Modeling the effect of reflective film calf hutch covers on reducing heat loss

Abstract Text: Many dairy operations are located in environments subject to periods of cold weather and calf hutches are popular method of protecting the calves from environmental extremes. This study determined if a reflective film could be useful in moderating the rate of heat loss from calves housed in polyethylene hutches during cold weather. An engineering approach was used in which rate of heat loss was modeled, using 38 liter water-filled steel drums covered by a yearling cow hide. Hides were collected the day before and cut to fit the drums so no metal was exposed. Duplicate loggers mounted in the center of each drum recorded temperature at 5-min intervals during each experiment. Two agitators circulated the water inside each drum. The reflective film (cover) consisted of aluminized 2.5 mil low-density polyethylene, full metal on olive color, with flat black spray paint covering the olive. The covers were 1.8 x 3 m finished size with the aluminized side facing the hutch and paint facing outward. Two of four hutches were either un-covered or had covers across the top and sides of the hutch, leaving the front, and back exposed. Water temperature ranged from 43.3°C to 32.2°C and there was an average 24 data points per experiment. Data loggers in each drum were averaged at each 5 min interval and averaged within treatments, and quadratic regression was used to predict rate of heat loss. During the cold night experiment, when ambient temperature was declining (mean temperature -13.6°C), the mean rate of temperature loss was -0.21°C per 5-min interval in the covered and -0.25°C in the uncovered (R²=0.99). During the daytime trial when the sun was shining and ambient temperature was rising (mean 14.3°C), mean rate of heat loss was -0.15°C per 5-min interval in the covered and -0.11°C in the uncovered (R²=0.99). Reflective film does appear to have potential to reduce the rate of heat loss when calves would be most at risk, cold nights. When the sun was shining on the hutches during mid-day, the uncovered warmed up more and hence, reduced the rate of heat loss when compared to the covered. Even with a black surface toward the sun, the covers did inhibit heating of the hutches, but calves would be able to move into the sun during those periods.  Improved materials and designs for hutch covers are presently being developed.

Keywords: dairy calf, cold stress, hutch