Thermal comfort evaluation of three genetic lines of nursery pigs using thermal images

Authors: BROWN-BRANDL, TAMI - University Of Nebraska; HAYES, MORGAN - University Of Kentucky; Rohrer, Gary; EIGENBERG, ROGER - Retired ARS Employee

Submitted to: Biosystems Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2022
Publication Date: 11/24/2022
Citation: Brown-Brandl, T.M., Hayes, M.D., Rohrer, G.A., Eigenberg, R.A. 2022. Thermal comfort evaluation of three genetic lines of nursery pigs using thermal images. Biosystems Engineering. 225:1-12. https://doi.org/10.1016/j.biosystemseng.2022.11.002.
DOI: https://doi.org/10.1016/j.biosystemseng.2022.11.002

Interpretive Summary: Understanding the thermal comfort zone of a pig is critical to maximize production. The standards that are currently used were determined approximately 40 years ago. Previous research found that swine heat production is 6 – 41% higher in modern pigs than documented in engineering standards. This higher heat production indicates the ideal temperature for pigs likely changed due to selection for increased growth and muscle mass. Therefore, a study was conducted using modern pig genetics to determine the thermal comfort zone for nursery aged pigs by evaluating skin temperature and animal behavior. A total of 180 nursery pigs sired by Duroc, Landrace, or Yorkshire sires were acutely exposed (~6-hours) to each of seven temperatures (20°C, 22.5°C, 25°C, 27.5°C, 30°C, 32.5°C, 35°C) over a 13-day period. Measurements were recorded on pen (10 pens of 18 pigs each) and individual pig (12 pigs/sire-breed – 36 total) images captured at each temperature. In addition, time-lapse images were taken every 5-minutes to document animal behavior. Average body surface temperatures were evaluated using an oval drawn over the center of the trunk of the pig. Temperatures along the midline of the ear were also evaluated for each pig as the second region of interest. Changes in the average body surface temperature were used to identify the thermal comfort zone for pigs sired by each breed. Threshold temperatures were determined to be 26.1°C for Duroc sired pigs, 27.9°C for Yorkshire sired pigs and 28.8°C for Landrace sired pigs. Animal behavior data supported the skin temperature analyses indicating pigs were most comfortable at approximately 27.5°C. Based on the results of this study the standard set point of 27.5°C is appropriate for nursery pigs; however, the temperature could be lowered slightly for Duroc-sired pigs.

Technical Abstract: Modern swine heat production is 6-41% higher than documented in engineering standards. This higher heat production indicates that the ideal thermal neutral temperature may have changed. Thermal comfort is critical to maximise production and well-being of modern swine. Measurements of posture, skin temperature, and ear temperature profile changes with air temperature were evaluated for three modern pig genetic lines. A total 180 nursery pigs (30 animal per sire - 3 breeds: Duroc, Landrace, and Yorkshire) were acutely exposed to each of seven temperatures (20°C, 22.5°C, 25°C, 27.5°C, 30°C, 32.5°C, 35°C) over a 13-day period. Time-lapse images were taken every 5-min of 10 pens with 18 pigs each to document posture and floor space. Individual thermal images were captured on 12 pigs/sire line - 36 total. Changes in the average trunk surface temperature were fit to two separate linear regression equations - above and below the standard temperature of 27.5°C. The two regression lines were solved simultaneously to estimate the thermoneutral temperature. The threshold temperatures were determined to be 26.1°C for Duroc sired pigs, 27.9°C for Yorkshire sired pigs and 28.8°C for Landrace sired pigs. Based on the results of this study the standard set point of 27.5°C is appropriate for nursery pigs.