Boar taint, meat quality and fail rate in entire male pigs and male pigs immunized against gonadotrophin releasing factor as related to body weight and feeding regime☆
Introduction
The Australian pork industry prefers to produce entire male pigs as they have a better feed conversion and less subcutaneous fat deposition compared to physically castrated pigs (Channon, D'Souza, & Dunshea, 2016). However the occurrence of boar taint which can reduce pork eating quality is an issue when producing entire male pigs (Andersson et al., 1999, Babol and Squires, 1995, EFSA Scientific Panel on Animal Health and Welare, 2004). Boar taint is an offensive smell and is primarily caused by the compounds skatole, androstenone and indole (Bonneau, 1982, Lundstrom and Zamaratskaia, 2006).
One way to eliminate boar taint is to immunize male pigs against gonadotrophin releasing factor (GnRF; immunocastrates). Immunization against GnRF involves immunization with an incomplete analogue of GnRF conjugated to a carrier protein in a low reactogenic-adjuvant system (Dunshea et al., 2001). It allows the pig to grow as an entire male until the second immunization against GnRF. Following the second immunization against GnRF the pig becomes more similar to a physical castrate and any boar taint substances present are progressively metabolized. Therefore, there are lower levels of skatole and androstenone in the subcutaneous fat (Channon and Warner, 2011, Dunshea et al., 2001).
Another suggested avenue to reduce the incidence of boar taint in Australia is to reduce the slaughter weight of pigs destined for the fresh pork market. There is a belief amongst some producers, processors and retailers in Australia that if entire male pigs are slaughtered at < 90 kg liveweight (LW) then there is no need for either physical castration or immunocastration because the incidence of boar taint is negligible (D'Souza et al., 2011). However, an Australian survey by D'Souza et al. (2011) showed a high proportion of pork samples exceeded the sensory threshold detection level for androstenone (1 μg/g) and skatole (0.2 μg/g) regardless of slaughter weight (73 to 115 kg LW). In addition, there was a poor correlation between carcass weight and androstenone and skatole (D'Souza et al., 2011). Although skatole and androstenone concentrations have been examined in light and heavy slaughter weight pigs, objective measurements and eating quality of both entire males and immunocastrated males have not been determined together under Australian conditions.
In addition to improving pork quality the Co-operative Research Centre for High Integrity Australian Pork aims to reduce fail rates of pork to < 10% through the implementation of an eating quality pathway (Channon & Warner, 2011). The boar taint issue facing the Australian pork industry is likely to result in higher fail rates in pork from entire male pigs, however as outlined above, an effective way to eliminate boar taint is by immunization against GnRF. This project aimed to investigate whether immunization against GnRF improved pork eating quality fail rates in male pigs.
Therefore, the objective of this experiment was to compare the pork quality of entire male pigs and pigs immunized against GnRF at both light and heavy LW's. The hypotheses were: i) that male pigs immunized against GnRF will have improved pork eating quality compared to entire males at both light and heavy slaughter weights and ii) immunization against GnRF will reduce pork eating quality fail rates compared to entire male pigs.
Section snippets
Care of animals
The experimental protocol used was approved by the Department of Agriculture and Food Western Australia's Animal Research Committee and by the Animal Ethics Committee (Activity number 2-12-11). The animals were handled according to the Australian code of practice for the care and use of animals for scientific purposes (National Health and Medical Research Council, 2004).
Experimental design
A total of 64 Large White × Landrace × Duroc entire male and immunocastrated male pigs were used in this experiment. The
Final liveweight, skatole and androstenone concentrations
Final LW's are given in Table 1. There was no difference in final LW between entire males and IC males (87.9 v. 86.3 kg; P > 0.05). Pig fed ad libitum were heavier than those fed the restricted diet (91.4 v. 82.8 kg; P < 0.001) and as expected heavy pigs weighed more than the light pigs (105.8 v. 64.8 kg; P < 0.001). Entire male pigs had significantly increased concentrations of skatole and androstenone than IC male pigs (P = 0.001 and P < 0.001, respectively). Androstenone concentration was also increased
Effect of sex
The hypothesis that pigs immunized against GnRF will have improved pork eating quality compared to entire males at both light and heavy slaughter weights was not supported. There was no difference in any eating quality parameters between entire males and IC males although there was a trend for the meat from IC males to be juicer than that from entire males. The lack of difference is in agreement with Channon et al. (2013) who also found no difference between entire males and IC males for any
Conclusions
In this experiment 37.5% of the light entire male pigs fed ad libitum had skatole levels that exceeded the sensory threshold of 0.2 μg/g. This provides further evidence that boar taint is still an issue at low carcass weights. This work also confirms that immunization against GnRF is effective at eliminating boar taint and reducing pork eating quality fail rates by approximately 10% compared to pork from entire male pigs.
Acknowledgements
The financial support provided by the Pork Cooperative Research Centre for High Integrity Pork is acknowledged (3A-101). The authors are appreciative of the technical assistance provided by staff from the Department of Agriculture and Food Western Australia and Linley Valley Fresh Pork. The biometrical services and the co-ordination and conduct of the consumer eating quality sessions by Anna Crump and Jessica Tan from the South Australian Research and Development Institute, Waite Campus, South
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Aspects of this work have been published as: Moore, K.L., Mullan, B.P., Kim, J.C., Trezona, M., & Dunshea, F.R. (2015). Immunization against gonadotrophin releasing factor reduces pork eating quality fail rates. Animal Production Science, 55, 1469.