Introduction
Taking into account the conducted studies, the null hypothesis is that the high weight of the pig at birth correlates positively with a large number of primary and secondary developed muscle fibers.
Alternative Hypothesis
On the contrary, it can be assumed that the high weight of the pig at birth does not affect the development of type I and types II muscle fibers.
Results
The central question guiding this study was the attempt to establish the nature of the mutual connection between the development of both types of muscle fibers and the weight of the pig at birth. The experiment was preceded by the division of the general sample into three groups depending on weight and nutrition type. This included a low birth weight (LBW) piglet fed on a PUFA diet (no. = 3), a normal weight (NBW) and a PUFA diet (no. = 6), and a control group with normal weight and not subjected to a diet (no. = 5). For each animal, the carcass mass was determined, the percentage of different muscle fiber types, and the mechanical and physical characteristics of the samples were identified. The values obtained were arithmetically averaged and then searched for a statistical standard error of the mean (SEM).
Table 1 presents numerical data on descriptive characteristics for pigs fed on a diet and without it. As can be seen from the second line of the table, the average weight of animals classified as LBW was 38.43 kg, while the NBW average weight was 40.77 kg. In parentheses, for each of the numbers, the standard error values of the mean are given. Results illustrating the relationship between muscle fiber types and swine mass have been beneficial for this study.
In particular, as shown in the third line in Table 1, the highest percentage of primary fibers identified by the mATPase typing method was found in animals with low body weight, which was 13.67%. In comparison, pigs of normal weight at birth had only 9.27% of slow twitch muscle fibers. This striking fact is confirmed by a study of the mechanical and physical properties of primary muscle fibers. As can be seen from the sixth line, there is a positive correlation between myocyte diameter and carcass weight: as the weight of a pig drops, the diameter of the primary muscle fiber increases to 41.32 µm. Table 3 illustrates the relationship between primary fiber quantity and quality in different groups. For example, it can be seen that the dominant figures are for LBW, while NBW’s type I fibers are 67.81% of LBW’s one. It should be noted that although this nship seems obvious, the effect of polyunsaturated fatty acids (PUFA) as a nutrient diet is difficult to characterize as linear. In particular, Figure 1 illustrates the unpredictability of the dependence of fiber diameter on the mass of the pig in combination with the diet. For instance, increasing animal weight does not necessarily reduce the size of primary muscle fibers: when fed on a PUFA diet, the diameter was 3.6 percent lower compared to the control group.
The results of the study were correlated with measurements of the physical and organoleptic properties of the meat, which additionally showed a preponderance of lower body weight pigs. Warner-Bratzler shear force for this group was 33.60 N, while for the normal weight group, it was only 25.93 N. At the same time, cooking losses from the LBW group were highest, at 20.33% compared to 18.01% for the NBW group and 19.91% for the control group.
The data on the secondary fibers are of additional research interest, as they illustrate a positive relationship to the pig’s body weight. As can be seen from Table 3, the pigs in the NBW group had an increased content of IIa fibers, while the control group showed a more significant amount of IIb fibers. On the other hand, secondary muscle fibers are most developed in underweight pigs, with NBW having a reduced fiber diameter by more than ten percent.
Discussion
The undoubted importance of these results is that they provide a qualitative assessment of the relationship between the mass of a pig at birth and the quantity and quality of muscle fibers. It is worth acknowledging that the predominance of valuable market characteristics in low birth weight piglets is an astonishing and even paradoxical phenomenon, as it may seem that low birth weight is associated with underdevelopment of the embryo. In general, as shown above, the number of primary fibers, their diameter, as well as the diameter of the secondary ones, absolutely prevailed among LBWs over other groups. When analyzing the available scientific literature, it is not difficult to notice that numerous authors clearly support these results (Gondret et al. 101; Handel and Stickland 314). It is also fair to note that some researchers have shown a negative correlation, indicating that animals with low weight are less muscular (Lee et al. 584). Returning to the results, it can be seen that higher numbers and dimensions of muscle fibers of the type I and type II are common among LBW category animals for specific reasons, and therefore, the fundamental interest is to find out the mechanism of forming more wide muscle fibers in LBW group pigs.
First of all, it must be noted that the primary muscle fibers, which are also slowly contracting, are responsible for the long-term exercise of aerobic nature. For this reason, the muscles of this type have a high mitochondrial density (Zhang et al. 1152). On the other hand, it should be noted that the linearity of the connection between fiber size and total muscle mass is well known: Staun postulates that the higher the thickness of the fibers, the more muscles are observed in the animal as a whole (304). Based on the above, it can be assumed that the delayed development caused by reduced body weight has an influence on the development of primary muscle fibers. One cannot rule out the possibility that this effect may be aimed at compensating for low weight, given the relatively low energy activation threshold. As Corona et al. have shown, severe animal trauma affecting muscle tissue can stimulate fiber development through the activity of myogenic host stem cells (9). In other words, piglets may have suffered during the perinatal period, which had the potential to provoke the development of type I and types II fibers.
On the other hand, a reduced number of muscle fibers of types IIa and IIb were found in pigs from the LBW group, while increasing their diameters. Secondary muscle fibers are known to be responsible for fast muscle twitch in the animal and hydrolyze ATP approximately twice as fast as Type I fibers (Types Of Muscle Fibers). Consequently, it may be assumed that the low weight of the piglet is negatively related to the development of fast fibers: the formation of Type I fibers is likely to inhibit secondary fiber development. As has been noticed in Handel and Stickland, if a piglet has a decrease in muscle mass, it is realized through the reduction of secondary fibers (311). However, the surprising discovery remains the fact that with comparatively fewer fast-twitched muscle fibers, their diameter remains dominant among all groups.
It has been observed that the LBW pigs had higher rates of mechanical Warner-Bratzler Shear Force. Given that this characteristic is closely associated with the strength of the specimen, the increased content may indicate a higher relative hardness of the meat due to the abundance of muscle mass (Novaković and Tomašević 2). However, Guo illustrated that small pigs of small breeds have less mechanical strength, which may indicate a high variability of this characteristic and low association with the subject of interest (1410). An additional effect reflected in this study was a relatively significant reduction in the weight of a piece of meat after culinary treatment. This is not surprising, as meat is known to be compressed by reducing the excess water contained in the all types of fibers. Given that LBW pigs had a cumulatively larger number of primary fibers and thicker secondary ones, this mass decreasing during cooking fits into the theoretical model.
Works Cited
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