Ve Vent ntil ilat ation ion an and Co d Cool olin ing in Ar - - PowerPoint PPT Presentation

Ve Vent ntil ilat ation ion an and Co d Cool

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Heat at St Stress ess Costs sts to to Dairy iry Pr Producers

• ducers
• Dairy Producers strive to achieve consistently high milk production, feed

efficiency and reproductive efficiency while maintaining the health of the dairy animal

• Dairy Cattle are sensitive to heat stress on account of the high metabolic

heat production during feed intake – rumen fermentation and milk yield

• Heat stress characterised by increased rectal temperature, elevated

respiration rate, decreased feed intakes which subsequently decreases milk yield

• Heat stress has a negative impact on a dairy farm’s future by reducing the

peak milk production of cows which go through the transition periods of heat stress

Wh When en are e Animals mals in Heat at Str tress ess

For lactating cows, temperatures above 23.9C start to have an impact

Wh When en are e Animals mals in Heat at Str tress ess

Mild Heat Stress Moderate Heat Stress Severe Heat Stress Dangerous Heat Stress Measures Temperature & Humidity Doesn’t Measure Radiant Heat Load under the roof & the Heat the Cow Generates

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Kn Know

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Enviro ironment nment

• More dairy farms being constructed throughout the world producers need

to select carefully the appropriate facility for the local climate

• Facility options vary depending on the severity of heat stress  capital

costs to construct a dairy farm will vary considerably based on the environmental conditions present

• In more sever climates greater effort is required to properly cool cows

How w to to Keep ep Cows ws Cool

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Enviro ironment nment

BWh B = Arid W = Desert h = Hot Arid

How w to to Keep ep Cows ws Cool

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Str trateg ategy y to to red educ uce e th the Im e Impa pact ct of

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eat

• Two Main Strategies

1. Reducing the heat load on dairy animals 2. Maximising heat loss from dairy cows

• Tools needed to reduce the heat load is;

1. Shade to reduce the solar heat load 2. Cooling to reduce the air and cow temperature and increases thermal gradient for cows to dissipate heat from the skin surface 3. Fans to increase convective air movement across the skin surface and increase convective heat loss

• Strategies for all buildings/class of animal need to be addressed

• Should be made available to cows
• Water at the parlour – lactating cows will consume 10% of their daily intake

if given the chance at the parlour

• Water space in the barn ~ 3-9 linear cm per cow

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Wat ater er

Shade

• Adequate shade in the housing area and the parlour
• Shade should be constructed at a height of at least 4.3m and ideally a 4/12

pitch

• Using porous materials such as shade cloth is not as effective as solid

shades

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Sha hade de

• Barns with a north-south orientation have a greater solar radiation

exposure than barns with an east-west.

• Cows seek shade during the summer  protection from direct sunlight

necessary

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Bar arn n Ori rien entation tation

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Direct Cooling - Soaking

• One of the most common and effective methods to promote heat loss
• Large droplets/low pressure which wets the cows hair coat and skin
• Fans force air over the cows body causing evaporative cooling on the skin

surface

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Respiration of cows cooled using different cooling strategies

40 50 60 70 80 90 100 110 5 15 25 35 45 55 65 75 85 95 Minutes from Start of Observation

Breaths/min

0 + F 15 15 + F 10 10 + F 5 5 + F

Soaking 1 minute every 5 minutes with fans has the biggest impact

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Indirect Cooling – High Pressure Fogging

• Cools the air around the cow
• High-Pressure Misters / High Pressure Fogging produce very small droplets

(1,000 psi)

• Fogging introduced into the air

stream of the fan

• Works well in arid climates

 water is evaporated into the air  temperature drops Humidity does increase as more water is being added to the air

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• In Extreme Climates it is necessary to use both soaking and high pressure

fogging

• Body temperature is directly lowered when feedlane soaking is used in

addition to cooling the air

• Cooling the air through evaporative cooling (high pressure fogging)

reduces the total hours of higher levels of THI

• Air movement is an important factor affecting both convective and

evaporative heat losses

• Air speed is critical – minimum target 3m/s
• Air exchange to remove moisture, pathogens and gasses
• Higher speeds produces higher rates of convective heat transfer  creating

wind chill

• Fan spacing is critical under the roof to ensure the maximum air speed can

be achieved in the peak of the heat

• Size of Fan Important Factor – bigger fans  great coverage  great

electricity efficiencies

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Me Mecha hanica nical l Ven enti tila lation tion

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