Indian Journal of Animal Research

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A Study on Changes of Carcass, Bones and Muscles of Ningxiang Pigs

Wei Zhang1, Yinglin Peng1,2,*, Qingming Cui2, Yitong Chang1, Yuan Deng2, Chen Chen2,*, Yingying Liu1,2
1College of Animal Science and Technology, Hunan Agricultural University, Changsha, Hunan, China.
2Hunan Institute of Animal and Veterinary Science, Changsha, Hunan, China.

ABSTRACT

Background: Ningxiang pigs are known for tasty meat and high intramuscular fat content. Currently, the slow growth rate and low lean meat rate of Ningxiang pigs have greatly restricted the development of its market. Therefore, the objective of this study is to explore the changes in carcass traits, meat quality, visceral organ weight indices, bones and muscles development with slaughter ages of Ningxiang pigs.

Methods: The experiment used 0, 60, 120, 180, 240, 300 and 360 days old Ningxiang pigs as the research objects, and 6 castrated male pigs in each group were randomly selected. The carcass traits, meat quality, visceral organs weights and skeletal muscle weights were measured. The correlation between carcass traits and meat quality were analyzed by bivariate analysis, and the regression equations between slaughter ages and these indicators were established.

Result: The results showed that pre-slaughter weight and weights of carcass, head, feet, skeleton and muscle, loin eye area, cooking yield, marbling and the large intestine weight index at 0 d, backfat thickness at 60 d, fat percentages at 60 and 120 d, and the lean meat percentage at 240 d, redness at 120 d of Ningxiang pigs were lowest, the heart, lung, kidney and small intestine weight percentages were highest at 0 d (P<0.05). Carcass traits and meat quality had different significant correlation at different slaughter ages. So the indices of carcass, meat quality, bones and muscles of Ningxiang pigs changed with slaughter ages. In general, the overall performance of 300 d Ningxiang pigs is better.

INTRODUCTION

The growth and development of animal muscles are related to the change of carcass performance and meat quality characteristics in livestock and poultry, which has a direct influence on the improvement of multiple performance indices and the economic benefits of animals (Chen et al., 2019). Ningxiang pigs, one of the four most renowned pig breeds in China, are known for tasty meat, high intramuscular fat and unsaturated fatty acid content (Gong et al., 2021; Li et al., 2021). Studies have shown that the distributions and depositions of bones, muscles and fat in animals present dynamic changes throughout the growth process, and these changes greatly affect the carcass traits and meat quality of animals (Guo et al., 2021; Malgwi et al., 2022; Zhang et al., 2024). Ilavarasan et al., (2017) showed that the muscle quality of young pigs was better than that of adult pigs. Guo et al., (2021) confirmed a significant increase in muscle pH24 and redness value in black-covered pigs with increasing body weight.
       
In recent years, the supply and demand of pork in the market is far from meeting the needs of consumers, so entrepreneurs to introduce many fast-growing and high-yielding breeds for hybrid improvement, so as to obtain greater economic benefits. With the continuous improvement of the scientific breeding system, the unique and outstanding traits such as bright red flesh color, tasty meat and thin muscle fibers of Ningxiang pigs was gradually excavated, which made the number of purebred individuals increase. Currently, there is a lack of research on the correlation between carcass traits and meat quality in Ningxiang pigs. Therefore, the experiment was conducted to study the changes of carcass, bones, and muscles, correlation analysis of carcass and meat quality and regression equations between slaughter ages and these indices of Ningxiang pigs.

MATERIALS AND METHODS

Experimental animals
 
The animal experiment conducted in this study was approved by the Institutional Animal Care and Use Committee of Hunan Agricultural University and was conducted in accordance with the Chinese Guideline for Ethical Review of Animal Welfare (ACC2019006, Changsha, China). The study was completed in Hunan Institute of Animal and Veterinary Science from 2022 to 2023. Forty-two castrated male Ningxiang pigs in seven developmental ages (0, 60, 120, 180, 240, 300, and 360 d) were used in this study. Six healthy individuals with similar body weight were selected for weighting and slaughtering in each developmental age. Seven groups of pigs were half-sibs, and the six samples in each developmental age were full-sibs. All the experimental pigs were reared under the standard environmental conditions in Hunan Liushahe Ecological Animal Husbandry Co., Ltd.
 
Carcass traits
 
Pre-slaughter body weight (BW) and weights of head, feet, carcass, carcass length, backfat thickness, and loin eye area at the 10th rib were measured immediately after slaughter (Ministry of Agriculture of the People’s Republic of China, 1987). Carcass straight length was measured from the first rib to the end of the pubic bone. Carcass oblique length was measured between the articulation of the first rib and the sternum to the end of the pubic bone. Backfat thickness using a vernier caliper, and the average measurements at three points: the first rib, last rib, and last lumbar vertebra were recorded. The left side of each carcass was weighed and then physically dissected into skin, skeletal muscle, fat and bone for the evaluation of carcass characteristics. These components were weighed, and the weights were multiplied by 2 to calculate the percentage of the whole carcass that each component constituted. The dressing percentage was calculated as carcass weight divided by pre-slaughter weight. Weights of skeletal muscles and bones were also recorded after carcass segmentation.
 
Visceral
 
After removing other tissues from the surface of internal organs, they were directly weighed and recorded (expressed as the percentage of pre-slaughter weight).
 
Meat quality
 
The 45 min pH (pH45) and 24 h pH (pH24) values at postmortem were measured in triplicate at the 6th to 7th rib position by using hand-held pH meter. Instrumental color measurements of lightness, redness, and yellowness were taken in triplicate at the 10th rib interface by using a Konica Minolta Chroma Meter with an 8 mm measuring port, D65 illuminant. On the slaughter ages, approximately 100 g fresh LD muscle was weighed and placed in a Whirl-Pak bag, suspended in a 4°C cooler for 24 h, reweighed, and drip loss was recorded. The muscle sample was weighed and covered in a container before cooking. Immediately after cooking for 45 min at 100°C, the sample was removed from the container and dried with a paper towel, then reweighed. Cooking yield = (cooked weight/raw weight)×100. After being placed in a plastic bag and cooked in an 80°C water bath until the internal temperature reached 70°C, muscle samples were cooled to room temperature, then measured using a texture analyzer equipped with a Warner-Bratzler shear force device (200 mm/min crosshead speed). Three samples with a diameter of 1.27 cm and a length of approximately 2 cm were cut with a cylindrical core borer from each of the cooked steaks, and then were sheared vertically to the muscle fibers to record the shear force value. Marbling was scored based on the procedure recommended by the National Pork Producers Council (NPPC) (2000), ranging from 1 (devoid) to 5 (abundant), 0.5 points were allowed between two scores. Meat quality of 0-day old piglets was not tested due to the small size of the LD muscle in newborn piglets.
 
Statistical analysis
 
After the test data were recorded and processed in Excel 2010, SPSS 21.0 and SAS 8.2 were used for significance analysis of all the original data and bivariate correlation analysis was conducted for carcass traits and meat quality indices at each age, and then regressions were fitted.

RESULTS AND DISCUSSION

Effect of slaughter ages on carcass traits and meat quality of ningxiang pigs
 
The study found that there was no significant change in skin percentage, the redness at 120-day age was significantly lower than that at other slaughter ages, shear force and drip loss increase first and then decrease with slaughter ages, the lean meat percentage, bone percentage, lightness and yellowness decreased gradually with slaughter ages, while other carcass and meat quality of Ningxiang pigs increased significantly (P<0.05). The results of lowest lean meat percentage on 240-day age in this study were inconsistent with the changing trend of the growth and development of pigs, which may be caused by the change of factors such as feeding management and environment. Carcass correlation analysis results were basically consistent with those of Ayuso et al., (2016) and Virgili et al., (2003), meat quality results were roughly similar to Virgili et al., (2003), indicating that the changes of these indices in the growth process of Ningxiang pigs were consistent with the growth law of pigs. However, the backfat thickness, loin eye area, shear force value, redness, lightness and yellowness results were different from Borah et al., (2016) and Ortiz et al., (2021), which may be due to the fact that muscle quality varies according to inherent differences such as breed, environment and sex in pigs (Table 1).
 

Table 1: Means of carcass traits and meat quality of ningxiang pigs at different slaughter ages.


 
Effect of slaughter ages on visceral organs weight and weights of bones and muscles of ningxiang pigs
 
In this experiment, the results demonstrated a significant decrease in the weight percentages of the heart, liver, lung, kidney and small intestine of Ningxiang pigs as slaughter ages, the weight percentage of large intestine increased significantly at 0-60 days. The spleen weight percentage increased significantly at 0-60 days, decreased significantly at 60-120 days, which was similar to the results of Jia et al., (2022) (Table 2). However, previous studies on the effects of different slaughter ages on the changes of visceral organ weight percentages are still lacking, and the evaluation of visceral organ weight percentages is an important biological characteristic used to assess the functional strength and developmental level of internal organs during the body growth process (Al-Khalaifa et al., 2019; Zhang et al., 2021). Therefore, it is very important for breeding work and future market development to explore the variation law of visceral organ weights at different slaughter ages.
 

Table 2: Mean visceral organ weights (as percentage of pre-slaughter weight) and weights of bones and muscles (in grams) of Ningxiang pigs at different ages of slaughter.


       
The results in this experiment revealed the weights of bones and muscles such as pectoral muscle, skull, lumbar spine of Ningxiang pigs significant increased with slaughter ages, which was roughly the same as the results of Zeng et al., (2022) (Table 2). Previous studies on the effects of different slaughter ages on the changes of bones and muscles weights are still lacking. However, compared to imported pig breeds, local pig breeds generally exhibit slower growth rates (Chen et al., 2023). Therefore, in the process of livestock production, the study of the change law of skeletal muscle weights with the increase of slaughter ages can lay a theoretical foundation for the improvement of economic benefits of livestock and poultry.
 
Correlations between various carcass traits at different ages of slaughter
 
The correlation coefficients between various carcass traits at different slaughter ages are presented in Fig 1.
 

Fig 1: Correlation analysis of main carcass traits of ningxiang pigs at different stages.


       
In line with the findings of Guo et al., (2021) and Wang et al., (2023), our experiment demonstrated significant positive correlations between pre-slaughter BW, dressing percentages at 60-day, 120-day and 180-day age and carcass weight in Ningxiang pigs. Pre-slaughter BW is one of the easiest indicators to measure and the data acquisition cost is low. Therefore, according to pre-slaughter BW, breeders can indirectly and quickly predict other important carcass indicators, especially dressing percentage and carcass weight, which will have important guiding significance for the selection of pigs with good carcass performance.
       
The correlation coefficients between various meat quality at different slaughter ages are presented in Fig 2. The pH45 of Ningxiang pigs in different slaughter ages was respectively correlated with shear force, pH24, drip loss and yellowness. The study results were consistent with the results of Wang et al., (2023). Research on the correlation of meat quality can enable breeders to indirectly select the related traits by measuring the main meat quality, which not only provides convenience for the determination of meat quality for breeders, but also provides a certain reference for the selection of pigs with excellent meat quality.
 

Fig 2: Correlation coefficients of meat quality of ningxiang pigs at different ages.


 
Regression analysis of carcass traits, visceral organ weight percentage, skeletal muscle weights, meat quality and slaughter ages of ningxiang pigs
 
In the study, there were significant regressions between the slaughter ages and these indices during the growth process of Ningxiang pigs (P<0.01) (Table 3). The study of Guo et al., (2021) are basically consistent with this experiment results, which were different from those of meat quality, might be due to the differences of animal species, slaughter weight and other basic factors, or related to differences in the speed of muscle color change caused by feeding management and environment. Previous studies on the regression analysis between visceral organ weight, skeletal muscle weights and slaughter ages were still lacking, however, the development degree of these indicators will also affect the economic benefits of livestock and poultry, so exploring the regression analysis between them were of great significance for the future development of pig industry (Cho et al., 2019; Shen et al., 2021; Ma et al., 2022).

Table 3: Regression equations for performance indices and slaughter ages of Ningxiang pigs.

CONCLUSION

The carcass traits, visceral organ weight percentages, weights of bones and muscles, and meat quality of Ningxiang pigs exhibited different changes as slaughter ages, and there were correlation among carcass traits and meat quality. The weight percentages of spleen, stomach and large intestine respectively reached the highest at 60-day, 120-day and 180-day-age, while the other organs weight percentages tended to be stable after sexual maturity (120~150 d) and body maturity (180~240 d). This study systematically analyzed the biological characteristics of the carcass traits and meat quality of Ningxiang pigs at different slaughter ages.

ACKNOWLEDGEMENT

Thanks for the financial support of the Natural Science Foundation of Hunan Province (2022JJ30317; 2021JJ30386), Hunan Innovation Platform and Talent Plan Project (2022NK4145), Science and Technology Major Project of Hunan Province (2021NK1009), Scientific and Technological Achievements Transformation and Industrialization Plan of Hunan Province (2022GK4016).

CONFLICT OF INTEREST

Authors declare no conflict of interest.

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