What do we still not know about cow cooling?

The negative effects of heat stress and ways to deal with them are currently among the most important research areas. The reason for this is clear, heat stress has become the greatest cause of economic losses to dairy herds, including in regions with a relatively temperate climate, which have only begun to feel the problem in recent years.

Evidence of the importance of the issue can be found in the following figure, taken from a recently published article and reviewing the sharp increase in the number of scientific papers on the “heat stress subject”, published in the professional press in recent years.

The figure shows the sharp increase in the number of articles published on the subject of heat stress and coping with it, especially in the last ten years.

And yet, do we already know everything about the subject? Is there still something to research and publish?

In this article, I would like to present what I believe are the knowledge gaps currently existing in this field and suggest ways to address them. These knowledge gaps arise mainly from the changes that the industry is undergoing worldwide, the main ones being the continuous increase in cow production (resulting from genetic, nutritional, and management changes in dairy farms), the migration of milk production from the traditional regions, characterized by temperate climate (Europe and North America), to regions with tropical and subtropical climates, where most of the increase in per capita consumption of milk and its products is occurring (Southeast Asia and Central America), and the increase in public awareness of the environmental consequences of coping with heat stress (mainly the increased use of water and electricity to cool the cows).

The need to cool cows in temperate climates has arisen mainly in recent years, mainly due to the increase in yield per cow (which means an increase in the heat that the cow must dissipate to the environment), and to a lesser extent, climate change (mainly, the increase in the frequency and duration of summer heat waves). The method of cooling cows in these regions may be different from that in hot regions, where cooling of cows is required continuously, at all hours of the day, for 3 to 8 months of the year. Summer in temperate regions is characterized by several heat waves during the summer that last several days each, and between them are periods of comfortable climate that do not necessarily require the use of cooling. Cooling cows under such conditions has not yet been studied, and therefore an examination of the optimal cooling method is required, both in terms of the intensity of cooling (the total of cumulative number of hours per day), and in terms of the method of operation (continuous operation throughout all the summer period, or operation during a heat wave event, when start and stop of cooling system operation being done gradually and based on meteorological station forecasts).

Until recent years, intensive milk production did not take place in these regions. The increase in demand for milk (due to the increase in the standard of living) on the one hand, and the increase in milk prices on the world market on the other hand, lead to the need to increase local production. In some cases, this involves establishing advanced dairy farms with high production potential cows (mainly the import of cows of European breeds), and with the intention of reaching high per cow production levels. Cows in these regions may be exposed to heat stress conditions almost all year round. Tropical regions are characterized by a large amount of precipitation during most months of the year and hence also by high humidity, which further burdens cows’ ability to dissipate heat. There is currently little knowledge (if any) about intensive milk production in such conditions, and about the consequences that cooling for such a long period of time may have on cow’s health in general, and on fur and hooves, in particular. It is also appropriate to examine whether it is possible under these conditions to achieve milk yields and conception rates that will allow reach similar results to those achieved in cooler regions and justify the large investment. The issue of feeding also requires attention. Tropical forage plants are considered nutritionally inferior compared to those grown in temperate climates and there is therefore a need to learn how to produce quality forages even under these conditions.

Efficiency of any kind of activity is always the right thing to do and desirable. There is an economic aspect to improving the efficiency of the cooling process (reducing production cost and improving farm profitability), as well as an environmental aspect (reducing pollution of water and air sources). There is still a large room for research to be done, that will enable cows to be kept at a normal body temperature throughout the year, with minimal use of water, electricity, and manpower. Recently, cooling systems have been developed that combine wetting and forced ventilation, which are operated using detecting sensors, in a way that the cooling system (fans and sprinklers) is activated only when cows are present at the cooling site, and sometimes, using computerized identification systems, that will operate the system only for those cows that “deserve” cooling. Research in this direction should be expanded. First of all, there is a need to ensure that all cows are indeed receiving the cooling treatment as required. Today, this can be done using data loggers, installed in various parts of cows’ bodies, which continuously monitor and transmit their body temperature, allowing farmers to evaluate the degree of effectiveness of this cooling treatment and give them the ability to make the changes and adjustments required to obtain optimal cooling. Later, it will be necessary to examine the extent to which these systems save money expenses on cooling resources, comparing these technologies with the conventional manner that is currently provided (cooling the cows on a group basis, bringing them to different cooling sites in the farm).

Cow cooling can be done directly (cooling the cow), or indirectly (cooling the barn). Nearly 80% of cows in the world who receive any cooling treatment are cooled by a direct cooling treatment that combines wetting and forced ventilation. The advantages of using direct cooling are the relatively low costs, as well as the ability to operate it in any type of climate.

The main disadvantages are the need to use water, which creates an environmental load and the need to “trouble” the cows, making them walk to the cooling sites a few times per day and stand there for several hours. Recently, some farms started cooling the cows in the feed line area (which was turned to be a “cooling yard”, by installing gates, two wetting lines, and curtains on both sides. Cooling in this way saves the investment and the necessity to “move” the cows several times a day to the cooling sites, but it does not save their standing there.

Indirect cooling may save the need to move the cows and their prolonged standing time, but it usually involves a higher financial investment in view of the need to completely close the barn in which the cows are housed. Currently, the most common indirect cooling of the cows is done by evaporating water inside the barn, using high-pressure foggers or “evaporative panels” and extracting fans to move the air and thereby evaporate water and lower the temperature inside the barn. The higher the relative humidity, the lower the ability to lower the temperature with this method, and in tropical regions, this method is not worthwhile at all. In dry or semi-dry regions (several hours with humidity of 50% or less), there may be justification for using this cooling method. In areas where cows need to be cooled for less than 6 months a year, the “barn volume” can be reduced by using plastic curtains on the sides of the shed and those that lower the ceiling to a height of 4 meters above the barn surface. This can reduce the barn volume that needs to be cooled to about 30% of the original area and save on cooling resources. In this way, cows can be properly and efficiently cooled during summer, and enjoy a barn with a high roof during the months when cooling is not required.

Cooling cows using an air conditioning system is the best thing you can think of. This is suitable for all weather conditions and allows the cows to maintain thermal comfort without having the necessity to walk and stand for long periods of time throughout the day. All that remains is to examine the economic feasibility of the matter. The last time that air conditioning for cows was tested was in the early 1970s by Dr. Bill Thatcher from the University of Florida. The study concluded that despite the improvement in cow performance, air conditioning is not economically justified. Since the study was published, there have been technical improvements that improve the efficiency of air conditioning systems on one hand, and on the other, due to the increase in cow productivity, the scope of economic losses caused by exposing cows to heat stress conditions and the economic benefit that may result from cooling the cows has increased. In light of this, I think there is room to reexamine the feasibility of the implementation of air conditioning for today’s cows.

Using the method of reducing the “barn volume” described earlier in this article may allow air conditioning to be operated in the barn only during the summer, and let cows enjoy high roof barn for the rest of the year, thus avoiding the necessity to construct unnecessarily expensive housing facilities.