Effect of floor cooling on behavior and heart rate of late lactation sows under acute heat stress

Authors: PAROIS, SEVERINE - Institut National De La Recherche Agronomique (INRA); CABEZÓN, FRANCISCO - Purdue University; SCHINCKEL, ALLAN - Purdue University; Johnson, Jay; STWALLEY, ROBERT - Purdue University; Marchant, Jeremy

Submitted to: Frontiers in Veterinary Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/28/2018
Publication Date: 9/21/2018
Citation: Parois, S.P., Cabezón, F., Schinckel, A.P., Johnson, J.S., Stwalley, R.M., Marchant Forde, J.N. 2018. Effect of floor cooling on behavior and heart rate of late lactation sows under acute heat stress. Frontiers in Veterinary Science. 5(223):1-8. DOI: 10.3389/fvets.2018.00223.
DOI: https://doi.org/10.3389/fvets.2018.00223

Interpretive Summary: Many sows in the United States are subject to heat stress in the hot, humid summers, especially during lactation when their own heat production is maximal. Exposure to heat stress is a welfare issue for the sows and their piglets and an economic issue for the farmers, with reduced feed intake, lower milk production and poorer piglet growth rate among many consequences. Many farms use evaporative cooling systems that add moisture to a humid environment, decreasing effectiveness and hygiene. Another option may be conductive cooling, which can be sow-focused, preventing chilling the piglets. The objectives of our study were to evaluate the impact of a water-cooled floor pad on sows’ behavioral and physiological responses to acute heat stress. We found that cooled sows were more restful, with fewer posture changes and less time spent drinker-pressing, standing and sitting than sows without cooling pads. Cooled sows also spent more time lying, especially lying on their side and their heart rates were lower. These results indicate that cooled sows were better able to cope with the acute heat stress and were more comfortable than the non-cooled sows, thereby improving their welfare. Longer duration studies will be needed to demonstrate an impact on production and economics.

Technical Abstract: Much U.S. swine production is in Köppen climate types classified as ‘hot-summer humid continental’ and ‘humid subtropical'. As a result, farrowing sows are often exposed to temperatures above their upper critical temperature. This heat stress (HS) can affect sow welfare and productivity and have a negative economic impact.The study objective was to evaluate the impact of a cooling pad on sows’ behavioral and heart rate responses to acute HS. Treatments were randomly allotted to ten multiparous sows to receive a constant cool water flow of 0.00 (CONTROL, n=4), 0.25 (LOW, n=2), 0.55 (MEDIUM, n=2) or 0.85 (HIGH, n=2) l/min for 100 min and replicated eight times, switching treatments so that each sow was exposed to each treatment. The cooling was initiated 1 hour after the room reached 35°C for 100 min. Eating, drinking and nursing behaviors, postures and heart rate were recorded before heating (Period 1), prior to cooling (Period 2), and during cooling (Period 3). There were no differences between LOW, MEDIUM and HIGH flow rates for any periods on all behavioral and heart rate traits, so data were pooled (COOLED). There were no differences in any of the measures during Periods 1 and 2, except for the ratio of short term to long term heart rate variability (SD1:SD2) with higher values for CONTROL than COOLED sows in Period 2. During Period 3, CONTROL sows changed postures more frequently (11.5 ±1.6 vs 5.1 ±1.6 changes per hour), spent more time drinker-pressing/drinking (4.4 ±0.5 vs 1.4 ±0.4% of time), standing (6.6 ±1.7 vs 3.8 ±1.6% of time), sitting (10.0 ±1.2 vs 4.0 ±1.1), less time lying (83.0 ±1.8 vs 92.0 ±1.7% of time), especially lying laterally (62.0 ±5.6 vs 75.0 ±5.3% of time), than sows in all three cooling treatments (all P < 0.001). Heart rate during Period 3 was lower for COOLED sows compared to the CONTROL sows (100.2 ±3.4 vs 119.0 ±4.0 beat per min, P<0.001). Sows response to increased thermal load can be effectively reduced using water-cooled cooling pads, thereby improving sow comfort and welfare. The beneficial effects on behavior are noticeable from the lowest flow rate.