1. Introduction
Growing consumer nutritional awareness has been accompanied by a demand for the availability of food products on the food market with high, stable, and scientifically verified nutritional and dietary value, for example, meat and offal, i.e., internal organs used in cuisines. The high nutritional value of these food products is determined by their chemical compositions of basic nutrients and their mineral profiles. The nutritional value of meat in poultry production can be modulated through controlled nutritional programs [
1,
2,
3]. One method for dietary modification of nutrient content, especially in terms of regulating the calorific value of poultry muscles and organs, is based on the inclusion of high-fat seeds to feed mixtures [
4,
5]. Consumers expect that regional feed materials or those common to traditional local cuisines are used in the production of foods of animal origin [
6]. Hence, seeds of local oilseed plants, for example, camelina, flax, or sunflower, seem to be valuable [
7,
8,
9].
One of the effects of poultry nutrition with camelina, flax, or sunflower seeds is the increased dietary value of poultry meat, i.e., lower fat content and an improved ratio of n-6/n-3 fatty acids [
10,
11,
12]. Researchers have also reported that supplementation of poultry diets with oilseeds has a positive effect on rearing performance and slaughter parameters [
13,
14].
The nutritional value of camelina, flax, and sunflower seeds in poultry production may be largely limited by their content of substances with antinutritional properties, for example, linatin, cyanogenic glycosides, phytins, trypsin inhibitors, lignins, and saponins [
15,
16]. They may, to some extent, limit the growth and production potential of broiler chickens [
11]. Methods employed for fodder processing can help to eliminate the negative impact of the antimetabolites contained in oilseeds. Thermal methods, such as micronisation, are a particularly effective solution to this problem [
17].
There is still little information in the literature about the effect of the addition of micronised oilseeds to chicken feed mixtures on the content of macronutrients and micronutrients in poultry meat and internal organs. Therefore, the aim of this study was to analyse the impact of the use of micronised high-fat seeds (camelina, flax, and sunflower) in feed mixtures for broiler chickens on the nutritional and dietary quality of meat and offal in terms of basic nutrient contents and mineral profiles. Additionally, the impact of the supplementation on basic slaughter and blood parameters reflecting the health status of the chickens was assessed.
4. Discussion
Oilseeds are regarded mainly as a source of fat, especially given their high content of valuable and health-enhancing polyunsaturated fatty acids (PUFA). They also contain antinutritional substances, which can substantially reduce the feed conversion ratio and nutrient availability. This, in turn, may lead to a decline in the efficiency of animal production. Raw flax and sunflower seeds contain trypsin inhibitors. Camelina seeds are additionally characterised by the presence of glucosinolates [
35]. In turn, flax seeds contain linamarin, mucilages, and other cyanogenic glycosides [
10]. Young birds are particularly sensitive to these factors, which may slow down the rearing process considerably [
6,
36]. Thermal processes, including micronisation, may effectively reduce the negative impact of antinutritional substances on the rearing performance, without elimination of the positive impact of the high nutritional value of fat on the dietary quality of meat and internal organs.
A beneficial effect of supplementation of feed mixtures with thermally processed oilseeds, i.e., reduction in the abdominal fat content of broiler carcass, was also reported by Parveen et al. [
36]. The authors used thermally processed flax seeds in poultry nutrition and observed reduced crude fat content in breast and thigh muscles. The results are in line with those presented in this study. As explained by Anjum et al. [
37], the reduced fat content in muscles and internal organs of broilers fed mixtures with thermally processed flax seeds was associated with the high availability of long-chain fatty acids in the feed. A similar phenomenon was also reported by Liu et al. [
38], who conducted an experiment on ducks and reported a significantly higher efficiency of conversion of longer-chain FAs C20:5(n-3) than in the case of C22:6(n-3). Ducks receiving a diet rich in this type of fat were characterised by high accumulation of lipid droplets in the liver. The authors suggested that the diets enriched with various fatty acids had a strong influence on PUFA deposition in tissue lipids. Supplementation with various levels of extruded flax seed was found to contribute to a significant reduction in the fat content of breast and thigh meat. A similar phenomenon, consistent with the present results, was also reported by Pietras and Orczewska [
39]. The authors showed that the inclusion of camelina oil to the feed mixture contributed to a reduction in abdominal fat of carcasses. A decrease in the fat content of breast and leg muscles in quails was also reported by Jakubowska et al. [
40] in experiments based on supplementation of feed mixtures with 4% and 7% of flax seed. The authors emphasised that the mechanism of the modification of adipose tissue deposition by the presence of PUFA in feed has not been fully elucidated.
PUFAs are also believed to be involved in the induction of mitochondrial uncoupling proteins, which may reduce the dietary energy in animals fed an n-3 PUFA-rich diet. This energy can be dissipated or can be used to increase protein deposition [
41,
42,
43]. The authors reported an increase in the protein content in breast muscles accompanied by reduced levels of fat, which confirmed this thesis. A similar mode of protein and fat deposition was also noted in the present study, especially in the internal organs (proventriculus and heart).
As explained by Parveen et al. [
36], the higher liver, heart, and kidney weights in the group of birds supplemented with extruded flax seeds were associated with increased protein synthesis in these tissues. These data correspond with the results presented in this study. As compared with the control group, the proventriculus weight was significantly higher in the experimental variants (CAM.IR, FLA.IR, and SUN.IR), and the liver and heart exhibited a tendency toward an increase in weight.
There is little information in the literature on the use of micronised oilseeds in poultry production. There are, however, reports of the effect of supplementation of poultry diets with thermally processed (e.g., extruded) oilseeds. In a study on broiler chickens, Anjum et al. [
37] analysed the effect of supplementation with extruded flax seeds. The authors found that the administration of extruded flax seeds in the chicken diet significantly improved the quality as well as the dietary and functional properties of poultry meat. Similar studies were conducted by Zhaleh et al. [
44], who analysed the effect of the addition of 5, 10, and 15% extruded flax seeds to the diet in the last rearing period (finisher). The authors concluded that the 10% dose of the experimental seeds in the broiler diet proved to be beneficial for production efficiency as compared with the birds fed with the standard mixture (control).
There is insufficient information in the literature about the effect of diets containing raw and thermally processed high-fat seeds on the mineral composition in muscles. The higher concentrations of Fe and Cu in the muscles, Cu in the proventriculus, and Fe in the heart in the CAM.IR, FLA.IR, and SUN.IR treatment groups may be associated with the high blood levels of these elements, to some extent reflecting their concentrations in the entire organism. The levels of iron and copper in an organism largely depend on the diet and the degree of gastrointestinal absorption [
45]. Equally interesting is the higher level of Ca in the breast muscles and liver of the CAM.IR and FLA.IR broiler chickens as compared with the control. As demonstrated by investigations of broiler chickens conducted by Gümüş et al. [
45], an adequate level of Ca in the diet inhibits the intensity of lipid peroxidation in meat with maintenance of adequate dietary nutrient proportions in meat. The authors proposed that the combination of Ca sources with natural antioxidants in the diet could be used to improve carcass characteristics and antioxidant capacity in broiler meat.
In the present study, the content of other minerals in the breast and drumstick muscles and the analysed organs did not differ significantly, irrespective of the energy source in the diet (infrared-irradiated camelina, flax, and sunflower seeds). This issue requires further multidirectional research. Nevertheless, the present results suggest some possibilities of modulation of the level of minerals, especially the haematopoietic micronutrients, in meat and internal organs used by consumers as the dietary source of these elements.
The analysis of selected haematological indices was performed to assess the possible adverse effects of the micronised oilseeds on the health status of the animals. The dietary inclusion of camelina and flax seeds to the diet significantly decreased the haemoglobin level and MCHC (haemoglobin-related index) as compared with those in the control diet and the sunflower seed treatment. Our previous study analysed the addition of raw oilseeds in broiler chicken nutrition also indicated a decrease in the haemoglobin level in supplemented groups [
46]. Other studies conducted with the use of two flaxseed varieties in rabbit nutrition have shown a decrease in RBC, HGB, MPV, and PCV in the blood of the experimental animals [
47]. The reduction in the level of haemoglobin and MCHC induced by the FLA.IR supplementation may be related to the content of cyanogenic glycosides (linamarin, linustatin, and neolinustatin) and enzymes (
β-bis-glucosidase,
β-monoglucosidase, and
α-hydroxynitrile lyase), which are involved in the hydrolysis of cyanogenic glycosides and the release of hydrocyanic acid [
35,
48,
49]. Hydrogen cyanide and cyanide salts are toxic to an organism, as they block cellular respiration enzymes and inhibit the activity of other enzymes due to their ability to bind with iron, manganese, or copper ions, which are part of the functional groups of many enzymes. Hydrogen cyanide has the ability to bind with blood haemoglobin to form cyanohaemoglobin, which does not dissociate into haemoglobin [
50,
51]. In turn, camelina seeds contain glucosinolates (glucoarabin, glucocamelinin, and 11-(methylsulfinyl)-undecylglucosinolate), which do not pose a threat to animal health, but their degradation products, for example, isothiocinate, nitrile, and thiocynate, exhibit multidirectional biological activity [
35].
The determination of metals and other elements in biological material, for example, in blood plasma, is highly important for assessing not only environmental exposure but also the proper supply and transformation of elements in organisms [
52,
53]. The FLA.IR treatment was observed to modify the content of Fe in the blood, muscles, and organs. The concentration of iron in blood depends on Fe abundance in the diet and on the absorption of this element in the gastrointestinal tract and the intensity of the decomposition and synthesis of haemoglobin [
54]. Probably, the presence of cyanogenic glycosides in flax seeds and their influence on the formation of cyanomethemoglobin mobilises iron stores and increases its blood plasma level. Other anti-nutrients present in oilseeds, for example, phytic acid, tannins, and glucosinolates, may affect the availability and status of these elements in an organism as well [
15,
16,
35,
40].