The topic of heat stress in dairy cows has been under study since the 1980s, when Israel Flamenbaum published an article in the Journal of Dairy Science. This work drew worldwide attention to the damage caused by the heat to dairy cows and proposed an innovative solution to address the problem.
According to Flamenbaum, dairy cows must dissipate as much heat as 16 100-watt incandescent lamps produce 30 kg of milk. However, when the outside temperature and relative humidity increase, cows have difficulty dissipating body heat.
We have seen that what drastically changes in summer compared to other seasons is the heat load that dairy cows undergo. The combination of high temperatures and humidity poses a significant challenge to the thermoregulation and overall well-being of cows. Cows' inability to sweat and their dependence on yawning to dissipate heat make them particularly vulnerable to heat stress.
When the temperature and humidity increase, dairy cows react in two distinct phases, with the main objective of maintaining the central body temperature, which is around 38.5 C. Initially, several behavioural and physiological changes are observed. Cows reduce food intake to minimize heat production from ruminal fermentation. Increase water consumption to facilitate heat dissipation through the respiratory system. They also reduce physical activity to minimize heat production by muscle metabolism. Yawning becomes more noticeable as the respiratory system works like a radiator to dissipate heat. These metabolic adaptations result in a reduction in milk production, fat and protein content, a decrease in oestrus behaviour and less rest time.
This condition may occur in early summer or during the entire warm period if the cooling systems for the animals are inadequate or non-existent. If the temperature-humidity index (THI) continues to rise and cooling systems are insufficient, some or all cows may experience heat stress. This pathological state can be diagnosed objectively by measuring rectal temperature and respiration rate. An increase in body temperature of just 0.5 ºC and a respiration rate of more than 80 breaths per minute indicate that a single cow or the entire herd is experiencing heat stress, indicating that the animals were unable to cope with the increase in THI.
To differentiate between individual and collective pathology, the criterion of 15% can be used. If more than 15% of the cows show an increase in rectal temperature and respiration rate, it indicates a collective risk factor in the barn. Otherwise, these are individual cows that cannot adapt to heat and that need to be managed individually.
In recent years, many farms have adopted animal cooling systems that have reduced some of the productivity and reproduction losses typically associated with summer and subsequent months. However, there is still much to be done, especially in genetic selection, to identify animals that are heat resistant and insensitive to photoperiod. Feeding and supplementing with proper supporting principles makes a difference in managing this important debilitating state of the herd.
During the summer, therefore, high temperatures can cause several problems in the dairy cow stables for the production of Parmigiano-Reggiano. Cows need a comfortable and cool environment to maintain their health and well-being, and to continue producing high-quality milk.
We know that the ideal temperatures for dairy cows are between 10 and 20 degrees, with a relative air humidity between 50% and 70%. However, during the summer, outdoor temperatures can easily exceed 30 degrees, making the interior of the barn too hot and humid for the cows.
There are several solutions that can be adopted to improve the productivity of the stables during the summer period. Some of these include:
1. Ventilation: installing a good ventilation system in the barn can help improve air circulation and reduce moisture, thus keeping the cows cool and dry.
2. Cooling: in some dairy cow sheds, a water cooling system may be used to reduce the temperature of the surrounding air.
3. Feeding: during the summer period, cows may eat less because of the high temperature. Farmers should provide them with high-quality, high-energy food to compensate for the decrease in calorie intake.
4. Water: it is important to provide cows with plenty of fresh, clean water to keep their body hydrated and regulate body temperature.
5. Milking time: farmers may change the cows' milking times during the summer period, avoiding the hottest hours of the day.
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