Effects of genetic selection for residual feed intake on behavioral reactivity of castrated male pigs to novel stimuli tests

Abstract

Increasing feed efficiency in swine is important for increasing sustainable food production and profitability for producers; therefore, this is often selected for at breeding. Residual feed intake (RFI) can be used for the genetic selection of pigs for feed efficiency. In our selection project, low-RFI pigs consume less feed for equal weight gain compared to their less efficient, high-RFI counterparts. However, little is known about how feed efficiency influences the pig's behavioral reactivity toward fear-eliciting stimuli. In this study, behavioral reactivity of pigs divergently selected for RFI was evaluated using human approach-(HAT) and novel object tests (NOT). Forty low-RFI (more feed efficient) and 40 high-RFI (less feed efficient) castrated male pigs (barrows; 46.5 ± 8.6 kg) from 8th generation Yorkshire RFI selection lines were randomly selected and evaluated once using HAT and once using NOT over a four week period utilizing a crossover experimental design. Each pig was individually tested within a 4.9 × 2.4 m test arena for 10 min; behavior was evaluated using live and video observations. The test arena floor was divided into four zones; zone 1 being oral, nasal, and/or facial contact with the human (HAT) or orange traffic cone (NOT) and zone 4 being furthest from the human or cone and included the point where the pig entered the arena. During both HAT and NOT, low-RFI pigs crossed fewer zones (P < 0.0001), had fewer head movements (P ≤ 0.02), defecated less frequently (P ≤ 0.03), displayed a shorter duration of freezing (P = 0.05), and froze less frequently (HAT: low-RFI = 4.9 ± 0.65 vs. high-RFI = 7.5 ± 0.96; NOT: low-RFI = 4.7 ± 0.66 vs. high-RFI = 7.2 ± 0.96; P < 0.0001) compared to high-RFI pigs. During HAT, low-RFI pigs also attempted to escape less frequently (low-RFI = 0.4 ± 0.14 vs. high-RFI = 1.1 ± 0.30; P = 0.001) compared to high-RFI pigs. In contrast, compared to the high-RFI pigs, low-RFI pigs took 48 s longer during HAT and 52 s longer during NOT to approach zone 1 (P ≤ 0.04). These results indicate that low-RFI pigs had decreased behavioral reactivity during HAT and NOT compared to high-RFI pigs. This may suggest that reducing a pig's behavioral reactivity is an important component of improving feed efficiency; however, it may have implications for animal handling and facility design. KeywordsSwine Feed Efficiency, Pig, Feed efficiency, Stress, Fear, Human approach, Novel object Disciplines Agriculture | Animal Sciences | Genetics and Genomics | Large or Food Animal and Equine Medicine CommentsThis is the author's version of a work that was accepted for publication in Applied Animal Behaviour Science. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. 21 NOTICE: this is the author's version of a work that was accepted for publication in Applied Animal Behaviour S...

A Hypothesis and Review of the Relationship between Selection for Improved Production Efficiency, Coping Behavior, and Domestication

“… Meunier-Salaün et al (2014) showed that a reduced physical activity in pigs from a line selected for low RFI contributed significantly to their improved feed efficiency. Sadler et al (2014) observed that gilts from a line selected for low RFI spent less time standing, more time sitting, and were less active overall than pigs from a control line, and Colpoys et al (2014) showed that low RFI male pigs were less active than those from a high RFI line. In growing cattle, variation in physical activity was estimated to account for approximately 10% of the variation in RFI ( Herd et al, 2004 ).…”

“…Efficient chickens have been reported to show a lower sensitivity to environmental disturbances than inefficient chickens ( Morrison and Leeson, 1978 ; Katle et al, 1984 ). In pig, Colpoys et al (2014) showed that male pigs from a line selected for low RFI displayed a shorter duration of freezing, froze less frequently, and attempted to escape less frequently than high-RFI pigs ( Colpoys et al, 2014 ). In the same pig lines, Sadler et al (2014) showed that gilts from the low-RFI line tended to have lower baseline cortisol concentrations and were less responsive to an ACTH challenge than gilts from the high-RFI line ( Jenkins et al, 2013 ).…”

The genetic basis and improvement of feed efficiency in lactating Holstein dairy cattle

“…In swine, feed efficient pigs from lines divergently selected for RFI demonstrated fewer arousal and fear behaviors and longer time to approach novel stimuli (Colpoys et al, 2014).…”

The genetic basis of feed efficiency in swine divergently selected for residual feed intake

“…In G8 and G9, pigs from the Low and High RFI lines were subjected to two tests (human approach and novel object tests) to measure behavioral reactivity to novel, feareliciting stimuli (Colpoys et al, 2014;Colpoys et al, 2015). In G8 and for both tests, barrows from the Low RFI line were observed to have fewer head movements (P ≤ 0.02), defecate less frequently (P ≤ 0.03), freeze in place for shorter amounts of time (P = 0.05), freeze less frequently (P < 0.0001), cross fewer zones (test area was split into 4 zones based on distance from novel object, P < 0.0001), and took longer (48 to 52 seconds) to approach the novel object (P ≤ 0.04) compared to High RFI barrows (Colpoys et al, 2014). During the human approach test, Low RFI barrows also tried to escape the area fewer times than High RFI barrows (P = 0.001).…”

“…Selection for lower RFI has also been reported to have limited negative impacts on meat quality , response to fear-eliciting stimuli and welfare (Colpoys et al, 2014;Colpoys et al, 2015), reproduction , and immune response (Mpetile et al, 2015), including response to porcine reproductive and respiratory virus (Dunkelberger et al, 2015). Additionally, various metabolic mechanisms have been found to contribute to the increased efficiency of the Low RFI line within the ISU selection project, including decreased degradation of protein , less reactive oxygen species production by mitochondrion in muscle and liver tissues , and increased energy and nutrient digestibility .…”