Healthy cattle can tolerate a wide range of temperatures if they are acclimatised and have sufficient feed and water. However, there are some important points to consider.
Some of the ways the weather can affect cattle
- Cattle reach their ‘critical’ temperature when the temperature-humidity index (THI) gets above 82. At this point, substantial heat stress leads to factors like reduced appetite, decreased weight gain, loss in milk production, lower calf birth weights and higher calf mortality rates.
- High humidity reduces the ability of cattle to use evaporation to dissipate heat. This is the main way cattle cool themselves in temperatures above 21°C.
- “Like most mammals, the dairy cow needs to maintain its core body temperature between 38.6°C and 39.3°C.”
- When there are hot environmental conditions such as high temperatures disrupting night cooling or heat dispersal, cows will use both behavioural and physiological strategies to offload heat. Behavioural strategies include seeking water and shade, reducing or even stopping feed intake to decrease rumen heat production, and sweating or panting.
- “Open mouth breathing, group seeking of shade and excessive drooling are all signs of prolonged heat stress and call for urgent attention.”
- Cows in hot environmental conditions will also respond with physiological changes which although unseen can have significant impacts of the health of the animal. These changes include rising core body temperatures, increased blood flow to the skin and decreased blood flow to internal organs.
- In Australia, hypothermia or cold stress is mainly a concern for new-born calves and occurs when body temperature is from about 37°C to less than 34°C but other at-risk cattle include calving cows or cattle that are sick or have low body condition.
- At 34°C body temperature, the calf’s processes and functions slow down, and blood is diverted to protect the vital organs. In these conditions, there are several implications including impaired brain function results.
- Cold stress has also been shown to decrease the rate of absorption of colostrum in newborn calves, compromising their immune system and potentially contributing to morbidity and mortality.