Bio-Energetics of Animals and Novel Ways of Cooling High-Producing Dairy Cows during Heat Stress

All processes of life -all physiological events -require energy expenditure. A climatic energy demand (food and water requirements) of an endotherm is a coupled heat and mass transfer problem and can be predicted using an energy balance model. To survive, animals need an environment that allows them to dispose of their excess metabolic heat. Thus, heat stress occurs when high ambient temperature or humidity leads to the animal having difficulty disposing of their metabolic heat. As body temperature begins to rise, a heat-stressed cow will breathe rapidly and start panting and sweating, all of which require additional energy expenditure and increase the total heat load the cow must dispense. Cows under heat stress will also have reduced feed intake and reduced milk output, with milk production falling in response to less incoming energy from feed consumption as well as other physiological factors. Heat stress tends to disproportionately affect higher producing cows since a higher producing cow will have higher metabolic heat production. Effects of heat stress can linger for several months as chronic heat stress leads to compromised immunity and fertility, and even a relatively short exposure to severe heat stress may damage a cow's milk production until the next time she freshens. The US dairy industry, a $37 billion industry in 2012, already loses more than $1.5 billion/yr. to the effects of heat stress. Climate change could exacerbate these losses. Current methods to alleviate heat stress are usually based on using fans to create forced convection as well as using misters or sprinklers to create evaporation. These methods of cooling cows take a lot of water and energy, and both fans and misters are less effective under humid conditions. High water consumption is especially a problem in the Western US, where water is scarce. Furthermore, use of water to cool cows leads to hygiene and disease concerns, which limits evaporative cooling applications near bedding areas. Increasing energy costs have also led to less return on investment for cooling systems that require significant energy use. Conductive cooling is an alternative animal cooling strategy that uses cold water to cool the beds that cows lie on, and thus conductively cool the cows. In this closed-loop system, all of the water is recirculated and re-cooled so no water is lost. Energy to run the system can potentially be recovered waste energy as well, making the system completely sustainable. Our results show that conductive cooling is very effective in relieving heat stress and increasing milk production as well as decreasing respiration rates and rectal temperatures. Cows conductively cooled also tend to spend more time lying down, and time spent lying down is positively correlated with milk production. This presentation will discuss bioenergetics (energy budget) of animals and novel ways of cooling cows in thermally stressful environments.