Application of extended feed withdrawal time preslaughter and its effects on animal welfare and carcass and meat quality of enriched-housed pigs
Introduction
Over the last years, the Canadian pork chain has undertaken numerous initiatives to improve the welfare of slaughter pigs by improving the farm design and the handling practices preslaughter. These initiatives resulted in lower total transport losses (dead on arrival and non-ambulatory pigs) on arrival at the plant, and reduced proportion of condemned carcasses at slaughter (Correa, 2011). However, these good results have not been always associated with improved pork quality. The analysis of meat quality data obtained on 2700 loins assessed in 11 trials carried out at the major Canadian slaughter plants over the last 10 years revealed, in fact, a high proportion of either pale (47%) or pale, soft and exudative (PSE; 25%) pork (Faucitano & Lambooij, 2019). A recent study (Rocha, Velarde, Dalmau, Saucier, & Faucitano, 2016) reported a greater proportion of red, soft and exudative (RSE), and PSE loins in pigs raised in enriched housing conditions (lower stocking density, straw-bedding, and frequent human contact) compared with those conventionally grown and finished (15 vs. 7%, and 27 vs. 14%, respectively). The greater post-mortem acidification and exudation rate observed in loins from pigs raised in enriched conditions has been explained by the higher residual glycogen level or glycolytic potential in the muscle at slaughter in some studies (Chevillon et al., 2005; Foury et al., 2005). This muscle metabolic status at slaughter may result from the reduced consumption of muscle energy reserves prior to slaughter due to the greater fitness or resilience to physical stress as pigs raised in enriched housing conditions have more opportunity for physical activity and are more accustomed to human handling (Chevillon et al., 2005; Foury et al., 2005; Geverink, de Jong, Lambooij, Blokhuis, & Wiegant, 1999; Tönepöhl et al., 2012) and social interactions (De Jong et al., 2000; Faucitano, 2018; Klont et al., 2001).
Among others, preslaughter feed withdrawal is seen as a tool for raising muscle ultimate pH and reducing the incidence of exudative pork through the reduction of muscle glycogen stores at slaughter (Faucitano, Chevillon, & Ellis, 2010; Sterten, Oksbjerg, Frøystein, Ekker, & Kjos, 2010). Faucitano et al. (2006) reported an increase in pHu of 0.07 units in the longissimus muscle of pigs fasted for 24 h compared to those fasted for 14 h. However, when the 24 h fasting interval is exceeded, losses in carcass weight (100 g/h; Chevillon, 2000) or yield (−1%; Faucitano et al., 2006) and increased risk for DFD (dark, firm, dry) pork production due to muscle glycogen exhaustion can occur, both resulting from increased fighting rate in mixed unfamiliar pigs and hunger (Gispert et al., 2000; Guàrdia et al., 2004; Guàrdia et al., 2009). For this reason, a period of 24 h between the last meal and slaughter appears to be an acceptable compromise to obtain optimal carcass yield and pork quality (Faucitano et al., 2010). However, research has also shown that this fasting interval does not truly apply to pigs with high muscle glycolytic potential, such as those carrying the RN− gene (Bidner et al., 1999; Bidner, Ellis, Witte, Carr, & McKeith, 2004) and heavier pigs (> 170 Kg; Nanni Costa, Lo Fiego, Dall'Olio, Davoli, & Russo, 2002), for which a longer feed withdrawal time (30 to 48 h vs 12 h) appears more appropriate to reduce the risk of PSE pork production at no detriment for carcass yield (Bidner et al., 1999; Bidner et al., 2004; Lo Fiego, Minelli, & Santoro, 1997). Similarly, pigs that are raised in enriched housing conditions may benefit from the application of a more extended fasting time to reduce their high glycogen stores to the level required at slaughter to produce normal meat quality. This practice would not affect carcass weight or yield losses, or animal welfare as the higher body energy stores should make them more resistant to the effects of fasting. In a recent study (Fàbrega et al., 2019), no major effects have been reported in pigs raised in enriched pens (including straw in a rack) and subjected to two preslaughter fasting times (0 vs. 12 h). The too mild stress conditions preslaughter (i.e., no mixing between unfamiliar boars in the truck and/or lairage) may explain the lack of significant interaction between on farm environmental enrichment and fasting time in this study.
The objective of this study is to assess the efficiency of a more extended fasting time preslaughter (32 vs 16 and 24 h) to reduce the glycolytic potential of the muscle at slaughter and to improve meat quality, without compromising carcass quality and the welfare of pigs raised in enriched production systems.
Section snippets
Material and methods
All experimental procedures performed in this study were approved by the institutional animal care committee at the Agriculture and Agri-Food Canada (AAFC) Sherbrooke Research and Development Centre (Sherbrooke, QC, Canada) based on the current guidelines of the Canadian Council on Animal Care (2009).
Effect of the raising system on growth rate
Differently from other studies (Casal-Plana, Manteca, Dalmau, & Fàbrega, 2017; Chevillon et al., 2005; Van der Wal et al., 1993) that did not report any difference in growth performance between pigs raised in indoors conventional and enriched conditions, in this study, keeping pigs in enriched pens (16E) instead of conventional ones (16C) resulted in heavier slaughter weight (as assessed at week 12; P = .02; Table 2). A greater body weight at slaughter in enriched-housed pigs vs.
Conclusions
The results of this study showed the benefits of growing-finishing pigs in indoors enriched environments, i.e., straw-bedding and lower density, in terms of greater ease of handling at loading, faster loading procedure, lower stress status at slaughter, and improved post-mortem muscle metabolic conditions and loin meat quality, although at slight detriment of carcass quality. Based on the negative effects on carcass quality and the lack of clear or major impact on stress response and meat
Declaration of Competing Interest
None.
Acknowledgements
We would like to thank the staff from AAFC for their work at the farm, M. St-Louis, L.M. Rocha and S. Lang for their help with data and sample collection and analyses. We are also grateful to S. Méthot for his assistance in the statistical analysis. Special thanks go to the Groupe Cérès Inc. for providing the pigs, and to Rousseau slaughterhouse for providing the slaughter facility and manpower. We appreciate the funding support (#J-001343) from the Science and Technology Branch of Agriculture
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Present address: Longhua Districts Central Hospital, 518,109, Shenzhen, China