Application of extended feed withdrawal time preslaughter and its effects on animal welfare and carcass and meat quality of enriched-housed pigs

Highlights

• Enriching the housing environment results in heavier and fatter pigs.

• Enriched-housed pigs are easier to handle and produce less exudative pork.

• Extending fasting time (from 16 to 32 h) does not result in better meat quality in this type of pigs.

Abstract

A total of 144 barrows were distributed into four treatment groups. One group was housed conventionally and fasted for 16 h preslaughter, while the other three groups were housed in enriched conditions (straw-bedding and low density) and fasted for 16, 24 and 32 h preslaughter. When compared with conventionally-housed pigs, enriched-housed pigs were heavier (P < .05) and fatter (P < .01), but easier to handle at loading (P < .05) and produced less exudative pork (P < .05) possibly resulting from a lower post-mortem muscle glycolytic potential (P = .10). Extending fasting time up to 32 h reduced dressing yield (P < .001) and increased skin lesion scores (P < .01), but did not result in any clear or major effect on muscle metabolism and meat quality. In conclusion, given the beneficial effects of enriched housing conditions on stress response and pork quality, the application of an extended fasting time (32h) preslaughter is not required for this production.

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.