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Increase metabolic rate Increased feed intake Increased insulation hair, wool, feathers, fat What happens at the warm and heat Invoke mechanisms to dissipate heat – Increase blood flow through vacillation – Reduce feed intake – Change posture, lie in shade Beyond warm zone to heat stress – Evaporate heat loss sweating and panting – Animals of higher metabolic needs due to size and production are disadvantaged and vice versa, because metabolism generates heat (pigs example) Continued heat stress (results in reduced efficiency) Low daily gains due to poor feed conversion Low reproduction because of embryonic deaths, poor sperm quality and reduced libido Reduced activity hence heat retention!
Increased consumption of water Increased urination Increased excretion Heat balance equation Integrates the different processes of heat gain & loss: = -??He +Home Has = heat storage in body, + for Db increase, – for Db decrease Hrs = net irradiative exchange, + for heat gain, – for heat loss HCI = conducive & connective exchange, + for heat gain, – for heat loss He = evaporate exchange, – as unidirectional, heat loss only ; Home = metabolic heat production, + as unidirectional, heat gain only ; Triangulation means minimizing change of Has, by altering the other four changes. Consequences of heat stress ; Heat Stress is a major source of production losses in the dairy and beef industry, billions have been lost all over the world.
In temperate countries heavy losses are in summer. ; Heat waves are also very devastating. ; Dairy cattle have become more heat sensitive as average milk yield has increased ; Global warming is a threat to livestock production (green house gases) Direct effects include altered production, reproduction and resistance or susceptibility to disease. ; Indirect effects include changes in pathogen and pest populations as well as animal behavior, that can cause increases in exposure to pathogens and pests, such as lying in muddy, wet areas to cool themselves when heat-stressed. Hanger! ; Finally, as we have improved our dairy breeds and their management milk yield has steadily risen.