Diet composition and slaughter age up to 24 weeks have minimal impact on pork eating quality of loin steaks and silverside roasts from female pigs
Introduction
Delivering consistently high eating quality pork, across a range of cuts prepared using different cooking methods, to drive consumer demand and ensure ongoing industry sustainability and competitiveness is a key focus of the Australian pork industry (Anon, 2014). However, the ability of any supply chain to consistently produce high quality pork is both difficult and complex due to individualised responses of pigs to the various management practices and environmental factors experienced throughout their lives, coupled with additional pre- and post-slaughter factors that may interact to further influence pork eating quality. It is also recognised that even with the close management of those pathway parameters known to negatively influence pork eating quality (Channon & Warner, 2011; Dunshea, D'Souza, Pethick, Harper, & Warner, 2005; Rosenvold & Andersen, 2003), eating quality inconsistencies may still be experienced due to cooking methods used, final internal temperatures achieved, cooking abilities of consumers and consumer confidence in preparing pork meals (Ngapo & Gariepy, 2008).
Channon, Hamilton, D'Souza, and Dunshea (2016) described a statistical approach using published data to assist with developing a cuts-based eating quality predictive model for Australian pork and highlighted that additional data are needed to quantify effects of multiple pathway factors on eating quality attributes and to extend these findings to other cuts in addition to the loin muscle. In response to this, the effects of ageing period, cooking method, cut type and final internal temperature have been determined in entire male, female and surgical castrated pigs (Channon, D'Souza, & Dunshea, 2016) and entire male and immunocastrated males (Channon, D'Souza, Hamilton, & Dunshea, 2013) slaughtered at 90–100 kg liveweight from one current Australian genotype. Across those factors investigated, the largest differences in eating quality were due to the interaction between cut (shoulder, loin or silverside) and cooking method (roast and stir fry (all cuts) or steak (loin only)). Overall, it was shown that loin steaks and silverside roasts had lower overall liking scores than the other cuts evaluated – presenting significant implications if this is not addressed given that these cuts are strongly demanded at the retail level by consumers. Ageing of these pork cuts at 2 °C for 7 days, compared with 2 days, was also relatively ineffective in both reducing fail rates and in consistently improving eating quality traits of various pork cuts (Channon et al., 2016). From these outcomes, it was not clear whether an ageing period of > 7 days may be needed to optimise tenderness of loin steaks and silverside roasts. Furthermore, few studies have compared whether an extended ageing period of 28 days, as can be experienced by vacuum packaged chilled pork to meet supply arrangements both when exported and for domestic retailers, may deliver pork eating quality benefits compared to an ageing period of 7 days.
Intramuscular fat content of between 2.0 and 3.5% in the loin has been shown to positively influence pork eating quality (Alonso, Campo, Provincial, Roncalés, & Beltrán, 2010; Bejerholm & Barton-Gade, 1986; DeVol et al., 1988; Fernandez, Monin, Talmant, Mourot, & Lebret, 1999; Touraille, Monin, & Legault, 1989). However, levels of intramuscular fat levels in the loin, in the vicinity of 0.8–1.5%, have typically been found in Australian pork loin muscles (Jose, Trezona Murray, Channon, & D'Souza, 2013; Channon, Taverner, D'Souza, & Warner, 2014: D'Souza et al., 2015; Moore, Mullan, & Dunshea, 2017), with higher levels of 2.5–3.5% in the loin recently reported by Channon et al. (2016). Increased liveweight at slaughter can increase the deposition of subcutaneous (Wood et al., 2008) and intramuscular fat (Čandek-Potokar, Žlender, Lefaucheur, & Bonneau, 1998; Heyer & Lebret, 2007). Pigs produced in the United States of America, Canada and the European Union are generally slaughtered at heavier weights of 90–130 kg compared with Australian pigs where they are typically slaughtered at 85–100 kg liveweight to meet preferred carcase weight and fat depth specifications. It is also recognised that diet formulations differ between countries, with a corn-soybean meal diet primarily used in North America whilst in the EU, diets for pigs must be free from restricted animal materials (meat meal, fish meal, blood meal etc.; RAM). The influence of these different diet types fed to Australian pigs grown to heavier liveweights on pork eating quality attributes has not previously been reported. Slaughtering pigs at higher liveweights in combination with different diet formulations may therefore present another option for Australian producers to consider in order to reduce pork eating quality variability.
This study aimed to evaluate whether diet composition (using feed ingredients typically used in North America and northern Europe) and age/final liveweight at slaughter can increase intramuscular fat levels compared with pork from pigs slaughtered at 20 weeks of age, whether extended ageing for 28 days post-slaughter, rather than for 7 days post-slaughter, can improve the eating quality consistency of loin steaks and silverside roasts and whether these pathway interventions may be additive or multiplicative in their effects on eating quality.
Section snippets
Materials and methods
Experimental protocols used in this study were managed through CHM Alliance Pty. Ltd.'s Animal Ethics Committee (Protocol CHM PP 32/12).
A total of 75 crossbred female pigs (25 per dietary treatment/slaughter age group), from a piggery located in South East Queensland, Australia were randomly allocated at 16 weeks of age to one of three nutritional treatments matched for digestible energy (13.6 MJ DE/kg) and total lysine (0.93–0.95%) (Table 1). The dietary treatments were A: 77% corn and 16%
Results
Pigs allocated to Treatment A were heavier at slaughter (P < 0.001) and produced heavier (P < 0.001), fatter (P < 0.001) carcases with higher dressing percentages (P < 0.001) compared with pigs allocated to treatments B and C (Table 2). Carcases in treatment C had a higher estimated chill loss (P = 0.019) than carcases in treatments A and B.
Discussion
The importance of flavour to overall liking was again shown, with the coefficient for flavour found to be three times as large as for juiciness and tenderness, supporting previous studies (Channon et al., 2014; Channon et al., 2016; Jaworska, Przybylski, Kajak-Siemaszko, & Czarniecka-Skubina, 2009). Positive correlations between tenderness, juiciness and flavour observed in this study also concur with previous studies (including Huff-Lonergan et al., 2002; Jeremiah et al., 1999).
Conclusion
As few differences in pork sensory quality resulted from finishing female pigs of 20 to 24 weeks of age, our findings support the inclusion of heavier carcases in a pathway based eating quality system for Australian pork. Feeding isoenergetic and isonitrogenous diets, formulated using dietary ingredients typically used in North America and northern Europe, to finisher pigs of a major Australian commercial genotype also did not result in markedly different eating quality performance. Ageing for 28
Acknowledgements
The High Integrity Australian Pork Co-operative Research Centre is gratefully acknowledged for providing funds to undertake this study (3A-105). The authors also acknowledge the producer and processor involved for their co-operation, technical assistance and support. Dr. Cameron Jose from the Department of Agriculture and Food Western Australia is acknowledged for his assistance with carcase and meat quality measures. The biometrical support and advice provided by Richard Jarrett and Jessica
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2018, Meat ScienceCitation Excerpt :The effects of various production, processing and post-slaughter factors on eating quality acceptability of pork were then investigated. These were: gender (entire male, female and physical castrates) (Channon, D'Souza, & Dunshea, 2016); entire male and immunocastrated males (Channon, D'Souza, & Dunshea, 2018b; Moore, Mullan, & Dunshea, 2017); entire male, female and immunocastrated males (Akit, Frobose, Channon, D'Souza, & Dunshea, 2014); entire male and females (Jose, Trezona Murray, Mullan, McNaughton, & D'Souza, 2013); final liveweight/diet composition (Channon, D'Souza, & Dunshea, 2018a); lecithin supplementation to pigs (Akit et al., 2011; Akit et al., 2014); hanging method (Channon, D'Souza, & Dunshea, 2015a); electrical stimulation (Channon, D'Souza, & Dunshea, 2015b, 2015c); moisture infusion (Channon et al., 2015a, 2015b, 2015c), ageing period post-slaughter (2 vs. 7 days) (Channon et al., 2015a, 2015c, 2018b; Channon, D'Souza, & Dunshea, 2016); 2 vs. 14 days (Channon et al., 2015b); 7 vs. 28 days (Channon et al., 2018a); endpoint temperature (70 and 75 °C) (Channon et al., 2018b; Channon, D'Souza, & Dunshea, 2016); muscle type (Channon et al., 2015a, 2015b, 2015c, 2018a, 2018b; Channon, D'Souza, & Dunshea, 2016); cut type × cooking method (Channon et al., 2015a, 2015b, 2015c; Channon et al., 2018b; Channon, D'Souza, & Dunshea, 2016) and final ultimate pH (Jose et al., 2013). Combined, these studies enabled a substantial multi-factorial dataset to be produced for further statistical analysis to commence the development of predictive algorithms that are able to reliably estimate the eating quality of pork.
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2018, Meat ScienceCitation Excerpt :A pathway based, non-prescriptive eating quality model is being developed by the Australian pork industry that, when implemented, will enable supply chains to choose various pathway interventions to deliver consistent, high quality pork to their domestic and export customers (Channon & Warner, 2011). In order to do this, a key industry focus has been to undertake research studies to address knowledge and data gaps identified from meta-analysis studies (Channon, D'Souza, & Dunshea, 2017; Channon, Hamilton, D'Souza, & Dunshea, 2016) to understand the effects of multiple pathway factors, including gender, final liveweight, ageing period, final internal temperature, cut type and cooking method on pork eating quality (Channon, D'Souza, & Dunshea, 2016; Channon, D'Souza, & Dunshea, 2018a; Moore, Mullan, & Dunshea, 2017). Entire male pigs immunised against gonadotrophin releasing factor (GnRF) produce pork that is more acceptable (D'Souza & Mullan, 2003; Font i Furnols et al., 2008), with lower shear force values (Jeong, Choi, Han, Lee, & Hennessy, 2008; Moore, Dunshea, Mullan, Hennessy, & D'Souza, 2009; Pauly, Spring, O'Doherty, Kragten, & Bee, 2009) and has a lower fail rate (Moore et al., 2017) than entire males.
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2018, Meat ScienceCitation Excerpt :Recent studies involving different Australian supply chains have not shown any eating quality improvements resulting from ageing for 7 days compared with 2 days across a number of different cut type x cooking method combinations (Channon, D'Souza, & Dunshea, 2016; Channon, D'Souza, & Dunshea, 2018b). Further, no differences due to ageing for 7 or 28 days post-slaughter were found for eating quality attributes of both loin steaks and silverside roasts, indicating that maximal ageing occurred by 7 days post-mortem (Channon, D'Souza, & Dunshea, 2018a). For ageing period to be included as a recommended intervention to improve eating quality, further data is required to validate whether it can be reliably applied to pork cuts.
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Aspects of this work has been previously published as: Channon et al. (2013). Diet and slaughter age have minimal impact on pork eating quality. In J. R. Pluske & J. Pluske (Eds.), Manipulating Pig Production XIV (p. 228) Australasian Pig Science Association Werribee, Australia.