Measures to reduce heat stress in the design of th

Measures to reduce heat stress in cowshed design

heat stress of dairy cows refers to the sum of nonspecific responses of dairy cows to environmental high temperature that is detrimental to their physiology. By changing various physiological and biochemical reactions of cows, it reduces the feed intake, production and reproductive performance and immunity of cows, which are also recognized by the majority of users in the dairy market, causing serious harm to the production of cows. Therefore, the research on the effects of heat stress on dairy cows and its countermeasures has been widely valued at home and abroad. When designing and building dairy houses, In particular, Professor Martin Dunn, another person in charge of the project (now the dean of the school of engineering and utilization Sciences at the University of Colorado Denver), said: "in general, the unreasonable climate conditions or the design of the cowshed itself cause the heat stress of cows.

an important criterion for judging heat stress is thi (temperature humidity index) 。 It is an index to evaluate the degree of heat by combining temperature and humidity. The calculation formula is:

thi=0.72* (dry bulb temperature + wet bulb temperature) + 403. Tensile test motor: 6

generally, when thi> 69, cows will suffer from heat stress symptoms such as reduced feed intake, reduced milk production, and reproductive performance disorders

China has a vast territory, with great differences in temperature, humidity and other climatic conditions between the north and the south. According to GB standard for building climate zoning, the building climate zoning in China is divided into seven regions. In the subtropical monsoon climate regions of southern China (Jianghuai, Anhui Jiangxi, Zhejiang Fujian and Huguang), the months with thi greater than 69 are months, and the days with daily average temperature greater than 30 ℃ in most regions are about 30 days, which has an adverse impact on the production and health of dairy cows. The cowshed construction in this area needs to be designed around reducing thi index. The measures to reduce the heat stress of dairy cows mainly include the following points:

1. Shading

shading is a necessary condition for dairy farms in hot climate areas, and it is one of the easiest methods to reduce solar radiation. It is estimated that well-designed shading can reduce% of the total heat load (bond et al., 1955); Compared with cows in non shaded environment, shaded cows have lower rectal temperature (38.9 and 39.4 ℃) and lower respiratory rate (54 and 82 times/min), and milk production is 10% more after shading (Roman Ponce et al., 1977)

Figure 1. There are two ways to increase the ventilation volume: natural ventilation and forced ventilation. Natural ventilation has no energy consumption and low operation cost. Therefore, when designing the cowshed, we should first consider the natural ventilation of the cowshed. When the natural ventilation cannot meet the heat dissipation needs of cows, turn on the forced ventilation. Through air convection, the purpose of cooling is achieved

the natural ventilation measures of cow houses generally include side windows and top windows. The most direct and cost-effective way to increase ventilation is to use side rolling shutter windows. The height of the rolling shutter windows of the cowshed with large ventilation can reach 6m. In hot summer, the sides of the whole cowshed can be fully opened, making full use of natural conditions to form convection. Take away the hot and humid air in the cowshed in time

the methods of forced ventilation mainly include negative pressure ventilation on the side wall and forced ventilation in the house. If possible, large ventilator and electric fan with large air volume (2m/s ~ 2.3m/s) can be installed in the cowshed to accelerate the speed of air flow in the cowshed. Generally, the peak temperature of cows appears in the evening, and the production capacity of aluminum lithium alloy in the United States is about 100000 tons/year. Therefore, when the temperature is higher than 29 ℃ and the humidity is more than 50%, it needs to be cooled from 5 a.m. to 1 p.m. There are many cows lying horizontally at night, so it can be changed to position ventilation and air supply. The side wall design of the cowshed also reduces the height of the retaining wall as much as possible to facilitate ventilation

3. The fan spray system

test shows that the cooling effect produced by the combination of fan and spray system is much better than that by using fan or spray system alone. Spraying is mainly to shower the slender water flow on the back of cattle. The water absorbs the sensible heat of animal surface and air and evaporates, which not only promotes the heat dissipation on the body surface, but also reduces the surrounding temperature. It is an ideal cooling method. Without the help of fan blowing, the cooling area of spraying is very limited, that is, within the spraying range of sprinkler. For large-area cowsheds, the sprinkler needs to be arranged with a very large density, and the pipeline is also lengthened, Increased investment in equipment. If you turn on the fan while spraying, and take away the heat in time through the blowing of the fan, you can quickly reduce the body surface temperature of the cow. In order to prevent the cow bed from getting wet or the air humidity is too high, intermittent spraying should be adopted. The time can be freely set according to the environmental conditions in the house. Generally, it takes one hour as the cycle, 10 minutes for spraying, and 50 minutes as the intermittent period

the fan spray system can be equipped with an intelligent monitoring device, which can automatically start the ventilation fan and spray operation according to the environmental index in the cowshed, and can automatically control the number of fans and spray time interval according to the environmental index

in addition, there are many ways to alleviate the heat stress of cows, such as increasing drinking water, adjusting the nutritional structure of feed, improving the genetic traits of cows and so on. Heat stress reduces the economic benefits of dairy farming, especially in areas with high summer temperatures. The most direct response of dairy cows to heat stress is to reduce feed intake and milk production. High temperature environment also reduces the reproductive performance of cows, resulting in low pregnancy rate and prolonged calving interval. Therefore, when designing the cow house, we should comprehensively consider a variety of factors, and design a more reasonable cow house on the basis of comprehensive input and output, so as to effectively reduce the occurrence of heat stress and improve the economic benefits of cow breeding. (end)