure
such as 10 psi. This inhibits the formation of unde-
sirable fine mist. An amount of water equal to 0.05
inches rainfall should be applied during each sprin-
kling. Care must be taken when using mist, fog, or
spinkling systems that the nozzles do not become
clogged. Trash and minerals in the water can be
harmful to pumps and nozzles. Proper nozzle,
pump and filter selection is important.


-I
r
/' I
' I


rn


S \ \ \
'' '


I I I
Figure 3. Fans and sprinklers.

Summary
If optimum production is to be achieved in
Florida, dairy cows must be provided relief from hot
summer conditions. Several methods are available
for doing this. The most cost effective is the use of
shade structures. Supplemental cooling will pro-
vide additional benefits, especially when it is used
at points of high heat stress, such as feed barns,
loafing areas, and holding areas. The cooling sys-
tem that has the widest application in Florida is
sprinkling combined with fans.


uNS
















































































COOPERATIVE EXTENSION SERVICE, UNIVERSITY OF FLORIDA, INSTITUTE OF FOOD AND AGRICULTURAL SCIENCES, JohnT. Woeste,
director, in cooperation with the United States Department of Agriculture, publishes this information to further the purpose of the May 8 and June
30,1914 Acts of Congress; and is authorized to provide research, educational information and other services only to individuals and institutions that
function withoutregard to race, color, sex, handicap or national origin. Single copies of extension publications (excluding 4-H and youth publications)
are available free to Florida residents from county extension offices. Information on bulk rates or copies for out-of-state purchasers is available from
C.M. Hinton, Publications Distribution Center, IFAS Building 664, University of Florida, Gainesville, Florida 32611. Before publicizing this publication,
editors should contact this address to determine availability. Printed 12/91.




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