One of the chief problems facing Israel’s Jordan and Beit Shean Valley dairy farmers is heat stress. The Jordan and Beit Shean Valleys are 700 ft below sea level and extend south from the southern shore of the Sea of Galilee. They are part of the Syrian-African Rift Valley and extend to the Dead Sea, which is the lowest point on earth at 1400 ft below sea level. Because of the low altitude in a subtropical climate and also because of the proximity to the Sea of Galilee, the climate in these valleys is extremely hot and fairly humid during the long summer. The average maximum daily temperature during the summer is over 100 degrees F, and the average minimum daily temperature is over 75 degrees F. The average maximum daily humidity is more than 70%. The average temperatures can be seen in Table 1. Almost one-third of Israel’s dairy farms are located in these interior valleys.
Table 1. Summer climatic conditions in the Jordan Valley
|Date||Temp (max)||Temp (min)||Humidity (max %)||Humidity (min %)|
As an example, we have gone to the lowest-producing herd in the area (and in the country) and made it a model. By improving the management, nutrition, feed trough practices, and specifically the heat stress management, within a 2 year period it became the highest-producing herd in the valley. This dairy farm raised its milk production by a 5,000-lb avg, in addition to lowering feed costs per kg. of dry matter. This could not have been done without proper heat stress management during the long, hot and humid summer.
Lowered milk production, lowered fertility rates and lowered food consumption are well-known effects of heat stress. These are acompanied by higher body temperature and higher respiration rates (Igono et al., 1985). The lower production is a direct result of the heat, but even more than that, it is a result of lowered food consumption. The combination of high environmental temperature, solar radiation and high humidity bring the cow to “heat stress” during a large segment of the day. Maintenance of high production at high temperatures is determined chiefly by the balance between metabolic heat production and heat loss. Metabolic heat production is relative to the amount of milk production plus the heat produced for maintenance. Higher milk yields, therefore, increase the thermal heat load (Flamenbaum et al., 1986).
Under condition of heat, the cow gives preference to thermoregulation over other functions such as milk production, growth or reproduction. This is the main reason for lowered production (Flamenbaum, 1990). The dairy cow, like all mammals, has a “comfort zone”: the temperature at which she can exist and produce without a change in her metabolic base. Changes in blood flow, in the thickness of insulation and in the behavior of the cow influence her ability to produce. Raising the environmental temperature above the “maximum critical level” encourages the cow to execute metabolic and physiological changes to help keep her comfortable. The upper critical temperature for lactating and dry cows is between 77 to 😯 degrees F (Collier et al., 1982). Above that, the cow enters “hyperthermia”, and rectal temperature exceeds 10 degrees F. In hyperthermia the first thing the cow will do is lower her food consumption and thus lower her heat production. Lowered food consumption is also a result of lowered gut motility and increased water consumption, which lead to”gut fill” (Collier et al., 1982).
Heat change between the cow and the environment is executed by four chief mechanisms : radiation, condensation, convection and evaportion. When the air temperature approaches the cow’s body heat, only evaporation remains to rid the cow of her excess heat. This is mostly by evaporation of water from the skin and upper respiratory airways (Flamenbaum et al., 1986).
Another point to remember about heat stress is that not only is the maximum daily temperature important in determining the extent of hyperthermia, but even more important is the minimum temperature at night. In arid desert areas where it is very hot at midday but cool at night, the cow succeeds in “radiating” heat to the cool air at night. The hyperthermia there is not as critical as in climactic conditions where the maximum daily temperature may not be as high, but at night the temperature rarely drops below about 75 degrees F, and the cow can never get rid of her excess heat. It must be pointed out that for the cow, humidity is more critical even than the temperature. For humans, THI (thermal heat stress) takes into account about one-half temperature and one-half humidity. For the cow, many researchers think the relative importance of humidity is two-thirds and temperature only one-third.
A survey of the Israeli Herd Book showed a 10% to 20% loss of milk in Israel in the summer months compared with winter (Bar Anan and Genizi, 1981). In the American Southwest up to 25% milk loss has been found. Most of this lost production occurs when the temperature exceeds 80 degrees F or the THI (thermal heat index) exceeds 72. Heat stress also changes milk composition. Casein composition seems to drop in heat stress. Milkfat percentage also drops in hot weather (Miller et al., 1951). Rumen pH declines during heat stress, as do electrolyte concentrations in rumid fluid, particularly potassium and sodium (Collier et al., 1982). There are also reductions in thyroxine, growth hormone and glucocorticoids in chronically heat-stressed cows (Collier et al., 1982).
In each herd the loss of production is greater in high producers than lower-producing cows (Bar Anan and Genizi, 1981).
In some studies the climatic factor accounted for almost 40% of the fluctuation of food consumption in the summer and for 50% of the variation of milk yield in these conditions (McDowell et al., 1969). The efficiency of changing digestible energy to milk dropped from 60% in 70 degrees F to half that after 14 d in 90 degrees F.
The conception rate in Israel in the summer is 24% compared with 52% in winter inseminations. In heat stress we have more “quiet heats”, unsynchronized ovulations, fertility failure and early embryonic death (Folman et al., 1979; Her et al., 1988). The concentration of P4 (progesterone) was lower in the luteal phase in cows in the summer than in the winter and in the cows cooled through evaporative sprinkling and ventilation (Flamenbaum, 1990). Thatcher (1974) showed heat stress in the first days after insemination caused fertility failure and early embryonic death.
Employing systems for easing heat stress improved conception rates in the summer. Keeping cows in the shade doubled conception rates compared with cows kept in direct sunlight (Roman-Ponce et al., 1977). In Israel, althouth all cows are kept freely in shade, there is still a drastic lowering of conception rates in the summer.
METHODS OF HEAT STRESS MANAGEMENT
Lowering or preventing heat stress of dairy cows in the summer requires the shielding of radiated heat and raising the loss of heat from the body to the environment. Shade permits reduction of more than 30% of all the heat radiated on cattle and is the single most important contribution for lowering heat stress (Bond et al., 1967).
In Israel (and, of course, in the Jordan and Beit Shean valleys) all dairies are open corral-like structures with free shade available all the time. Most feed bunks are also shaded. To lower radiation, roofs should be high (4 m at least at the lowest point) and made of reflective material. Whitewashing roofs in the summer to increase reflection is an inexpensive and useful practice.
Cool, shaded water must be supplied all day, and superior nutritional practices for lowering heat increment in the rumen should be employed.
In areas of extreme heat, it is even more important for cows to give birth in good body condition because after parturition their dry matter intake will be lowered by heat stress, as well as the usual low intake immediately after calving.
Forced ventilation in the corrals is also a widespread and useful practice for lowering heat stress. Forced ventilation of cows in Israel in the summer lowered by half the rate of body temperature increases compared with cows in the control group (Berman et al., 1985) and helped raise milk yield and fertility of higher-producing cows (Folman et al., 1979). Body temperature of these cows was still more than 0.5 degrees F higher than in similar-producing cows in the winter.
The limiting factor of the efficiency of lowering heat by evaporation is high humidity; therefore, a combination of sprinkling and forced ventilation doubled the lowering of body temperatures of hyperthermic cows as compared with either system used separately (Seath and Miller, 1948).
The systems we use in the interior valleys are based on this principle and fit open-structure housing and high temperature and humidity conditions.
In the holding pens of the milking parlor, cows are given intermittent showers and ventilation. One-half minute of sprinkling and then 4.5 min of fan ventilation by an automatic timer are used. This is continued for 20 min, which is the time it takes for cows to reach their normal body temperature without standing too long in the holding pen. The sprinklers used in the holding pen should give about 150 to 200 gal of water per hour per sprinkler and be wide-nozzled. They should thoroughly soak the cow. The sprinklers in the holding pen should have a 360 degrees circumference. The air flow of the fans must be approximately 3 m/s. It is very imprtant in any evaporative cooling system for the drops to be large enough to penetrate the cow’s coat. If the drops are mist-like, a layer of hot, humid air may form around the cow and elevate the cow’s heat stress, especially in humid climates. In dairies that have no evaporative cooling system at the feed troughs, the cows are brought to the holding pen 4x/d to 5x/d during the daylight hours for cooling. In dairies with cooling showers at the feed bunk as well as the holding pen, cows are cooled in the holding pen of the milking parlor only before milking 3x/d. This is done because in the crowded holding pen without showers, the heat stress is made worse by the radiation of body heat from the cows themselves.
Was found in the Jordan Valley that showers in the holding pen only were not enough to cool cows to normal body temperature all day during the summer, although in climates with less extreme conditions, 4 to 5 “showers” a day did alleviate almost all heat stress. Also, many dairy farmers hesitate to bring their cows two extra times a day to the holding pen in order to cool them because it is not recommended to have cows so long on concrete in the holding pen and away from food, rest, etc. For dairies with twice-a-day milking, this is also a problem. Therefore, we have initiated evaporative cooling over the shaded feed bunks as well.
Above the feed mangers, we use sprinklers that give only approximately 30 gal of water/h at 2 atmospheres. The sprinklers should have a 180÷ (half-circle) radius and be spaced about every 2 m (6.6 ft) apart and 1.5 m above the cow’s back. Again, the drops must be large enough to penetrate the cow’s coat. Fans should be spaced every 30 ft apart and should operate continuously whenever the system is operating. The fans here (and in the holding parlor) can be about ½ HP and 36` in diameter. The sprinklers should be operating automatically for 1/2 min. every 5 min. The system should use a thermostat that turns it on whenever the air temperature exceeds 80÷ F. In less humid areas, the fans may not be necessary. Of course, for the system to work well, there must be adequate drainage, although this system above the feed trough is economical with its use of water. This system should be used only above feed mangers with concrete floors. The idea is to wet the cows, evaporate-dry them, and then as soon as the cows are almost dry, wet them again and continue the cycle. This gives maximum cooling potential.
In the Jordan Valley, we have improved milk production by 4.5 lb/d using feed bunk sprinkling plus holding pen cooling as compard with holding pen cooling only. The only really expensive items in feed bunk cooling are the fans, which may only be necessary in humid climates.
It is also recommended to cool the dry herd as well. We have shown in experiments in the valley that dry cows that were cooled during the day gave more milk in their subsequent lactation. This makes sense when we realize that cows in order to cool off send their blood flow to the periphery to “radiate” the heat, and this takes blood away from the udder as well as the uterus. By measuring the cirumference of the cow’s udder with and without cooling in the dry period, we have seen the cow’s udder to be larger (after parturition) as a result of increased blood flow if the cow was cooled in the dry period.
Besides systems of evaporative cooling, there are other systems in use based on different principles. One such system is based on sprinkling the roofs of cows’ corrals. By cooling the structure, the cows’ microclimate is made cooler and more comfortable. While this may lower the temperature somewhat, it is much less efficient than evaporation directly on the cow’s body. Each gram of water that turns to steam uses 540 cal of heat to do so. Herefore, the most efficient use of water to cool cows is maximum evaporation directly on their bodies.
Another method of helping cows avoid heat stress is feeding them cooled water, but this also is not the most efficient system of cooling. In experiments we have carried out, we saw a decrease in water intake as a result of feeding cooled water. This is, of course, undesirable. Cooling water is also an expensive method and not usually cost-efficient.
A series of experiments were carried out in the Negev Desert to judge the effects of evaporative cooling in the holding pen. It was determined that with intervals of 1/2 min sprinkling to 4.5 min of forced air, body temperatures were lowered by 2 degrees F 30 min after cooling, and 2 hr. after cooling were still almost 1÷ F lower than uncooled cows. In these experiments cooling was tested for 15, 30 or 45 min, and the body temperature was lower 1.2, 1.4 2 degrees F, respectively (Flamenbaum et al., 1986).
It was found in experiments carried out in the desert that cooling is made more efficient by decreasing crowding in the holding pen. By decreasing crowding in the holding pen from only 1.9 sq.m./cow to 3.2 sq.m./cow, the efficiency of the cooling was doubled (Flamenbaum et al., 1986).
In another experiment in Bet Dagan, evaporative cooling in the holding pen significantly raised milk production by 4.5 lb, and in periods of particular heat stress, raised milk yield by 10-12 lb.
In experiments we have carried out in the Jordan Valley, we compared four-times-a-day showers in the holding pen in the control group to the same in the treated group, with the latter also receiving evaporative cooling in the feed bunks. The extra cooling in the feed bunk lowered body temperature, and the cows in the treated group never reached a state of “hyperthermia” (Rosen and Cohen, 1990). Without any evaporative cooling at all, the cow’s temperature exceeds 105 degrees F in the afternoon in the summer. We also significantly raised the daily feed consumption by almost 1 kg dry matter. We received a 2-kg (4.4-lb) increase in milk production as a result of the extra cooling. We also witnessed a great change in the cow’s eating practices. By providing only one-half of the feed bunk with cooling, the cows could choose where they would rather eat, and we watched and monitored their behavior. They spent much more time in the cooled feed bunk, partly to eat but also partly just to “cool-off”. Between 70% to 80% of the cows chose to eat in the half of the feed bunk that was “cooled” rather than the uncooled side when food was provided free-choice on the whole feed bunk. In evaporative cooling in the feed bunk, we believe it is only to necessary to cool about half the trough’s length, provided that the cows are also cooled in the holding pen before milking. This way, the cows can “choose” when they want to cool-off. We have seen some cows go to the showers just to “cool-off” and go to the uncooled side to eat. At night. very few cows from both groups ate, but the uncooled cows in our experiments did not eat more at night that the cooled cows and thus did not make up for less food consumption during the day.
In our experments cooling has not raised the milkfat percentage but has tended to increase the milk protein concentration, although not usually at a statistically significant rate.
In some experements there was more of a reaction in cows more than 60 days after parturition, possibly because of the heavy hormonal demand to give milk at the beginning of lactation (Flamenbaum, 1990).
In experiments with cooling dry cows, calves of cows cooled in the dry period were almost 6.6 lb heavier than those of uncooled cows. Milk was also raised significantly by 5 lb in the subsequent lactation (Flamenbaum, 1990).
Cooling the cows decreased the days to first observed heat by 17 d, and behavioral heat was about 2 h longer than in uncooled cows in one experiment. In this experiment evaporative cooling raised the conception rate from 17% to 59%. The level of progesterone in the luteal phase tended to be higher in cooled cows (Flamenbaum, 1990).
We have also carried out experiments in beef steers. Here we have not seen an improvement in growth rates in steers given evaporative cooling. For these steers, apparently shade was enough, although lower growth rates are reported in the summer. In some experiments carried out outside Israel, cooling steers improved their rate of weight gain and food consumption and significantly lowered rectal temperature.
In temperatures above 78 to 80 degrees F, lactating cows enter hyperthermia and “heat stress” and suffer from lowered food consumption, lowered milk production, lowered milkfat and protein concentration, lowered fertility rates, higher body temperatures and elevated respiration rates. Shade must be provided freely, as well as fresh water and good ventilation. Superior summer nutritional practices should be employed. In areas of extreme heat or humidity, this is not sufficient, and evaporative cooling must be practiced in order to lower body temperatures, lower respiration rates and maintain full food consumption and productive capability. Evaporative cooling means subsequent wetting and forced drying of the cow’s coat to maximize the cooling effect. Milking parlors with adequate holding pens can employ the use of subequent sprinkling and forced air in the pens. In dairies with adequate drainage and housing, evaporative cooling can be provided above the feed bunks in addition to or instead of in the holding pen.