Immunisation against gonadotrophin releasing factor reduces pork eating quality fail rates

The Cooperative Research Centre for High Integrity Australian Pork is aiming to achieve consumer fail rates of less than 10% for pork through the implementation of various eating quality pathways. An issue facing the Australian pork industry is boar taint (Channon and Warner 2011), which is likely to result in higher fail rates in pork from entire male pigs. An effective way to eliminate boar taint is through immunisation of entire male pigs against gonadotrophin releasing factor (GnRF). The hypothesis was that immunisation against GnRF will reduce pork eating quality fail rates compared to entire male pigs at both light and heavy slaughter weights.

Sixty-four Large White × Landrace × Duroc pigs were used in a 2 × 2 × 2 factorial experiment (n = 8) with the main treatments being: 1) sex [entire male pigs vs male pigs immunised against GnRF (immunised; Improvac^®; Zoetis Australia, Rhodes NSW)]; 2) weight at second immunisation [50 kg (light) vs 80 kg (heavy) live weight (LW)]; and 3) feeding regime (2.5 times maintenance vs ad libitum). Pigs were housed individually. The diets were fed for, and the second immunisation of GnRF was given, 28 days before slaughter (68.4 kg LW for light pigs and 106 kg LW for heavy pigs). At 24 hours after slaughter, 2-cm thick steaks were cut from the Longissimusthoracis for sensory analysis. Consumers graded the pork steaks into one of five quality/re-purchase intention categories: 1) unsatisfactory/definitely would not buy it; 2) below average/would probably not buy it; 3) average/might buy it); 4) above average/would probably buy it, and 5) excellent/would definitely buy it. Steaks were deemed to have failed if the score was ≤2. Skatole and androstenone concentrations were measured in belly fat using high performance liquid chromatography. Data were analysed by Chi-square and ANOVA (GenStat, 15th Edition; UK).

Fail rates were reduced by 9.1% and 12% for pork from immunised males for quality grade (P = 0.007) and re-purchase intention (P = 0.001), respectively, compared to pork from entire male pigs (Table 1). Skatole (P = 0.001) and androstenone (P < 0.001) levels in belly fat were higher in entire male pigs than immunised male pigs, which may in part help to explain the higher fail rates in pork from the entire males compared to the immunised males (data not shown). In addition, 37.5% of the light entire male pigs fed ad libitum showed skatole levels that exceeded the sensory threshold of 0.2 µg skatole/g, providing further evidence to the work of D’Souza et al. (2011) that boar taint is still an issue at lower carcass weights. This work confirms that immunisation against GnRF is effective in eliminating boar taint and reducing pork eating quality fail rates by approximately 10% compared to pork from entire male pigs.

Table 1.  Percentage of consumer scores for quality grade and re-purchase intention for entire male pigs and immunised male pigs (n = 240)