Beef Species Symposium II: Handling Heat in Beef Cattle Production- Sponsored by ARPAS
By: Meghan Thorndyke
Dr. Robert Rhodes from Virginia Tech was the first speaker. His topic, the physiology of heat stress, tackled the indirect and direct animal health mechanisms for dealing with heat stress. His group found that metabolic flexibility decreases during heat stress indicating fatty acids are unable to blunt carbohydrate use. As well that fatty acid oxidation and maximal mitochondrial respiration are impaired during heat stress and that muscle cells in culture retain in vivo phenotype. In conclusion Dr. Rhodes addressed that heat stressed animals fail to maintain metabolic flexibility limiting fuel substrates switch and use which may begin to explain the direct effects of heat on production. He indicated that one possibility may relate to impaired cellular metabolism and mitochondrial dysfunction as exhibited by skeletal muscle.
Dr. Frank Mitloehner from UC Davis discussed the impact of heat stress on feedlot operations with an emphasis on design and management to reduce its impact. Dr. Mitloehner talked about a few studies conducted his group conducted comparing heat stress mitigation techniques and the influence these strategies had on carcass characteristics, health, and economical impact. In conclusion the performance losses were predominantly a result of decreased DMI, but when provided performance levels can be maintained during heat stress. They also found that the yearly occurring implement of shade structures provided on cattle performance is equaled to $18/head/ yr, and dome shade structures had the highest net economic returns as well as the carbon footprint decreases with shade and fans because the animals reached a final weights sooner because animals performance wasn’t inhibited by heat stress.
Finally, Dr. Jenny Jennings from the Texas AM AgriLife Research who wrapped up the symposium discussed the impact of heat stress on feedlot operations; nutritional and breeding options to reduce its impact. She reviewed old and new research on the topics and further implementation of the research. The first study she reviewed was strategies to reduce feedlot cattle heat stress effects on tympanic temperature indicating that switching from a morning to afternoon feeding could be beneficial in reducing body temperature, and that restricting feeding regimens led to a decrease in body temperature. The effects of diet type and metabolizable energy intake on tympanic temperature of steers fed during summer and winter seasons. For the implementation of this study the response for unshaded angus steers was approximately 15% reduction. The return to pre-heat stress intakes took between zero and six days although some of the delay was management induces. Panting score works well for assessing heat tolerance of Bos Indicus, Bos Taurus, and crossed cattle over a range of geographical locations and climate conditions. The spot measure HLI is a good indicator of heat load can be used in conjunction with PSD to assess heat tolerance. Inc conclusion changing bunk management, time feeding and dietary energy density can all be considered when trying to manage heat stress.