Heat stress is considered one of the most influential factors in the profitability of dairy farms, especially in the hot regions of the world. In the conferences and publications that I have published over the years, I mainly dealt with the economic benefits that may arise from the proper installation and operation of the means to dissipate the heat generated by the cows.
The purpose of this article is to raise awareness that the inability to cope with heat stress is of financial importance, reflected in a loss of about one third and more, of the expected annual net income.
In the first part of my article, I will describe the way in which heat stress impairs farm performance, from a professional and economic point of view. In the second part, I will show how proper cooling can reduce the negative impact of heat stress and its contribution to farm profitability.
Heat stress leads cows to a series of behavioral and physiological responses, each of which leads to a reduction in production efficiency and financial losses for the dairy farm.
Decrease in food consumption: under conditions of heat stress, food consumption decreases, which leads to a reduction in the supply of nutrients, required for milk production. This results in a decrease in the annual production of cow's milk.
Feed efficiency: under conditions of heat stress, metabolic changes occur that lead to reduced availability of nutrients for productive purposes. At the same time, a part of the energy consumed is used for the activation of body mechanisms for heat dissipation (generally ineffective), while reducing the energy available for production. Unlike the previous section, where food consumption decreases, here, some of the food that is served and consumed, simply does not serve productive purposes and, in fact, is wasted.
Reduced fertility: heat stress reduces the duration and intensity of the "heat signals" of the cow. In parallel, the effectiveness of artificial insemination is reduced. After these two, the "open days" interval extends beyond the optimum, a fact that reduces production efficiency and increases the "unplanned" culling rate, due to sterility reasons, which negatively affect farm's genetic improvement.
Impairment of the immune system: in severe stressful conditions, including heat stress, the immune system is impaired and there is an increase in the frequency of "morbidity events", especially near the time of delivery. It is known that "calving diseases" are an important cause of economic losses, mainly due to their negative effect on the determination of cow's lactation curve and total milk production.
Following the description presented above, I will try to present how each of these channels is damaging the cow's performance and quantify its economic losses.
Reduction of cow's annual milk production: the higher cow's yield, the "feed efficiency" is improved (smaller amount of feed is required for the production of milk unit). This can be explained by the fact that the requirement of food for body maintenance is constant and does not depend on the height of the level of production, so that the higher the yield, maintenance food is "distributed" in more liters.
In a survey conducted several years ago in Israel, using data from 40 large-scale dairy farms, over 20 years, an increase of 2,000 liters in average annual milk yield per cow was observed (growing from 9,000 to 11,000 kg, annually). Consequently, the food requirement for the production of 1 kg of milk was reduced from 0.83 to 0.76 kg of dry matter, an improvement of approximately 10% in feed efficiency. Assuming a daily feeding cost of 5 USD, an average of 330 days of milking per lactation and an expected production loss of 1000 Kg of milk per lactation, due to the fact that cannot cope with heat stress, will "cost" the producer about USD 180 per cow, annually.
Reduction of feed efficiency: recent studies and surveys conducted in the USA showed that exposing cows to heat stress conditions has reduced feed efficiency (converting feed into milk) by 15%. Assuming an average daily feeding cost per cow of 5 USD, and 120 summer days per year, not coping with heat stress will "cost" the producer approximately USD 100 per cow, annually.
Fertility losses due to the prolongation of "calving interval": cows generally reach a conception rate of 40% when they are inseminated in the winter months. The conception rate falls to less than 20% in the summer, if cows do not cope with heat stress. The decrease to such low levels, for several months a year, increases the period of "open days", beyond the desired, by at least 20 days. Estimating a "price" of each "open day" at approximately USD 5, farmers' losses will reach approximately USD 100 per cow, annually.
Increased frequency of morbidity events: according to Israeli veterinary studies, 5-10% of cows in the herd suffer from udder infection annually, 30% of cows suffer from uterine infection, 20% of them suffer from ketosis and 10% of cows suffer from retained placenta. Almost 5 to 10% of the cows in the herd abort and 5% of the cows leave the herd involuntarily due to sterility. Under the conditions of the Israeli herd, the economic loss of each udder infection case is USD 300, each uterine infection costs the farmer USD 180, each case of ketosis costs USD 85 and the retained placenta causes the loss of USD 170. An aborted cow costs the farmer 500 USD and for each cow involuntarily culled from the herd, the producer "loses" 1800 USD. Assuming that the rate of these events will increase by only 10%, due to the fact that producers cannot cope with summer heat stress, the losses will reach USD 30 per cow, annually.
Adding the total losses per cow, due to the inability of Israeli farmers to cope with summer heat stress, can reach the sum of more than USD 350 per cow, annually, representing the loss of more than 20% of total net income per cow.
Dr. Vincent St. Pierre, an economist and researcher at the University of Ohio, conducted a survey, examining the impact of weather conditions in different parts of the US., In the performance and profitability of various sectors of animal production (dairy and beef cattle, pigs and poultry). The researcher analyzed data from 250 different weather stations in the US., and in the last 50 years, and characterized the "intensity of heat stress" in the different states, using the Temperature Humidity Index (THI), with the value 72 as the limit between thermal comfort and heat stress conditions. The climate of each of the US states was characterized by calculating the percentage of hours in the year, where THI exceeds 72. The results of this survey show that, on average, 14% of the hours in the year in the US., are considered as stressful for the cows. This figure differs between the northern states, where these conditions are not met at all, or at very low rates, compared to other states (mainly in the south), where cows are exposed to heat stress conditions for almost half of the year time.
The increase in the percentage of cows culled from the herd was 16 times higher in the warm states compared to the cold ones (0.6 and 8%, respectively), as was the percentage of cow mortality, which increased 17 times (0.1 % and 1.7%, respectively). The number of "open days" beyond that planned, was 9 and 60, respectively, in the cold and hot states, respectively. Differences were also observed in feed consumption of the cow, milk production and profitability. In the cold and hot states, there was a fall of 90 and 900 kg of per cow annual dry matter consumption, loss of 180 and 1780 in per cow annual milk production, and a loss of USD 70 and 675 in annual per cow net income, respectively. The average US cow (there are 9 million of them) loses USD 170 of its potential annual income, totaling $ 1.5 billion a year, as the financial damage from summer heat stress for the US., dairy industry.
If we thought that the problem of heat stress in cattle only belonged to the warm parts of the world, then recently a French paper was published that shows that this is not the case, so that European countries also "joined the club" . This is probably due to a combination of climate change and the increase in the frequency of heat waves in Europe, on the one hand, and a significant increase in the performance of cows, achieved in recent years (which means an increase in the amount of metabolic heat that these cows generate and should dissipate). The French researchers characterized the climatic conditions in different European countries, using local weather stations, and calculated the number of hours per day during the summer months, during which heat stress conditions prevailed (above the THI 68 threshold). According to the findings of previous Arizona research, climatic conditions were classified as mild (4 hours of heat stress per day), medium (9 hours per day) and heavy (14 hours of heat stress or more). Expected milk loss in the inventions of these climatic conditions is of 1.1, 2.7 and 3.9 kg per day, for mild, medium and heavy heat stress conditions, respectively. Based on the Arizona work, summer milk losses were calculated in different European countries. The degree of decline in England was the lowest, with approximately two hours of heat stress and an expected milk loss of 0.7 kg per cow per day. In France, the duration of heat stress reached 6 hours, with a loss of milk of 1.8 kg per day. In Poland, the duration of heat stress was 10 hours a day and milk loss reached 3 kg per day. Heat stress conditions in Spain lasted 13 hours per day and milk loss was calculated at 4 kg per day, while the highest losses were recorded in northern Italy, with 18 hours of heat stress and 5 kg of milk lost per day.
When reviewing the literature dealing with the means of heat reduction and its contribution to cow performance and farm profitability, it was concluded that the application of existing knowledge US dairy farms has the potential to reduce by almost 40% the losses in milk production, caused by heat stress conditions and described earlier in this article. Total losses for the US dairy industry are expected to drop from 1.5 to 0.9 billion USD per year, when cooling systems are used properly and adapted to the climatic conditions of each state. It is likely that the reconsideration of this problem today, with the advances and improvements made in the cooling systems during the last twenty years, the implementation of intensive cooling can reduce the losses caused by heat stress in the summer in greater measure.
This topic will be presented and discussed in the second part of this article, where the contribution of cooling in the improvement of cow performance and farm profitability will be presented.
Here you can read the second part of this article: https://en.engormix.com/dairy-cattle/articles/heat-stress-cooling-effects-t44315.htm