1 t +44 (0) 1725 511422 e info@hydor.co.uk heat stress & the dairy cow w www.hydor.co.uk
As a result of Man s thirst for knowledge, our understanding of our domestic livestock is continuously expanding and improving. This is especially true in the case of the effect of heat stress on dairy cows. There is a wide range of published research examining every aspect of this subject. This paper summaries the latest thinking on this subject and examines the effect of heat stress, its impact on production and health and what strategies and available for its control, with particular focus on ventilation and evaporation cooling technology.
contents 4 5 6 7 8 9 What is heat stress? Heat stress chart The consequences of heat stress Fans for dairy cows Evaporative cooling Fans and evaporative cooling 10 10 References Additional thanks
4 what is heat stress? All animals have what is known as a Thermal Comfort Zone. This is a range of temperature within which the animal s comfort is optimal. In the case of the dairy cow this zone is between -13 C and +25 C with a body temperature of between 38.4 and 39.1 C. (Lefebvre and Plamondon 2003). All warm blooded animals generate heat as a result of internal metabolic processes that maintain the body and permit growth and production. A lactating dairy cow produces the equivalent of sixteen 100 watt light bulbs as a result of these metabolic processes and this must be dissipated if heat stress is to be avoided (McFarlane 1997). Indeed in high yielding cows this heat output may be higher due to increased metabolic rate as they are producing more milk. Hence these high yielders may be more prone to heat stress. During hot weather the likelihood of heat stress is a consequence of more than just temperature. Heat stress is a result of a complex relationship between temperature and humidity. For any given temperature, the apparent temperature (how hot we feel) will increase as the humidity rises, in the same way as a sauna operates. The relationship between these two factors has been developed into a Temperature Humidity Index (THI) specifically for the dairy cow as shown adjacent. (F. Wierama. University Of Arizona 1990). hydor Heat Stress & The Dairy Cow
5 heat stress chart When the index exceeds 71 cows will start to suffer mild stress. As the temperature or humidity increases so will the level of stress until at above 86 there is a real risk of death as a consequence of extreme heat and humidity. It is also important to remember that your high yield animals are likely to suffer stress at a lower temperature and humidity than this. F C 116 46.7 113 110 45.0 43.3 fatal 107 41.7 104 101 40.0 38.3 severe stress Temperature 98 95 92 36.7 35.0 33.3 distressed 89 31.7 86 83 30.0 28.3 mild stress 80 26.7 77 74 25.0 23.3 no stress 71 21.7 0 10 20 30 40 50 60 70 80 90 100 Relative Humidity % t +44 (0) 1725 511422 e info@hydor.co.uk w www.hydor.co.uk
6 the consequences of heat stress In times of heat stress cows will make adjustments to both their behaviour and body chemistry in an attempt to maintain their body temperature. Water consumption will increase by as much as 50% as the animal uses moisture to increase evaporative heat loss. This is achieved by increasing subcutaneous blood flow, panting and drooling. At 35 C these measures increase considerably and maintenance energy needs increase by 20% (Lallemand Animal Nutrition 2007). The result of this is for any given food intake, there is a reduction in available energy for milk production and milk yields will fall. Cows can also reduce heat production by reducing the metabolic processes within the body; the cow essentially takes her foot off the throttle. This manifests itself principally in reduced food intake. However the consequences of this for the rumen function can go much further; As food intake falls higher proportions of fermentable carbohydrates tend to be eaten. Less bulk fibre is consumed so saliva production falls and as a result the ph of the rumen declines, impairing fibre digestion. This chain of events can lead to acidosis which can have serious consequences for the cow s health. All these changes impact upon the cow s health and productive output. Jones and Stallings (2008) found that heat stress could lead to 1 2m HV belt drive fan showing suspended installation 1 Reduced food intake 2 Increased water intake 3 Reduced yield 4 Lower conception rates 5 Lower calf weights 6 Increased mastitis 7 Increased Laminitis The pattern of weather conditions can also be important. Evidence from Denmark suggests that short, sudden hot weather periods can result in reduced food intake coupled with rapid increases in water intake. This can lead to a fall in milk solids content, which often fail to recover once normal weather patterns resume. hydor Heat Stress & The Dairy Cow
7 fans for dairy cows Common-place in the poultry sector, fans are now increasingly being applied to the dairy the sector to improve the welfare and productivity of cows. The use of fans to provide positive control of air speed and direction has a number of benefits: 1 Stale air is removed and fresh air brought in 2 Heat and moisture generated by the cows is removed thus reducing the temperature and humidity 3 Consistent air flow can be maintained regardless of external conditions During hot weather increasing the air speed in the building not only increases the rate of air change, it also improves the effectiveness of evaporative heat loss from the cows; It s the same principle as raising a wetted finger in the breeze. Modern Dairy housing is typically characterised by wide buildings with low pitched roofs and exposed purlins and trusses, all of which reduce the potential for natural ventilation. Indeed smoke testing in such buildings shows air movement to be typically slow and random in nature not ideal during spells of high temperature. Such designs do lend themselves to positive control, fan driven ventilation systems; known as Tunnel Ventilation. This is a simple concept where the building is used as a tube down which air is moved at a controlled rate. The objective is to bring in fresh air and remove stale air. As the temperature rises then increasing the number of functioning fans increases the air flow rate; just like you do with your car ventilation on a hot day. The Hydor range of belt driven HV fans are perfect for this task; they are capable of moving large volumes of air with minimal energy consumption. Available in a range of 2 1.25m HV belt drive fan showing end wall installation designs they can be built into end walls or suspended in the building to provide consistent air movement as shown in Fig 1 and Fig 2. Research indicates that air speeds as high as 600ft per minute can reduce the THI by 7.5 units. (McFarlane 1997). It is common in poultry installations to have a series of fans that are sequentially controlled, as the temperature increases so the number of fans operating increases, thereby increasing the air speed. Similar control systems can be applied to dairy installations; indeed Hydor have a team of engineers who produce such control equipment for various applications within the agricultural sector. t +44 (0) 1725 511422 e info@hydor.co.uk w www.hydor.co.uk
8 evaporative cooling There is one obvious limitation with fans, they cannot cool the air lower than the ambient temperature. Is it possible to reduce air temperature on hot days in large dairy houses? This is where evaporative cooling can help. The system introduces very small water droplets (3 Microns) into a hot air mass. As the water evaporates it rapidly cools the air mass. As the air mass cools it also falls as it is more dense than hot air. A practical example is the sensation experienced when a sudden cooling effect travels down ones body. The Hydor system uses an ultra high pressure pump; 70 bar coupled with stainless steel pipe-work and precision 0.3mm nozzles. See Fig 3. The benefit of this is that the water evaporates quicker than low pressure nozzles because the droplet size is much smaller. This increases the rate of air cooling and gives complete evaporation of the water so no surface wetting occurs. With all evaporative cooling systems care must be exercised during very humid weather because as humidity increases so the potential for evaporative cooling decreases. Thankfully the Hydor system is available with a control panel to monitor atmospheric conditions in-order to ensure maximum efficiency and safety. 3 Evaporative cooling nozzle In typical installations nozzles are placed at a height of 3m and at 3m spacing in cubicle areas and feed passages. Under normal conditions it is possible to reduce the internal temperature from 30 C to 25 C when the ambient humidity is 50%. The system has an additional benefit in that all installations are completely bespoke and nozzles can be placed in any area required. For example, additional nozzles could be placed in collecting yards and the parlour. By using solenoid control valves and a variable speed pump it is possible to control these zones independently of each other so that nozzles in the collecting yard and parlour only operate during milking. hydor Heat Stress & The Dairy Cow
9 fans & evaporative cooling With Hydor s technology and experience in the design and manufacture of environment control systems, we feel there is great potential for a fully integrated climate control system inclusive of fans and evaporative cooling to provide progressive climate management for dairy cow housing. During normal weather first stage fans will maintain a pre set air flow in the building to provide a constant air change in-order to remove stale air and bring in fresh air. As the temperature increases additional fans will increase the air speed further to increase the cooling effect and the evaporative cooling system will reduce the air temperature further. Finally by clustering solenoid controlled nozzles around strategically placed fans we are able to inject water droplets directly into the air stream thus maximising potential cooling. Many large-scale dairy herds have evolved from smaller units, driven by economies of scale as costs rise at a time when milk prices are often static or worse. The more progressive farms are now realising that ventilation has often been neglected or not considered at all, the use of fans is becoming more common place. With a detailed understanding of the cow s environmental requirements, coupled with Hydor s technical knowledge and range of specialist equipment, it is possible to bring cow welfare to the top of the list of priorities and provide considerable benefits in productive output, cow health and your financial bottom line. t +44 (0) 1725 511422 e info@hydor.co.uk w www.hydor.co.uk
10 references Lefebvre D, Planondon P., 2003 Le Producteur de Lait Quebecois, juin 2003. Mc Farlane J. Hot Weather s here!, 1997. Wierama F., University of Arizona. 1990. Lallemand Animal Nutrition, Heat Stress in Dairy Cows: Implications and Nutritional Management., June 2007. Jones G. M., Stallings C. C., Reducing Heat Stress In Dairy Cattle., November 2008. additional thanks Kemble Farms, The Royal Cornwall Showground and Ivy House Farm for the photographs used in this text. hydor Heat Stress & The Dairy Cow
Date 26 / 4 / 2011
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