7
Heat stress has negative effects on sow productivity and reproductive performance. It has multiple impacts on animal metabolism and physiology. These include: increased body core temperature, increased blood flow to the skin to dissipate radiant heat, increased respiration rates to remove the excess heat, and reduced feed intake as a strategy to reduce heat production. Consequently, sows under heat stress have reduced milk production and litter weight gain. Sows with excessive body protein loss during lactation have increased days from weaning to estrus and reduced conception rates.
During the last three decades, continuous selection for increased litter size and milk production has increased the heat production of sows and reduced their upper critical temperature. This selection has also resulted in decreased piglet birth weights and less body energy reserves at birth, requiring greater farrowing room temperatures and the use of heat pads or heat lamps to provide local heat for piglets.
The Animal Sciences and Agricultural Biological Engineering Departments at Purdue University and the USDA-ARS Livestock Behavior Research Unit have been working together for the last three years to develop a cooling pad able to efficiently remove excess of heat from lactating sows.
Floor cooling is based on the conduction of heat from the source (the animal) to a sink (chilled water running through the pipes), while the animal is lying down. Aluminum and copper are able to effectively transfer heat between the two temperatures. The cooling pad has been built with a heavy-duty aluminum plate in the surface, high-density polyethylene base and copper water pipes attached to the aluminum plate (Figure 1). From these initial tests, pad dimensions were enlarged, and the range of constant flow rates, time between flushes and desired upper set temperatures for different environmental conditions were refined.
The refined cooling pad designs have been used in sow lactation trials, shown in Figure 2. Sows with no cooling spent more time in a “dog like posture” to increase body heat dissipation to the environment, less time on the feeder and less time milking in comparison to the sows with an active cooling. After 80 min of cooling, sows with active cooling had lower respiration rates (45 versus 122 breaths/min), heart rates (100 versus 119 beats/min), vaginal temperature (39.2 versus 40.1ºC), rectal temperature (39.0 versus 40.0ºC) and skin temperature (38.6 versus 39.4 ºC) than sows with no active cooling, respectively. The heat removal rate was three to four times greater than previous cooling pad designs made of concrete and steel pipes, covering entire floor sections.
The effectiveness of the sow cooling pads for an entire lactation was evaluated under mild and moderate heat stress conditions. The moderate heat stress room was targeted to achieve 32ºC from 0800-1600 h and 27ºC for the rest of the 24-hour day. The mild heat stress room was targeted to achieve 27ºC and 22ºC for the same periods, respectively. Yorkshire-Landrace sows were blocked by parity and BW, and assigned to two farrowing rooms which differed only in environmental temperature. Each sow was provided an eight–row cooling pad. Sows received either a constant cool water flow of 0.00 L/min (CONTROL, n = 9), 0.25 L/min (LOW, n = 12), or 0.50 (HIGH, n = 10) L/min. Water inlet and outlet temperatures and flow rates were recorded to estimate heat removal. Respiration rates (RR), rectal temperatures (RT) and skin temperatures (ST) were recorded daily (0700 and 1500 h) from the second day in the farrowing room to weaning at a mean age of 19 days. The sow cooling pads reduced the measures of heat stress. The LOW flow rate was adequate for the mild heat stress room and the HIGH flow rate was needed for the moderate heat stress rooms. Figures 3 and 4 show the effect of the Purdue hog cooling pads on RR, while Figures 5 and 6 show the effect on RT.
| Variable | Pad Treatment | Mild – 700 h | Moderate – 700 h | Mild – 1500 h | Moderate – 1500 h |
| Respiration rate | CONTROL | 23 | 56 | 41 | 89 |
| LOW | 21 | 24 | 29 | 41 | |
| HIGH | 18 | 20 | 24 | 27 | |
| Skin temp | CONTROL | 35.4 | 37.3 | 37.2 | 37.3 |
| LOW | 34.4 | 36.5 | 36.6 | 36.5 | |
| HIGH | 33.7 | 36.2 | 36.5 | 36.2 | |
| Rectal temp | CONTROL | 38.8 | 39.0 | 39.2 | 39.6 |
| LOW | 38.8 | 38.8 | 39.1 | 39.0 | |
| HIGH | 38.8 | 38.8 | 39.1 | 39.0 |
Acknowledgements
This research was funded by Purdue University as part of AgSEED Crossroads funding to support Indiana’s Agriculture and Rural Development and by USDA-ARS Project 5020-32000-013-00-D – Protecting the Welfare of Food Producing Animals. The authors also would like to thank Daniel Madson and Aaron Doke for their work in the building and refinement of the cooling pad devices.
