Physiology of heat stress in cattle and sheep Project number LIVE.209 Report prepared for MLA and LiveCorp by: Anne Barnesa, David Beattya, Eric Taylora, Catherine Stockmana, Shane Maloneyb and Michael McCarthyc aSchool

of Veterinary and Biomedical Sciences,

Murdoch University, bSchool of Biomedical and Chemical Science, University of Western Australia, cProfessional Agricultural Services Meat & Livestock Australia Limited ABN: 39 081 678 364 ISBN 1 74036 524 0

March 2004 MLA and LiveCorp make no representation as to the accuracy of any information or advice contained in this document and excludes all liability, whether in contract, tort (including negligence or breach of statutory duty) or otherwise as a result of reliance by any person on such information or advice. © Meat and Livestock Australia (2004)

The livestock export program is jointly funded by the livestock exporters and producers of Australia

Physiology of heat stress in cattle and sheep

Table of Contents Abstract .........................................................................................................................................................3 Executive Summary ......................................................................................................................................3 1 Main Research Report ...............................................................................................................................5 1.1 Background..........................................................................................................................................5 1.2 Heat stress of exported animals ..........................................................................................................5 1.3 Physiological responses to heat stress ...............................................................................................6 1.4 Implications for therapy of transported animals...................................................................................7 2 Experimental Methods................................................................................................................................9 2.1 Climate controlled rooms .....................................................................................................................9 2.1.1 Room conditions .........................................................................................................................10 2.2 Measurements and monitoring ..........................................................................................................10 2.2.1 Core temperature ........................................................................................................................10 3 Experimental schedule .............................................................................................................................11 3.1 The Physiology of Heat Stress in Bos taurus and Bos indicus: Experiments 1, 2 and 3 ..................11 3.1.1 Materials and Methods................................................................................................................11 3.1.1.1 Animals.................................................................................................................................11 3.1.1.2 Preparation ...........................................................................................................................12 3.1.1.3 Feed and water.....................................................................................................................12 3.1.1.4 Room conditions...................................................................................................................12 3.1.1.5 Body weight ..........................................................................................................................12 3.1.1.6 Monitoring.............................................................................................................................12 3.1.2 Results ........................................................................................................................................13 3.1.2.1 Room conditions...................................................................................................................13 3.1.2.2 Clinical signs.........................................................................................................................13 3.1.2.3 Core and rectal temperatures...............................................................................................13 3.1.2.4 Feed and water intake, body weight.....................................................................................14 3.1.2.5 Respiratory rate, blood gas ..................................................................................................14 3.1.2.6 Electrolytes ...........................................................................................................................14 3.1.3 Discussion and proposed electrolyte supplement ......................................................................15 3.2 The Efficacy of an Electrolyte Replacement Therapy : Experiments 4 and 6 ...................................16 3.2.1 Materials and Methods................................................................................................................16 3.2.1.1 Animals.................................................................................................................................16 3.2.1.2 Preparation ...........................................................................................................................16 3.2.1.3 Feed and water.....................................................................................................................16 3.2.1.4 Measurements......................................................................................................................16 3.2.1.5 Room conditions...................................................................................................................16 3.2.2 Results ........................................................................................................................................17 3.2.2.1 Room conditions...................................................................................................................17 3.2.2.2 Clinical signs.........................................................................................................................17 3.2.2.3 Core and rectal temperature ................................................................................................17 3.2.2.4 Feed and water intake..........................................................................................................18 3.2.2.5 Body weight ..........................................................................................................................18 3.2.2.6 Respiratory rate, blood gas ..................................................................................................18 3.2.2.7 Electrolytes ...........................................................................................................................18 3.3 Shipboard trial of electrolyte supplement : Experiment 7 ..................................................................19 3.3.1 Background .................................................................................................................................19 3.3.2 Materials and Methods................................................................................................................19 3.3.2.1 Animals.................................................................................................................................19 3.3.2.2 Pen assignment....................................................................................................................19 3.3.2.3 Feed and water.....................................................................................................................19 3.3.2.4 Measurements......................................................................................................................19 3.3.3 Results ........................................................................................................................................20 3.3.3.1 Environmental conditions .....................................................................................................20 3.3.3.2 Clinical signs and observations ............................................................................................20 3.3.3.3 Water and feed intake ..........................................................................................................21 3.3.3.4 Body weight ..........................................................................................................................21 3.3.3.5 Urine and bedding ................................................................................................................21 1

Physiology of heat stress in cattle and sheep

3.3.4 Discussion...................................................................................................................................21 3.4 The physiology of heat stress in sheep : Experiment 5.....................................................................22 3.4.1 Materials and Methods................................................................................................................22 3.4.1.1 Animals.................................................................................................................................22 3.4.1.2 Preparation ...........................................................................................................................22 3.4.1.3 Feed and water.....................................................................................................................22 3.4.1.4 Room conditions...................................................................................................................22 3.4.1.5 Measurements......................................................................................................................22 3.4.2 Results ........................................................................................................................................23 3.4.2.1 Room Conditions ..................................................................................................................23 3.4.2.2 Core and rectal temperature ................................................................................................23 3.4.2.3 Clinical signs.........................................................................................................................24 3.4.2.4 Feed and water intake..........................................................................................................24 3.4.2.5 Respiratory rate, blood gas ..................................................................................................24 3.4.2.6 Electrolytes ...........................................................................................................................24 3.4.3 Discussion...................................................................................................................................25 3.5 Feeding experiment, two different pelleted feeds for cattle : Experiment 8 ......................................25 3.5.1 Background .................................................................................................................................25 3.5.2 Materials and Methods................................................................................................................26 3.5.2.1 Animals and preparation ......................................................................................................26 3.5.2.2 Feed .....................................................................................................................................26 3.5.2.3 Measurements......................................................................................................................26 3.5.3 Results ........................................................................................................................................26 3.5.3.1 Room conditions...................................................................................................................26 3.5.3.2 Feed and water intake, body weight.....................................................................................26 3.5.3.3 Temperature – rectal, core, rumen.......................................................................................26 3.5.3.4 Physical parameters .............................................................................................................27 3.5.4 Discussion...................................................................................................................................27 4 Success in achieving objectives...............................................................................................................28 5 Impact on Meat and Livestock Industry....................................................................................................29 6 Conclusions and recommendations .........................................................................................................29 7 Bibliography..............................................................................................................................................31 8 Appendices...............................................................................................................................................33 Appendix 1........................................................................................................................................33 Appendix 2........................................................................................................................................33 Appendix 3........................................................................................................................................34 Appendix 4........................................................................................................................................35

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Physiology of heat stress in cattle and sheep

ABSTRACT The physiology of clinical heat stress in cattle and sheep was defined under experimental animal house conditions. Changes in body temperature, feed and water intake, respiratory and heart rates, and acidbase and electrolyte balance were measured. This work has helped define the heat stress threshold for Bos taurus and Bos indicus heifers, Merino wethers and Awassi rams. An electrolyte supplement was proposed on the basis of measured changes in the cattle, and tested with positive results on urine pH indicating improved buffering capacity, and a body weight advantage. On the basis of these results, it is recommended that Bos taurus receive appropriate electrolyte supplements in the water when shipped on long haul voyages when they are exposed to high heat and humidity, for potential health and economic benefits. Future work could further clarify the nature and repeatability of these benefits.

EXECUTIVE SUMMARY Experiments were conducted to define the physiology of heat stress in cattle and sheep considering particularly the physiological and biochemical changes that affect electrolyte balance in the animals, with a view to formulating appropriate supplementation of electrolytes. An experimental animal house facility with specifically modified climate controlled rooms was used to subject animals to sustained periods of high heat and humidity, as experienced by livestock exported by ship on long haul voyages to northern hemisphere destinations during the northern summer. Three baseline experiments were conducted with six cattle each (two with Bos taurus and one with Bos indicus) and one experiment was conducted with 18 sheep (12 Merino wethers and six Awassi rams). These baseline experiments indicated the wet bulb temperatures at which the cattle were no longer able to maintain their normal body temperature (“heat stress threshold”). These data can be used in predictive models for heat stress management. The Bos taurus had a more pronounced panting response at lower wet bulb temperatures compared to the Bos indicus, which led to greater alterations in acid-base balance. However, once the Bos indicus passed their heat stress threshold, the responses and physiological changes were essentially the same as those measured in the Bos taurus. There was a marked reduction in feed intake by the Bos taurus once their body temperature rose to the stage where the experimental animals were eating almost nothing. This severe inappetence has not been previously described, but has serious production and economic implications. The water intake of these heat stressed animals was very high, in some cases over 15% of body weight per day, indicating that animals will require good access to water at all times when exposed to hot, humid conditions. From these intensive experiments, the alterations in electrolytes could be determined for animals subject to clinical heat stress, and a supplement was designed to replace the deficits. The electrolyte supplement was delivered in the drinking water, containing 1.8g/L sodium bicarbonate and 3.5g/L potassium chloride, and it was tested in three experiments on Bos taurus, two within the climate controlled rooms (12 animals in total), and one experiment on a commercial ship with 80 animals. All three experiments showed a similar result: that compared to control animals, supplemented animals drank more, had more alkaline urine, and had a weight advantage at the end of the experiment. For cattle experiencing clinical heat stress in the climate controlled rooms, treated animals lost 5.1% of their starting body weight, while control animals lost 7.9% of starting body weight. The cattle on the commercial shipment did not show clinical heat stress, and the treated animals gained 2.9 ± 1.7 % more weight than the control animals (P