The hot summer is approaching.
In this season, cows often experience heat stress.
Heat stress increases the incidence of mastitis in dairy cows.
What is the reason for this?
Let's take a look together today~
Cow heat stress and mastitis
Heat stress refers to the total amount of non-specific physiological responses made by the body when the heat load (internal and environmental) generated by the animal exceeds the heat dissipation capacity in a high temperature and high humidity environment (Bernabucci et al. , 2010).
The most commonly used dairy cows in dairy production are Holstein cows from Northern Europe, which have the characteristics of large body size, small heat dissipation area per unit weight, and underdeveloped sweat gland function. At the same time, with the continuous improvement of production performance, the calories produced by the body's metabolism and lactation of dairy cows have also increased significantly. Therefore, weak heat dissipation performance and large heat production make dairy cows particularly sensitive to heat stress (Bernabucci et al., 2014). Although a series of measures to relieve heat stress are currently used, the problem of heat stress in summer cows cannot be solved.


Among the many negative effects brought about by heat stress, mastitis is the more prominent one.


We know that the three major factors affecting breast health are:
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Breast epithelial cell integrity
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Somatic defense
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Bacteria challenge
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So during the heat stress, what is different from other seasonal changes that make mastitis more likely to occur in summer?
What are the characteristics of the bacteria that cause mastitis in summer?
The growth of bacteria requires nutrients, moisture, proper pH and temperature. In summer, humidity and temperature are more suitable for bacterial growth, and environmental microbes can multiply, increasing the chance and risk of milk cow mammary gland infection.
The important management methods for alleviating heat stress in pastures usually include physical cooling measures such as shade, spray + fan.
The key areas for spraying are the waiting room and the cow house. The large amount of water increases the humidity of the cow house and increases the amount of water in the manure passage. There is also a risk of being wetted behind the bed. The spray in the waiting room often has the risk of water flowing to the udders. If the milker does not fully dry the nipples of the cows after entering the milking room, it is easy to cause slippery cups and affect the quality of milk. The flow of water also provides for the transfer of bacteria. convenient.


When it comes to stress, everyone may agree that it will cause a decline in the body's immunity. And how to quantify the change of immunity in physiological indicators, and what is the relationship with the occurrence of diseases, let's take a look at the conclusions of two experimental studies.


In 2011, Thompson et al. further studied the difference in the immune response caused by the infection of Streptococcus uberis in the milk area of dairy cows when heat stress occurs. In the study, there were 15 Holstein cows in the heat stress treatment group and the control group. The heat stress treatment time was also in the dry milk period. The two groups were reared and managed in the same environment after calving. Each 5 cows were artificially infected with Streptococcus uberis in the milk area, and then blood samples were collected for analysis.
Regardless of the white blood cell count or the neutrophil count, the control group was significantly higher than the heat stress group. After being infected by bacteria under the same conditions, the immune system of the control group can function faster/stronger.
It can be seen from the above two studies that heat stress can significantly reduce the number of white blood cells (neutrophils) and reduce the bactericidal activity of neutrophils. This may be related to the fact that heat stress reduces the comfort of cows, which causes the cortisol hormone (stress hormone) to rise and immunosuppression occurs. Even if the same amount of bacteria infect the body, due to the reduced ability of white blood cells (neutrophils) to recognize, engulf and kill pathogens, the body is more prone to infectious diseases such as mastitis.
Taking early lactation as an example, there are more cases of severe E. coli mastitis at this stage.
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One of the reasons is that the speed of neutrophils entering the milk area is slowed down, and at the same time, calving stress and other factors cause the immunity of the breast to decrease, and the ability to inhibit bacterial reproduction is significantly weakened;
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Similarly, after a bacterial infection occurs in the milk area of a cow during heat stress, the release of neutrophils is slowed, the immune response is delayed, and the sterilization ability is weakened, and it is difficult to quickly exert the non-specific immune function of the mammary glands, and even bacteria The number may rise to a higher level, causing serious damage to the breast tissue.
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In addition, many studies have pointed out that the dry matter intake of dairy cows is significantly reduced when heat stress occurs. In the Arizona study, it was found that it can be reduced by 30%. During heat stress, cows’ energy intake is insufficient, and negative energy balance is prone to occur, and heat consumption increases significantly, which further aggravates the challenge of energy distribution and tests the body’s immunity against invading infections.
in conclusion
In summary, during heat stress, management such as heatstroke prevention and cooling must be done to alleviate the negative effects brought by it as much as possible to ensure that the immunity of cows is not severely challenged and mastitis occurs.
For the mastitis that has occurred, the treatment must follow the principle of "sterilization + anti-inflammatory", rational use of antibiotics to kill bacteria, and at the same time with non-steroidal anti-inflammatory drugs (such as Medaga) to control the inflammatory response. Especially under heat stress conditions, the immune response of dairy cows is delayed, the free speed of white blood cells and neutrophils is slowed down, and the risk of endotoxin entering the blood is higher, which reminds us that we must pay attention to the control of inflammatory response when treating mastitis.