Dairy cattle powerpoint

• A magnitude of forces external to the body which tend to
displace its system from resting or ground state. (Youself,
1985)
• Heat stress happens in animals when there is problem in
thermoregulation. When there is an imbalance between
heat production (gain) within the body and its dissipation
(loss) from the body.

What is STRESS
http://en.engormix.com/MA-dairy-cattle/articles/heat-stress-dairy-animals-t1019/p0.htm

Factors that determine the level of environmental
heat loss or gain:
•Air temperature and relative humidity
•Amount of solar radiation
•Degree of night cooling
•Ventilation and air flow
•Length of the hot conditions

* Domestic livestock have evolved a range of physiological strategies to
off-load heat to cope in hot environmental conditions. Problems may occur
if temperatures and humidity remain high and cows do not have
opportunities to get rid of excess heat.

http://en.engormix.com/MA-dairy-cattle/management/articles/heat-stress-in-dairy-t2165/124-p0.htm

Environmental Stress Physiological Nutritional Management
Toxic metal pollutants Heat Stress Acidosis Handling
Chemical Fertilizers Advance pregnancy Bloat Transportation
Pesticide Dehydration Hypocalcaemia Seasonal change
contamination Cold stress Ketosis
Hypomagnesaemia
Mycotoxin/Plant-
toxins

• Heat stress accounts for a large portion of dairy cattle culled.

The four types of stress

• Based on maximizing available routes of heat exchange with
• Convection
• Conduction
• Radiation
• Evaporation.
• When ambient temperature conditions approach body temperature, the only
viable route of heat loss is evaporation; if ambient conditions exceed body
temperature, heat flow will reverse and the animal becomes a heat sink.
• THI allows us to estimating the thermal environment around animals. This
index takes into account ambient air temperature and humidity.

Successful cooling strategies for
lactating dairy cows

The Stress levels and THI
number

Lactating cows prefer an ambient temperature between 5 and 25º C, the
thermo-neutral zone (TNZ). Heat stress is caused by both temperature as
well as humidity


The two main strategies to improve heat stress during
summer months in animals
1. Management Approach
• Shades : It is the cheapest way to avoid heat stress in cattle.
• Milking times: On hot days we must milk and feed animals before 8 am in the
morning.
• In hot summer months sprinkling of dairy animals before morning and evening
milking period.
• Drinking water
2. Nutritional Approach
• During summer period, it is recommended that 75 % of green fodder feeding.
• Feeding of total mixed rations I
• Increase the energy density of diet.
• Increase the feeding frequency during cooler period of the day
• Feeding of by-pass nutrients helps to improve nutrient density and availability
for better milk production
• Further, supplementation of nutrients which play role as antioxidants
http://en.engormix.com/MA-dairy-cattle/articles/tips-keeping-dairy-cows-t989/p0.htm

Heat stress, with its physiological and behavioral
consequences, increases the risks of rumen acidosis.
http://www.thecattlesite.com/articles/1053/heat-stress-in-dairy-cows-implications-and-nutritional-management

Non-visual heat stress
• Sub-clinical rumen acidosis increases
• Blood flow to internal organs decreases
• Reproduction performance decreases
• Decreased levels of blood bicarbonate
• Significant drop in pregnancy rate
• Death loss increases
• Blood flow to skin increases

Visual heat stress
• Daily feed intake decreases
• Water intake increases
• Respiration rates increase
• Acute health problems
• Milk production decreases
• High incidence of abortions
• Decreased saliva production
• Increased drooling

http://www.formafeed.com/products/products_dairy_hydrola
c.htm

• Ideal ambient temperature for dairy cattle is between 41° and 77°F.
• Cows are stressed when their respiration rate rises above 75-80 breaths per
minute.
• Contribute to heat stress
• High humidity levels
• low air velocities
• solar radiation
http://en.engormix.com/MA-
dairy-cattle/articles/tips-
keeping-dairy-cows-
t989/p0.htm

http://www.formafeed.com/products/products_dairy_hydrol
ac.htm

• Lactating dairy cows feel
heat stress when the rectal
temperature is higher than
39.4C
• THI = 0.72 (W+D) +40.6,
Where W = Wet bulb temperature oC and D=
Dry bulb temperature oC

• THI values:
• 70F or less are considered comfortable
• 75-78F stressful
• >78F causes extreme distress with
lactating cows being unable to
maintain thermo regulatory
mechanisms

• Heat stressed cows generally exhibit altered blood acid-base chemistry as
a result of the shift in cooling from conductive, convective, and radiation
to evaporative cooling (Kibler and Brody, 1950).
• Panting and sweating increase as the reliance on evaporative cooling
increases.
• Panting sharply increases the loss of CO2 via pulmonary ventilation, reducing
the blood concentration of carbonic acid.
• For lactating dairy cows the ambient temperatures above 25C are
associated with lower feed intake, drops in milk production and reduced
metabolic rate (Berman, 1968).
• Clean drinking water is arguably the most important nutrient for the
dairy cow
• *Texas research work demonstrated that offering chilled drinking water
enhanced milk yield for lactating cows (Milam et al., 1986) by reducing
body temperature through absorbed heat energy.

Effects of Heat Stress on Physiology

Temperature Humidity Index for Dairy Cows, if the temperature is 95°F and the humidity is 75%
humidity the cow is under “severe” stress.

http://en.engormix.com/MA-dairy-cattle/articles/tips-keeping-dairy-cows-t989/p0.htm

Temp - - - - - - - - Relative Humidity, % - - - - - - - -

(F) 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100

- - - - - - - - - - - - - - - - - - - - - THI - - - - - - - - - - - - - - - - - -

70 64 64 64 65 65 65 66 66 66 67 67 67 68 68 68 69 69 69 70 70

71 64 65 65 65 66 66 66 67 67 67 68 68 68 69 69 70 70 70 71 71 Heat
Stress
72 65 65 65 66 66 67 67 67 68 68 69 69 69 70 70 70 71 71 72 72 Begins

73 65 66 66 66 67 67 68 68 68 69 69 70 70 71 71 71 72 72 73 73

74 66 66 67 67 67 68 68 69 69 70 70 70 71 71 72 72 73 73 74 74

75 67 67 67 68 68 68 69 69 70 70 71 71 72 72 73 73 74 74 75 75

76 67 67 68 68 69 69 70 70 71 71 72 72 73 73 74 74 75 75 76 76 Sharp
drops in
77 67 68 68 69 69 70 70 71 71 72 72 73 73 74 74 75 75 76 76 77 productio
n occur
78 68 68 69 69 70 70 71 71 72 73 73 74 74 75 75 76 76 77 77 78

79 68 69 69 70 70 71 71 72 73 73 74 74 75 76 76 77 77 78 78 79

80 69 69 70 70 71 72 72 73 73 74 75 75 76 76 77 78 78 79 79 80

81 69 70 70 71 72 72 73 73 74 75 75 76 77 77 78 78 79 80 80 81

82 69 70 71 71 72 73 73 74 75 75 76 77 77 78 79 79 80 81 81 82 Danger
Zone
83 70 71 71 72 73 73 74 75 75 76 77 78 78 79 80 80 81 82 82 83

http://en.engormix.com/MA-dairy-cattle/management/articles/heat-stress-in-dairy-t2165/124-p0.htm THI chart

• When THI values are between 72 and 86, physical signs
of heat stress with cattle are visible. When the THI is
greater than 86, severe heat stress can be exhibited.

http://www.formafeed.com/reference%20pages/hydrolac_heat_index_chart.htm

How to evaluate heat stress?

Body temperature (rectal) >
39.4ºC
Respiratory frequency >100/mn
DM intake decreases:
-10% = high stress
- 25% = severe stress

• The dairy cattle thermal comfort zone is -13ºC - +25ºC.
• A normal body temperature is between 38.4ºC and 39.1ºC (Lefebvre
and Plamondon, 2003)

http://www.thecattlesite.com/articles/1053/heat-stress-in-dairy-cows-implications-and-
nutritional-management

Until recently, a 72 THI was considered the point when heat and humidity began to stress dairy
cows. University of Arizona researchers have found a 68 THI is a better indicator. Ontario, 2011

Calves the optimal thermal environment is between 55 to 78°F in still air. 78°F and
above, they must burn more energy to drive off heat from the body by sweating and
increasing respiratory rate.

Broadwater, 2010

• Signs of heat stress become evident in dairy cows when the THI exceeds 72.

http://www.milkproduction.com/Library/Scientific-articles/Housing/Coping-with-summer-weather/

• Temperature and humidity index do not include
• air velocity
• radiant heat
• metabolic heat production
• hair coat
• skin water loss
• posture effects
Replacing a heat stress index based on air temperature and
humidity by one based on equations including animal and
environmental variables will help to determine the magnitude of
the stress.

The Problem with THI

Wet- and Dry- Bulb Temp

• Wet-bulb dry temperature (WBDT)79) 0.4Tw+0.6Ta
http://www.jniosh.go.jp/en/indu_hel/pdf/indhealth_44_3_388.pdf

• Acclimation involves changes in hormonal signals as
well as alteration in target tissue responsiveness to
hormonal stimuli.
• Determination that adaptation of animals to thermal stress
is a homeorhetic process
• endocrine control is an innovative way to use of endocrine
regulation as means of improving thermal tolerance.

Acclimation/Conditioning
http://www.ncbi.nlm.nih.gov/pubmed/16537957

• Cows increase respiration rate in order to promote heat loss via
evaporation. Respiration rate can be the most practical way to identify
heat stress, as flank movements are easy to count.
• Respiration rate increase in response to heat load with little or no lag in
time (Brown-Brandl et al., 2005).
• feedlot cattle, respiration rate increased from approximately 65
breaths/min when THI < 76 to 93 breaths/min when THI ≥ 84.
• Cows are stressed when their respiration rate rises above 75-80 breaths
per minute.

Respiration Rate (RR)
http://jas.fass.org/content/83/6/1377.full#ref-29

Innovative Technology
• Intravaginal probes to track
core body temperature (CBT)
continuous by attaching to the
intravaginal drug release
(CIDR) device
• measures core body temperature
(CBT) every 60 seconds for up to 6
days.
• This technology allows cows’ CBT
to be monitored and recorded 24h/d
as they move throughout all areas
of a dairy facility.

• Infrared thermography guns has been shown to be a cheap and effective way
to figure the actual skin surface temperature of an animal.
• If the skin surface temperature is below 35°C, the temperature gradient
between the core and skin is large enough for the animals to effectively use
all 4 routes of heat exchange.
• Infrared skin temperature is highly correlated with respiration rates and is a
good measure of the microenvironment around the animal.


Infrared image of a dairy cow lying down at night. The temperature scale is in Fahrenheit.
• Standing has been shown to increase heat loss by increasing the amount of
skin exposed to air flow or wind.
• Recumbent animals may develop heat stress at lower ambient temperatures
than standing animals.

http://www.thedairysite.com/articles/2404/behavioural-responses-to-heat-stress

Cooling
Ponds
• Cooling ponds did have a lower percentage of successful
breedings
• Fewer days dry
• A higher percentage of cows in milk compared with dairy herds
that used other forms of cooling.

“cooling ponds may provide relief from heat stress without
adversely affecting most important measures of herd performance.”


• Cortisol level will be 10 times higher than normal during periods of elevated environmental
temperature and humidity. Heat stress takes heavy toll to dairy performance by way of
making changes in feed intake, immunity and milk production.
• The increase in body temperature affects the reproductive tract and the early embryo. These
changes in the reproductive tract influence the ability of a cow to become pregnant during
heat stress.
• “Higher producing cows exhibit humidity ranging more signs of heat stress than lower
producing cows because higher pro-rapid shallow breathing, producing cows generate
more heat as they eat more feed for higher production.” (Pennington)
http://www.uaex.edu/other_areas/publications/pdf/fsa-3040.pdf
• *Texas research work demonstrated that offering chilled drinking water enhanced
milk yield for lactating cows by reducing body temperature through absorbed heat
energy (Milam et al., 1986) .

Extras

In order to maintain milk production, stress
minimization was required for an unusually
long period of time.
Australian Government: Bureau of Meteorology

http://www.milkproduction.com/Library/Scientific-articles/Housing/Coping-with-summer-weather/

• Tunnel Ventilation
• These systems have large exhaust fans located at one end of the barn, drawing the air into the
building on the opposite end.
• It provides both air exchange and airflow past the animals at higher air velocities in the barn
during the summer’s hottest days. Although an excellent system, the electrical costs to run the
fans can be high.
• The inlet needs to be sized adequately to handle the airflow. Tunnel ventilation is not used in cold
weather so tie-stall barns need a well-designed cold weather ventilation system.

• Shade
• A portable or temporary shade can reduce the amount of solar radiation that reaches cows on hot
sunny days. Shade height should be 14ft or higher for maximum effectiveness to allow for good
airflow under them.
• Shade cloth is less expensive than solid roofing material but does not provide as much protection
from solar radiation. If using a shade structure, feed and water must be available under the shade
and a manure management system must be planned.
• Cows will often lie down in the shade so some of the shaded area should be maintained for good
cow comfort

http://www.wxforecastnow.com/wxbase/index.php
option=com_content&view=article&id=12&Itemid=18

Proposed systems for rating heat stress and strain (heat stress indices)
Year Index Author(s)

1905 Wet-bulb temperature (Tw) Haldane19)
1916 Katathermometer Hill et al.47)
1923 Effective temperature (ET) Houghton & Yaglou23)
1929 Equivalent temperature (Teq) Dufton48)
1932 Corrected effective temperature (CET) Vernon & Warner24)
1937 Operative temperature (OpT) Winslow et al.49)
1945 Thermal acceptance ratio (TAR) Ionides et al.50)
1945 Index of physiological effect (Ep) Robinson et al.51)
1946 Corrected effective temperature (CET) Bedford52)
1947 Predicted 4-h sweat rate (P4SR) McArdel et al.53)
1948 Resultant temperature (RT) Missenard et al.54)
1950 Craig index (I) Craig55)
1955 Heat stress index (HIS) Belding & Hatch7)
1957 Wet-bulb globe temperature (WBGT) Yaglou & Minard25)
1957 Oxford index (WD) Lind & Hellon34)
1957 Discomfort index (DI) Thom36)
1958 Thermal strain index (TSI) Lee & Henschel56)
1959 Discomfort index (DI) Tennenbaum et al.39)
1960 Cumulative discomfort index (CumDI) Tennenbaum et al.39)
1960 Index of physiological strain (Is) Hall & Polte57)
1962 Index of thermal stress (ITS) Givoni58)
1966 Heat strain index (corrected) (HSI) McKarns & Brief59)
1966 Prediction of heart rate (HR) Fuller & Brouha60)

1967 Effective radiant field (ERF) Gagge et al.61)
1970 Predicted mean vote (PMV) Fanger9)
Threshold limit value (TLV)
1970 Prescriptive zone Lind62)
1971 New effective temperature (ET*) Gagge et al.63)
1971 Wet globe temperature (WGT) Botsford64)
1971 Humid operative temperature Nishi & Gagge65)
1972 Predicted body core temperature Givoni & Goldman66)
1972 Skin wettedness Kerslake67)
1973 Standard effective temperature (SET) Gagge et al.68)
1973 Predicted heart rate Givoni & Goldman69)
1978 Skin wettedness Gonzales et al.70)
1979 Fighter index of thermal stress (FITS) Nunneley & Stribley71)
1981 Effective heat strain index (EHSI) Kamon & Ryan72)
1982 Predicted sweat loss (msw) Shapiro et al.73)
1985 Required sweating (SWreq) ISO 793374)
1986 Predicted mean vote (modified) (PMV*) Gagge et al.75)
1996 Cumulative heat strain index (CHSI) Frank et al.76)
1998 Physiological strain index (PSI) Moran et al.77)
1999 Modified discomfort index (MDI) Moran et al.78)
2001 Environmental stress index (ESI) Moran et al.79)
2005 Wet-bulb dry temperature (WBDT) Wallace et al.80)
2005 Relative humidity dry temperature (RHDT) Wallace et al.80)

• http://en.engormix.com/MA-dairy-cattle/articles/heat-stress-dairy-animals-t1019/p0.htm
• •http://en.engormix.com/MA-dairy-cattle/management/articles/heat-stress-in-dairy-t2165/124-
p0.htm
• •http://en.engormix.com/MA-dairy-cattle/articles/heat-stress-dairy-animals-t1019/p0.htm
p0.htm
p0.htm
• •http://en.engormix.com/MA-dairy-cattle/articles/tips-keeping-dairy-cows-t989/p0.htm
•http://www.thecattlesite.com/articles/1053/heat-stress-in-dairy-cows-implications-and-nutritional-
management
• •http://www.formafeed.com/products/products_dairy_hydrolac.htm
•http://www.formafeed.com/products/products_dairy_hydrolac.htm
•http://en.engormix.com/MA-dairy-cattle/management/articles/heat-stress-in-dairy-t2165/124-
p0.htm
• •http://www.formafeed.com/reference pages/hydrolac_heat_index_chart.htm
• •http://www.jniosh.go.jp/en/indu_hel/pdf/indhealth_44_3_388.pdf
• •http://www.milkproduction.com/Library/Scientific-articles/Housing/Coping-with-summer-weather/
•http://www.ncbi.nlm.nih.gov/pubmed/16537957 •http://jas.fass.org/content/83/6/1377.full
• •http://www.thecattlesite.com/articles/1053/heat-stress-in-dairy-cows-implications-and-nutritional-
management

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