# Broiler House Cross Ventilation: Design and Management ## Key Takeaways - Cross ventilation is optimal for cool to mild weather (below 70-75°F) to manage moisture and air quality, not for cooling. It moves air horizontally across the house using fans on one wall and inlets on the opposite, creating negative pressure to draw air through. - Proper inlet sizing is critical; a ratio of 1 sq ft of inlet opening per 300-500 CFM of fan capacity is recommended to achieve target static pressure (0.05-0.10 inches of water column) for optimal air mixing at ceiling level. - Minimum ventilation fans should operate on a timer cycle (e.g., 1 minute per 5 minutes) to control moisture and ammonia without chilling birds, with settings adjusted based on litter moisture (target 20-30%) and ammonia levels (ideally <10 ppm). - Transition to tunnel ventilation when outside temperatures exceed the bird comfort zone (above 70-75°F) and cross ventilation fans run continuously without adequately lowering house temperature, to provide higher air speeds (500-800+ ft/min) for effective heat removal. - Regular maintenance, including monthly checks of belts, shutters, and blades, and cleaning between flocks, is essential for maintaining fan efficiency and inlet function, directly impacting static pressure and airflow. - Accurate recordkeeping of timer settings, static pressure, litter moisture, ammonia levels, and bird behavior is crucial for informed adjustments and optimizing ventilation strategies throughout the flock's lifecycle. --- Getting air movement right inside a broiler house is one of the most important jobs a poultry farmer has. Birds grow faster today than ever before, and that means they produce more heat and moisture that must be removed from the building. When air stalls, litter gets wet, ammonia builds up, and bird health suffers. Cross ventilation is the simplest and most common system for moving air through a poultry house, and when it is designed and managed correctly, it keeps birds comfortable and houses dry in cool and moderate weather. This guide explains what cross ventilation is, how it works, when to use it, and how to design a system for a new or existing broiler house. It covers fan placement, air inlet sizing, static pressure, controller settings, common mistakes, and how to know when it is time to switch to tunnel ventilation. The information is written for broiler producers, farm managers, and poultry workers who want practical, actionable guidance. It is not a substitute for advice from a poultry veterinarian, an agricultural engineer, or your local extension service. ## At a Glance - Cross ventilation moves air horizontally across the house from one side wall to the other, using fans on one wall and inlets on the opposite wall. - It is best suited for cool and mild weather when outside temperature is below about 70 to 75 degrees Fahrenheit and minimum ventilation is needed. - Place fans on one side wall and air inlets on the opposite wall, spaced evenly along the length of the house. - Inlet opening area should match fan capacity. A good starting point is 1 square foot of inlet opening for every 300 to 500 cubic feet per minute of fan capacity. - Static pressure should typically run between 0.05 and 0.10 inches of water column in cross ventilation mode. - Operate minimum ventilation fans on a timer cycle, not continuously, to control moisture and air quality without chilling the birds. - Do not use cross ventilation when outside temperature rises above the bird comfort zone. Switch to tunnel ventilation instead. - Check belts, shutters, and fan blades monthly, and clean fans and inlets between flocks. - Keep accurate records of timer settings, static pressure, litter moisture, ammonia levels, and bird behavior so you can adjust your system with confidence. ## Why Cross Ventilation Matters Broiler houses are sealed, controlled environments. The birds inside produce heat, moisture, and carbon dioxide, and the litter produces ammonia as it breaks down. Without ventilation, the air inside a house quickly becomes hot, humid, and toxic. Cross ventilation is the first line of defense against these problems. In a cross ventilated house, fans pull air in through inlets on one side wall and exhaust it through fans on the opposite wall. The air moves across the house in a fairly uniform sheet, picking up moisture, heat, and gases as it travels. This air movement does three essential jobs. It removes excess moisture from the litter and the air. It brings in fresh oxygen and dilutes ammonia and carbon dioxide. And it helps equalize temperature across the house so birds in all areas experience similar conditions. Cross ventilation is the standard system for minimum ventilation in most broiler houses. Minimum ventilation is the lowest amount of air exchange needed to keep litter dry and air quality acceptable, even when it is cold outside. It is not about cooling the birds. It is about removing moisture and gases. In cool weather, a house that is too tightly sealed will accumulate moisture from bird respiration and manure, and the litter will become wet and caked. Wet litter leads to ammonia, foot pad lesions, breast blisters, and poor bird performance. Cross ventilation prevents this by continuously exchanging the air. The system also plays a role in transitional weather, when outside temperatures are moderate and the birds need a little more air movement than minimum ventilation provides. In this mode, more fans run and more air moves through the house, helping to remove excess heat without creating drafts at bird level. ## How Cross Ventilation Works Cross ventilation relies on a simple principle. Fans on one side of the house create a negative pressure inside the building. That negative pressure pulls outside air through inlets on the opposite wall. The air enters the inlet at high speed, travels across the ceiling toward the fans, and mixes with the warmer, moister air inside the house before it is exhausted. The key to good cross ventilation is controlling where the air goes after it enters the inlet. If the inlet is sized and angled correctly, the incoming air shoots across the ceiling and mixes with the hot air that collects there. This mixing action pushes warm, moist air down to bird level and eventually out through the fans. If the inlet is too large or angled downward, the cold air falls directly onto the birds, causing drafts and chilling. If the inlet is too small, air speed is excessive and static pressure climbs, reducing fan performance. Negative pressure is what makes the system work. The fans are rated to move a certain volume of air, measured in cubic feet per minute (CFM), at a specific static pressure. Static pressure is the resistance the fan must overcome to move air through the building. In a cross ventilated house, static pressure is created by the restriction of the inlets. When inlets are partially closed, pressure rises. When they are fully open, pressure falls. The controller measures static pressure and adjusts the inlets automatically to maintain the target setting. The goal is to have the incoming air enter at a speed of about 800 to 1,200 feet per minute. At this speed, the air jet travels across the ceiling and mixes thoroughly before it reaches bird level. If the air enters too slowly, it drops quickly and creates cold spots. If it enters too fast, it may create excessive pressure and reduce fan output. ## When to Use Cross Ventilation Cross ventilation is not the right choice for every season or every weather condition. It is most effective when outside temperature is below the bird comfort zone, which for broilers is roughly 70 to 80 degrees Fahrenheit depending on bird age. In cool weather, cross ventilation provides minimum air exchange without over-cooling the birds. In mild weather, it can be used for transitional ventilation to remove excess heat. The decision to use cross ventilation versus tunnel ventilation depends on outside temperature, bird age, and bird weight. Young birds need less air movement because they produce less heat and are more sensitive to drafts. Older, heavier birds produce more heat and need more air exchange to stay comfortable. As a general rule, use cross ventilation when outside temperature is below about 70 to 75 degrees Fahrenheit. When the temperature rises above this range, begin transitioning to tunnel ventilation. The exact threshold depends on the age and weight of your birds. A house full of day-old chicks needs very little air movement, so cross ventilation may be appropriate even on a warm day. A house full of 6-pound birds produces a great deal of heat, so you may need to switch to tunnel ventilation at a lower outside temperature. Many producers use a combination approach. They run cross ventilation for minimum ventilation in the cool hours of the day, then switch to tunnel ventilation when temperatures climb. This is normal and expected. The controller should be programmed to make this transition automatically based on temperature settings. ## Designing a Cross Ventilation System A well-designed cross ventilation system starts with the right equipment in the right places. Whether you are building a new house or retrofitting an existing one, the same principles apply. ### Fan Placement Fans should be placed on one side wall of the house, spaced evenly along its length. The number of fans you need depends on the size of the house and the ventilation rate required. Most broiler houses have multiple fans on the side wall, with additional fans on the end wall for tunnel ventilation. For cross ventilation, the fans on the side wall are usually 36-inch or 48-inch fans, each rated to move 10,000 to 20,000 CFM at 0.10 inches of static pressure. The fans should be positioned so that air moves across the house in a straight line, not in a diagonal or swirling pattern. Place fans no closer than 4 feet from the corners of the house. This prevents dead air zones where moisture and ammonia can accumulate. Space the fans evenly so that air distribution is uniform along the length of the building. ### Inlet Placement Air inlets belong on the wall opposite the fans. The most common type is a counterbalanced ceiling inlet, which is mounted in the ceiling near the side wall. These inlets are hinged on one side and open downward, directing incoming air across the ceiling toward the center of the house. Inlets should be spaced evenly along the length of the house, matching the spacing of the fans. The goal is to have a uniform curtain of air entering the house and moving across the ceiling. If inlets are clustered in one area, the air distribution will be uneven, and some parts of the house will be poorly ventilated. The total inlet area should match the total fan capacity. A common rule of thumb is to provide 1 square foot of inlet opening for every 300 to 500 CFM of fan capacity. For example, if you have four 48-inch fans rated at 20,000 CFM each, the total fan capacity is 80,000 CFM. You would need between 160 and 267 square feet of inlet opening area. ### Inlet Adjustment Each inlet should be adjustable so you can fine tune the amount of air entering the house. Most modern houses use a controller that automatically adjusts all inlets together based on static pressure. The controller opens the inlets wider when static pressure is too high and closes them when pressure is too low. The inlets should also have adjustable baffles that direct the angle of the incoming air. In cold weather, aim the air jet toward the ceiling so it mixes thoroughly before reaching the birds. In warmer weather, you can aim the air slightly more downward to provide a little more air movement at bird level, but be careful not to create drafts. ### Static Pressure Control Static pressure is the single most important control parameter in cross ventilation. The controller measures the pressure difference between the inside of the house and the outside air. This pressure difference is what drives air through the inlets at the correct speed. For cross ventilation, the target static pressure is typically between 0.05 and 0.10 inches of water column. At this pressure, air enters the inlets at about 800 to 1,200 feet per minute, which is the ideal speed for good mixing. The exact target depends on your house design, inlet type, and fan capacity. Work with your controller manual and your extension agent to determine the best setting for your specific house. Once you find the right setting, maintain it consistently. ### Controller Settings The controller is the brain of the ventilation system. It operates the fans, adjusts the inlets, and monitors temperature and static pressure. For cross ventilation, the controller should be set up to operate fans on a timer cycle during minimum ventilation. Minimum ventilation fans should run on a timer, not continuously. The timer is set to run the fans for a certain number of minutes out of each 5-minute or 10-minute cycle. For example, you might set the fans to run for 1 minute out of every 5 minutes. This provides the minimum air exchange needed to control moisture without over-cooling the house. The timer setting depends on outside temperature, bird age, and litter condition. Start with a conservative setting and adjust based on litter moisture and air quality. If the litter is getting wet, increase the timer run time. If the house is getting too cold, decrease it. The controller should also have a temperature sensor that can override the timer. If the house temperature rises above the target, the controller should run the fans continuously or bring on additional fans to provide more air movement. ## Step by Step: Setting Up Cross Ventilation Follow these steps to set up and manage cross ventilation in a broiler house. ### Step 1: Check the Fans Before each flock, inspect all fans on the side wall. Clean the fan blades, shutters, and guards. Check the belts for wear and proper tension. A loose belt reduces fan speed and air output. Verify that the shutters open freely and close tightly when the fan is off. Lubricate bearings according to the manufacturer instructions. Turn each fan on briefly to confirm it runs smoothly and moves air in the correct direction. The fan should pull air out of the house, not push air in. ### Step 2: Check the Inlets Inspect all inlets along the wall opposite the fans. Clean any dust, cobwebs, or debris that could block airflow. Verify that the hinges move freely and the baffles are intact. Check that the inlet cables or actuators are connected and operating correctly. Close all inlets manually, then open them with the controller to confirm they move together and open to the correct angle. ### Step 3: Calibrate the Controller Check the controller settings before placing birds. Verify the temperature sensors are located at bird level and are reading accurately. Calibrate the sensors if needed. Set the minimum ventilation timer, the target static pressure, and the temperature set points. Make sure the controller is set to operate the side wall fans for cross ventilation, not the tunnel fans. The tunnel fans should only come on when the house enters tunnel mode. ### Step 4: Set the Minimum Ventilation Rate The minimum ventilation rate is the amount of air exchange needed to keep litter dry and air quality acceptable. A common starting point is 0.5 to 1.0 CFM per bird for chicks, increasing to 2 to 3 CFM per bird as they grow. Work with your extension agent or poultry company to determine the right rate for your specific conditions. Set the timer so the fans run for the calculated number of minutes per cycle. For example, if you need 20,000 CFM of ventilation and your fan moves 20,000 CFM, the fan needs to run for 1 minute out of every 5 minutes to achieve the required air exchange. ### Step 5: Adjust the Inlets With the minimum ventilation fans running, check the static pressure reading on the controller. Adjust the inlet opening so the static pressure is in the target range. The controller should do this automatically, but you should verify that the inlets are opening and closing as expected. Check the air distribution by walking through the house. You should feel a gentle air movement across the ceiling, not drafts at bird level. Use a smoke pencil or a thin strip of plastic to visualize the air pattern. The air should move across the ceiling and mix before descending to bird level. ### Step 6: Monitor and Adjust After the birds are placed, monitor the house conditions daily. Check litter moisture, ammonia levels, and bird behavior. Adjust the timer settings as needed to keep litter dry and air quality good. As the birds grow, they produce more heat and moisture, so the ventilation rate must increase. Increase the timer run time gradually as the flock develops. Monitor the house temperature and adjust the set points to keep the birds comfortable. ## Managing Cross Ventilation Through the Flock Managing cross ventilation is not a set it and forget it job. Conditions change every day as the birds grow and as the weather changes. A good manager checks the system regularly and makes small adjustments before problems develop. ### Daily Checks Walk through the house at least twice a day, once in the morning and once in the afternoon. Look for signs of poor ventilation, including damp litter, ammonia smell, and birds panting or huddling. Check the fans to make sure they are running and the shutters are opening properly. Look at the inlets to confirm they are opening and closing as the controller commands. Check the static pressure reading on the controller. If it is outside the target range, investigate the cause. Inlets may be stuck, fans may be underperforming, or the controller may need adjustment. ### Litter Moisture Litter moisture is the best indicator of ventilation adequacy. The goal is to keep litter moisture between 20 and 30 percent. Litter that is too dry can create dust, which irritates the birds respiratory systems. Litter that is too wet leads to ammonia and foot pad problems. To check litter moisture, pick up a handful and squeeze it. If it forms a ball that holds together when you open your hand, it is too wet. If it crumbles easily and feels dry, it is in good condition. If it is dusty and powdery, it is too dry. Adjust the minimum ventilation timer to keep litter in the target range. Increase ventilation if litter is wet. Decrease it if litter is too dry and dusty. ### Ammonia Control Ammonia is produced when bacteria break down uric acid in the litter. High ammonia levels irritate the birds eyes and respiratory tracts, reduce feed intake, and increase susceptibility to disease. The recommended maximum ammonia level in a broiler house is 25 parts per million, and many experts recommend keeping it below 10 parts per million. You can smell ammonia at levels above about 10 to 15 parts per million. If you can smell it, the ventilation rate is too low. Increase the minimum ventilation timer or add additional fan cycles to remove the ammonia. ### Bird Behavior Birds are the best indicator of whether the ventilation is working. Watch how they behave and where they gather in the house. If birds are spread evenly throughout the house, the ventilation is probably good. If they are huddling in groups, the house may be too cold or there may be drafts. If they are panting and holding their wings away from their bodies, the house is too hot. If they are clustered near the inlets, the air quality may be poor in other parts of the house. Adjust the ventilation settings based on bird behavior. The goal is to keep birds comfortable and evenly distributed. ## Common Mistakes in Cross Ventilation Many ventilation problems come from the same handful of mistakes. Knowing what these are can help you avoid them. ### Inlets Too Wide Open One of the most common mistakes is opening the inlets too wide. When inlets are too open, static pressure drops, and the incoming air speed slows down. The air falls to the floor before it mixes with the warm air in the house, creating cold drafts at bird level and leaving warm, moist air trapped near the ceiling. Keep the inlets restricted enough to maintain the target static pressure. The air should enter at high speed and travel across the ceiling before mixing. ### Inlets Too Closed The opposite problem is having inlets too closed. When inlets are too restricted, static pressure climbs, and the fans have to work harder to move air. Fan output drops, and the ventilation rate falls below what is needed. If static pressure is above the target range, open the inlets wider. The controller should do this automatically, but verify that the inlets are actually moving and not stuck. ### Poor Inlet Placement Inlets that are not spaced evenly or are located in the wrong places create dead air zones and uneven ventilation. Some parts of the house get too much air, while others get too little. If you are building a new house or retrofitting an existing one, take the time to plan the inlet placement carefully. Evenly spaced inlets along the entire length of the wall opposite the fans are the goal. ### Fans Too Small or Too Few Underpowered ventilation is a common problem in older houses. If the fans cannot move enough air, the house will have high humidity, wet litter, and ammonia problems no matter how well everything else is managed. Calculate the ventilation requirement for your house and bird capacity, and verify that your fan capacity meets that requirement. If it does not, you may need to add fans or upgrade to larger models. ### Ignoring Static Pressure Some producers set the inlets once and never check the static pressure again. This is a mistake. Static pressure changes as fans wear, belts stretch, and inlets accumulate dust. Check the static pressure regularly and adjust the inlets as needed. ### Not Adjusting for Bird Age Ventilation needs change dramatically as birds grow. A house full of day-old chicks needs very little air movement, while a house full of 6-pound birds needs a great deal. Some producers set the timer once and never adjust it, leading to poor conditions as the flock matures. Increase the ventilation rate gradually as the birds grow. Check litter moisture and air quality daily and adjust the timer settings accordingly. ### Switching to Tunnel Too Late Cross ventilation has its limits. When outside temperature rises above about 75 degrees Fahrenheit and the birds are heavy, cross ventilation cannot remove enough heat to keep the birds comfortable. Waiting too long to switch to tunnel ventilation can cause heat stress, reduced feed intake, and increased mortality. Monitor the house temperature and bird behavior. When the house temperature climbs above the target and the cross ventilation fans are running continuously, switch to tunnel ventilation. ## Cross Ventilation vs Tunnel Ventilation Understanding the difference between cross ventilation and tunnel ventilation helps you know when to use each system. Cross ventilation moves air from one side of the house to the other. The air path is short, so air speed at bird level is low, typically 100 to 300 feet per minute. This makes it ideal for minimum ventilation in cool weather, when you want to exchange air without chilling the birds. Tunnel ventilation moves air from one end of the house to the other. The air path is long, so air speed at bird level is high, typically 500 to 800 feet per minute or more. This creates a wind chill effect that removes heat from the birds, making it ideal for hot weather. The two systems use different fans. Cross ventilation uses fans on the side wall. Tunnel ventilation uses fans on the end wall, usually large fans rated at 20,000 to 30,000 CFM or more. The inlets are also different. Cross ventilation uses inlets on the side wall opposite the fans. Tunnel ventilation uses inlets on the end wall opposite the fans. Many houses have both systems installed. The side wall fans handle minimum and transitional ventilation, and the end wall fans handle tunnel ventilation. The controller switches between the two systems automatically based on temperature. The switch from cross to tunnel ventilation should happen when the house temperature rises above the target and the side wall fans cannot keep up. A common threshold is when the house temperature is 5 degrees or more above the target with all side wall fans running. At this point, the tunnel fans should come on and the side wall inlets should close. ## Monitoring and Recordkeeping Good ventilation management requires good records. Without records, you cannot know what settings worked in the past or what adjustments are needed in the future. Keep a daily log for each house that includes the following information: - Date and bird age - Outside temperature and humidity - House temperature at several locations - Static pressure reading - Fan timer settings - Number of fans running - Inlet position - Litter moisture rating - Ammonia level - Bird behavior observations - Any equipment problems or maintenance performed Review the records at the end of each flock to identify patterns. If you had litter problems in week 4, look back at the ventilation settings during that period. If you had high ammonia in the morning, check whether the timer settings were adequate for overnight conditions. Use the records to plan improvements for the next flock. If you consistently had wet litter in the winter, you may need to increase the minimum ventilation rate or improve the insulation in the house. ## When to Call a Professional Most ventilation problems can be solved with careful observation and adjustment. But there are times when you should call in help. Call your poultry company service technician or your extension agent if you have ventilation problems that you cannot solve on your own. This includes persistent wet litter, high ammonia, uneven temperatures, or high mortality that you cannot explain. Call a veterinarian if birds show signs of respiratory disease, such as coughing, sneezing, nasal discharge, or swelling around the eyes. Poor ventilation can cause these signs, but so can infectious diseases. A veterinarian can help you tell the difference and recommend treatment if needed. Call an agricultural engineer or ventilation specialist if you are planning major changes to your ventilation system, such as adding fans, moving inlets, or upgrading your controller. A professional can help you design a system that meets the specific needs of your house. If you see signs of a notifiable disease, such as sudden high mortality, severe depression, or swelling of the head and wattles, contact your state veterinarian or the USDA Animal and Plant Health Inspection Service immediately. [Avian influenza](/knowledge/bacteria/avian-bacteria/avian-influenza-cdc-global-surveillance) and other reportable diseases require prompt reporting. ## Frequently Asked Questions ### How do I know if my cross ventilation is working properly? The best indicators are litter moisture, air quality, and bird behavior. Litter should be crumbly and dry to the touch, not wet or sticky. You should not be able to smell ammonia when you walk into the house. Birds should be spread evenly throughout the house, not huddled in groups or clustered near the inlets. If any of these indicators are off, the ventilation needs adjustment. ### What static pressure should I run for cross ventilation? The target static pressure for most cross ventilated broiler houses is between 0.05 and 0.10 inches of water column. The exact setting depends on your inlet type, fan capacity, and house design. Start within this range and adjust based on air distribution and bird comfort. Check the static pressure regularly and adjust the inlets to maintain the target. ### How much ventilation do my birds need? The minimum ventilation rate depends on bird age, weight, and outside temperature. A common starting point is 0.5 to 1.0 CFM per bird for day-old chicks, increasing to 2 to 3 CFM per bird at market age. Your poultry company or extension agent can help you calculate the right rate for your specific conditions. Adjust the rate based on litter moisture and air quality. ### Why is my litter getting wet even though the fans are running? Wet litter usually means the ventilation rate is too low for the amount of moisture the birds are producing. Increase the minimum ventilation timer run time. Also check that the fans are moving the rated amount of air. Clean fan blades, check belt tension, and verify that shutters are opening fully. Check that the inlets are not blocked and that the air is mixing properly before it reaches the litter. ### When should I switch from cross to tunnel ventilation? Switch to tunnel ventilation when the house temperature rises above the target and the cross ventilation fans cannot keep up. A common threshold is when the house temperature is 5 degrees or more above the target with all side wall fans running. This usually happens when outside temperature is above about 70 to 75 degrees Fahrenheit, depending on bird age and weight. ### Can I use cross ventilation in hot weather? Cross ventilation is not effective for cooling in hot weather. It moves air at low speed, so it does not create enough wind chill to remove heat from the birds. Use tunnel ventilation when outside temperature is above the bird comfort zone. Cross ventilation should be used for minimum ventilation in cool weather and for transitional ventilation in mild weather. ### How often should I clean my fans and inlets? Clean fans and inlets before each flock and inspect them monthly during the flock. Dust and debris accumulate on fan blades, reducing their efficiency and air output. Dirty inlets may not open or close properly. Clean the fan blades, shutters, and guards with a brush or compressed air. Wipe down the inlet surfaces and check that the hinges and cables move freely. ### What should I do if I smell ammonia in the house? If you can smell ammonia, the ventilation rate is too low. Increase the minimum ventilation timer run time to bring in more fresh air. Check that all fans are running and that the inlets are open. If the ammonia level is high and the birds are showing signs of respiratory distress, increase ventilation immediately and call your veterinarian if the problem persists. ## Related Farming Guides This section will be populated with links to related poultry housing, ventilation, and management guides. Check back for additional resources on [broiler house design](/knowledge/animal-farming/farm-management/poultry-broiler-house-design-floor-space-ventilation), tunnel ventilation, litter management, and bird health. ## Related Clinical & Scientific Guides * [Poultry Farm Fencing: Materials, Design, and Predator Exclusion](/knowledge/animal-farming/poultry/poultry-farm-fencing-materials-design-predator-exclusion) * [Broiler House Wind Speed and Airflow Measurement](/knowledge/animal-farming/poultry/broiler-house-wind-speed-airflow-measurement) * [Broiler House Heating Systems: Types and Efficiency](/knowledge/animal-farming/poultry/broiler-house-heating-systems-types-efficiency) ## References - FAO Poultry Production: https://www.fao.org/poultry-production-products/en/ - USDA APHIS Poultry Health: https://www.aphis.usda.gov/livestock-poultry-disease/avian - WOAH [Avian Influenza](/knowledge/bacteria/avian-bacteria/avian-influenza-cdc-guidelines-poultry-pandemic-preparedness): https://www.woah.org/en/disease/avian-influenza/ - FAO Animal Production and Health: https://www.fao.org/animal-production/en/ - WOAH (World Organisation for Animal Health): https://www.woah.org/en/home/ > This article is educational and is not a substitute for veterinary diagnosis, treatment, public-health guidance, or regulatory reporting.