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Mitigating heat stress in dairy cattle via conductive cooling
The US dairy industry, a $37 billion per year industry (2012), loses more than $1.5 billion in a typical year to the effects of heat stress on lactating dairy cattle. High ambient temperature or humidity leads to cows having trouble disposing of metabolic heat, causing an increase in respiration rates and body temperature along with a decrease in milk production. Our objective was to design, build, and test a conductive cooling system for relieving heat stress in lactating dairy cattle.
Our study used 8 1stlactation Holstein cows producing 34.4 +/- 3.7 kg/d of milk at 166 +/- 28 d in milk. Cows were milked twice per day at 06:00 and 18:00. Cows were exposed to heat stress in a climate controlled room from 09:30 until 17:30 daily but moved to well-ventilated pens at night. During the time the heat stress occurred, each of the 4 experimental cows was conductively cooled by pumping chilled water through a waterbed in her stall, but the 4 control cows were given no heat stress relief. The cooling system was tested at two different heat stress levels (THI = 81.3 +/- 0.7 and THI = 79.7 +/- 0.8) as well as two different chilled water temperatures (4.5 °C and 10 °C) for a total of 4 treatments. Each treatment lasted for 7 days. Milk production, feed consumption, and rectal temperature were recorded twice daily. Respiration rates and skin temperatures were measured 5 times per day. Data loggers recorded the cooling water temperature, the ambient temperature and humidity, and the vaginal temperature as well as standing and lying behavior of each cow.
Results from the higher heat stress/lower water temperature treatment show that conductive cooling removed ~850 Watts (about 60% of the total metabolic heat from a lactating Holstein cow) whenever the cow was lying down. This significantly reduced the effects of the heat stress, with cooled cows producing 35.5 +/- 2.0 kg/d of milk while control cows produced 26.2 +/- 4.7 kg/d of milk (p = 0.024). Rectal temperatures for cooled cows were 39.2 +/- 0.6 °C while control cows were 40.3 +/- 0.6 °C (p = 0.039). Respiration rates were 64 +/- 10 breaths/min for cooled cows compared to 84 +/- 10 for control cows (p = 0.033). Such results indicate that conductive cooling shows promise for mitigating heat stress in lactating dairy cattle.
Keywords: Conductive cooling, heat stress, milk production