ASAE Journal Article
Shade Management Systems to Reduce Heat Stress for Dairy Cows in Hot, Humid Climates
D. E. Buffington, R. J. Collier, G. H. Canton
Published in Transactions of the ASAE Vol. 26 (6): 1798-1802 ( Copyright 1983 American Society of Agricultural Engineers ).
ABSTRACT THE benefits of providing shade for dairy cows are reported based on over 8 yr of research. Production benefits that are attributable to a well-designed shade management system are increases in milk production, reproductive efficiency and milk production in subsequent lactation. Major design and management considerations for shade management structures that are presented and discussed are orientation, space, floor, height, ventilation, roof construction, feeding and watering facilities, and waste management system.
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INTRODUCTION The influential factors in animal production are nutrition, disease, and environment (Baxter, 1969). These three factors are not discrete, but rather they demonstrate a three-way interaction. These factors together influence how closely an animal will produce to its genetic potential. Theoretically, if an animal could be provided ideal nutrition, reared under completely disease-free conditions and provided an ideal environment, the animal should produce to its full genetic potential. The goal of environmental modification is to provide an environment conducive to high productive efficiency for the animals. When under a high degree of thermal stress, an animal will reduce feed intake and expend energy to maintain homeothermy. The expended energy would otherwise be available for useful production. Problems often associated with thermal stress in addition to a decline in productivity are a general decline in reproductive efficiency and an increase in disease susceptibility. Indices of environmental conditions have been developed and used to predict comfort, or discomfort. Generally, the only two environmental parameters considered have been dry-bulb temperature and humidity. During periods of heat stress, an unshaded cow often is exposed to a radiant heat load greater than its metabolic heat production (Bond et al., 1967). THI cannot be effectively employed to predict discomfort and subsequent losses in production and reproduction in dairy cows when the radiant heat load becomes a significant portion of the total heat that the cow must dissipate, especially during periods of little air movement. To create an index integrating dry-bulb temperature, humidity, net radiation and air movement, the Black Globe-Humidity Index (BGHI) was developed by inserting black globe temperature in the THI equation in lieu of the dry-bulb temperature. As documented in several studies reported by Buffington et al. (1981) and Oliveira and Esmay (1981), the BGHI is a more accurate indicator of the severity of heat-stressing environmental conditions, especially when incident solar radiation and/or air movement are high. Under conditions of little or moderate heat stress, BGHI and THI are about equally effective as indices of heat stress. Several environmental modification strategies that can be utilized for reducing the severity of heat stress conditions are mechanical refrigeration, evaporative cooling, zone cooling, and various shade structures. Homeothermy in the dairy cow can best be achieved by mechanical refrigeration. Thatcher et al. (1974) reported that a 9.3% increase of 4% fat-corrected milk was achieved with mechanical refrigeration; however, totally refrigerated structures could not be economically justified because of high operating expenses. Other limitations restricting the use of total air conditioning are dust filtration, odor-ammonia accumulation, and problems associated with recirculating air. Evaporative cooling is an adiabatic process in which no heat is added to or removed from the environment, but removal of sensible heat required to evaporate water lowers the ambient temperature. Increased moisture content of the air results. Evaporative cooling is effective in certain regions where relatively high dry-bulb and low wet-bulb temperatures are experienced (Wiersma and Stott, 1966 and Stott and Wiersma, 1974). In hot, humid climates, only limited applications of evaporative cooling are practical (Hahn and Osburn, 1969). Zone cooling involves cooling the cow's head and neck, and therefore, the air that the cow inspires. Heat dissipation through the respiratory system assumes significant proportions when the effective temperature relegates minimal importance to sensible modes of heat exchange. Canton et al. (1982) reported that inspired-air temperatures below 18 °C effectively reduced heat stress in dairy cows as monitored by rectal temperature and respiration rates. However, economical justification of such an environmental modification system would be needed. Another effective means of aiding an animal maintain temperature regulation in a hot climate is to provide some control over the incoming thermal radiation. Shades—defined as thermal radiation shields—change the radiation balance of an animal but do not affect air temperature or humidity (Buffington et al., 1981; Esmay, 1969). The primary purpose of a shade is to protect the animal under it from intense direct solar radiation and diffuse and reflected radiation. A simple shade structure can reduce the radiant heat load on a cow by 30% or more by intercepting the direct solar radiation (Bond et al., 1967). Milk production and physiological responses achieved by providing shade for dairy cows have been inconsistent. Johnston et al. (1966) observed, in Louisiana, an improvement in milk production of shaded cows from 4 to 7% in comparison to unshaded cows, but no significant differences in body temperature were observed. Nelson et al. (1961) encountered lower rectal temperatures in shaded cows but no improvement in milk production. More recently in Louisiana, Guthrie et al. (1967) observed lower rectal temperatures and respiration rates in shaded cows, but no improvement in milk yield and composition. Dairy producers in California experienced critical heat stress for a period of about a week during August, 1977. Throughout this period, daily maximum temperatures were 31 to 35.5 °C and minimum temperature were about 21 °C. Afternoon relative humidities averaged 40 to 50%, and humidities during late evening and early morning hours averaged 90 to 95%. Approximately 700 dairy cows died because of the heat stress, and the milk production of all the dairy cows was substantially reduced. Cooling systems evaluated for their performance in terms of reducing death losses and milk production losses were shades, foggers, several different barn types, and washing systems. The main conclusion reached by the researchers was "shades were much more effective than any other method for reducing production and death losses" (Bishop et al., 1978). The objectives of this study were to document the performance benefits realized by providing shade structures for dairy cows and to develop design criteria for shade structures for dairy cows in hot, humid climates. STUDIES CONDUCTED The research was conducted beginning in the summer of 1975 and continuing thereafter at the University of Florida Dairy Research Unit near Hague, Florida. Dairy cows had free access to either a 9.1 m by 24.4 m gable-roofed shade structure or an adjacent open pasture. The metal roof sloped from 3.7 m to a peak height of 5.2 m and was insulated on the underside with 38 mm polystyrene insulation. The control group, located in an adjacent pasture with no shade, and the shaded group each consisted of 30 cows. These groups of cows were compared on the basis of milk production, reproductive efficiency, feed and water consumption, rectal temperature, respiration rate and basic physiological parameters of uterine blood flow, rumen contractions and blood analyses. Blood analyses consisted of hematocrit, plasma protein, plasma prolactin and aldosterone. Ambient dry-bulb and dewpoint temperatures were measured as well as black-globe temperatures in both shade and no shade locations. Black-globe temperatures were measured with a four-junction thermopile inserted in the center of a 0.15 m copper sphere painted flat black. DISCUSSION AND RECOMMENDATIONS Dairy Cow Performance Benefits In 1975, production of the cows having access to the shade structure was 10.9% more fat-corrected milk than the no-shade cows. All milk production records were adjusted to common stages of pregnancy, lactation, and experimental week. Conception rate to all inseminations was significantly higher (P < 0.05) for the cows with shade access. Conception rate, defined as number of confirmed pregnancies divided by total number of inseminations for the group, was 44.4% for the shade cows versus 25.3% for no shade cows. In 1976, cows in the shade group produced 5.5% more fat-corrected milk than cows in no-shade group. Conception rate was 38.2% for shaded cows versus 14.3% for no shade cows. Both increases were significant (P < 0.05). Although the milk production benefits realized from the shade are important economically, the marked improvements in reproductive efficiencies are more significant economically. Later studies focused on examining the role of shade structures in influencing the physiological performance of the cows. Rectal temperatures, uterine temperatures and respiration rates of cows in the no-shade locations were always significantly higher (P < 0.05) than the corresponding values of the shade cows during the heat stressing portions of the days. Rectal temperatures averaged 1 °C higher and respiration rates averaged 37 respirations per minute higher for the no shade cows. Conception rates were documented to be inversely related to uterine temperatures. The physiological parameters were correlated with the black-globe temperatures of the shade and no shade locations. Increases in black-globe temperatures were associated with depressed milk yields 24 and 48 h later. Major benefits of providing sufficient shading for cows are related to indirect effects such as increases in feed intake, digestive tract performance and uterine blood flow rate. Direct environmental effects on the ability of the mammary gland, digestive system or reproductive system to function properly during periods of heat stress were not observed. Benefits of providing shade for dry cows and heifers in the last trimester of their pregnancies also were observed. At parturition, all cows in the milking herd were managed uniformly. Calf birth weights were 3 kg lower (P < 0.05) for cows in the no-shade group. Milk yield was correlated positively in a linear manner with calf birth weight, and cows in the shade group produced more milk in the commencing lactation. The 100-day milk yield difference and the predicted 305-day adjusted milk yield difference between the shade and no-shade animals were 116 kg and 810 kg, respectively. Detailed analyses of these and other performance benefits observed in the University of Florida studies are reported by Collier et al. (1981, 1982), Roman-Ponce et al. (1977) and Thatcher et al. (1980). Shade Structure Design Parameters The only factor that the differences in milk production, reproductive efficiency, and basic physiological parameters of the cows in shade and no shade locations can be attributed to is the level of incident radiation. The 30 cows assigned to each group were selected carefully on the basis of previous performances and genetic merit to minimize differences between the shade and no-shade cows. Cows in both groups were handled by the same people and received the same nutrition and management programs. The shade cows maintained a higher level of feed intake than the no-shade cows, resulting in higher milk yields for the shade cows. Rectal temperatures and respiration rates of no-shade cows were always higher than the shade cows during the heat stressing portion of the day. Summarization of the dry-bulb, dewpoint, and black-globe temperatures measured over the course of several summers was presented by Buffington et al. (1981). The mean ambient dry-bulb, dewpoint, and black globe temperatures from June 22 to September 12 in 1978 are shown in Fig. 1. It is interesting to note that the climatic conditions experienced in California (as discussed in the Introduction) that were termed "critical heat stress'' are similar to what is frequently experienced through the period of May 15 to September 15 in Florida. In fact, many Florida summer days are even more heat stressing. Shade structures must be well-designed and engineered in order to obtain the maximum economic benefits that can be realized. The major design considerations for shade structures are: (a) orientation, (b) space, (c) floor, (d) height, (e) ventilation, (f) roof construction, (g) feeding and water facilities, and (h) waste management system. The design parameters discussed below were developed on the basis of research results at the University's Dairy Research Unit over an 8-yr period and farm visits to many Florida dairies having a variety of shading systems. Orientation: The orientation of a shade structure is crucial. The preferred orientation is east-west, i.e. the long axis of the building runs in an east-west direction. The east-west orientation is recommended because both feeding and watering facilities can be provided that are shaded nearly all day during the summer months and that are under the protection of the shade structure. It is important that animals have access to feed and water without leaving the shaded area. With a shade structure having a north-south orientation, the feeding and watering facilities located under the structure would be sunlit for nearly a half day every day through the summer months. However, if the prime objective is to maintain the floor of a shade structure as dry as possible during the summer months, then the north-south orientation is preferable. The shading patterns ofa9.1 m X 24.4m X 3.65 m high shade structure oriented north-south and east-west are shown in Figs. 2 to 4 for the 21st day of the months of June, March/September, and December, respectively, for the Orlando, Florida vicinity (28 deg N. Latitude; 81 deg W. Longitude). As depicted in the figures, a higher percentage of the shadow lies under the shade structure with an east-west orientation as compared to a north-south orientation during the summer months. In the winter, the percentage of the floor area that is sunlit to achieve drying is very nearly the same for both orientations. The shading patterns of a shade structure or any object for that matter are plotted for values of shade projection factor and azimuth angle for a given hour and day for a specified location. A simplified procedure for determining shade patterns has been presented by Buffmgton et al. (1981b). Space: The shade structure should provide at least 4.2 m2 of floor space per cow and preferably up to 5.6 m2. Many dairy producers try to ''economize'' by providing only 1.4 to 2.3 m2 floor space per cow. Although cows crowd under the shade during heat stressing periods, few production benefits are realized because of the adverse environmental conditions created by crowding. Floor: The floor of a shade structure in a hot, humid climate needs to be made of at least 0.1 m of reinforced concrete on a 1.5 to 2% grade. An earthen floor cannot be used under hot and humid conditions because it would soon become muddy. Because cows position themselves in the shadow rather than under the shade structure itself, areas adjacent to shade structures become muddy also. Such conditions pose serious problems especially in low-lying areas with high rainfall. Under such conditions, it is advisable to fence the cows under the shade on a concrete pad. However, the area fenced and concreted needs to be larger than the floor area of the shade structure because sufficient shadow area will not always be under the structure. Any installed fencing should extend at least 2.4 m on the north side, 6.1 m on the east and west sides, and 1.2 m on the south side. Such a fencing arrangement will allow the cows to have access to the total shaded area from about 9:30 am to 5:00 pm EDT during the summer months in the Orlando, Florida vicinity shown in Figs. 2 and 3. Height: Shade structure height needs to be selected with two opposing criteria in mind: (a) the higher the shade, the greater the air movement under the shade, and (b) the lower the shade, the smaller the diffuse and reflected radiation loads on the cows. For Florida conditions, a minimum height of 3.6 m from ground level to lowest point of the roof is recommended to encourage sufficient natural ventilation through the structure. If a shade structure is quite narrow (less than 6 m), then the recommended height is 3.3 m. Ventilation: Shade structures generally have length to width ratios ranging from about 2:1 to over 10:1. When the width of a shade structure exceeds about 12 to 15 m, the air movement under the shade structure is sharply reduced, especially in the center. If a wide structure is desired, it is recommended to have several continuous roof openings to allow better circulation of air. Gable-roofed shade structures should have a continuous open ridge to promote natural ventilation. To enhance natural ventilation in shade structures, the selected site should have no trees, other buildings, or obstructions within at least 15 m of all sides. Roof Construction: Various types of roofing materials can be used for shade structures. The most effective in terms of reducing radiant heat load on the animals under the shade is a reflective roof such as white galvanized or aluminum roof with about 25 mm of insulation directly beneath the metal roofing. The question as to whether or not to include insulation on the underside of the metal roofing is controversial. The rationale for including insulation is to practically eliminate the infrared radiant load on the cows from the underside of the roof. The argument advanced for not including insulation is that the benefits are too minimal to justify the costs. Fig. 5 shows the mean temperature on the underside of insulated and uninsulated portions of the metal roof of the shade structure for 38 summer days in 1976. For the hottest day experienced during that period, the temperatures on the underside of the insulated and uninsulated metal roof were 37 and 57 °C, respectively. Obviously, animals congregating under an insulated shade structure will be exposed to far less infrared radiation than those animals under a bare metal roof structure. For the case of a bare metal roof temperature of 57 °C, insulated metal roof temperature of 37 °C, cow's body surface temperature of 35 °C, radiation shape factor of 0.75, effective exposed area of 3 m2, and absorptivity of cow of 0.9, the cow under the uninsulated roof would have an increased radiant heat load of 303 W. Modifications of shade structures with metal-clad roofs include galvanized metal-cable roofing systems for flat-roofed shades. The metal-cable system consists of sheets of galvanized roofing sandwiched between cables under high tension. The sheets are spaced with a gap of 10 to 20 cm between them. A metal-cable shade is not as effective as a shade structure with solid roof for reducing radiation loads. The advantage of such a system is a lower initial investment; however, it is not known how well such a roof would withstand strong winds. Shade cloth fabrics with various weave openings providing actual shade from 30% up to 90% are available for use as animal shades. Most commonly used are fabrics with about 80% actual shade. With shade cloth used as roofing material, the structure is definitely cheaper than any other roofing system commonly used. However, the shade cloth does not provide as much protection from solar radiation for the cows. Studies at the Dairy Research Unit show that the black-globe temperature under 80% shade cloth averaged 3 °C higher (P < 0.05) than under a shade structure with insulated metal roof during the early afternoon hours of heat stressing days. Shade cloth is quite durable if it is properly installed under tension so the wind cannot freely whip it. It is necessary to maintain the tension in the fabric in order to realize many years of service from the material. Feeding and Watering Facilities: To achieve maximum benefit of the shade structure, feed and water must be available to the cows in the shade. When feed and water are supplied in an unshaded area, the animals need to sacrifice some comfort in order to eat and drink, resulting in a reduction in feed intake and consequently lower milk production. In the research conducted in the 1960's as discussed in the Introduction, the cows preferred shade, but they did not produce significantly more milk when provided with shade. In all those studies, the cows did not have access to feed and water under the shades. The benefits of providing feed under the shade are minimized if the cows have access to feed only during early morning and evening hours. Cows might actually be discouraged from feeding at night under shaded areas because they would not have radiation exposure to the night sky. In many large commercial dairies, groups of cows are often fed throughout the day and night because adequate bunk space is not available to feed all cows just during early morning and evening hours. Waste Management System: Waste management must be planned as an integral part of any shade structure system. The concrete floor of a shade can be cleaned by flushing with dump tanks, hosing manually with high pressure water, or scraping with a small tractor. Such cleaning needs to be done daily in order to maintain high standards of sanitation and corresponding low incidence levels of mastitis. With some planning, the value of the waste material can be utilized in a re-feeding program or in a fertilization/irrigation program for cropland. SUMMARY A shade management system is an economically feasible environmental modification for dairy cows in Florida. For cows with a production level of 13 to 16 kg/day, a 10% increase in milk production during the summer provides a yearly increase of about 170 to 200 kg milk/cow. The economics of a shade management system become even more feasible when one considers the improved conception rate and higher milk production in subsequent lactations of dairy cows with access to shade throughout their entire lactation and gestation periods. References 1. Baxter, S. H. 1969. The environmental complex in livestock housing - a review. Scottish Farm Bldg. Investigation Unit (Aberdeen), Farm Bldg. Report No. 4. 2. Bishop, S. E., J. C. Oliver, and H. Hellman. 1978. Heat stress survey results. Southern California Dairy Technology, June. University of California, Berkeley. 3. Bond, T. E., C. F. Kelly, S. R. Morrison, and N. Pereira. 1967. Solar, atmospheric, and terrestrial radiation received by shaded and unshaded animals. TRANSACTIONS of the ASAE 10(5):622-625, 627. 4. Buffington, D. E., A. Collazo-Arocho, G. H. Canton, D. Pitt, W. W. Thatcher, and R. J. Collier. 1981. Black globe-humidity index (BGHI) as comfort equation for dairy cows. TRANSACTIONS of the ASAE24(3):711-714. 5. Buffington, D. E., S. K. Sastry, and R. J. Black. 1981. Factors for determining shading patterns in Florida—Orlando and vicinity. Landscaping for Energy Conservation Series, Circular No. 505, University of Florida, Gainesville. 6. Canton, G. H., D. E. Buffington, and R. J. Collier. 1982. Inspired air cooling for dairy cows. TRANSACTIONS of the ASAE 25(3):730-734. 7. Collier, R. J., R. M. Eley, A. K. Sharma, R. M. Pereira, and D. E. Buffington. 1981. Shade management in subtropical environment for milk yield and composition in Holstein and Jersey cows. J. of Dairy Sci. 64:844-849. 8. Collier, R. J., S. G. Doelger, H. H. Head, W. W. Thatcher, and C. J. Wilcox. 1982. Effects of heat stress during pregnancy on maternal hormone concentrations, calf birth weight, and postpartum milk yield of Holstein cows. J. of Animal Sci. 54:309-319. 9. Esmay, M. L. 1969. Principles of Animal Environment. AVI Publishing Co., Inc., Westport, Conn. 10. Guthrie, L. D., J. E. Johnston, J. Rainey, and J. A. Lee. 1967. Effects of solar radiation and levels of fiber on production and composition of Holstein cow's milk. J. Dairy Sci. 50:608-609. 11. Hahn, G. L. and D. D. Osburn. 1969. Feasibility of evaporative cooling for dairy cattle based on expected production losses. TRANSACTIONS of the ASAE 13(3):289-294. 12. Johnston, J. E., E. J. Stone, and J. B. Frye, Jr. 1966. Effect of hot weather on the production function of dairy cows. Louisiana State Experiment Station Research Bull. 608, Baton Rouge. 13. Nelson, G. L., G. W. A. Mahoney, and E. K. Berousek. 1961. Hot weather shelter for lactating dairy cattle. Tech. Bull. T-87, Oklahoma State University, Stillwater. 14. Oliveira, J. L. and M. L. Esmay. 1981. Systems model analysis of hot weather housing for livestock. ASAE Paper No. 81-4564, ASAE, St. Joseph, MI 49085. 15. Roman-Ponce, H., W. W. Thatcher, D. E. Buffington, C. J. Wilcox, and H. H. Van Horn. 1977. Physiological and production responses of dairy cattle to a shade structure in a subtropical environment. J. of Dairy Sci. 60:424-430. 16. Stott, G. H. and F. Wiersma. 1974. Response of dairy cattle to an evaporative cooled environment. Proc. of First Int'l. Livestock Environment Sym., 88, ASAE, St. Joseph, MI 49085. 17. Thatcher, W. W., F. C. Gwazdauskas, C. J. Wilcox, J. Toms, H. H. Head, D. E. Buffington, and W. B. Fredrickson. 1974. Milking performance and reproductive efficiency of dairy cows in an environmentally controlled structure. J. Dairy Sci. 57:304-307. 18. Thatcher, W. W. and R. J. Collier. 1980. Effect of heat on animal productivity. CRC Handbook on Food and Human Nutrition, Chemical Rubber Co., Cleveland, OH. 19. Wiersma, F. and G. H. Stott. 1966. Microclimate modification for hot-weather stress relief of dairy cattle. TRANSACTIONS of the ASAE 9(2):309-312.
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