Analysis of Sodium and Potassium Content in Selected Tissues of Mallard Ducks (Anas platyrhynchos L.) Depending on the Hunting District and the Sex of the Birds

Abstract

Changes in the habitat of wild mallard ducks (Anas platyrhynchos L.) and thus in their diet can result in significant differences in the content of sodium and potassium in their tissues and organs. There is little data in the available literature regarding the qualitative analysis of mallard meat and organs. The aim of the study was to determine the sodium and potassium content in biological material (breast muscle, leg muscles, and liver) from wild mallards and the effect of sex and place of origin (hunting district) on these parameters. Sodium and potassium in the biological material were analyzed by inductively coupled plasma atomic emission spectroscopy (ICP-OES). The sodium and potassium levels in the tissues were shown to be influenced by the sex of the mallards and the site where they were harvested. Sodium content was significantly higher in the liver of male mallards than in females. In most cases, the tissues and organs of mallards harvested in the Siedlce hunting district had higher levels of sodium and potassium, apart from potassium content in the breast muscle. This may indicate greater abundance of these elements in this district.

1. Introduction

Consumers are increasingly interested in safe, healthy food products [1]. They expect meat products available on the market to have the required nutritional value and to be healthy, fresh, and low in fat [2]. The production and consumption of duck meat around the world dates back many centuries [3]. Contemporary farmed ducks grow more rapidly, owing to genetic selection, efficient rearing systems, and improved nutrition. However, selection for rapid growth and high yield can have adverse effects on the functional and sensory properties of meat [4]. In contrast, the nutritional value of wild mallard ducks is beneficial due to their high protein content and favourable proportions of fatty acids [5,6,7,8,9,10]. Wild mallard meat is of high quality, and seasonal hunting can provide meat with beneficial nutritional characteristics which attract consumers [11]. Cobos et al. [12] showed that the meat of wild birds, including mallards, is nourishing, with high protein content and low content of total fat and saturated fatty acids. It is also relatively rich in valuable nutrients such as eicosapentaenoic acid, docosahexaenoic fatty acids, and iron. Mallard meat has good nutritional potential as a component of a varied diet or as a delicacy. Animal products, including the meat of game animals, are an important source of mineral salts in the diet. Minerals are unevenly distributed through the body, and their content in individual tissues depends on multiple factors, including the species of animal and its activity, the function of a given tissue, the animals’ diet, and pre-slaughter handling [13]. Slaughter animals and game animals differ in the levels of mineral salts in their tissues. This may be due to the fact that wild animals, which move across considerable distances, seek natural food and selectively eat what they need and what is available in their environment at a given moment. Slaughter animals in large-scale production, on the other hand, are kept in strictly defined environmental conditions and receive the same diet, balanced for their nutritional needs, throughout the production cycle. Dzierżyńska-Cybulko and Fruziński [13] reported that the differences between the contents of individual mineral salts in meat can easily be seen in white and red muscles. The former have a higher content of phosphorus compounds, while the latter have more compounds containing chlorine, zinc, potassium, sodium and calcium.

Sodium (Na) is a soft, silvery-white, highly reactive mineral. It is one of the most common elements in the Earth’s crust. In higher organisms, it is mainly present in extracellular and body fluids. Its biological role is very broad. It regulates the osmotic pressure and pH of the plasma, is essential to the functioning of the sodium–potassium pump, and takes part in protein biosynthesis and mineralization [14]. It is essential to the functioning of the nervous and muscular systems [15]. Sodium deficiency (hyponatraemia) in higher organisms leads to disturbances of the water–electrolyte balance, functional changes in cells, disturbances of protein synthesis, a decrease in blood pressure, and gradual cerebral oedema [14,16]. It can also lead to convulsions and coma. In animals, reduced feed efficiency is observed as well. An excess of sodium (hypernatremia) is toxic to the body and leads to serious poisoning. In humans, excessive sodium in the diet can cause circulatory failure, chronic glomerular disease, stroke, stomach cancer, and death [15]. Symptoms observed in birds include increased irritability, nasal discharge, and a fluid-filled crop, leading to a dramatic increase in mortality [14].

Potassium (K) is a soft, silvery-grey mineral and one of the most common elements in nature. Potassium is an intracellular cation, and within cells it performs a function similar to that of sodium in body fluids. Potassium is the main component of cellular protoplasm [15]. It is an essential element for cardiac function. In addition, it maintains appropriate osmotic pressure in the body, regulates the body’s pH and water–electrolyte balance, activates the activity of intracellular enzymes, and regulates muscle contractility [14]. Potassium increases cell membrane permeability, regulating the degree to which amino acids such as glycine and lysine pass through the membrane to the interior of cells. Deficiencies of this element (hypokalaemia) in the body may arise due to vomiting, diarrhoea, or treatment with diuretic drugs. Symptoms of potassium deficiency in people and animals can lead to disturbances in cardiac function and in the nervous and muscular systems. Hyperkalaemia (excess potassium in the body) is manifested in humans as slowed cardiac activity and nervous or muscular disorders [15], while an excess of this element in animals leads to tibial dyschondroplasia and diarrhoea [14].

Sodium and potassium were chosen for the research because they perform important physiological functions. Their content is regulated by the sodium–potassium pump. These elements regulate osmotic pressure in humans and animals. The scientific literature lacks information on the availability and quantity of sodium and potassium in the meat of wild mallards. This is due to the fact that the meat of this species is not very popular due to its difficulty in obtaining and its specific taste. However, the growing trend of culinary tourism, in which tourists embark on a journey to discover the wildlife and traditions of a given region, makes mallard meat an attractive culinary ingredient. Changes in habitat and diet can result in considerable differences in sodium and potassium content in the tissues and organs of these birds. Given the scarcity of research devoted to qualitative analysis of the tissues and organs of wild mallards, the aim of the study was to determine the sodium and potassium content in biological material from wild mallards (Anas platyrhynchos L.), i.e., in the breast muscle, leg muscles, and liver, and to assess the effect of sex and place of origin (hunting district) on these parameters.

2. Materials and Methods

2.1. Animals and Sample Collection

The experiment was conducted using tissues and organs from wild mallards (Anas platyrhynchos L.) harvested in two study areas. The first area was the Siedlce hunting district, and the second was the Leszno hunting district. The two areas have different environmental resources and different levels of contamination with heavy metals, so it was important to compare the results from the two areas. A detailed description of the environmental differences in the studied hunting areas was presented in the work of Bombik et al., 2023 [17]. The period for obtaining material from mallards in these areas was limited to the first two months of the hunting season for the species, i.e., from 15 August to 15 October, before the birds had begun to migrate. Six males and six females from the Siedlce hunting district and eight males and eight females from the Leszno hunting district were obtained for the research. The research material was obtained, as part of the annual hunting plan, by hunters who have statutory powers to manage the game animal population. The exact method of obtaining wild mallard ducks for research is presented in the work: Bombik et al. [18].

2.2. Laboratory Analysis

Sodium and potassium in the breast muscle, leg muscles, and liver were determined by inductively coupled plasma atomic emission spectroscopy (ICP-OES) using the Perkin Elmer Optima 2000 DV spectrometer (Springfield, IL, USA) following digestion of the material in the Anton Paar Microwave system (Graz, Austria). After thawing, the material was homogenized in an agate mortar. Weighted samples of about 1 g were transferred to quartz pressure vessels, to which 5.0 mL of 65% HNO3 (SuprapurTM, Merck, Rahway, NJ, USA) and 1 mL of 30% H₂O₂ (SuprapurTM, Merck) were added. The vessels were tightly sealed and placed in the mineralizer, which was equipped with a constant temperature- and pressure-control system. The cooled and degassed (CO₂, NO₂) digest was made up to 10 mL in class A volumetric flasks (BRAND, Wertheim, Germany) [7]. The analytical wavelengths and instrument detection limits: Na 568,263 nm; DL 1.5 μg·L⁻¹, K 766,491 nm; DL 1.5 μg·L⁻¹. Radiation emissions were measured in the prepared solutions, reading radially (across the plasma) for Na and K. Content of Na and K were determined in mg·kg⁻¹ w.w. (wet weight).

2.3. Statistics

For each trait in each group, i.e., for hunting districts and sexes, basic measures of descriptive statistics were determined, i.e., arithmetic mean ($\overline{\mathrm{x}}$), range of variation (x_min.–x_max.), standard deviation (s), and coefficient of variation (V%).

In addition, non-orthogonal two-way analysis of variance (the Fisher F-test) with interaction was carried out according to the following mathematical model:

y_ijl = m + a_i + b_j + ab_ij + e_ijl,

where

y_ijl—value of trait for ith hunting district (a = 2), jth sex (b = 2) and lth replicate (measurement)

m—grand mean

a_i, b_j—effects of the main factors, i.e., hunting district and sex

ab_ij—effect of the interaction of hunting district and sex

e_ijl—sampling error

Significant effects were compared by Tukey’s test, for a significance level of 0.05.

Statistical analysis of the results was carried out using Statistica 13.0.

3. Results

The results of the analyses of sodium content in selected tissues and organs of mallards (Anas platyrhynchos L.) depending on sex and hunting district are presented in

Table 1. Mean sodium content in selected tissues and organs of mallards (Anas platyrhynchos L.) (mg·kg⁻¹ w.w.) by sex and hunting district.

Tissue/Organ	Basic Statistics	Sex		LSD0.05	Hunting District		LSD0.05
		Female (n = 14)	Male (n = 14)		Siedlce (n = 12)	Leszno (n = 16)
Breast muscle	$\overline{\mathrm{x}}$ min.–max. s V%	252.1 a 165.3–362.1 58.55 23.23	266.7 a 180.0–413.4 77.34 29.01	n. s.	319.8 b 222.5–413.4 58.54 18.30	214.0 a 165.3–272.6 31.01 14.49	37.3
Leg muscles	$\overline{\mathrm{x}}$ min.–max. s V%	320.7 a 190.8–451.1 77.66 24.21	332.1 a 232.8–459.5 77.29 23.27	n. s.	388.1 b 250.7–459.5 61.1 15.76	280.1 a 190.8–379.8 52.50 18.74	47.6
Liver	$\overline{\mathrm{x}}$ min.–max. s V%	430.8 a 331.1–587.1 78.49 18.22	511.2 b 324.7–710.0 99.53 19.47	70.554	474.9 a 331.1–646.7 107.1 22.55	468.1 a 324.7–710.0 90.95 19.43	n. s.

Legend: $\overline{\mathrm{x}}$—arithmetic mean; min.–max.—extreme values; s—standard deviation; V%—coefficient of variation; LSD_0.05—least significant difference (p ≤ 0.05); ^a, ^b—means marked with different letters for sex and hunting district are significantly different (p ≤ 0.05).

, and the results for sex within hunting districts are given in

Table 2. Mean sodium content in selected tissues and organs of mallards (Anas platyrhynchos L.) (mg·kg⁻¹ w.w.) by sex within hunting district.

Tissue/Organ	Basic Statistics	Hunting District				LSD0.05 Femp. p
		Siedlce		Leszno
		Female (n = 6)	Male (n = 6)	Female (n = 8)	Male (n = 8)
Breast muscle	$\overline{\mathrm{x}}$ min.–max. s V%	303.7 a 233.2–362.1 43.69 14.38	335.9 a 222.5–413.4 66.54 19.81	213.3 a 165.3–254.5 32.63 15.30	214.7 a 180.0–272.6 29.29 13.64	n. s. 0.28 0.333
Leg muscles	$\overline{\mathrm{x}}$ min.–max. s V%	388.8 a 328.0–451.1 43.29 11.13	387.4 a 250.7–459.5 74.86 19.32	269.6 a 190.8–361.8 55.35 20.53	290.6 a 232.8–379.8 47.23 16.26	n. s. 0.34 0.355
Liver	$\overline{\mathrm{x}}$ min.–max. s V%	397.2 a 331.1–562.6 78.53 19.77	552.6 a 445.6–646.7 68.51 12.40	455.9 a 383.7–587.1 68.39 15.00	480.2 a 324.7–710.0 107.58 22.40	n. s. 0.46 0.479

Legend as for Table 1, F_emp—F-statistics, p—probability p.

.

Analysis of the mean sodium content in the breast muscle of mallards (Table 1) showed a higher level in males (266.7 mg·kg⁻¹ w.w.) than in females (252.1 mg·kg⁻¹ w.w.), although these differences were not statistically significant. A significantly higher average sodium level was recorded in mallards harvested in the Siedlce hunting district (319.8 mg·kg⁻¹ w.w.) than in those harvested in the Leszno hunting district (214.0 mg·kg⁻¹ w.w.). The coefficient of variation for the sodium content in the breast muscle of mallards for the hunting districts was 14.49% in the Leszno hunting district and 18.30% in the Siedlce hunting district. In both hunting districts (Table 2), the average sodium content was higher in the breast muscle of male mallards than in females, although these differences were not statistically significant.

Analysis of the sodium content in the leg muscles of mallards (Table 1) showed a higher average level in males (332.1 mg·kg⁻¹ w.w.) than in females (320.7 mg·kg⁻¹ w.w.), although these were not statistically significant differences. The average sodium content in the leg muscles of mallards harvested in the Siedlce hunting district (388.1 mg·kg⁻¹ w.w.) was significantly higher than in birds from the Leszno hunting district (280.1 mg·kg⁻¹ w.w.). The coefficient of variation for the sodium content in the leg muscles of mallards for the hunting districts was 15.76% in the Siedlce hunting district and 18.74% in the Leszno hunting district. In the Siedlce hunting district (Table 2), the average sodium level in the leg muscles of female mallards was higher than in males, while in the Leszno hunting district, the average value for this trait was higher in males than in females. These differences were not statistically significant in either hunting district.

The average sodium content (Table 1) in the liver was shown to be significantly higher in males (511.2 mg·kg⁻¹ w.w.) than in females (430.8 mg·kg⁻¹ w.w.). The coefficients of variation for the sodium content in the liver of mallards for sex were similar: 18.22% for females and 19.47% for males. Mallards harvested in the Siedlce hunting district had a higher average sodium level in the liver (474.9 mg·kg⁻¹ w.w.) than birds from the Leszno hunting district (468.1 mg·kg⁻¹ w.w.), but these differences were not statistically significant. In the Siedlce and Leszno hunting districts (Table 2), the average sodium contents in the liver of male mallards were higher than in females, but the differences were statistically non-significant.

The results of the analyses of potassium content in selected tissues and organs of mallards (Anas platyrhynchos L.) depending on sex and hunting district are presented in

Table 3. Mean potassium content in selected tissues and organs of mallards (Anas platyrhynchos L.) (mg·kg⁻¹ w.w.) by sex and hunting district.

Tissue/Organ	Basic Statistics	Sex		LSD0.05	Hunting District		LSD0.05
		Female (n = 14)	Male (n = 14)		Siedlce (n = 12)	Leszno (n = 16)
Breast muscle	$\overline{\mathrm{x}}$ min.–max. s V%	2268 a 2084–2647 126.36 5.57	2315 a 2126–2473 105.85 4.57	n. s.	2273 a 2084–2473 106.49 4.69	2306 a 2126–2647 125.49 5.44	n. s.
Leg muscles	$\overline{\mathrm{x}}$ min.–max. s V%	2106 a 1937–2724 189.83 9.01	2160 a 1940–2523 171.27 7.93	n. s.	2166 a 1948–2523 179.91 8.30	2108 a 1937–2724 180.98 8.58	n. s.
Liver	$\overline{\mathrm{x}}$ min.–max. s V%	1556 a 1306–1790 141.57 9.10	1643 a 1282–2004 166.59 10.14	n. s.	1658 a 1387–2004 150.91 9.10	1556 a 1282–1790 153.41 9.86	n. s.

Legend as for Table 1.

, and the results for sex within each hunting district are shown in

Table 4. Mean potassium content in selected tissues and organs of mallards (Anas platyrhynchos L.) (mg·kg⁻¹ w.w.) by sex within hunting districts.

Tissue/Organ	Basic Statistics	Hunting District				LSD0.05 Femp. p
		Siedlce		Leszno
		Female (n = 6)	Male (n = 6)	Female (n = 8)	Male (n = 8)
Breast muscle	$\overline{\mathrm{x}}$ min.–max. s V%	2231 a 2084–2386 98.84 4.43	2314 a 2170–2473 97.21 4.20	2296 a 2192–2647 137.11 5.97	2315 a 2126–2457 111.88 4.83	n. s. 0.98 0.789
Leg muscles	$\overline{\mathrm{x}}$ min.–max. s V%	2055 a 1948–2219 94.07 4.58	2277 b 2038–2523 176.74 7.76	2145 a 1937–2724 230.21 10.73	2072 a 1940–2191 99.36 4.80	195 4.28 0.003
Liver	$\overline{\mathrm{x}}$ min.–max. s V%	1599 a 1387–1744 117.98 7.38	1715 a 1495–2004 157.50 9.18	1524 a 1306–1790 149.03 9.78	1587 a 1282–1722 151.19 9.52	n. s. 0.76 0.688

Legend as for Table 1 and Table 2.

.

The highest potassium content, among all tested mallard tissues and organs, was noted in the breast muscle (Table 3). The average potassium level in the breast muscle was higher in males (2315 mg·kg⁻¹ w.w.) than in females (2268 mg·kg⁻¹ w.w.), although these differences were not statistically significant. The average potassium content in the breast muscle was higher in mallards harvested in the Leszno hunting district (2306 mg·kg⁻¹ w.w.) than in birds from the Siedlce hunting district (2273 mg·kg⁻¹ w.w.), but the differences were not statistically significant. The coefficients of variation for this trait, for sexes and hunting districts, were low and did not exceed 6%. In both hunting districts (Table 4), the average potassium level in the breast muscle was higher, though not statistically significantly, in males than in females.

Differences were noted in the average potassium level in the leg muscles of mallards (Table 3) between males (2160 mg·kg⁻¹ w.w.) and females (2106 mg·kg⁻¹ w.w.), but they were not statistically significant. The average potassium level in the leg muscles of mallards harvested in the Siedlce hunting district (2166 mg·kg⁻¹ w.w.) was higher than in birds from the Leszno hunting district (2108 mg·kg⁻¹ w.w.), although these were not statistically significant differences. Male mallards harvested in the Siedlce hunting district had a significantly higher average potassium level in the leg muscles (2277 mg·kg⁻¹ w.w.) than females (2055 mg·kg⁻¹ w.w.) (Table 4). In the Leszno hunting district, the level of this element was higher in the leg muscles of females (2145 mg·kg⁻¹ w.w.) than in males (2072 mg·kg⁻¹ w.w.), but in this district the differences were not statistically significant. The coefficient of variation for the potassium level in the leg muscles took on the most extreme values for females, ranging from 4.58% in the Siedlce hunting district to 10.73% in the Leszno hunting district.

The average potassium level in the liver of mallards (Table 3) was higher in males (1643 mg·kg⁻¹ w.w.) than in females (1556 mg·kg⁻¹ w.w.), although the differences were not statistically significant. The average potassium content in the liver of mallards was higher, though not statistically significantly, in birds harvested in the Siedlce hunting district (1658 mg·kg⁻¹ w.w.) than birds from the Leszno hunting district (1556 mg·kg⁻¹ w.w.). In both hunting districts (Table 4), the average level of this element in the liver was higher in males than in females, although significance of differences was not shown. Variation for this trait, measured as the coefficient of variation, was similar for both sex and hunting district, at about 10%.

4. Discussion

According to Kokoszyński and Bernacki [19] sodium levels in the breast and leg muscles of Pekin ducks ranged from 4.07 g·kg⁻¹ d.w(1140 mg·kg⁻¹ w.w.) to 5.48 g·kg⁻¹ d.w.(1530 mg·kg⁻¹ w.w.) and from 3.97 g·kg⁻¹ d.w.(1110 mg·kg⁻¹ w.w.) to 4.58 g·kg⁻¹ d.w(1280 mg·kg⁻¹ w.w.) Kokoszyński et al. [20] reported that the average content of this macronutrient in these muscles in Pekin ducks ranged from 3.28 mg·kg⁻¹ d.w.(0.92 mg·kg⁻¹ w.w.) to 4.47 mg·kg⁻¹ d.w.(1.25 mg·kg⁻¹ w.w.) and from 3.17 mg·kg⁻¹ d.w.(0.89 mg·kg⁻¹ w.w.) to 3.96 mg·kg⁻¹ d.w.(1.11 mg·kg⁻¹ w.w.). In the breast muscle of wild quail (Coturnix coturnix), the average sodium content was 50.38 mg·100 g⁻¹ meat, which was higher than in the present study. Farmed quail, on the other hand, had a 10.0% lower sodium content than its wild counterpart [21]. Herkel et al. [22] in Hybrid XL turkeys fed a diet supplemented with essential oils and fructooligosaccharides, observed an increase in the average sodium content in the thigh muscles and a decrease in the liver, from 2.75 g·kg⁻¹ d.w.(770 mg·kg⁻¹ w.w.) to 2.97 g·kg⁻¹ d.w.(830 mg·kg⁻¹ w.w.) and from 3.49 g·kg⁻¹ d.w.(1050 mg·kg⁻¹ w.w.) to 2.94 g·kg⁻¹ d.w.(880 mg·kg⁻¹ w.w.), respectively. Kokoszyński et al. [23], in a comparison of certain quality traits of the meat and liver of Muscovy ducks and mule ducks, showed that genotype had a significant (p < 0.05) effect on sodium content in the breast muscle. In comparison with the present study, the authors showed a significantly higher sodium content in the breast muscle of male and female Muscovy ducks (94.3 mg·100 g⁻¹ and 90.1 mg·100 g⁻¹, respectively) and mule ducks (50.7 mg·100 g⁻¹ and 50.9 mg·100 g⁻¹, respectively). The sodium content in the leg muscles of male Muscovy ducks was significantly higher than in females (70.7 mg·100 g⁻¹ and 54.3 mg·100 g⁻¹, respectively), and these values were higher than in the present study. Similar relationships were shown for sodium levels in the liver of male and female Muscovy ducks (103.0 mg·100 g⁻¹ and 85.5 mg·100 g⁻¹, respectively) and mule ducks (75.5 and 56.2 mg·100 g⁻¹, respectively). Majewska et al. [24] showed the highest sodium level in the liver of ostriches (1026.67 mg·kg⁻¹ w.w.), followed by turkeys (921.84 mg·kg⁻¹ w.w.) and broiler chickens (811.0 mg·kg⁻¹ w.w.).

According to Kokoszyński and Bernacki [19], the potassium level in the breast and leg muscles of Pekin ducks ranged from 15,050 mg·kg⁻¹ d.w.(4214 mg·kg⁻¹ w.w.) to 15,770 mg·kg⁻¹ d.w.(4415 mg·kg⁻¹ w.w.) and from 13,700 mg·kg⁻¹ d.w.(3836 mg·kg⁻¹ w.w.) to 15,280 mg·kg⁻¹ d.w.(4278 mg·kg⁻¹ w.w.), respectively. Kokoszyński et al. [20] reported that the average potassium content in these muscles in Pekin ducks ranged from 13.8 mg·kg⁻¹ d.w.(3.86 mg·kg⁻¹ w.w.) to 15.2 mg·kg⁻¹ d.w.(4.26 mg·kg⁻¹ w.w.) and from 12.0 mg·kg⁻¹ d.w.(3.36 mg·kg⁻¹ w.w.) to 14.1 mg·kg⁻¹ d.w.(3.95 mg·kg⁻¹ w.w.), respectively. Kokoszyński et al. [23], in their analysis of quality traits of the meat and liver of Muscovy ducks and mule ducks, showed higher potassium content in the breast muscle of male Muscovy ducks (359.4 mg·100 g⁻¹) than in females (352.2 mg·100 g⁻¹). The reverse pattern was noted for potassium levels in the breast muscle of mule ducks (321.4 mg·100 g⁻¹ in males and 344.6 mg·100 g⁻¹ in females); these values were much higher than those obtained in the present study. The potassium content in the leg muscles of Muscovy ducks was higher than in mule ducks. The authors showed higher potassium levels in these muscles in females than in males (331.2 mg·100 g⁻¹ and 330.0 mg·100 g⁻¹, respectively, for Muscovy ducks and 286.2 mg·100 g⁻¹ and 276.1 mg·100 g⁻¹ for mule ducks). The authors showed a higher potassium content in the liver of male Muscovy ducks and mule ducks than in females (220.0 mg·100 g⁻¹ and 203.0 mg·100 g⁻¹ and 219.1 mg·100 g⁻¹ and 195.4 mg·100 g⁻¹, respectively).

Kokoszyński et al. [25] compared some quality traits of the meat and liver of Muscovy and Pekin ducks and showed that the sex of the birds influenced the potassium content (in mg·100 g⁻¹) in the breast muscle and the sodium and potassium content in the leg muscles, while it had no significant effect on their content in the liver. The present study, on the other hand, showed a significantly higher sodium content in the liver of male mallards. The authors cited reported higher sodium content in the breast muscle of Pekin and Muscovy ducks in comparison with the present study. Similar tendencies were shown for the sodium level in the leg muscles and liver of these ducks. The potassium level in the breast muscle, leg muscles and liver of Pekin and Muscovy ducks was higher than in the mallards analyzed in the present study. The breast muscle of wild quail (Coturnix coturnix) had significantly higher average potassium content than the values obtained in the present study, amounting to 523.36 mg·100 g⁻¹ meat. The highest potassium content, 579.8 mg·100 g⁻¹ meat, was shown in the breast muscle of farmed Japanese quail (Coturnix japonica domestica) [19]. Wójcik et al. [26] demonstrated that the average potassium content in the breast muscle is influenced by transport. According to the authors, transport of broiler chickens over a distance of 300 km caused a decrease in the potassium level from 3.87 mg·g⁻¹ d.w.(1.08 mg·g⁻¹ w.w.) to 3.00 mg·g⁻¹ d.w.(0.84 mg·g⁻¹ w.w.) compared to the group that was not transported. According to Herkel et al. [22] the average potassium contents in Hybrid XL turkey hens ranged from 13,010 mg·kg⁻¹ d.w.(3643 mg·kg⁻¹ w.w.) to 13,630 mg·kg⁻¹ d.w.(3816 mg·kg⁻¹ w.w.) in the breast muscle, from 11,900 mg·kg⁻¹ d.w.(3332 mg·kg⁻¹ w.w.) to 12,780 mg·kg⁻¹ d.w.(3578 mg·kg⁻¹ w.w.) in the thigh muscles, and from 9670 mg·kg⁻¹ d.w.(2707 mg·kg⁻¹ w.w.) to 10,750 mg·kg⁻¹ d.w.(3010 mg·kg⁻¹ w.w.) in the liver. Majewska et al. [24] showed the highest average potassium contents in the liver of turkeys (2153.05 mg·kg⁻¹ w.w.), broiler chickens (1963.80 mg·kg⁻¹ w.w.), and ostriches (1938.61 mg·kg⁻¹ w.w.). Kokoszyński et al. [27] analyzed the effect of replacing part of a commercial feed with whole triticale grain on the quality of pheasant meat. They found higher sodium and potassium values in the breast and leg muscles of pheasants than was shown in mallards in the present study.

Consumption of mineral fertilizers (NPK) in the Greater Poland Voivodeship, where the Leszno hunting district is located, was greater than in the Masovian Voivodeship, which contains the Siedlce hunting district [17]. Excessive potassium application may have led to excessive K accumulation in plants and affected the electrolyte balance in the birds tested in the study. High K content in the plants may have inhibited sodium (Na) uptake by plants and reduced its content in the birds. Excessive nitrogen levels may also have reduced the sodium content in plants and disturbed the cation balance (K:Na and K:Mg) in wild mallard ducks.

5. Conclusions

The variation in sodium and potassium content in the tissues and organs of wild mallards (Anas platyrhynchos L.) may have been influenced by the abundance of these minerals in the environment and the birds’ diet. Diet composition is a factor that modifies the content of minerals in the meat and internal organs of birds. The sex of the wild mallards and the location where they were harvested were found to influence the sodium and potassium content in the tissues. The sodium level in the liver of males was significantly higher than in females. In the remaining cases, sodium and potassium content were higher in the tissues of males, but these were not statistically significant differences. In most cases, the tissues and organs of wild mallards harvested in the Siedlce hunting district were shown to have higher sodium and potassium content, except for potassium content in the breast muscle. The significantly higher sodium content in the breast and leg muscles of wild mallards in the Siedlce hunting district may indicate that the nutritional value of the meat of these birds is higher in this district.