A Comprehensive Analysis of Novel Dairy Cooling Systems, Their Cooling Efficiency and Impact on Lactating Dairy Cow Physiology and Performance

Transcription

1 A Comprehensive Analysis of Novel Dairy Cooling Systems, Their Cooling Efficiency and Impact on Lactating Dairy Cow Physiology and Performance Item Type text; Electronic Dissertation Authors Ortiz de Janon, Xavier Alejandro Publisher The University of Arizona. Rights Copyright is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. Download date 12/07/ :53:05 Link to Item

2 A C O M P R E H E N S I V E A N A L Y S I S O F N O V E L D A I R Y C O O L I N G S Y S T E M S, T H E I R C O O L I N G E F F I C I E N C Y A N D I M P A C T O N L A C T A T I N G D A I R Y C O W P H Y S I O L O G Y A N D P E R F O R M A N C E by Xavier Alejandro Ortiz de Janon A Dissertation Submitted to the Faculty of the S C H O O L O F A N I M A L A N D C O M P A R A T I V E B I O M E D I C A L S C I E N C E S In Partial Fulfillment of the Requirements for the Degree of D O C T O R O F P H I L O S O P H Y I N A N I M A L S C I E N C E S In the Graduate College T H E U N I V E R S I T Y O F A R I Z O N A 2016

3 T H E U N I V E R S I T Y O F A R I Z O N A G R A D U A T E C O L L E G E As members of the Dissertation Committee, we certify that we have read the dissertation prepared by Xavier Alejandro Ortiz de Janon, titled A Comprehensive Analysis of Novel Cooling Systems, their Cooling Efficiency and Impact on Lactating Dairy Cow Physiology and Performance and recommend that it be accepted as fulfilling the dissertation requirement for the Degree of Doctor of Philosophy in Animal Sciences. DATE: 11/17/2015 ROBERT J. COLLIER DATE: 11/17/2015 SEAN W. LIMESAND DATE: 11/17/2015 MURAT KACIRA DATE: 11/17/2015 PEDER S. CUNEO DATE: 11/17/2015 DAN B. FAULKNER Final approval and acceptance of this dissertation is contingent upon the candidate s submission of the final copies of the dissertation to the Graduate College. I hereby certify that I have read this dissertation prepared under my direction and recommend that it be accepted as fulfilling the dissertation requirement. DATE: 11/17/2015 DISSERTATION DIRECTOR: ROBERT J. COLLIER 2

4 S T A T E M E N T B Y A U T H O R This dissertation has been submitted in partial fulfillment of the requirements for an advanced degree at the University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library. Brief quotations from this dissertation are allowable without special permission, provided that an accurate acknowledgement of the source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his or her judgment the proposed use of the material is in the interests of scholarship. In all other instances, however, permission must be obtained from the author. SIGNED: Xavier Alejandro Ortiz de Janon 3

5 A C K N O W L E D G E M E N T S I would like to acknowledge Al-Safi Dairy Company, GEA Farm Technologies, Schaefer Ventilation Equipment and Peter Orradre for their economic support in the development of these experiments. Additionally, I would like to thank all the people that assisted in the development of these experiments at the University of Arizona and at Al-Safi Dairy Company. I would also like to express my enormous gratitude to Dr. Robert Collier and Jayne Collier for their patience, guidance and training. Their effort prepared me for future challenges. 4

6 D E D I C A T I O N I would like to dedicate my dissertation to my beautiful wife, Renate Diaz Gill. Without her support and love this work wouldn t have been possible. For her encouragement to be a better person, her companionship during this journey, and her unconditional care and love. I would also like to dedicate this work to my father in law, Gustavo Diaz Gill. For welcoming me with open arms into his family and sharing with me so many stories, jokes and wisdom. He left a huge mark in my life that will endure over time. Finally, to Dr. John Smith, for giving me the opportunity to finish my studies and letting me learn from him. It was an honor for me to work with him and I will always remember him as a great mentor and professional, but over all an amazing friend. 5

7 T A B L E O F C O N T E N T S L I S T S O F F I G U R E S A N D T A B L E S...9 A B S T R A C T Literature Review I N T R O D U C T I O N H E A T S T R E S S I N D I C A T O R S Temperature Humidity Index Skin Temperatures Respiration Rates Body Temperature Animal Behavior T H E R M O R E G U L A T O R Y M E C H A N I S M S Conduction Convection Radiant Exchanges Evaporation E F F E C T S O F H E A T S T R E S S Nutrition Reproduction M I L K Y I E L D Health M E T H O D S T O R E D U C E H E A T S T R E S S Genetics Facilities C O N C L U S I O N S

8 R E F E R E N C E S Evaluation of conductive cooling of lactating dairy cows under controlled environmental conditions A B S T R A C T I N T R O D U C T I O N M A T E R I A L S A N D M E T H O D S Stall Preparation Statistical Analysis R E S U L T S D I S C U S S I O N R E F E R E N C E S An evaluation of bedding type on efficiency of heat exchangers to cool high producing dairy cows during thermal stress A B S T R A C T I M P L I C A T I O N I N T R O D U C T I O N M A T E R I A L S A N D M E T H O D S Stall Preparation Statistical Analysis R E S U L T S D I S C U S S I O N C O N C L U S I O N R E F E R E N C E S Energy balance of conductive cooled lactating dairy cows in heat stress conditions

9 A B S T R A C T I N T R O D U C T I O N M A T E R I A L S A N D M E T H O D S Energy balance of lactating cows R E S U L T S A N D D I S C U S S I O N R E F E R E N C E S A comparison of 2 evaporative cooling systems on a commercial dairy farm in Saudi Arabia A B S T R A C T I N T R O D U C T I O N M A T E R I A L S A N D M E T H O D S Experimental Design Statistical Analysis R E S U L T S D I S C U S S I O N R E F E R E N C E S Summary R E F E R E N C E S

10 L I S T S O F F I G U R E S A N D T A B L E S Table 2.1 Ingredients and chemical composition of diet Figure 2.1 Sequence of climates and acclimation phases for each of 2 periods of the study. TN = thermo neutral, HD = hot and dry, and HH = hot and humid Figure 2.2 Description of bed treatments, location, bedding type, and sensor placement within the environmental room. Temp = temperature, RH = relative humidity Figure 2.3 Water supply and return through heat exchangers in stalls of the environmental room Figure 2.4 Placement of sensors in each stall. H = height, L = length Figure 2.5 Average ambient temperature, relative humidity (RH), and temperature humidity index (THI) by hour for the hot and dry environment Figure 2.6 Average ambient temperature, relative humidity (RH), and temperature humidity index (THI) by hour for the thermo-neutral environment Figure 2.7 Average ambient temperature, relative humidity (RH), and temperature humidity index (THI) by hour for the hot and humid environment Table 2.2 Effect of bedding type and cooled water flow (on vs. off) on bed temperatures (surface and 25-cm depth) and heat flux between the heat exchanger and the cow Table 2.3 Effect of environment, water flow (on vs. off) through the heat exchangers, and bedding type on mean 24-h core body temperature (CBT), feed intake, milk yield, and resting time Figure 2.8 Effect of bedding type on circadian core body temperature (CBT) pattern in a hot and dry environment. DRM = dried manure. Treatment-by-time interaction: P < ; SEM =

11 Figure 2.9 Effect of bedding type on circadian core body temperature (CBT) pattern in thermoneutral environment. DRM = dried manure. Treatment-by-time interaction: P < ; SEM = Figure 2.10 Effect of bedding type on circadian core body temperature (CBT) pattern in hot and humid environment. DRM = dried manure. Treatment-by-time interaction: P < ; SEM = Table 2.4 Effect of environment and bedding on skin and rectal temperature and respiration rate (RR) in lactating Holstein cows Table 2.5 Effect of environment and bedding on milk composition of Holstein cows Table 2.6 Percentages of milk composition of cows in 4 types of bed treatments and 3 different climates Figure 2.11 Percentage of moisture content of 4 types of bed treatments at 3 different depths (0, 13, and 25 cm below the surface). DRM = dried manure Figure 2.12 Mean temperature of water returning from the heat exchangers in 3 different climates. a,b Bed treatments with different letters are significantly different (P < 0.05) in their respective climate Table 3.1 Ingredients and chemical composition of diet Figure 3.1 Sequence of climates and acclimation phases for each of 2 periods of the study. TN = thermo neutral, HD = hot and dry, and HH = hot and humid Figure 3.2 Description of bed treatments, location, bedding type, and sensor placement within the environmental room. Temp = temperature, RH = relative humidity Figure 3.3 Water supply and return through heat exchangers in stalls of the environmental room Figure 3.4 Placement of sensors in each stall. H = height, L = length

12 Figure 3.5 Average ambient temperature, relative humidity (RH), and temperature humidity index (THI) by hour for the hot and dry environment Figure 3.6 Average ambient temperature, relative humidity (RH), and temperature humidity index (THI) by hour for the thermo-neutral environment Figure 3.7 Average ambient temperature, relative humidity (RH), and temperature humidity index (THI) by hour for the hot and humid environment Table 3.2 Effect of environment, water flow (on vs. off) through the heat exchangers, and bedding type on Mean 24-h core body temperature (CBT), feed intake, milk yield, somatic cell count (SCC) and resting time. DRM=Dried manure Figure 3.8 Effect of bedding type on circadian core body temperature (CBT) pattern in a hot and dry environment. DRM = dried manure. Treatment-by-time interaction: P < ; SEM = Figure 3.9 Effect of bedding type on circadian core body temperature (CBT) pattern in thermoneutral environment. DRM = dried manure. Treatment-by-time interaction: P < ; SEM = Figure 3.10 Effect of bedding type on circadian core body temperature (CBT) pattern in hot and humid environment. DRM = dried manure. Treatment-by-time interaction: P < ; SEM = Table 3.3 Effect of environment and bedding on skin and rectal temperature and respiration rate (RR) in lactating Holstein cows. DRM= Dried manure Table 3.4 Effect of environment and bedding on milk composition of Holstein cows. DRM= Dried manure Table 3.5 Percentages of milk composition of cows in 4 types of bed treatments and 3 different climates. DRM= Dried manure

13 Table 3.6 Effect of bedding type and cooled water flow (on vs. off) on bed temperatures (surface and 12.7cm depth) and heat flux between the heat exchanger and the cow. DRM= Dried manure Figure 3.11 Percentage of moisture content of 4 types of bed treatments at 3 different depths (0, 13, and 25 cm below the surface). DRM = dried manure Figure 3.12 Mean temperature of water returning from the heat exchangers in 3 different climates. a,b Bed treatments with different letters are significantly different (P < 0.05) in their respective climate Table 4.1 Physiological responses of cows in two previously developed studies evaluating conductive cooling in three environments (hot-dry, thermo neutral and hot-humid) two bedding materials (sand and dried manure) and two heat exchanger depths (25 vs.12.5cm). Core body temperature (CBT) DRM (dried manure bedding) Table 4.2 Milk production (Kg/d) and milk composition (%) of cows in two studies evaluating conductive cooling in three environments (hot-dry, thermo neutral and hot-humid) two bedding materials (sand and dried manure) and two heat exchanger depths (25 vs.12.5cm). DRM (dried manure bedding) Figure 4.1 Calculated surface temperature of cows as function of ambient temperatures from two studies evaluating conductive cooling in hot-dry conditions with two bedding materials (sand and dried manure) and two heat exchanger depths (25 vs.12.5cm). DRM (dried manure bedding) Figure 4.2 Calculated respiration rates of cows as function of ambient temperatures two previously developed studies evaluating conductive cooling in hot-dry conditions with two bedding materials (sand and dried manure) and two heat exchanger depths (25 vs.12.5cm). DRM (dried manure bedding) Table 4.3 Energy balance of cows in two studies evaluating conductive cooling in two environments (hot-dry and hot-humid) two bedding materials (sand and dried manure) and two heat exchanger depths (25 vs.12.5cm). DRM (dried manure bedding)

14 Figure 4.3 Twenty-four-hour mean heat storage of cows in two studies evaluating conductive cooling in hot-dry conditions with two bedding materials (sand and dried manure) and two heat exchanger depths (25 vs.12.5cm). DRM (dried manure bedding) Figure 4.4 Twenty-four-hour mean heat storage of cows in two studies evaluating conductive cooling in hot-humid conditions with two bedding materials (sand and dried manure) and two heat exchanger depths (25 vs.12.5cm). DRM (dried manure bedding) Table 4.4 Percentage of total heat loss through conduction, convection, radiation and evaporation of cows in two studies evaluating conductive cooling in two environments (hot-dry and hot-humid) two bedding materials (sand and dried manure) and two heat exchanger depths (25 vs.12.5cm). DRM (dried manure bedding) Figure 4.5 Sensibility analysis of sand bedding material at different thermal conductivities (0.33, 0.41, 0.49, 0.57, 0.66 W/m C ) and distance (10, 15, 20 and 25cm) between the heat exchanger and cows Figure 4.6 Sensibility analysis of dried manure bedding material at different thermal conductivities (0.1, 0.2 and 0.3 W/m C ) and distance (10, 15, 20 and 25cm) between the heat exchanger and cows Table 5.1 Ingredients and chemical composition of diets Figure 5.1 Calorimetric grid for the distribution of sensors under both cooling systems: Korral Kool (Korral Kool Inc., Mesa, AZ) and FlipFan (Schaefer Ventilation Equipment LLC, Sauk Rapids, MN). Temp = temperature; RH = relative humidity; S = distance Figure 5.2 Average ambient temperature (TEMP), relative humidity (RH), and temperaturehumidity index (THI) by hour (June). SEM: TEMP = 0.15, RH = 0.24, and THI = Table 5.2 Effect of 2 cooling systems on mean DMI, milk yield, and services per cow (June to August)

15 Figure 5.3 Weekly milk production of cows during 3 mo for both treatments KK and FF. KK = Korral Kool (Korral Kool Inc., Mesa, AZ); FF = FlipFan (Schaefer Ventilation Equipment LLC, Sauk Rapids, MN). SEM (error bars) = Figure 5.4 Average weekly feed intake. KK = Korral Kool (Korral Kool Inc., Mesa, AZ); FF = FlipFan (Schaefer Ventilation Equipment LLC, Sauk Rapids, MN). Letters (a, b) indicate treatment interaction: P < 0.05; SEM = Table 5.3 Effect of 2 cooling systems on core body temperature (CBT), respiration rates, surface temperature, and resting time in the months of June and July Table 5.4 Effect of cooling systems on respiration rates (breaths/min) by hour for the months of June and July Table 5.5 Effect of cooling systems on surface temperatures ( C) by hour for the months of June and July Figure 5.5 Continuous core body temperature (CBT) of cows in 2 different cooling systems in the month of June. KK = Korral Kool (Korral Kool Inc., Mesa, AZ); FF = FlipFan (Schaefer Ventilation Equipment LLC, Sauk Rapids, MN). Letters (a, b) indicate treatment time interaction: P < 0.05; SEM = Figure 5.6 Average ambient temperature (TEMP), relative humidity (RH), and temperaturehumidity index (THI) by hour (July). SEM: TEMP = 0.07, RH = 0.11, and THI = Figure 5.7 Continuous core body temperature (CBT) of cows in 2 different cooling systems in the month of July. KK = Korral Kool (Korral Kool Inc., Mesa, AZ); FF = FlipFan (Schaefer Ventilation Equipment LLC, Sauk Rapids, MN). Letters (a, b) indicate treatment time interaction: P < 0.05; SEM = Table. 5.6 Water and electricity usage of both cooling systems in the months of June and July

16 Table 5.7 Ambient temperature, wind speed, and convective heat transferred of FF and KK cooling systems Figure 5.8 Calorimetric analysis of KK system for the month of June (KK = Korral Kool, Korral Kool Inc., Mesa, AZ) Figure 5.9 Calorimetric analysis of KK system for the month of July (KK = Korral Kool, Korral Kool Inc., Mesa, AZ) Figure 5.10 Calorimetric analysis of FF system for the month of June (FF = FlipFan, Schaefer Ventilation Equipment LLC, Sauk Rapids, MN) Figure 5.11 Calorimetric analysis of FF system for the month of July (FF = FlipFan, Schaefer Ventilation Equipment LLC, Sauk Rapids, MN)

17 A B S T R A C T Cooling systems used to reduce heat stress in dairy operations require high energy, water usage, or both. Steady increases in electricity costs and reduction of water availability and an increase in water usage regulations require evaluation of passive cooling systems to cool cows and reduce use of water and electricity. A series of experiments were conducted to evaluate the use of heat exchangers buried as components in a conductive system for cooling cows. In the first experiment six cows were housed in environmentally controlled rooms with tiestall beds, which were equipped with a heat exchanger and filled with 25 cm of either sand or dried manure. Beds were connected to supply and return lines and individually controlled. Two beds (one per each kind of bedding material) constituted a control group (water off), and the other 4 (2 sand and 2 dried manure) used water at 7 C passing through the heat exchangers (water on). The experiment was divided in 2 periods of 40 d, and each period involved 3 repetitions of 3 different climates (hot and dry, thermo neutral, and hot and humid). Each cow was randomly assigned to a different treatment after each repetition was over. Sand bedding remained cooler than dried manure bedding in all environments and at all levels of cooling (water on or off). Results from this experiment demonstrated that bed temperatures were lower and heat flux higher during the bed treatment with sand and water on. We also detected a reduction in core body temperatures, respiration rates, rectal temperatures, and skin temperatures of those cows during the sand and water on treatment. Feed intake and milk yield numerically increased during the bed treatment with sand and water on for all climates. No major changes were observed in the lying time of cows or the composition of the milk produced. 16

18 The efficiency of conductive cooling as a heat abatement technique in dairy production is highly correlated with the distance between the cooling system and the skin of the cow and the type of bedding material used. A second experiment was conducted to identify possible improvements in the utilization of conductive cooling for cooling cows. Heat exchangers buried 12.7cm below the surface as components in a conductive system ware evaluated in this study. Six cows were housed in environmentally controlled rooms with tie-stall beds, which were equipped with a heat exchanger and filled with 12.7cm of either sand or dried manure. Beds were connected to supply and return lines and individually controlled. Two beds (one per bedding material type) constituted a control group (water OFF), and the other four (two sand and two dried manure) used water at 7 C passing through the heat exchangers (water ON). The experiment was divided into two periods of 40 days and each period involved three repetitions of three different climates hot dry (HD), thermo neutral (TN) and hot humid (HH). Each cow was randomly assigned to a different treatment after each repetition was over. The sand and water on treatment was the most efficient treatment under heat stress conditions (humid or dry heat). Cows in stalls with the sand and water on treatment demonstrated lower rectal temperatures, respiration rates, skin surface temperatures and core body temperatures compared to the other three treatments. Additionally, the sand and water on treatment increased milk yield and resting time of cows under heat stress. Also, the sand and water on treatment had the lowest bed surface temperatures and highest heat exchange compared to the other treatments. From these two experiments we confirm that heat exchangers are a viable heat abatement technique that could reduce the heat load of heat stressed cows; however, this system should be paired with additional cooling systems (e.g. fans and or misters) to most efficiently reduce the negative effects of heat stress on dairy production. Additionally, Sand was superior to dried manure as a bedding material in combination with heat exchangers. 17

19 To make further recommendations of the use of heat exchangers in commercial dairy farm, a third study was developed. Based on the data obtained in the previous experiments, a comprehensive energy balance was developed to fully understand conductive cooling in two different environments (HD and HH), two bedding materials (sand and dried manure) and two depths between cows and the heat exchangers (25 vs. 12.5cm). The energy balance estimates indicated that sand is the most efficient bedding material when utilized as bedding material with conductive cooling in both hot dry and hot humid environments. In the hot-dry environment there was an increase in the conductive heat exchanged with the reduction in bedding depth to 12.5cm, however this did not result in a reduction in the heat storage of cows. In the hot-humid environment when heat exchangers were placed 12.5cm from the top of the bed there was an increase in both the conductive heat loss and heat storage of cows when compared to 25cm. Additionally, results demonstrated that the efficiency of heat exchangers as measured by heat flux was improved when heat exchangers were at a depth of 12.5cm. The sensibility analysis indicated that a reduction in the depth and/or an increase in the thermal conductivity of both bedding materials would maximize conductive heat exchange. These results should be utilized as recommendations for the utilization of heat exchangers and conductive cooling in commercial dairy farms. Evaporative cooling is widely used in dairy farms located in arid environments. Even though, these cooling systems have been shown to effectively reduce the heat stress of lactating dairy cows, a growing shortage of water and rising cost of electricity compromise its future usage. An experiment was developed to compare two evaporative cooling systems, their interaction with lactating dairy cows and their usage of natural resources. The efficacy of 2 evaporative cooling systems (Korral Kool, KK, Korral Kool Inc., Mesa, AZ; FlipFan dairy system, FF, Schaefer Ventilation Equipment LLC, Sauk Rapids, MN) was estimated utilizing 400 multiparous Holstein 18

20 dairy cows randomly assigned to 1 of 4 cooled California-style shade pens (2 shade pens per cooling system). Each shaded pen contained 100 cows (days in milk = 58 ± 39, milk production = 56 ± 18 kg/d, and lactation = 3 ± 1). Production data (milk yield and reproductive performance) were collected during 3 months (June August, 2013) and physiological responses (core body temperature, respiration rates, surface temperatures, and resting time) were measured in June and July to estimate responses of cows to the 2 different cooling systems. Water and electricity consumption were recorded for each system. Cows in the KK system displayed slightly lower respiration rates in the month of June and lower surface temperatures in June and July. However, no differences were observed in the core body temperature of cows, resting time, feed intake, milk yield, services/cow, and conception rate between systems. The FF system used less water and electricity during this study. In conclusion, both cooling systems (KK and FF) were effective in mitigating the negative effects of heat stress on cows housed in arid environments, whereas the FF system consumed less water and electricity and did not require use of curtains on the shade structure. Results of this research indicate that effective use of conductive cooling in combination with efficient evaporative cooling systems offer opportunities to reduce both water and electricity consumption on dairy farms under both hot dry and hot humid environments. 19

21 C H A P T E R 1 Literature Review I N T R O D U C T I O N In the dairy industry one of the biggest problem is the increasing susceptibility of dairy cows to heat stress. Every year, animals are more vulnerable to changes in weather caused by global warming (Klinedinst et al., 1993). In addition, the majority of the biggest dairy farms in the US are located in regions where seasonal stressors adversely influence productivity (Collier et al., 2006). These challenges have created more interest in the development of mitigation measures and techniques that prevent heat stressed animals. Water consumption and availability for heat abatement systems pose major challenges for today s dairy operators. The depletion of clean water supplies and the increasing cost of water and electricity in the U.S is becoming a limiting issue in some states. Additionally, regulations concerning water availability for livestock production will likely be more restrictive in future years. New passive methods for cooling livestock need to be investigated in order to maintain high levels of milk production while increasing the efficiency of water and electricity consumption. An animal in thermoneutrality, or zone of thermal comfort (ZTC), is in the range of maximum sensation comfort. At this stage the environmental factors promote maximum performance and least stress for the animal. Berman et al. (1985) suggested that for lactating dairy cows, the upper limit of the ZTC vary between 25 and 26 C. When temperature is beyond 20 C, environmental factors compromise the animal s zone of thermal comfort affecting the performance and 20

22 maintenance requirements of animals (NRC, 2001). Relative humidity plays an important role in the variation of ZTC; as relative humidity increases, the ability of animals to exchange heat with the environment decreases, meaning that at lower temperatures animals could be under heat stress. Heat stress is defined as the negative balance between the amount of energy an animal exchanges with the environment, and the amount of heat energy produced by the animal as a result of metabolic reactions. The regulation of this balance is made by environmental factors (ambient temperature, relative humidity, solar radiation, air movement, and precipitation), and animal properties (rate of metabolism, moisture loss) as well as thermoregulatory mechanisms of the animal with the surrounding environment (non evaporative and evaporative) (Armstrong, 1994, St-Pierre et al., 2003, Bohmanova et al., 2007). H E A T S T R E S S I N D I C A T O R S For dairy managers it is extremely important to realize when their animals are under high thermal conditions. The awareness of animals under heat stress helps producers to take heat stress preventive measures. Currently the most used heat stress indicators are: Temperature Humidity Index (THI), skin temperatures, respiration rates, body temperature, and animal behavior. Temperature Humidity Index Researchers developed a method to estimate and control the impact of environmental conditions over livestock. This index is called Temperature Humidity Index (THI), and it takes into consideration the thermal stress of the animals related with all the environmental information available such as ambient temperature, relative humidity and solar radiation. 21

23 According to Ravagnolo and Misztal (2000), the formula to calculate THI for dairy cattle is: THI = ((1.8 x Tdb) + 32) ( x RH) x (1.8 x Tdb -26) Where: Tdb : Temperature dry bulb in degrees Celsius, RH : Relative humidity in percentage. New investigations have shown that each species has a different value of THI, and it should be calculated depending on the methods and characteristics of the thermoregulatory mechanisms as well as the sensitivity of each specie to environmental conditions. According to Zimbelman et al. (2009), when THI exceeds 68 an environment is considered stressful for dairy cattle. Skin Temperatures Even though these values of THI are used to estimate the impact of heat stress on animals, cows are exposed to different microenvironments created by the cooling systems and the position of the cows in the pens (Collier et al., 2006). Therefore new technology has been used to estimate if animals are adequately cooled. One approach is the use of infrared thermography guns, which measure the actual skin surface temperature of animals. If the skin surface temperature is below 35 C, the difference between the skin temperature and the core body temperature is large enough to effectively exchange heat from the body with the surrounding environment (Collier et al., 2006). Although this approach does not require restricting movements of cows and it also takes in consideration the different microenvironments that cows are exposed (Collier et al., 2006), the accuracy of the predictions can be limited by the variability in skin surface moisture at a given point in time (VanBaale et al., 2006). 22

24 Respiration Rates Respiration rate is a gross indicator of heat load in animals during hot weather, due to the high correlation between the respiration rate and the thermal condition of the animal. Thermal stress induces physiological changes, including increased respiration rates in order to maintain a thermal equilibrium (Kadzere et al., 2002). In cool conditions the reported amount of breaths is 20 breaths/min which increases to 100 or more per minute at severe heat stress (Silanikove, 2000). Regardless that high temperatures play a more important role affecting the respiration rate of dairy animals, high relative humidity decrease the effectiveness of evaporative mechanisms of thermal regulation, decreasing the ability of animals to exchange heat with the environment. Body Temperature An increase in body temperature is the result of the imbalance between the heat energy produced by the animal and the amount of heat dissipated. Body temperature is the best indicator to assess the physiological response to high thermal environments in dairy cows, because it is nearly constant under normal conditions. The range for normal body temperatures for dairy cattle vary from 38 C to 39.3 C with an average of 38.6 C as normal (Dukes, 1947). A rise of 1 C or less in body temperature is enough to reduce performance in most livestock species (Kadzere et al., 2002). Even though the use of core body temperature is widely used in animal research, its application is limited for commercial uses due to the difficulty in taking measurements without using invasive sensors. The use of data loggers attached to a continuous intravaginal drug release (CIDR) device is a common practice in research procedures. These devises remain inside the cow s vagina measuring 23

25 and recording core body temperature (CBT) 24h/d as they move throughout all areas of a dairy facility (VanBaale et al., 2006). An alternative is the use of ruminal boluses, which have the capacity to wirelessly transmit the information to a base station. Although these sensors seem to have a wider opportunity in commercial facilities, the accuracy of these sensors can be compromised by feeding and drinking episodes (Ipema et al., 2008, AlZahal et al., 2011). Animal Behavior Heat stress in dairy cattle not only alters the physiology and performance, but it also affects the behavior of animals. According to (Jones and Stallings, 1999), some of the behavioral changes due to heat stress are: increased water intake, seeking shade, reduced feed intake, altered estrous behavior, standing rather than lying down and an increase in respiration behavior. Drinking behavior will increase due to the dehydration of the animal; Garcia (2006) mentioned that water helps the animal to transfer heat from the body to the environment. As the temperature rises from 30 to 35 C, water intake may increase from 21 to 32 gallons per day (Garcia, 2006). Cook et al. (2007) reported an increase from 0.3 to 0.5 h/d in the drinking behavior at a THI of 68 units. Cows are more likely to seek shade during elevated temperature waves. This type of behavior could be preferred by animals instead of drinking or eating behavior (Jones and Stallings, 1999). Reduced feeding behavior is another symptom of heat stress. The animal decreases this behavior to regulate the amount of metabolic heat produced. Feed intake of a dairy cow may be compromised when ambient temperatures are above the comfort zone of the cow (5 to 25 C). When ambient temperatures go beyond 25 C, cows typically demonstrate decreased appetite by reduced dry matter intake (NRC, 2001). 24

26 Perera et al. (1986) reported that eating activity in winter was 5.6 h/d and decreased to 4.2 h/d during summer months. Respiratory behavior was considered the best indicator of climatic heat stress. According to Hahn (1999), an animal with heat stress increases the respiration rate to maintain homeothermy by dissipating excess heat as other ways of heat exchange become insufficient. According to Albright and Arave (1997), resting behavior is decreased with heat stress. Cattle trying to dissipate more body heat tend to stand rather than to lie down and ruminate. Cook et al. (2007) reported a decrease in resting behavior from 10.9 to 7.9 h/d at a THI of 68 units. Hillman et al. (2005) and Allen et al. (2015) reported a change in behavior from resting to standing behavior when the THI reaches 68 and the CBT of cows is higher than 38.9 C. During periods of heat stress, dairy cattle develop a series of changes (anatomical, physiological and behavioral), but most of these changes are the result of the animal s effort to acclimatize with the environment. This process takes place in neurons that are temperature sensitive located throughout the animal s body (Mount, 1979). These peripheral temperature receptors in the skin send information to central temperature receptors in the hypothalamus, in the midbrain, and in the spinal cord. Information from both peripheral and central receptors influences the control of body temperature, centrally mediated in the hypothalamus, which invokes numerous acclimation responses (Mount, 1979). During heat stress, animals decrease feed intake to reduce the metabolic heat produced by fermentation. Due to the decrease in feed intake, the animal looses weight, its body condition decreases, the energy balance is affected, milk composition is compromised and milk production decreases. 25

27 The reproductive performance of cows decrease during thermal stress, the expression of estrous is reduced and fertility decreases in lactating dairy cows. During thermal stress, hormonal changes may be responsible for the changes in estrous expression (Rensis and Scaramuzzi, 2003). Due to the change of thermal conditions, animals change their normal behavior to cope with the environment. As a result of these changes in behavior, animals are more susceptible to laminitis and hoof diseases (Cook et al., 2007). In the United States during periods of heat stress, the diverse physiological, behavioral and nutritional changes that animals go through have a big impact on the profitability of dairy cattle. According to St-Pierre et al. (2003) and Scharf (2014), across the United States heat stress results in an estimated $897 to $1500 million in losses per year in the dairy industry. T H E R M O R E G U L A T O R Y M E C H A N I S M S The equilibrium between the metabolic heat production and the heat dissipation form the cows to the environment regulates the core body temperature of animals (Hansen, 2004). Cattle can exchange heat with their surrounding environment in four ways: conduction, convection, radiation and evaporation. Conduction, convection and radiation engage differences in the temperatures of materials involved and depend on a thermal gradient. As environmental temperature rises above a critical point, the thermal gradient is reduced and heat dissipation via conduction, convection and radiation is less effective. With increasing ambient temperature, evaporative cooling becomes more important than non-evaporative and more heat flow is exchanged by evaporative pathways (Kibler and Brody., 1950, Maia et al., 2005). 26

28 Conduction The definition of conductive heat exchange is the flow of heat between two media or bodies in direct physical contact. The energy in conduction is transmitted through the collision of neighboring molecules. There are three types of media material: gases (air surrounding the animal), solid or liquids. If the media materials are gases or liquids, the conductive heat exchange is affected by convection of those materials with the animal. The flow of heat by conduction is affected by differences in media temperature as well as the thermal conductivity of the material and the area of contact. As an example, cows will tend to stand during hot environments to reduce contact with the ground, and increase their surface area. The net heat gains via air are small due to the low thermal conductivity of air (Yousef, 1985). If air temperature or ground temperature on which the animal is lying is greater than skin temperature the animal will gain heat by conduction, adding to metabolic heat load (Yousef, 1985). On the other hand, if a cool wet area is available, cows will lie in it depending on the conductance of the liquid as well as the temperature difference and magnitude of the area of contact relative to the total surface area (Kadzere et al., 2002). The conductive heat loss of a dairy cow can be described by the following equation was used (Blaxter, 1989): H cond = ka x (T 2 T 1 ) Where: H cond : heat of conduction (W), k = thermal conductivity of the material W/m C, A = area of contact (m2), x = thickness of material (m), T2 = skin temperature ( C), T1 = bed temperature ( C). 27

29 Convection Convection is defined as the exchange of heat with air surrounding the surface of the body. Convection is a thermo regulatory mechanism which could increase or decrease the temperature of the animal s body, depending on the ambient temperature surrounding the animal and the temperature of the animal s surface. If the ambient temperature is lower than the temperature of the surface of the animal, the heat from the surface of the animal is exchanged with the temperature of the air creating a heated layer of air surrounding the surface of the body and thereby cooling the body through the process of convection (Kadzere et al., 2002). Dairy cows in hot environments increase their skin circulation (vasodilatation) to enhance heat loss and prevent a rise in core body temperature. This method is unlikely to be a major method of heat dissipation in cattle because of their large body mass, but convection helps to decrease the temperature on the surface of the body (Berman et al., 1985). The convective heat exchange can be calculated according to the equation (NRC, 1971): H conv = h c A c (T s T air ) Where: H conv = heat of convection (kcal/hr), hc = convection coefficient of heat transfer (kcal/hr m2 / C, Ac = area available for convection (m2), Ts = skin temperature ( C), Tair = air temperature ( C). Radiant Exchanges This method exchanges heat loads by the amount of radiant heat that an animal can receive from solar energy (short wave), and from radiation exchange between the animal and its environment (long wave) (Yousef, 1985). Long waves are characterized by exchanging more heat 28

30 away from the cow, helping the animal to decrease its temperature. According to Cena and Monteith (1975) the amount of heat gain by radiation depends on the temperature of the animal or object, and also on its color and texture. Dark surfaces radiate and absorb more heat than light colored surfaces. Stewart and Brody (1954) reported that the type and color of Brahman s coat decreases its susceptibility to solar radiation compared with Jersey and Holstein cattle. To measure the amount of radiant flux between cows and the environment the following equation is available (NRC, 1971): H rad = A F a F e σ (T 4 s T 4 air ) Where H rad = radiant flux (kcal/hr), F a = shape factor, F e = emissivity factor, σ = radiation constant (4.93x10-8 kcal/hr m2 K 4 ). Evaporation The evaporative heat exchange mechanism varies with the breed of cattle. Evaporation in dairy cattle is considered the most important thermoregulatory mechanism during hot temperature and low relative humidity. During this process 2.43 joules of heat are lost for each gram of water that evaporates (Silanikove, 2000). Cows accomplish the process of evaporation in two ways: through the diffusion of water through the skin (sweating), and by loss of water vapor from the respiratory tract (panting). Water loses from sweating and panting can reach a critical level of dehydration, becoming a threat to thermoregulation and cardiovascular function (Silanikove, 1994). Evaporation effectiveness is compromised when relative humidity or temperature increases. According to (Maia et al., 2005), under natural conditions and at temperatures between 10 and 20 C more than 20% of the heat is lost via sweating. At 30 C, about 85% of the heat is lost through sweating and 15% is lost via panting. 29

31 Sweating Sweating can be considered the most important thermoregulatory mechanism in high temperature environments. Cattle have apocrine sweat glands and they are associated with hair fiber (Yousef, 1985). There are two types of sweating in dairy cattle, the first is insensible sweating of perspiration that leaves the body at all times, unless relative humidity increases. The second type of sweating occurs when ambient temperature rises and it is the principal evaporative cooling mechanism of the cow. According to Collier et al. (2008) there are physical (wind speed, ambient temperature, and relative humidity) and animal factors (sweat gland density and function, hair coat density and thickness, hair length and color, skin color, and regulation of epidermal vascular supply) affecting the efficacy of sweating. While Berman (2005) estimated the maximal sweating rate of cattle between 200 to 300 g/m 2 per hour, Maia et al. (2005) reported a variation in the sweating rate of Holstein cows between 50 to 300 g/m 2 per hour when the relative humidity increased from 30 to 75%. Additionally, the increase in sweating rate leads to an increase in the loss of water and ions like potassium, sodium and chlorine (Mallonee et al., 1985, Kadzere et al., 2002). To predict the heat loss through sweating, Maia et al. (2005) reported the following equation based on the skin temperature of cows. H sweat. = e (t sd33.11) 2.73 Where: H sweat.= heat loss though sweating (Kcal/m 2 ). Panting Panting is the exchange of heat with the environment via respiration. It can be accomplished by two methods, through evaporation of water in the lungs and by increasing the temperature of the inhaled air (Brouk et al., 2001). The amount of heat exchanged via respiration depends on the number of breaths per minute and the temperature and humidity difference between the inhaled and 30

32 exhaled air (Brouk et al., 2001). In the case of high relative humidity, sweating is limited but respiratory cooling may still be effective. One of the consequences of panting during hot climatic conditions is the respiratory alkalosis created by the elevated blood ph. This change in blood ph is the result of a carbonic acid deficit created by carbon dioxide (CO 2 ) expired due to panting (Dale and Brody, 1954). When the cow pants, bicarbonate (HCO 3 ) is converted to carbonic acid, which is broken down to carbon dioxide and water for exhalation and excretion (Dale and Brody, 1954). When panting increases, the loss of CO 2 via pulmonary ventilation reduces the blood concentration of carbonic acid creating a critical imbalance between carbonic acid and bicarbonate, affecting blood ph and resulting in respiratory alkalosis (Benjamin, 1981). In their effort to maintain the blood ph equilibrium during respiratory alkalosis, cows increase urinary excretion of bicarbonate and Na, and increase the renal conservation of K. The decrease in blood bicarbonate concentration results in a decrease in the bicarbonate pool available for buffering the rumen, lowering the ruminal ph of cows during heat stress (Bandaranayaka and Holmes, 1976) and during cooler evening hours creating metabolic acidosis (West, 2003). The heat loss though panting can be calculated based on the following equation (Berman, 2005) H resp = T a T a 2 1P w T a P w Where: H resp = heat loss through respiration (Mcal/day), T a =ambient temperature ( C ), P w = vapor pressure (Kpa). 31

33 E F F E C T S O F H E A T S T R E S S Some of the major responses of animals to thermal stress include changes in nutrition, reproduction, health and decrease in production. Nutrition The main nutritional impact of hot environments on lactating dairy cows is the decrease in feed intake. This reduction in feed intake contributes to control the heat production by ruminal fermentation and metabolic processes (Sanchez et al., 1994). Feed intake begins to decline at ambient temperatures between C (Ames et al., 1981). However, a decrease in feed consumption has been reported on dairy cows at lower temperatures and high relative humidity (Johnson et al., 1963). According to Brobeck (1960), heat stress causes the rostral cooling center of the hypothalamus to stimulate the medial satiety center which inhibits the lateral appetite center, resulting in reduced feed intake and consequently lower milk production. Even though the reduction in feed intake is not completely understood, some authors have reported that the reduction in feed intake is the result of changes in elevated body temperature, the reduction in blood flow and may be related to gut fill (McGuire et al., 1989, Lough et al., 1990, Silanikove, 2000). The decrease in feed intake may induce a negative nitrogen balance in the animal decreasing the protein available for production (Hassan and Roussel, 1975, Higginbotham et al., 1989). During thermal stress, the concentration of volatile fatty acids (VFA) in the rumen decreases (Kelley et al., 1967), due to the decrease of rumen motility (Attebery and Johnson, 1969), and decrease in fiber intake, which may lead to decreased acetate production as well as the acetate and propionate ratio (Weldy et al., 1964). Despite that cows have their best performance on a lower fiber 32

34 diet in hot weather due to the reduced heat production in the digestion of high concentrate rations, ruminal ph is reduced as a consequence of propionate and lactic acid production from increased high energy feed intake (Pitt et al., 1996). The decline of ph often increases the number of cases of cows with rumen acidosis (Collier et al., 2006). During hot conditions dehydration by sweating increases the need of animals to consume water. Water is one of the most important nutrient for dairy cattle due to the correlation with feed intake and milk production. Murphy et al. (1983) mentioned that water may increase by 1.2 kg/ C increase in minimum ambient temperature. The composition of cattle s sweat is high in potassium and low in sodium. It has been estimated that potassium requirements increase by as much as 12% in heat stressed cows (Collier et al., 2006). Reproduction Heat stress has a negative impact on reproduction in dairy cattle and even though many studies have been developed to understand the physiology of the reproductive changes that animals go through during thermal stress, the knowledge is not enough to control and prevent the reproductive effects. Some of the most important consequences in dairy cows reproduction due to heat stress are: decreased expression of estrous behavior, reduced duration of estrus, altered follicular dynamics, decreased oocyte quality for an extended interval after thermal stress is removed, decreased conception rate, early embryonic mortality and decreased pregnancy rate (Kadzere et al., 2002, Rensis and Scaramuzzi, 2003, Thatcher et al., 2010). 33

35 Heat detection (expression of estrous behavior) The reproductive performance on a dairy farm is greatly influenced by the ability to accurately detect heat. Failing to detect heat will contribute to longer calving intervals and a decrease in income (Barr, 1975). During periods of thermal stress, the duration and intensity of behavioral estrus decreases and the incidence of anestrus and silent ovulation are increased, leading to a decreased detection of estrus (Gwazdauskas et al., 1981, Pennington et al., 1985, Thatcher and Collier, 1986). According to Rensis and Scaramuzzi (2003), the reduction in fertility due to poor expression of estrus is a consequence of the reported hormonal change that cows go through during heat stress. Follicular development Follicular dynamics are also affected with elevated environmental temperatures. Wolfenson et al. (1995) in their investigations reported an impaired follicular development, a depression of follicular dominance correlated with a significant increase in large follicles, a decrease in number of medium-sized follicles and the decline of plasma estradiol concentration of heat stressed cows. Despite the fact that the average size of dominant follicles did not differ in the first wave, the decline in size is sooner during thermal stress. On the other hand, the emergence of the preovulatory follicle, or second wave, is sooner, suggesting that the dominant follicle in the second wave may be an aged follicle at ovulation, compromising the quality of the oocyte and follicular steroidogenesis (Howell et al., 1994, Wolfenson et al., 1995, Jordan, 2003). This reduction in oocyte quality lasts for an extended interval of days after thermal stress is removed, suggesting the reason for decreased fertility of dairy cows during cooler autumn months (Roth et al., 2001, Rensis and Scaramuzzi, 2003, Collier et al., 2006). 34