MINIMUM VENTILATION FOR REARING TURKEYS

Transcription

1 MINIMUM VENTILATION FOR REARING TURKEYS DEFINITION The ventilation of the turkey house has several important functions essential for the welfare and performance of the turkeys: 1. To control house temperature. 2. To supply the birds with oxygen. 3. To remove pollutants, i.e. carbon dioxide, ammonia, dust and carbon monoxide. 4. To maintain litter quality through the removal of moisture. In a fan-ventilated house, the ventilation rate will vary between a minimum and a maximum setting to control the temperature (Figure 1). The minimum ventilation setting is the lowest ventilation required to ensure that the birds have enough oxygen, pollutants are removed and litter quality maintained and is the subject of this Technical Advice Sheet. The fans used to provide minimum ventilation are often called manual, hand or stage 1 fans and these will run continuously ensuring that good air quality is maintained. In contrast to these manual fans, other fans are usually installed to help maintain the target temperature and operate automatically to control an increase in house temperature. Head Office Chowley Five Chowley Oak Business Park Tattenhall Cheshire CH3 9GA United Kingdom Telephone +44 (0) Fax +44 (0) But.uk@ aviagen.com Website Figure 1 - Relationship Between Minimum & Maximum House Ventilation Ventilation rate m 3 /h Maximum Minimum Ventilation to maintain air quality only. If supplementary heating is not provided, house temperature will fall below the target temperature set Ventilation rate adjusts as temperature changes Ventilation can only keep house temperature at external temperature plus 3 to 5 O C (depending on insulation value of the house) Cooling aids may be necessary as temperature increases External Temperature O C Minimum ventilation is provided by the manual only, whilst Maximum ventilation is provided by all fans in the house Page 1 of 8

2 OBJECTIVES To ventilate turkey houses to maintain air quality within suggested limits, see Table 1 below: Table 1. Ventilation objectives Supply / Remove Component Acceptable Levels Supply Oxygen 19 to 21 % Remove Carbon monoxide Effectively 0 ppm Remove Water Vapour Poults 65 70% RH* Older birds < 70% RH* Remove Carbon dioxide < 0.1 % Remove Ammonia < 20 ppm** Remove Dust < 5 mg/m 3 Remove Airbourne diseases Minimal Remove Heat To a set temperature target * RH - relative humidity **Note: Check local regulations for guidance on permitted Ammonia levels To maintain good air quality and the correct use of supplementary heat (see Technical Advice Sheet Controlling Litter Moisture Linking Fans to Heaters a ), to maintain good litter conditions and healthy birds. To calculate the correct level of minimum ventilation for a given turkey flock taking into account its age. To provide the calculated minimum ventilation by means of manually controlled fans, i.e., fans that are totally independent of any temperature control system. To provide targets for acceptable air quality in naturally ventilated houses. PROCEDURE Methods Used For Calculating Minimum Ventilation The primary factor in most practical situations that determines the minimum ventilation required is the moisture content of the air. For every one kg of food consumed by the birds they will drink approximately two kg of water. A flock of 1,000 commercial males at 20 weeks of age will produce between 1.2 and 1.4 tonnes of water per day depending on the strain. Most of this water ends up in either the litter or the poultry house air. Page 2 of 8

3 This water is removed from the house by the ventilation system, replacing the moist house air with dry air from the outside. The effectiveness of this process is determined by the relative humidity (RH) of the incoming air and house temperature. When the incoming air is saturated (i.e. RH = 100%) heat must be used in order to condition the air to increase its water holding capacity and enable it to remove excess moisture. This topic is dealt with in Technical Advice Sheet, Controlling Litter Moisture Linking Fans to Heaters a. The actual volume of fresh air required to provide sufficient oxygen for turkeys and to remove carbon monoxide, carbon dioxide, ammonia, dust particles and pathogens etc., to provide an acceptable environment is usually much smaller than the volume of air needed to control moisture content. Therefore, these other parameters are controlled by default in most situations by managing the air moisture content within the turkey house. However, in hot countries with low ambient relative humidity or when managing older turkeys such as replacement breeder females, care should taken because excess dust may be the pollutant that determines the rate of minimum ventilation. In some conditions, care needs to be taken to ensure ammonia concentrations in the air are below the accepted maximum. This applies especially if mechanical turning of the litter is practiced or diets with excess concentrations of protein are accidentally fed. There are three widely practiced methods for calculation of the minimum ventilation requirement: 1. An equation based on metabolic bodyweight: 2. Ventilation requirement (m 3 /s) = 1.95 x 10-4 m 3 /s/kg weight A simple factor based on feed intake known as Metres cubed per Second per Tonne of feed eaten per Day, or MSTD. This preferred method uses feed intake (predicted or measured) as an indicator of water use and as a basis to calculate minimum ventilation requirements to control moisture. In most climates, a MSTD of 2 is sufficient to keep turkeys alive, but in practice a MSTD value of 3 will help to keep litter dry and birds healthy, providing that there is sufficient supplementary heat, i.e. brooders, to maintain the internal temperature target. 1. A variation on method 2 based on linking the minimum ventilation rate to measured daily water input to the house, however, it is not commonly used and is therefore not discussed in detail within this Technical Advice Sheet. Page 3 of 8 The relationship between these two methods of calculation can be seen in Figure 2. The ventilation requirement will vary with the feed intake method according to the type of diet fed (e.g. energy level will affect feed intake) and the chosen MSTD factor, whilst the body weight method will provide a consistent result. However, the body weight equation can be difficult to calculate correctly or explain on farm and the concept of metabolic body weight is not easily understood. Using the MSTD is far simpler to remember and is often the preferred method on farm. TAS Issue 15/05/2006 MINIMUM VENTILATION FOR REARING TURKEYS

4 Using a feed intake method is also more dynamic because the minimum ventilation rate can be adjusted to suit a real life situation, for example a disease challenge when the birds stop eating and heat production in the house decreases. In this scenario the body weight method does not reflect daily variations in ventilation requirement and is too inflexible. Another advantage of using the feed intake method is that by adjusting the MSTD factor it is possible to ensure that water removal is properly taken into account. In practice an MSTD factor of 3 is recommended but successful management of minimum ventilation will focus on identifying the most appropriate MSTD factor for specific farms and seasons. The calculation of minimum ventilation rate using measured water use (method 3) is often used for broiler chicken ventilation. It is satisfactory if water use is measured and recorded accurately and is beneficial if other sources of water in the house such as spillage from drinkers are a particular problem. This water adds to the total house water load produced by the birds and needs to be removed. In many practical situations water intake is not measured accurately or is too variable from day to day to enable practical control of minimum ventilation. However, daily measurement of water intake is considered good practice, as sudden drops in water intake can be a good early indicator of a disease challenge. Calculating the Minimum Ventilation Requirement Before any of the above methods can be used to calculate minimum ventilation requirement, it is important that the volume of air moved by one fan is determined by measuring its capacity in the turkey house. This is done using a hand held vane anemometer and preferably a model that integrates a number of readings. See Technical Advice Sheet on this Measuring Ventilation b. It is essential for the correct calculation of both minimum and maximum ventilation that a fan capacity measurement (in m 3 /s) is made for each individual turkey house. For minimum ventilation, it is also important that the fan(s) measured are those actually used to provide the minimum ventilation. The procedure for calculation of minimum ventilation using the MSTD method is shown in Example 1 to calculate minimum ventilation rates for a house of 8- week-old turkeys. In this example, predicted feed intake data have been used (BUT T8 Performance goals, edition 5, feed programme B). It is recommended that actual feed intake data be used where available, as this will more accurately reflect the type of diet being used and the influence of ambient temperature. Page 4 of 8

5 Example 1 Minimum Ventilation required for a house containing 6,300 females & 6,300 males 8 week old BUT T8. Females Males No of animals 6,300 6,300 Feed Intake per bird (kg/day) Flock feed intake (tonne/day) (No. birds x intake per bird/1000) x 6300 /1000 = x 6300 /1000 = MSTD (m 3 /s/tonne/day) 3 3 Minimum ventilation rate required (m 3 /s) (MSTD x flock feed intake) 3 x = x = Fan Capacity (m 3 /s) Total No. fans needed (Minimum ventilation required / Fan capacity) / 2.8 = / 2.8 = Total fans required for house = = 3.28 (Equivalent to a ventilation rate of 3.28 x 2.8 x 60 x 60 = 33,062 m 3 /hour) The result of this calculation will usually yield a part fan, e.g fans. In this situation the part fan is either rounded up or down to the nearest whole fan using the following rule: In summer round up at or above 0.4 of a fan, i.e. 3.3 = 3 fans and 3.4 = 4 fans In winter round up at or above 0.7 of a fan, i.e. 3.6 = 3 fans and 3.7 = 4 fans This rule applies for fans which have a capacity of less than 3.5 m 3 /s. For fans with a capacity greater than 3.5 m 3 /s see Example 2 below. By using this rule, the risk of chilling birds by over ventilating or using unnecessarily extra heating in winter is minimised. As the risk of this chilling in summer is low, it is recommended to use this rule to provide extra ventilation. Some sophisticated ventilation control systems can be adjusted to provide the exact amount of ventilation required by precisely adjusting fan speed or the time fans operate. Using these controls to provide the required minimum ventilation should only be considered if the operator is competent in adjusting the controls. If in doubt it is better to manually ensure the required number of fans operate continuously. Page 5 of 8

6 A predicted requirement for less than one fan creates a specific problem where rounding up to one whole fan running continuously may pose serious risks to maintaining house temperature. This problem is most likely to occur when brooding day old poults and is usually addressed by either operating one or more fans at reduced speed or by using a cycle timer linked to one manually controlled fan. Therefore, if 0.25 of a fan is required this can be achieved by running one fan for 1.25 out of every 5.0 minutes (i.e minutes off). Operating fans at reduced speed presents specific problems because it assumes that the relationship between fan performance and fan speed is known. This relationship is rarely measured in practice and is affected by many factors such as fan design, external wind speed, light baffle design and fan bell-mouth design. Unless the fan control system can allow for these factors, it is recommended that the cycle timer system is used. In tunnel and transitional ventilation systems large capacity fans are most often fitted, e.g. 900mm diameter belt driven fans with an air movement value of around 5.5m 3 /s (19,8005m 3 /hr). With these systems speed control is frequently used to provide the level of minimum ventilation requirement as shown in Example 2. Example 2 In this example, predicted feed intake data has been used as follows - BUT Big 6 Performance goals, edition 5, feed programme A. Minimum Ventilation required for a house containing 4,500 females & 4,500 males 8 week BUT B6 Females Males No of animals 4,500 4,500 Feed Intake per bird (kg/day) Flock feed intake (tonne/day) (No. birds x intake per bird/1000) x 4500 / 1000 = x 4500 /1000 = MSTD (m 3 /s/tonne/day) 3 3 Minimum ventilation rate required (m 3 /s) (MSTD x flock feed intake) 3 x = x = Fan Capacity (m 3 /s) Total No. fans needed (Minimum ventilation required / Fan capacity) / 5.5 = / 5.5 = Total fans required for house = = With large fans it is more usual to run two fans at reduced speed rather than to round the fan number up or down as in Example 1 where smaller fans are used. Thus in this example, fans equates to 2 fans running at a reduced speed of 64% of maximum. Page 6 of 8

7 A number of points need to be taken into account when large fans only are used to provide minimum ventilation: The relationship between the speed that fan runs at and the amount of air moved needs to be determined as this is not linear and will vary depending on each installation. It is often the case that these fans do no perform well at low speed. Caution should be exercised when large capacity fans are running at high speed as they can create raised local air speeds that can adversely affect poult behaviour. In some systems small capacity fans are often installed to provide minimum ventilation as they provide better control. Minimum ventilation should be recalculated each week to take into account the growth / increase feed consumption of the birds. It should also be recalculated when bird numbers change due to mortality, birds being removed or birds being added. It should be noted that all non operating fans should be fitted with effective back draught shutters as this will prevent these fans acting as inlets and also prevent the ingress of unwanted light. Related Technical Advice Sheets: a. Controlling Litter Moisture Linking Fans to Heaters b. Measuring Ventilation Further reading: 1. Charles D. & Walker A. Poultry Environment Problems A guide to solutions. Nottingham University Press The Climatic Environment of Poultry Houses. UK MAFF - ADAS Bulletin The contents of this Technical Advice Sheet are British United Turkeys Limited and the advice contained herein is given as a guide and may need to be varied to meet a specific customer operation; in any event this advice should not be regarded as a form of guarantee. Page 7 of 8

8 Figure 2 - Minimum Ventilation Requirement; the Relationship Between Calculation Methods for an example flock of 5000 males No. fans (capacity 2.5 m/s) Age (weeks) BUT 5th Edition Liveweight & Feed Consumption (B diet) based on 5,000 T8 males Feed 2 MSTD Feed 3 MSTD Body weight Page 8 of 8