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Dairy Cattle Management in a Hot Environment
Mitsunori Kurihara and Shigeru Shioya*
Department of Animal Physiology and Nutrition,
National Institute of Livestock and Grassland Science,
Tsukuba, Ibaraki 305-0901, Japan
*Department of Animal Feeding and Management,
National Insitute of Livestock and Grassland Science,
Nishinasuno, Todhigi 329-2793, Japan, 2003-09-01

Abstract

In Southeast Asian countries, with the consistent increase in milk consumption, it is important to develop new technologies for higher milk production. However, the performance of dairy cows, including the yield and composition of milk, are depressed by heat stress. This Bulletin reviews factors affecting the thermal balance and production of lactating Holstein cows in hot environments. Thermal environments have several aspects, including air temperature, humidity, air movement, and radiation rate. However, the effective temperature (ET) is a simple and useful indicator for estimating the performance of lactating Holstein cows. Shade, fans, mist and fan systems, and night grazing and their effects, are presented as methods of modifying the environments of dairy cattle. Although heat stress causes a decline in dry matter intake, the cow's energy and protein requirements in hot environments increase. Therefore, it is important to increase the energy and by-pass protein contents of diets in order to maintain the performance of dairy cows in a hot environment. Problems regarding a decrease in dairy cattle performance, especially milk yield and fertility, still exist in many hot regions. Further investigation is required in order to clarify the combined effect of environmental modification and nutritional management on dairy cattle performance in hot environments.

Introduction

Hot environments affect the performance of dairy cattle both directly and indirectly. To attain the fullest genetic performance, environmental conditions and diets should be modified. Thermal factors consist of air temperature, humidity, air movement, and radiation rate. In lactating Holstein cows, the comfortable temperature is within the range 4-24oC (Hahn 1981). The effects of heat stress on the cows begin to be observed above 24oC, and milk yield decreases markedly above 27oC (Johnson 1965).

A decline in milk yield, fertility, and growth rate in hot environments is closely related to an increase in body temperature (BT). BT results from the balance between heat production (HP) and heat loss (HL). Since humidity affects the HL from an animal under high temperature conditions, dairy cattle performance falls markedly in hot, humid summers. Moreover, HP is associated with feed intake level, which in turn affects the production level. In high-producing cows, the HP is higher, and the effect of a hot environment is more pronounced.

Preventing an increase in body temperature in hot environments can be approached in three ways (Shibata 1996):

  • Lowering the environmental temperature by modifying the structure of the shed where the cattle are kept, or by introducing cooling facilities.
  • Increasing heat loss from animals by sprinkling them with water, using fans and so on.
  • Increasing the efficiency of feed energy utilization, and reducing the heat increment of animals from feeding.

The objectives of this report are to clarify the thermal effects on the production of lactating Holstein cows, and to introduce methods used to modify the environmental and nutritional management of Holstein cows in Japan.

Effect of Hot Environments on Animal Performance

Air Temperature and Humidity

Moisture in the air influences the rate of evaporative heat loss from animals through both skin and the respiratory tract. Mukai et al. (1984 unpublished) reported humidity should be taken into account in order to predict the production responses of lactating cows in a hot environment of more than 24oC. Table 1(1192) shows the effects of air temperature and relative humidity (RH) on the performance of lactating Holstein cows (Shioya et al. 1997).

There were no significant differences in live-weight, body temperature (BT), and respiration rate (RR) between 28oC-40% RH and 28oC-80% RH. However, the effect of 28oC had more effect on the cows' feed intake (on a dry matter basis), milk yield, milk composition, heat production (HP), evaporative heat loss (EHL), and time spent lying down at a high humidity (80% RH) than when humidity was low (40% RH). The ratio of evaporative heat loss to heat production at 28oC-40% RH was 65%, while at 28oC-80% it was 53%. In the latter case, cattle spent more time standing. This increased the area of the body surface exposed to the air, which in turn increased their heat loss.

Radiation

Radiant heat from both the sun and the animal's surroundings affects the rate of heat loss from radiation, convection, and conduction. In particular, the level of radiant heat from the roof of a livestock barn is very high in summer, and its effect on milk production is very important. Table 2(1089) shows the effects of radiant heat (0.2 cal/cm2/min) on the performance of lactating cows at an air temperature of 28oC (Shioya et al. 1997). The skin surface temperature, BT, and RR of cows exposed to the radiant heat were significantly higher than in those not exposed. On the other hand, the dry matter (DM) intake and heat production (HP) fell in cows exposed to radiant heat. As a result, the milk yield fell by 17% among the cows exposed to radiant heat, compared to those which were not.

Air Movement

Wind affects the heat loss from the body surface of an animal by the processes of convection and evaporation. At 10oC, the effect of wind on the milk production of Holstein cows was not significant (Johnson and Vanjonack 1976). However, at 27oC, the effect of wind moving only 2 meters/second (m/s) beneficial. There was no difference between the effect of a wind speed of 2.24 m/s, and one of 4.02m/s.

Assessing the Thermal Environment

Thermal effects on animals result from a combination of air temperature, humidity, radiation and air movement. The heat production of the animal itself is also considered a source of heat stress under hot conditions. Some scientists have presented the following model to assess the thermal environment:

ETE = k1*DBT + k2*WBT + k3*AM + k4*RD + k5*EI (Yamamoto 1983)

Where ETE, effective thermal environment; k1 _ K5, factors; DBT, dry-bulb temperature (C); WBT, wet-bulb temperature (C); AM, air movement; RD, radiation; EI energy intake.

THI = DBT + 0.36*DPT+41.2 (Johnson 1987)

Where THI indicates temperature humidity index, and DPT the dew point temperature.

ET = 0.35*DBT + 0.65*WBT

(Bianca 1962)

Where ET indicates effective temperature.

Yamamoto's equation includes all parameters related to the thermal effect on animals. However, a single acceptable index comprising all of the parameters is not yet available. Based on an investigation using the THI, (temperature humidity index), milk yield starts to decline at a mean THI of 72 (21oC at moderate humidity). A marked decline occurs at around 76 _ 78 mean THI. For each unit increase in THI, there is a decrease in milk yield of 0.26 kg/day, and a fall in hay consumption of 0.23 kg/day.

Recently, Toda et al. (1998, 1999, 2002) reported the effect of ET (effective temperature) on milk production and other physiological responses in Holstein cows. The respiration rate began to increase at an daily mean effective temperature (ET) of 20oC, while the body temperature began to increase at an ET of 22oC. Daily feed intake (dry matter basis) began to decline at 21.7oC ET, while daily milk yield began to fall at an ET of 22.2oC.

The impact of daily mean ET values was affected by the level of milk yield. The respiration rate and body temperature of high-producing cows began to increase at a lower ET, as did daily feed intake and milk yield.

There was a significant negative relationship between the level of milk yield (X) and the daily mean ET (Y) at which the milk began to decrease, as shown in the following equation: Y = -0.1695*X + 25.979.

According to this equation, the milk yield of Holstein cows which produce 10 kg of milk/day, begins to decrease at 24oC. Those which produce 30 kg of milk/day show a decline in milk yield at 21oC.

Effect of Production Level on Animal Performance in Hot Environments

Physiological Responses

Hagiwara et al. (2002) reported that the ET at which the respiration rate started to increase was lower (17oC) for high-producing cows (>35 kg milk/day) than that (22oC) of low-producing cows. The body temperature of high-producing cows rose to a higher level than that of low-producing cows, because of the higher metabolic rate and heat production of the more productive cows.

DRY Matter (DM) Intake and Milk Production

Sinde et al. (1994) reported that the food intake (dry matter (DM) basis) of cows which ate more than 20 kg of feed (DM basis) per day started to decrease at 25oC of ET. The ratio of forage to concentrates also decreased. However, the feed intake of cows with a feed intake of less than 20 kg/day (DM basis) was relatively constant. These cows were fed a high-quality diet of corn silage, timothy hay and concentrates, in which the level of total digestible nutrients (TDN) was 75 _ 77%. NDF, the level of neutral detergent fiber (NDF) supplied by roughage, was less than 35%.

The milk production of cows which consumed more than 20 kg of feed per day (DM basis) decreased with a rise in ET. Milk production also fell, especially when the ET rose to 25oC. On the other hand, no significant differences were seen with a higher ET in the milk production of cows which consumed less than 20 kg of feed (DM) per day.

Milk yields in summer in Japan show a more marked fall in more productive dairy cows (Toda et al. 2002). In other words, the decline in milk yield at higher temperatives is more marked in cows that produce more milk. A significant relationship exists between the level of milk yield (X, kg/day) and the decline in milk yield with each increase in daily mean ET (Y, kg/day/oC) as follows:

Y = -0.04*X + 0.18 (r = -0.53, P = 0.03).

This equation shows that the decline in milk yield seen in lactating Holstein cows with each increase in ET of one degree C was 0.6 kg/day in cows producing 20 kg milk/day, 1.0 kg/day in cows producing 30 kg/day, and 1.4 kg/day in cows producing 40 kg/milk/day.

Modification of the Environment

Careful management which can alleviate heat stress is the best way to maintain high production levels in lactating cows in a hot environment. Good management includes the modification of the surrounding environment to reduce the impact of the environment and/or to promote heat loss from the animals (Shibata 1996).

Fans are the most common type of cooling device used in Japan. Fans were used by 98% of farmers in the Kyushu area in the southern part of Japan, with an average of 5 (2-8) cows per fan. The percentage of farmers who own mist equipment has increased markedly in recent years. Some farmers prefer to use sprinklers, installed on the roof or at various places in the barn (Terada 1996).

Shade

Simple shade is the basic method in summer of protecting animals from direct solar radiation during the day. The most effective sources of shade are trees and other plants. They provide not only protection from sunlight, but also create a cooling effect through the evaporation of moisture from their leaves (Hahn 1985).

Shade has a beneficial effect on the physiological response of dairy cattle to heat. The body temperature, heart rate, and respiration rate all decreased when shade was provided during the summer in the Kyushu area of Japan ( Table 3(1156)).

Fans

Air movement increases the rate of heat loss from a cow's body surface, as long as the air temperature is lower than the animal's skin temperature. Table 4(1119) shows the effects of spot wind (air blasting around the head and neck) of lactating cows during the daytime and at night, in terms of animal performance. Spot wind reduced both the body temperature and the respiration rate, and improved the weight gain, milk yield and milk composition. However, if the air temperature is higher than the skin temperature, the skin will gain heat from the surrounding air. At air temperatures above 39oC, moving air becomes a source of heat stress for dairy cows.

The idea of cooling part of the animal's body (the head and neck) by cool air (zone cooling) has been tested. Table 5(1233) shows the effects of zone cooling on the performance of dairy cows. Zone cooling increased the feed intake (the hours of eating) and milk production, while reducing the body temperature and respiration rate (Saitou et al. 1989).

Mist and Fan System

Aii et al. (1998) have described an evaporative system which uses water mist and a fan ( Fig. 1(1272)). Mist particles are sprayed onto the cow's body to wet the hair. A fan is then used to evaporate the moisture, as a way of cooling the cows. The results showed an increase in milk production of 0.66 _ 1.90 kg/day for cows producing 20 _ 25 kg/day. An economic analysis showed that the break-even point of this system in Japan would be a 0.81 kg/day increase in milk production.

Night Grazing

Although air temperature and the level of solar radiation begin to fall after about 2 pm, the temperature of the roof remains high. As a result, the body temperature and respiration rate both rise. Cattle kept in a shed maintained a rapid heart beat during the night. However, when the cattle were allowed out into a pasture at night, these physiological responses decreased immediately. This is the result, both of the reduction in radiation heat from the surrounding cattle, and the rise in heat loss from the cattle.

Nutrient Requirements of Dairy Cows in a Hot Environment

It is important to predict dry matter (DM) intake, in order to formulate an adequate diet for cattle in a hot environment. Although there are some reliable equations regarding DM intake in regard to the thermo-neutral zone, reasonable equations regarding hot environments are few. Shioya et al. (1997) gives a good prediction equation.

DMI = 0.0198*LW + 0.231*FCM + 0.179*TMAX _ 0.187*TDN,

Where LW, live-weight (kg); FCM, 4% fat corrected milk (kg); TMAX, maximum air temperature (C); TDN, total digestible nutrients. The data used for this analysis were as follows: DMI, 13.2 _ 21.9 kg/day; LW, 456 _ 748 kg; FCM, 16.6 _ 30.1 kg/day; TMAX, 28.2 _ 34.4 C; TDN, 68.9 _ 75.5%.

From this equation, with the goal of maintaining the live-weight and milk production (FCM) of Holstein cows in hot environments, we must increase the DM intake by 0.179 kg for each 1oC rise in TMAX. This value (0.179 kg-DM) is 1.05% of the mean DM intake used for this analysis. This means that the energy needs of cattle for maintenance and production should increase in a hot environment, while the gross energy efficiency should fall.

After energy balance trials, Kurihara (1996) reported that the net energy requirement for the maintenance of dry Holstein cows tended to increase by 5% at 36oC, compared to energy needs at 18 _ 32oC. The metabolizable energy requirements for maintenance (MEm) increased by 10% at 26 and 32oC. The increase in MEm tended to be lower in the case of diets that were easy for the cattle to metabolize (i.e. high in energy, low in roughage).

The energy requirements of lactating cows also increased under high temperature conditions, but this increase seemed to be caused mainly by the increase in MEm. Using Shioya's equation, if the DMI, LW, and TDN are constant, the FCM decreases by 0.775 kg with each 1oC rise of TMAX over 28oC. Similarly, the FCM increases by 0.81 kg with a 1% rise of TDN.

Effect of High-Energy Diets

Although the MEm of dairy cows increases in a hot environment, heat stress depresses feed intake. For this reason, it is important to increase the energy content of the diet of dairy cows, in order to maintain their energy intake under hot conditions.

Shioya (2002) reported that when Holstein cows were fed a diet which contained a high level (77%) of TND (total digestible nutrients), their body temperature and respiration rate were significantly lower than those of cows fed on a diet with a low TDN content (70 and 74%). Kurihara (1996) has reported that the heat increment, which is an internal heat stressor in hot environments, is lower in more highly metabolizable diets. Thus, it is though that the heat increment from a high TDN diet is lower than that from a low TDN diet. This is why the body temperature and respiration rate of the cows fed on a 77% TDN diet were relatively low. In contrast, the TDN intake and production efficiency (FCM/TDN intake) of cows fed on a 77% TDN diet were significantly higher. This was found to be especially important in the increase in FCM yield during postpartum days 10 _ 30.

Furthermore, Terada (1996) recommends the use of fatty feeds, or the calcium salts of fatty acids, as way of improving the energy supply for cows in summer. Cows fed such a diet in hot weather had a higher milk yield, and a lower body temperature and respiration rate.

Effect of by-Pass Protein

It is well known that excessive protein intake increase HP and decreases reproductive performance. However, since in a hot environment the protein requirement of cows increases and DM intake decreases, the protein supplied to lactating cows during summer is not always sufficient. Table 8(1276) shows that the DM intake, milk yield, milk fat content, and ruminal NH3-N of lactating cows which produce above 25 kg milk per day and are fed on 17.5% CP diets tend to be higher than those of cows fed on 14.5% CP diets. Furthermore, by using fish meal which is by-pass protein, the milk yield and milk protein content of cows increased while ruminal NH3-N decreased. Terada (1996) also reported that fish meal supplementation led to a decrease in both urinary nitrogen excretion and BT. These results mean that fish meal protein resulted in more greater milk production.

Many researchers have investigated methods for reducing heat stress to dairy cattle and nutritional modification in regard to hot environments. However, problems concerning the decrease in dairy cattle performance, especially milk yield and fertility, still exist in many hot regions including Southern Asian countries and Japan. Therefore more research is needed to develop a more efficient and sustainable production system for dairy cattle in hot environments. This research should focus on the effects of a combination of environmental modification and nutritional management in hot environments.

References

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Index of Images

Figure 1 Effect of Air Temperature on Milk Production

Figure 1 Effect of Air Temperature on Milk Production

Table 1 Effects of Air Temperature and Relative Humidity on the Performance of Lactating Holstein Cows

Table 1 Effects of Air Temperature and Relative Humidity on the Performance of Lactating Holstein Cows

Figure 2 Mist and Fan System for Cooling Dairy Cattle

Figure 2 Mist and Fan System for Cooling Dairy Cattle

Figure 3 Effect of Night Grazing (after 6 PM) on Physiological Parameters of Cattle

Figure 3 Effect of Night Grazing (after 6 PM) on Physiological Parameters of Cattle

Table 2 Effects of Radiant Heat on the Performance of Lactating Holstein Cows in a Hot Environment

Table 2 Effects of Radiant Heat on the Performance of Lactating Holstein Cows in a Hot Environment

Table 3 Effect of Butter Muslin and Shaded Arbor on the Physiological Response of Cattle in a Hot Environment

Table 3 Effect of Butter Muslin and Shaded Arbor on the Physiological Response of Cattle in a Hot Environment

Table 4 Effect of Fans during Daytime and at Night on Animal Performance

Table 4 Effect of Fans during Daytime and at Night on Animal Performance

Table 5 Effect of Zone Cooling on Animal Performance

Table 5 Effect of Zone Cooling on Animal Performance

Table 6 Effect of Mist and Fan System on Animal Performance

Table 6 Effect of Mist and Fan System on Animal Performance

Table 7 Effect of Dietary TDN Content on Animal Performance during Early Lactation (5-60 Days)

Table 7 Effect of Dietary TDN Content on Animal Performance during Early Lactation (5-60 Days)

Table 8 Effects of Crude Protein (

Table 8 Effects of Crude Protein (

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