Heat stress is primarily a concern during the summer and early fall months, but it can occur at any time during the year given the right conditions. Signs of heat stress include nasal flaring, open-mouthed breathing, increased breathing rate and/or effort, drooling, depression or dullness, not eating, scrotal swelling in intact males, weakness, trembling, and a rectal temperature greater than 104 degrees F.
There are two generally accepted ways to predict the likelihood of heat stress, the Heat Stress Index (HSI) and the Livestock Temperature Humidity Index (THI). The livestock THI, developed for ruminants, is the most applicable to alpacas.
To calculate the livestock Temperature Humidity Index the following formula is used: Temperature in Celsius + (0.36 * Dew point Temperature in Celsius) + 41.2. (For reference, a chart of the THI is located at the bottom of this news brief.) For example, today the Temperature was 77°F (25°C) and the Humidity was 61% (making the dew point Temp 17°C), so the THI for today would have been 72.32. A THI of less than 72 will not result in heat stress. Between 72-78, there is the potential for mild stress, 79-84 would result in moderate stress, and 85-100 would result in severe stress. Please visit our website if you need assistance calculating this index.
Of course, factors that will also contribute to the possibility of heat stress developing include the amount of fleece the animal is carrying, their color, access to shade, ventilation and water, activity level, and pregnancy status.
Heat stress can result in poor growth, a greater incidence of illness or death. It can develop rapidly. Observation is the key to preventing or successfully treating heat stress. Call immediately if you are concerned that your alpacas are experiencing heat stress.