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Heat stress in beef cattle

Heat stress in beef cattle

Explanation and consequences

Heat stress is the result of an imbalance between the heat produced and the heat dissipated by the animals, and the consequences vary from mild involvement to death in the most vulnerable animals. During the summer period heat stress manifests itself as hyperthermia and the consequences are manifold:

  • increased respiratory and cardiac rates;
  • increased sweating with loss of large amounts of electrolytes and consequent dehydration;
  • decreased ingestion up to 15-20% and increased energy requirements up to 20-30% to maintain body temperature;
  • reduction in daily weight gain (Chester-Jones report a 37% reduction in weight gain in animals subjected to heat stress over a long period);
  • increased oxidative stress and immunodepression;
  • increased frequency of DFD (Dark Firm Dry) meat at slaughter due to low muscle glycogen reserves;
  • increased incidence of disease and mortality.

The level of stress that animals experience is a combination of several factors:

  • environmental: temperatures and relative humidity, wind speed and solar radiation;
  • susceptibility of the individual: race, sex, temperament, genetics and pervious illnesses;
  • management: access to food and water, animal handling and manipulation.

From an economic point of view, heat stress causes losses in the order of millions of dollars in the United States, and the situation in Europe is absolutely comparable.

Knowing therefore the environmental conditions in which the herd is in a situation of maximum well-being allows us to intervene by adopting strategies to mitigate the effects of the hottest season.

However, it is not enough to refer only to the environmental temperature, but the combination of the latter with relative humidity, expressed as THI (temperature humidity index), allows us to better evaluate the degree of stress suffered by the animals.

In beef cattle, the THI threshold defining the beginning of a stress condition is higher than for dairy cows. The latter, due to the large amount of metabolic heat linked to milk production, begin to show the negative effects of heat stress already at THI values of 68-70 and for the most productive cows the threshold is even lowered to 65.

In the case of beef cattle the threshold is set at 75-78, but even in this case the individual susceptibility leads some individuals to show symptoms of stress already at THI values of 72.

Possible interventions

All this makes clear the importance of intervening to optimize environmental conditions also in beef farming. Therefore, several strategies have been developed over time to improve animal welfare during the summer season and can be classified into:

  • managing access to food and water;
  • optimization of animal handling;
  • shading;
  • forced ventilation;

Paying particular attention to food and water management helps to counteract the drop in intake typical of the warmer season. In particular, it is necessary to guarantee free access to water by installing an adequate number of drinking points with a proper flow rate. As far as the unified is concerned, stimulate ingestion by using high quality, easily digestible feed and organizing the discharges (preferably more than one during the day) during the cooler hours.

It is also essential to reduce handling and all operations involving the handling of animals. In cases that cannot be avoided, always choose the coolest hours of the day as the movement and muscular activity itself results in the production of heat.

From the environmental point of view, it is first of all necessary to avoid overcrowding in order to avoid competition, but also to optimize the quality of the shelters trying to reduce the presence of flies and parasites.

Regarding structures, natural ventilation must be well evaluated at the time of construction and, in addition, shading is essential to prevent the animals from being exposed to excessive sunlight. Often, however, shading and natural ventilation are not sufficient to guarantee welfare conditions. It therefore becomes essential to combine a forced ventilation system with horizontal fans.

The installation of these systems to support natural ventilation has a positive influence on several aspects:

  • improvement of air quality by reducing the concentration of harmful gases;
  • improvement of the quality of the shelters due to the lower humidity and with the consequent reduction of the quantity of material used for the bedding;
  • reduction in the presence of flies;
  • increased heat loss from animals.

All this allows therefore an important improvement of welfare conditions avoiding the decrease of ingestion and obtaining a drastic reduction of pathologies and mortality.