Abstract
Muscle growth in pigs occurs in two stages: prenatal and the final postnatal phase. The prenatal phase is characterized by massive cell differentiation leading to an increase in the number of fibers. In contrast, postnatal development results from the enlargement of fibers and minimal hypertrophy (Hoon et al., 2016). This study assesses muscle growth’s influence on the final pork quality and factors that inhibit carcass growth. The pig breed, diet, age, and location affect its protein accretion and carcass value. Consumers’ preference for pork is influenced by the carcass leanness, juiciness, flavor, and tenderness. Management practices can be enhanced to improve the carcass quality and mass that will fetch high profits.
Muscle texture and flavor are pork characteristics that have a positive effect on carcass acceptance in the market. Therefore, they affect the competitiveness of the carcass in the meat industry. The pig’s age at slaughter also determines the pork quality, and only mature ones should be taken for slaughter. Farmers must choose pigs that will give high yields.
Keywords: postnatal, tenderness, prenatal, leanness, muscle.
Introduction
Modern pig production focuses on various breeds and piglet weights, which can offer high productivity and efficiency. The pork’s quality entirely depends on intramuscular fat (IMF) and fatty acid contents, which affect the strain genes, location, diet, and age (Molik et al., 2018). During prenatal muscle growth, preadipocyte division is very active but slows down with age. During the postnatal stage, hypertrophy is an important issue determining IMF content. Pork offers a variety of nutritional benefits to people, and its production needs to be improved.
Prenatal Muscle Development
Myogenesis is a process through which muscles are formed at the prenatal stage. Myofibres are created from mitotic stem cells generated from the embryonic mesoderm (Molik et al., 2018). Muscle growth is the development of density, shape, mass, and function of mitotic cells. Myotubes look like many sticks wrapped up for firewood (Santos et al., 2020). In contrast, myofibrils are a cylindrical group of filaments consisting of sarcomeres fundamental to fiber relaxation and contraction.
Prenatal muscle growth in pigs occurs majorly due to increased fibers; a phenomenon referred to as hyperplasia. However, cell growth is a factor of cell division, DNA (Molik et al., 2018). The DNA, protein, and weight of the cell all increase proportionally and ultimately increase the cell size. The myoblasts that remain unused during fusion are stored in the fiber as long as the muscle is not damaged: a point at which they differentiate into new cells to replace the dead or damaged ones. During the prenatal stage of mass development, initial fibers called primary fibers are formed (Hoon et al., 2016). The primary fibers then establish a surface for attachment and fusion of the myoblasts as they create the secondary ones. This forms the basis for postnatal muscle development.
Postnatal Muscle Development
While prenatal muscle growth results from the increment in the number of fibers, postnatal mass development is achieved due to enlarged circumference and the existing hypertrophy length of myofibres. Postnatal muscle development is achieved by combining DNA hyperplasia and a rise in the DNA protein. The soar in the protein ratio represents the rise in the cell size (Hoon et al., 2016). During this stage, there is little or no hyperplasia occurring in the pig’s carcass. However, there is a rapid hypertrophy of DNA. Biochemical processes majorly drive hyperplasia during the postnatal phase (Hoon et al., 2016). An enlargement in DNA leads to a corresponding rise in the number of nuclei that a given muscle fiber contains, building more mass and a more massive carcass, which provides quality pork.
However, various pig strains experience a different rate of muscle growth. The variation in the rate of growth is linked to the duration of a growth phase. Small pig strains have reduced growth and smaller carcass mass, suggesting that they possess tiny myofibers than the larger ones. Barrows with larger muscles take exceptionally more extended periods to reach their potential growth; hence take a long time to be ready for the market. However, barrows always have larger weights than miniature pigs (Molik et al., 2018). Though the number of fiber remains constant past the neonatal phase, pork muscles contain satellite cells that can differentiate, fuse, and increase adjacent fibbers.
The nucleus of the satellite cells is added to the muscle fibers. These satellite cells are distributed across the body of muscle fibers. Their numbers vary depending on the type of nature and fiber available. However, they are majorly in young pigs compared to the older ones (Hoon et al., 2016). The level of their activity is a factor of several protein hormones. They are likely to be responsible for the state of the cells. Growth enhancers can overcome environmental and nutritional factors that can affect muscle fiber development.
How Primary and Secondary Muscle Fibre Affect Carcass Size
Pigs experience biphasic muscle growth, which involves establishing many primary myofibres in the presumptive organ areas. Later, tiny secondary fibers from the fusion of myoblast form on the surfaces of the natural fibers. The primary fibers exhibit slow contraction properties, while the secondary ones experience faster contraction properties (Molik et al., 2018). The number of primary myofibres always remains constant in pork. In contrast, the secondary myofibrils populations are aspects of many environmental factors and growth proteins. Pigs that are starving tend to have a reduced number of secondary myofibres. In this case, a pig receives certain harmful hormones that restrict the formation of the myoblasts.
The carcass size of pork is an indication of protein accretion. The pigs require a considerate level of carbohydrates and other essential nutrients for energy purposes. Furthermore, when intake is low, proteins are metabolized to provide energy. This reduces protein content in the body, as there is low protein retention; hence, the carcass size reduces. Large muscle indicates a more extensive lean meat content in livestock, translating into enormous carcass weight (Hoon et al., 2016). It is crucial to determine the fiber size, and choosing the sizes involves measuring the muscle diameter. Larger fiber diameters represent hypertrophic growth, which proceeds until the pig attains its potential size.
Birth Weight
Pigs are either having a small or big birth weight; it is necessary to determine which of the two is more beneficial to the carcass size and quality. This is because a piglet weight translates to its profitability to the farmer when it has reached its potential. Piglets’ birthweight falls either below or above 1.4 KG (Rekiel et al., 2015). When a pig weighs 1.4 or more, it is likely to reach its market potentials and fewer growth complications. Piglets with weights less than 1.4KG are likely to die pre or during weaning stages. According to data presented at the American Society of Animal Science meeting, the average litter size is 14.3 piglets, out of which 13.1 are live born (Rekiel et al., 2015). The average weight at birth is 1.46 kg. According to the data, total mortality is 17.5%, and the mass of 1.13 kilograms represents a breaking point and determines the offspring’s pre-meaning survival chances. Above this weight, the survival percentage is 92%, while the chances are 58% (Santos et al., 2020). The table below shows the effect of birth weight and rearing methods piglets on sampled slaughter traits of pigs. It shows that piglets with a high birth weight can produce a high muscle percentage that gives quality lean meat compared to those with fewer weights.
Table 1: Effects of birthweight on piglet muscle, backfat and loin eye area (Rekiel et al.,2015)
Increasing the weight at birth is, therefore, a prerequisite to obtaining highly quality piglets. It is achieved by increasing quality feeding to the sow. Birthweight is also affected by various factors, which include the age and size of the gilt. The sow’s overall health condition also affects the growth of the litter (Molik et al., 2018). The sow’s feeding regime and feeding practices affect the offspring’s muscle growth.
How Collagen Affects Muscle Tenderness
Collagens facilitate flexibility and elasticity in muscles, tendons, ligaments, and other connective tissues. This tissue positively contributes to pork texture and tenderness. Collagens are closely wrapped together to provide strength and structure. They form reducible crosslinks, but they mature as the pig ages (Santos et al., 2020). Development leads to the toughness and roughness of the muscles. Therefore, older pigs possess mature collagen crosslinks compared to the tender ones; this makes their muscles more rigid. Population summary statistics for carcass traits, the data adopted from (Barducci et al.,2020) It shows that carcass weight and muscle depth is positively related to lean yield while fat depth is negatively correlated with pork leanness. Therefore, it suggests that deeper muscle growth is necessary for a high-quality lean meat.
Table 2: Showing statistics of carcass strains.
A high growth rate also results in mature crosslinks in the pork muscles, reducing the pork’s quality. Therefore, it is necessary to consider pork quality in the breeding selection of the first growing strains. The availability of food and the genetic base of a given breed also affect meat tenderness. Energy or amino acid intake, genotype, sex, and other environmental factors influence meat leanness and tenderness (Hoon et al., 2016). However, ecological stresses are majorly crucial in the growth of lean meat. It needs management efforts to control these factors to improve carcass quality.
Market Preference for Pork Quality
Customers assess the final carcass quality in terms of meat tenderness, leanness, and flavor when cooked. The firmness and texture of muscles, to a greater extent, affect pork quality (Santos et al., 2020). Consumers’ quality of pork is linked with their taste measurements of tenderness, flavor, leanness, and texture. However, the overall visual appearance plays a significant role while evaluating carcass quality by observation.
The varying pork tastes result from three factors: breed, diet, and other traits associated with meat quality, including color, fat content, and pH. Meat with a pH between 5.8 and 6.0 gives high-quality texture, taste, and tenderness, which many consumers accept (Hoon et al., 2016). High contents of fatty acid in the carcass also possess a juicy flavor and a lump of tender meat that visually satisfies consumers’ demand. Pork consumption varies in different countries and individuals depending on ethnic and religious inclinations. Some religious beliefs discourage the consumption of pork, for example, the Islamic communities.
Meat leanness indicates low-fat content in the carcass, which may be a factor of nutritional feeds, genetic base, and pig strain, affecting muscle growth and development. Muscle growth is a matter of fusion myoblasts; retaining more proteins in the carcass produces fatty pork. While conversion of these proteins into energy exchanges these fats into leans. It requires more than 3.5 times more energy to deposit fat (Nevrkla et al., 2017). After converting all fats, lean growth increases, and the available feeds used for maintenance.
Comparison between the Effects of Slaughter Time Pork Leanness
Aging affects the carcass content, intramuscular fate, and meat quality at the slaughter time. The old pigs have pH that is accepted, and their meat does not reduce during cooking compared to the younger ones (Hoon et al., 2016). The appropriate age for pig slaughter is at least ten months because it has larger muscles with lean meat. Pigs aged ten months or more produce redder and have a dark appearance that attracts the customers. Young hams of age eight months or less have fewer muscles in their carcass, and their pork is watery; such meat does not have a flavor sensation when eaten (Rekiel et al., 2015). Therefore, it is more profitable to rear barrows that will reach maturity very fast, and their fibers are maturing after a short period.
Effects of Feeding Regulation on Meat Leanness
The nature and quantity of feeds given to pigs ultimately influence their meat leanness. A fat pig has more fatty acid content and therefore does not have lean pork. They can adjust their nutritional intake to respond to their energy imbalances (Gondret, et al., 2006). When there is low energy in the body, pigs consume more food to regain energy balance. When a barrow and gilts are experimented with and subjected to a different level of feedings, the well-fed barrows will have higher carcass weight than the less fed gilts. Pork acceptance for consumption is higher for the barrows than the gilts (Hoon et al., 2016). Meat from the barrows contains a low amount of PUFA in their subcutaneous fat and a higher amount of intramuscular fat than beef from gilts.
Feeds rich in omega3 fatty acids increase the muscles’ firmness and improve the final grade; fatty acids diet, however, reduces firmness. A pig approaching slaughter time needs to experience reduced feeding, as continued feeding is likely to negatively affect the meat tenderness (Hoon et al., 2016). During this stage, feeding protein-deficient foods will improve the fat contents’ marbling making the carcass leaner and juicier with less water content.
Effects of Breed and Sex on Meat Quality
Pork meat is an ingredient for a healthy nation, hence developing breeds that can provide high-quality output is essential. The castrated pigs always have higher carcass weight and fat content than the gilts. Male pigs are castrated to enhance their meat production characteristics (Hoon et al., 2016). However, they pose increased risks of sexual behavior and aggression. Immuno-castration is currently done to male pigs by surgical means.
The immuno-castrates have competitive muscle production, which gives a high-quality carcass. Further, pork from immuno-castrates is similar to those of barrows, and the boars have a leaner carcass than the castrates (Handel & Stickland, 1987). A crossbreed always provides higher muscle mass than the native breeds; however, these local breeds are used for crossbreeding because they ate mostly preferred by most consumers.
Estimation of Carcass Leanness
It is necessary to classify the carcass based on traits such as leanness, tenderness, color, and texture for market purposes. In Europe, pork is classified based on its lean meat composition using an established classification sys classifying the carcass based on the fat thickness and muscle. The system uses alphabetical letters to classify the meat example (E, U, R, O, AND P) according to the table below.
Table 3: Showing classes of pork according to European Classification system. This data was adopted from the website of American Meat Science Association page 144
(Walstra, 1992)
Pork is an excellent source of nutrients for human consumption. It contains essential minerals and vitamins necessary to maintain body muscle during old age and those trying to lose weight. Carcass provides selenium, niacin, thiamin, vitamin B12, and B6 (Hoon et al., 2016). It is also a good source of iron, potassium, zinc, and magnesium. Pork also gives the body quality protein and helps in muscle building and weight gain. However, it is advisable to consume the carcass’s leanest cut, as it is the richest in nutritional requirements.
Conclusion
In conclusion, muscle development is responsible for quality carcasses in pigs and other livestock. The satisfaction of customers and consumer preferences is a vital determinant of their likelihood of purchasing pork. Therefore, pig farmers must concentrate on improving muscle growth and quality to ensure high valued body. This will ensure that there is the pork industry’s continued operation and earn the farmers extra income.
References
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