The effects of thermal efficiency index on growth performance, feeding pattern, and carcass quality in grow-finish pigs

Abstract

The thermal Efficiency Index (TEI) estimated through infrared thermography has been used to predict metabolic efficiency in pigs. This study evaluated the effect of thermal efficiency on growth performance, feed efficiency, feeding pattern, and carcass characteristics of grow-finish pigs. It was hypothesized that high TEI pigs lose more energy as radiant heat and leaving less energy available for growth, whereas low TEI pigs lose less energy as heat, allowing more energy to be partitioned toward growth. Eight-week-old pigs (N = 176) were enrolled in a 12-week experiment, with 88 pigs per block (replicated once over time) under a randomized complete block design. At nursery exit, pigs were scanned using an infrared camera and mean dorsal surface temperature was recorded and used to calculate TEI (dorsal temperature divided by metabolic body weight, BW^0.75). In each block, 44 pigs were selected into high (HIGH; TEI: 4.29 ± 0.39; body weight 15.62 ± 1.43kg) and low (LOW; TEI: 3.48 ± 0.35; body weight 20.28 ± 1.82kg) TEI categories, and group housed separately (11 pigs/ pen). The study was partitioned into three phases: Grower (10-12 weeks), Finisher 1 (12-16 weeks), and Finisher 2 (16-20 weeks). Growth performance, feed intake, and feeding patterns were recorded for each pig individually and calculated by phase. LOW pigs showed greater average daily gain (p = 0.01) and final body weight (p < 0.01) than HIGH pigs. Feed efficiency indices did not differ during early phases but in Finisher 2, LOW pigs had higher residual intake and gain (p < 0.003) and tended to have lower residual feed intake (p = 0.076). For feeding patterns, LOW pigs showed fewer visits, longer feeding duration, and higher feeding rates (p < 0.001). Carcass backfat was also greater in LOW pigs (p = 0.018). Collectively, these findings demonstrate that TEI is closely related to growth efficiency that reflects differences in energy retention and heat energy dissipation and the advantage in feed efficiency is more pronounced in the late finishing phase.