Influence of Slaughter Weight, Sex and Intramuscular Fat Content of the MLLT on the Carcass Value of Hybrid Pigs

Hybridisation programs have the goal of achieving hybrid populations with optimal reproductive traits and productive traits including carcass value. According to Miar et al., (2014), the selection on suitable breeds of pig during hybridisation is a critical factor for improving the economic properties of pork. The lean meat content and fat tissue varies according to the slaughter weight of hybrid pigs, thereby changing the carcass value (Kim et al., 2005, Alvarez-Rodríguez and Teixeirab, 2019, Wang et al., 2019, Lertpatarakomol, et al., 2019). Factors, influencing the quality of carcases, are in many respects linked to three main factors, i.e. sex, genotype and slaughter weight.
       
According to Wang et al., (2019), the IMF content has reduced in recent years as a result of breeding for an increased lean meat content, whereas more primitive breeds of pig achieve a higher IMF content.
       
These findings stimulated efforts to increase the IMF content of pork from breeds farmed in conventional facilities in order to improve the flavour of the pork. IMF is an important qualitative property of pork that affects both its sensory properties and nutritional value (Suzuki et al., 2005, Wood et al., 2008, Wang et al., 2019).
       
Font-i-Furnols et al., (2019) observed that the IMF content depends on the sex, genotype and nutritional intake of pigs. Many studies have discussed the relationship between IMF content and the sensory properties of pork (Brewer et al., 2002, Rincker et al., 2008, Moeller et al., 2010). Meat without sufficient marbling is considered insufficiently juicy or flavourful to be acceptable to consumers. Excessive IMF content is also refused, as it causes the energy content of the meat to be too high.

The experiment was conducted in 2019 in commercial pig breeding in Rudíkov in the Czech Republic. Analyses of pork samples were performed in the laboratory at Mendel University in Brno in the Czech Republic.
       
Operational testing of hybrid pigs was used to obtain the monitored indicators. F1 generation hybrids of Czech Large White × Czech Landrace were used as mothers and were bred by insemination to boars of the Duroc  breed to produce experimental hybrid combination (Czech Large White × Czech Landrace) × Duroc, referred to as (CLW × CL) × D. As many as 78 pigs intended for slaughter, these being 48 barrows and 30 gilts were included in the experiment.
       
After birth, piglets were tagged with an identification number and their sex was recorded. Pre-fattening and fattening of the pigs took place separately depending on the sex of the pigs, using normal commercial feed mixtures. All pigs kept in identical environments.
       
Once fattening was achieved, test animals were slaughtered. The lean meat content was established by inserting a Fat-O-Meater (FOM) probe between the 2^nd and 3^rd from last left ribs, 70 mm laterally from the halving cut. Data pertaining to lean meat content (%), muscle thickness (mm) and backfat thickness (mm) was obtained from each carcass measurement.
       
For the purposes of this experiment, half of each slaughtered pig was butchered into the main cuts of meat (shoulder, neck, loin and ham) and each individual cut was weighed electronically.
       
During butchering, 300 g samples were taken from the MLLT at the point of the last thoracic vertebra to assess the quality of the meat.  Based on the qualitative indicators of pork, we focused on determining the percentage of IMF in the MLLT, drip loss and the colour of the pork. IMF content was determined in a laboratory using the method of extraction by ether according to Soxhlet.
       
Parameters in the CIELab colour system were monitored to evaluate the colour of the pork. Lightness (L*) and the proportion of meat in the red (a*) and yellow (b*) spectrum was determined using a Konica Minolta CM - 2600 d spectrometer (Konica Minolta, Japan). To ensure standard conditions, gauge aperture was set to 8 mm, the source of daylight was - D65, 10° standard observer angle and SCI mode were set.
       
Carcass data was recorded by sex, with groups created according to slaughter weight and further sub-divided by percentage of IMF in the MLLT.
       
STATISTICA 10 software was used for statistical evaluation. A Scheffe test was used to determine the significance of differences between groups at a lavel of P<0.05 and P<0.001.

Table 1 shows the carcass value indicators in the hybrid (CLW × CL) × D pigs according to sex. The average slaughter weight was significantly higher (P<0.05) in barrows (122.66 kg) compared to gilts (116.70 kg). The backfat thickness was also higher in barrows (17.71 mm) than in gilts (16.55 mm). Lertpatarakomol et al., (2019) measured higher values of backfat in both barrows and gilts in (Large White × Landrace) × Duroc pigs in comparison with our experiment. Qualitative indicators of carcass value in pigs of the hybrid combination (CLW × CL) × D were also addressed in their experiments by Ilavarasan and Abraham (2018) and Lei et al., (2019).
 

       
We found the average lean meat content to be higher in gilts (56.51%) compared to barrows (55.89%), where as the average IMF was 3.76% in barrows and 3.42% in gilts.
 
Matoušek et al., (2006) came to the same conclusion, observing that barrows had a 0.25% greater IMF than gilts (1.35% versus 1.09%). Alvarez-Rodríguez and Teixeirab (2019) also recorded a higher IMF content in barrows (1.44%) compared with gilts (1.20%) from the Bisaro breed. We measured a higher drip loss of meat (1.70%) in gilts than in barrows (1.61%) and found the average weight of the main cuts of meat to be higher in barrow than gilts.
       
The values of the colour parameters (L*, a*, b*) of the MLLT were similar in both barrows and gilts. Corino et al., (2008) also found no statistically significant differences monitored in the quality of the meat of (Goland × Hypor) hybrids according to sex.
       
Our monitoring found higher average values in barrows compared to gilts in the weights of the main cuts of meat.
       
The slaughtered hybrid (CLW × CL) × D pigs had an average slaughter weight of 119.68 kg, the average lean meat content of the carcasses was 56.20% and the average backfat thickness was 17.13 mm. Lertpatarakomol et al., (2019) states that in Thailand the Duroc breed is extensively used for three-breed utility hybridisation in the (Large White × Landrace) × Duroc combination.
       
The average IMF content in our (CLW × CL) × D test animals was 3.63%. Matoušeket_al(2006) found lower IMF values with (Czech Landrace × Czech Large White) × (Duroc × Pietrain) hybrids (1.56%). Duroc breed hybrids generally have a higher IMF content than hybrids of other breeds (Armero et al., 1998, Suzuki et al., 2005).
       
We observed a higher average value (58.59) for the lightness of the colour of meat (L*) than reported by Suzuki et al., (2005). Lertpatarakomol et al., (2019) also reported a lower L* (51.19) in (Large White × Landrace) × Duroc pigs than observed here, although they obtained a similar percentage of meat in the yellow spectrum b* (11.47) to that in our experiment (11.68). Kim et al., (2019) recorded an average value of L* (48.60) in their experiment with the Berkshire breed.
       
Table 2 shows the carcass value indicators in the hybrid (CLW × CL) × D pigs according to slaughter weight. We observed that pigs with a higher slaughter weight had alower lean meat content in the carcass. The backfat thickness increased linearly with increasing slaughter weight.
 

       
The lowest drip loss of meat (1.55%) was measured in pigs with an average slaughter weight of 104.91 kg, whereas the greatest drip loss was registered in pigs weighing less than 100 kg.
       
The meat lightness parameter L* ranged on average from 57.68 to 58.13. The average values of the yellow spectrum indicator b* were similar in all weight groups.
       
Significant differences were found between the values of all indicators for the main cuts of meat, apart from the weight of the loin. These results demonstrate that a higher slaughter weight corresponds to a higher weight of the main meat cuts.
       
The results in Table 3 indicate that the IMF content of the MLLT has a small impact on carcass value indicators but that this does not reach significance.  Conclusive impacts of sex, slaughter weight and genotype on the IMF content of pork have been described (Brewer et al., 2002, Latorre et al., 2003). However, other studies report that slaughter weight has no impact on the IMF content of pork (Moon et al., 2003). In general, a higher slaughter weight (121.61 kg, 120.68 kg) was observed in pigs with a higher average IMF content (3.52%, 5.20%).
 

       
With regard to the colour of the meat, the lightness parameter value L* was similar in all IMF groups (57.92 - 58.37), with the exception of those with an IMF greater than
4%, where this value was 59.58.
       
No differences were registered between the established carcass values of individual main cuts of meat according to the IMF content groups.

This data demonstrates that the (Czech Large White × Czech Landrace) × Duroc hybrid pigs have exhibits very high meat quality asmeasured by the IMF content (3.63%) of the MLLT. A higher lean meat content was attained in gilts than in barrows. With regard to the quality of the meat, a higher IMF content was registered in barrows than in gilts. No impact of sex or slaughter weight was observed on any indicator of meat colour.
       
Slaughter weight did have an impact on the IMF content of the MLLT. A higher slaughter weight was observed in pigs subsequently found to have a higher IMF content.
               
The IMF content of the MLLT did not impact carcass value indicators, although those with a higher IMF content demonstrated a lighter meat colour.