Epsilon Archive for Student Projects

Abstract

När man i tidigare undersökningar studerat betesgång för mjölkkor har klimatet på betet inte
beaktats. En höglakterande ko producerar mycket värme som hon måste avge till sin
omgivning för att kunna bibehålla sin kroppstemperatur. De sätt som djuret kan avge värme
på är begränsade och påverkas av flera klimatfaktorer samt djurets genetiska och biologiska
förutsättningar.
Antalet dagar som registreringar gjordes under denna studie blev av flera olika anledningar få,
18 dagar. Klimatet utomhus under studien registrerat som globtemperatur varierade från 22,4
till 34,7ºC.
Då djurskyddslagen skall främja djurens hälsa och djurets naturliga beteende fick en grupp
126 höglakterande kor möjlighet att välja uppehållsplats under tiden 26 juli till 11 augusti.
2004. Korna fördes ut på betet vid niotiden på förmiddagen och var därefter fria att gå in och
ur stallet efter egen vilja tills de togs in för kvällsmjölkning omkring klockan tre
påeftermiddagen. Kornas val av uppehållsplats registrerades automatiskt med hjälp av kons
transponder och antennportaler vid utgången från stallet. Även kornas besök i
kraftfoderautomater registrerades automatiskt. Ytterklimatet registrerades med hjälp av en
väderstation (registrerade lufttemperatur, globtemperatur, relativ fuktighet, vindriktning och
vindhastighet samt solinstrålning). Inne i stallet registrerades temperatur och relativ fuktighet.
Studien skulle även registrera parametrar som avspeglar graden av värmestress hos korna.
Detta gjordes genom att manuellt registrera andningsfrekvenser och yttemperaturer hos 10
utvalda fokaldjur när de befann sig på betet.
Djuren utfodrades på stall och fodergivan tog ingen hänsyn till vad korna åt på betet.
Betestillgången under hela försöket var god.
Resultatet visar att klimatfaktorer på betet som temperatur, solinstrålning, THI (Temperatur
Humidity Index baserat på globtemperatur), och skillnaden mellan ute och stallklimat inte
påverkade kornas vilja att gå in i stallet. Resultatet visade dock att det under alla
klimatbetingelser alltid fanns kor som gick in i stallet. Av de kor som gick in i stallet uppsökte
alltid en del kor kraftfoderautomat inom en kort tid och man kan sluta sig till att de primärt
gick in i stallet för att äta. Klimatfaktorer påverkade dock inte andelen kor som åt inom en
kort tid av de kor som gick in. Klimatet påverkar inte heller kornas beteende att gå ut från
stallet till betet.
När globtemperaturen steg ökade kons andningsfrekvens och yttemperatur Vad det gäller
yttemperaturer visar resultatet i enlighet med litteraturen att en svart ko blir varmare (är mer
värmebelastad) än en vit ko vid samma globtemperatur. Detta betyder inte att den vita kon har
lägre andningsfrekvens, vilket kan förklaras av det faktum att den teoretiskt framräknade
värmeproduktionen har antaganden om en viss energieffektivitet vad det gäller metabolism,
mjölkproduktion och dräktighet. Eftersom utfodringen av den enskilda kon inte är
kontrollerad kan en ko avvika kraftigt från denna norm och därmed kan resultat som visar att
en ko med låg teoretisk värmeproduktion (pga. ex. låg mjölkproduktion) uppvisa starkare
värmestress (högre andningsfrekvens) än en annan ko med hög teoretisk värmeproduktion.
Uppmätta yttemperaturer hos korna jämfördes med simulerade yttemperaturer i programmet
ANIBAL. ANIBAL simulerar med antaganden att djuret står upp och befinner sig i ett stall
(ingen solinstrålning). De simulerade värdena för yttemperaturen blir därför i de flesta fallen lägre än den uppmätta. Simuleringar i ANIBAL visade att den latenta värmeavgivningen ökar
med en ökad solinstrålning. Detta stöder resultatet med ökade andningsfrekvenser med ökad
globtemperatur.
Den energi som tillförs kon via solinstrålning är i många fall mycket hög. I en situation som
på betet, tillförs energi via solinstrålning och bortförs via konvektionsförluster. När dessa
jämfördes visade resultatet att i många fall så överstiger den tillförda strålningsenergin vida
konvektionsförlusterna. Bara i någon enstaka jämförelse var konvektionsförlusten större.
Olika sätt att karaktärisera klimatet användes i studien. THI beräknades på två sätt, ett med
lufttemperaturen som bas och det andra med globtemperatur som bas. Då solinstrålningen på
ett betydande sätt påverkar hur mycket kon värmebelastas borde det andra alternativet ge en
rättvisare bild. Effekten av strålning ses även i jämförelser med lufttemperatur och
globtemperatur. Wet Bulb Globe Temperatur (WBGT) visar effekten av lufttemperatur,
globtemperatur samt luftens relativa fuktighet. Studier med denna temperatur finns dock inte
gjorda på nöt och kan inte jämföras med studier på människa då våra biologiska
förutsättningar att avge värme är så vitt skilda från kornas.
I framtida studier av kornas val att vara på bete eller gå in i stallet bör man ha en säkrare
registrering i portalerna. Tidpunkterna när korna släpps ut och tas in från bete skall inte skilja
sig från dag till dag. Man skulle även kunna ytterligare studera vilka kor som går in och äter
kraftfoder och hur detta påverkar kons hela kraftfoderkonsumtion. Korna bör även släppas ut
under alla klimatbetingelser för att kunna se effekter av riktigt varma eller regniga dagar.

SUMMARY

Earlier studies of grazing dairy cattle have not taken the climate under consideration. A high
lactating dairy cow produces a great amount of heat which she has to dissipate in order to
maintain her deep body temperature. The ways of heat dissipation are affected by several
climatic factors as well as the biological and genetic prerequisites.
The number of days for data collecting in this study got by several reasons rather few, 18
days. The outside globe temperature varied during this study varied from 22.4 to 34.7ºC.
The Swedish Animal Protection Act is promoting animal health and animal natural behaviour
and states compulsory grazing for dairy cows. Hence in this project a group of 126 high
lactating dairy cows were given opportunity to choose between pasture or inside during day
time between the 26 of July till 11 of August 2004. All cows were taken out on pasture at 9
am and were thereafter free to go in and out of the barn as they wanted until they were all
taken in for milking around 3 pm. The cows´ choices of location were automatically
registered by the necklace transponder in antenna- portals located at the barn exit. The cows´
visits in the automatic concentrate feeders were automatically registered as well. Outside
climate parameters (air temperature, globe temperature, relative humidity, wind angle and
wind speed and solar radiation) were recorded in a weather-station. Inside the barn air
temperature and relative humidity were recorded. The study also collected parameters
reflecting the level of heat stress on the animals. This was done manually by observing
respiration rates and measure skin temperatures on 10 selected animals during grazing. The
sward access during the study was good.
The result shows that climate factors as temperature, solar radiation, THI (Temperature
Humidity Index based on globe temperature and relative humidity), and the difference
between the outside and inside climate does not affect cow's willingness to go inside the barn.
However, during all climatic situations there were always cows that went into the barn. Some
of these cows went shortly after their entry to consume concentrate and you can conclude they
primarily went inside to consume concentrate. Climate factors did not affect the number of
cows who consume concentrate shortly after their entry. The climate did not affect the cows´
behaviour of going out from the barn to the pasture area.
As the globe temperature rises the cow's respiration rate and skin temperature increase. The
results from the skin temperature measurements were in accordance with literature and that a
black coated cow gets warmer (is more heat stressed than a white coated cow at the same
globe temperature). This does not mean that the white coated cow has a lower respiration rate
compared to the black cow. This can be explained of their nutritional status. The assumptions
regarding feed intake, metabolism, milk production and pregnancy for the theoretically
calculated heat production of the particular cow must be fulfilled to make proper comparison
about heat stress. As the feed intake of one particular cow is not controlled one cow can show
big differences from the assumptions based on feeding norms and the result will show that a
cow with low theoretical heat production (low lactating) shows a stronger heat stress (higher
respiration rate) than another cow with a high theoretical heat production.
Measured cow skin temperatures were compared with simulated skin temperatures in the
computer simulation program ANIBAL. ANIBAL simulates assuming the cow is standing up
in a barn (no solar radiation load). The simulated values of skin temperatures get thereby inmost cases lower then the registered. Simulations with ANIBAL showed an increasing
amount of latent heat loss as solar radiation rises which support the result with increasing
respiration rates as a function of rising globe temperature.
The solar radiation heat load is in many cases high. In a situation as on the pasture energy is
transferred into the cow by solar radiation and from the cow by convection losses. When these
were compared the result showed that the solar radiation gain often widely exceed the
convection losses. Only some situations showed otherwise.
Different ways of describing climate where used in the study. THI were calculated in two
ways, one with air temperature and the other with globe temperature as base. As solar
radiation principally always affects the thermal condition for the cow the globe temperature
alternative should give a more adequate description. The effect of solar radiation load is also
seen in comparisons between air temperature and globe temperature. Wet Bulb Globe
Temperature (WBGT) shows the impact of air temperature, radiation, and the relative
humidity of the air. Studies using this temperature are however not done on cattle and can not
be compared with studies done on humans as our capacity of loosing heat by evaporation
widely differs from cattle.
In future studies of cows´ choice of being on pasture or inside the barn you must have a more
accurate and reliable recording in the portals. The time of letting cows out and in from the
pasture should not differ day by day. You could also study which cows that goes back into the
barn to eat concentrate and how this affects the total feed consumption of the cow. The herd
should be let out to pasture in all climates to be able to see the effect of really hot or rainy
days.

Earlier studies of grazing dairy cattle have not taken the climate under consideration. A high
lactating dairy cow produces a great amount of heat which she has to dissipate in order to
maintain her deep body temperature. The ways of heat dissipation are affected by several
climatic factors as well as the biological and genetic prerequisites.
The number of days for data collecting in this study got by several reasons rather few, 18
days. The outside globe temperature varied during this study varied from 22.4 to 34.7ºC.
The Swedish Animal Protection Act is promoting animal health and animal natural behaviour
and states compulsory grazing for dairy cows. Hence in this project a group of 126 high
lactating dairy cows were given opportunity to choose between pasture or inside during day
time between the 26 of July till 11 of August 2004. All cows were taken out on pasture at 9
am and were thereafter free to go in and out of the barn as they wanted until they were all
taken in for milking around 3 pm. The cows´ choices of location were automatically
registered by the necklace transponder in antenna- portals located at the barn exit. The cows´
visits in the automatic concentrate feeders were automatically registered as well. Outside
climate parameters (air temperature, globe temperature, relative humidity, wind angle and
wind speed and solar radiation) were recorded in a weather-station. Inside the barn air
temperature and relative humidity were recorded. The study also collected parameters
reflecting the level of heat stress on the animals. This was done manually by observing
respiration rates and measure skin temperatures on 10 selected animals during grazing. The
sward access during the study was good.
The result shows that climate factors as temperature, solar radiation, THI (Temperature
Humidity Index based on globe temperature and relative humidity), and the difference
between the outside and inside climate does not affect cow’s willingness to go inside the barn.
However, during all climatic situations there were always cows that went into the barn. Some
of these cows went shortly after their entry to consume concentrate and you can conclude they
primarily went inside to consume concentrate. Climate factors did not affect the number of
cows who consume concentrate shortly after their entry. The climate did not affect the cows´
behaviour of going out from the barn to the pasture area.
As the globe temperature rises the cow’s respiration rate and skin temperature increase. The
results from the skin temperature measurements were in accordance with literature and that a
black coated cow gets warmer (is more heat stressed than a white coated cow at the same
globe temperature). This does not mean that the white coated cow has a lower respiration rate
compared to the black cow. This can be explained of their nutritional status. The assumptions
regarding feed intake, metabolism, milk production and pregnancy for the theoretically
calculated heat production of the particular cow must be fulfilled to make proper comparison
about heat stress. As the feed intake of one particular cow is not controlled one cow can show
big differences from the assumptions based on feeding norms and the result will show that a
cow with low theoretical heat production (low lactating) shows a stronger heat stress (higher
respiration rate) than another cow with a high theoretical heat production.
Measured cow skin temperatures were compared with simulated skin temperatures in the
computer simulation program ANIBAL. ANIBAL simulates assuming the cow is standing up
in a barn (no solar radiation load). The simulated values of skin temperatures get thereby in
6
most cases lower then the registered. Simulations with ANIBAL showed an increasing
amount of latent heat loss as solar radiation rises which support the result with increasing
respiration rates as a function of rising globe temperature.
The solar radiation heat load is in many cases high. In a situation as on the pasture energy is
transferred into the cow by solar radiation and from the cow by convection losses. When these
were compared the result showed that the solar radiation gain often widely exceed the
convection losses. Only some situations showed otherwise.
Different ways of describing climate where used in the study. THI were calculated in two
ways, one with air temperature and the other with globe temperature as base. As solar
radiation principally always affects the thermal condition for the cow the globe temperature
alternative should give a more adequate description. The effect of solar radiation load is also
seen in comparisons between air temperature and globe temperature. Wet Bulb Globe
Temperature (WBGT) shows the impact of air temperature, radiation, and the relative
humidity of the air. Studies using this temperature are however not done on cattle and can not
be compared with studies done on humans as our capacity of loosing heat by evaporation
widely differs from cattle.
In future studies of cows´ choice of being on pasture or inside the barn you must have a more
accurate and reliable recording in the portals. The time of letting cows out and in from the
pasture should not differ day by day. You could also study which cows that goes back into the
barn to eat concentrate and how this affects the total feed consumption of the cow. The herd
should be let out to pasture in all climates to be able to see the effect of really hot or rainy
days.