1. Introduction
The utilization of herbs in animal production is in line with global trends for improving animal husbandry and breeding systems. The phytobiotic compounds present in herbs have a positive effect in improving health and increasing antioxidant potential, which contributes to the improvement of growth performance [
1,
2].
Milk thistle (
Silybum marianum L.) is a cosmopolitan plant native to the Mediterranean. This plant is rich in bioactive substances such as silymarin and taxifolin [
3]. Most of these compounds are found in the fruit and achenes [
4]. Milk thistle seeds contain a number of substances that improve the homeostasis of the body, i.e., silibinin, silidianin, isosilichristin, silichristin, and isosilibin A and B [
4,
5]. Additionally, the high concentration of vitamin E in the seeds has a positive effect on antioxidant protection and metabolism [
6]. Silymarin, along with other compounds contained in milk thistle seeds, have anti-hepatotoxic, antioxidant, anti-carcinogenic, and anti-inflammatory properties [
7,
8]. In addition, milk thistle, used in the diets of chickens, improves appetite, increases the secretion of digestive juices, and improves the functioning of the circulatory system and liver [
9,
10]. In previous studies, various authors have proposed different ways of administering milk thistle or its active ingredients to animals, in the form of seeds [
11], cake [
12], flour [
13], or an extract [
10].
In addition, it is worth taking note of the latest global trends that aim to reduce the number of medications used in animal production. The use of herbs in livestock therapy fits perfectly into the current direction of livestock production. The price of most easily available herbs for use in nutritional prophylaxis is definitely lower than most pharmacological substances. Taking into account the presence of the above-mentioned active compounds in milk thistle, it can be concluded that its use, in the right amount, will positively affect the health of chickens and the quality of the obtained product, meat. There is a paucity of information on the effects of milk thistle on the growth performance and welfare of broilers. Thus, the aim of this work was to examine the effects of milk thistle on growth performance, welfare, physicochemical properties, meat quality, and antioxidants in broilers.
4. Discussion
Apart from the visual assessment of foot pad quality in terms of FPD changes, one of the methods to assess the welfare of chickens is the gait score test [
15]. The treatment birds participating in this study obtained best gait ratings, enabling them to show natural behavior. Significant differences were found between groups C and E1 as well as C and E2 (
p ≤ 0.05). The best gait index indicating for the birds administered with milk thistle may be because of the adding milk thistle and increasing dose of milk thistle from 0.24 g to 0.36 g that will reduce the severity of FPD. The gait results obtained for the control group may be because these chickens had the lowest body weights [
24,
25], as the vast majority of these birds (61%), despite not having access to the milk thistle infusion, scored 0 or 1. Improved gait quality associated with lower body weight has also been confirmed by other authors [
26,
27].
Inflammation of the foot pad (FPD) significantly affects the welfare of chickens, production results, and the selling price of livestock; hen pododermatitis is a very desirable raw material in Asian countries. The genesis of FPD is complex, as it is believed that it may be due to several factors, but it is related particularly to litter moisture, lack of balanced nutrition, and genetic susceptibility. A conceivable cross-link between the dietary treatments and litter quality may well be inferred due to the changes observed in bacterial composition of cecal digesta, which to an incredible extent contributed to the general litter conditions. The disease is caused by inflammation that affects the epidermis and the superficial layer of the skin. The disease begins with micro-trauma followed by a bacterial infection. Insufficient blood supply to the bird’s pododermatitis causes necrosis and keratosis of the epidermis, especially in the last period of the bird’s growth. Therefore, in this study, both GS and FPD assessments were carried out in the last stage of rearing, when birds are most susceptible to motion disturbances due to high body weight and litter parameters [
16]. It was found that birds that received a drinking infusion of 0.36 g/day/animal differed significantly (
p < 0.05) from group C in the foot pad quality assessment. In addition, the obtained results for all groups, in which the majority of chickens scored 0, testify to the proper welfare and appropriate microclimate conditions present during the rearing period. The maximum concentration of milk thistle infusion, administered in drinking water, may reduce FPD lesions.
It was found that milk thistle infusion significantly increased the weight of the chickens in groups E1 and E2. Birds fed milk thistle by 0.24 dosage had the highest body weight (p < 0.01) which is significantly more than birds fed with E2 and control group. Moreover, body weight before the 24th day of age was not significantly different (p > 0.05) between treatments. Conversely, after 24 days of age, the body weights for birds fed with milk thistle were significantly (p < 0.01) higher in comparison to the control.
Additionally, it was found that the addition of milk thistle in the E1 group reduced the feed conversion rate by 1.9% compared to the control group. However, the addition of an increased dose of milk thistle in the E2 group increased this coefficient; in the case of this experiment, the coefficient increased by 6.37% compared to the control group. These results may have been due to the presence of active compounds in the milk thistle seeds, mainly silymarin, which has a positive effect on liver prophylaxis antioxidant, as well as anti-carcinogenic properties [
7,
8].
Chickens receiving the milk thistle infusion in their drinking water had a 1 or 2 percentage points lower slaughter efficiency (depending on the group) compared to the control group. Similar results have been described in works by other authors investigating the effects of silymarin on slaughter yield [
28]. The carcass weights of treatment groups E1 and E2 were significantly higher in comparison with control group. Moreover, the weight of breast and leg muscles in E1 and E2 were higher than C. There were no significant differences between E2 and C. Conversely, slaughter yield for control group was higher than E1. This finding is consistent with the work of Šťastník et al. [
29], who reported that the highest slaughter yield was shown with the control group. The conducted research showed a lower proportion of abdominal fat in groups E1 and E2. It is estimated that the content of the carbohydrate fat accounted for 20% of the total body fat mass of a chicken [
30,
31]. Chicken broilers tend to store this fat during growth, but this type of fat is considered undesirable [
32] and can cause economic losses for the producer [
33]. Thanks to the addition of milk thistle extract to the water, the proportion of this fat was decreased. This may have been due to better metabolism and improved liver function [
34]. It has been found that the addition of milk thistle expeller reduced blood cholesterol levels, which, according to other authors, improves the health of the birds [
35].
Differences between the groups regarding pH24 were found when analyzing the quality parameters of the meat. The addition of milk thistle infusion reduced the amount of hydrogen ions in the analyzed pectoral muscles, which resulted in better quality meat. Meat acidity determines the technological usefulness of the meat—it determines the ability of the meat to retain its own water, tenderness, and color. If pH24 is below 5.72, chicken meat has a lower ability to bind water and retain it during thermal processing [
36]. The E1 group was the only one to have the desired range of hydrogen ion content.
The metabolic processes in the cells of the body of chickens depend on the rate of synthesis and degradation of basic energy compounds: proteins, fats, and carbohydrates [
37]. These processes are controlled by, inter alia, the activity of glycosidase enzymes [
38]. The increased number of aminopeptidases due to the addition of milk thistle infusion increased the circulation of proteins in the chickens’ bodies. Increased protein circulation results in the improved growth performance of the animals, which can be seen in groups E1 and E2. In addition, the higher aminopeptidase content found in the breast muscles of the birds from the E1 and E2 groups may indicate that milk thistle has a positive effect on the maintenance of the homeostasis of the breast muscles. [
39,
40]. Beta glucosidase is involved in the removal of non-reducing glycosyl residues from saccharides and glycosides [
41]. They are also involved in the metabolism of glycolipids [
41]. The addition of milk thistle caused an increase in BGRD in the blood serum, which had a positive effect on the functioning of the chicken organism due to the decomposition of potentially harmful compounds.
Meat that is rich in polyunsaturated fatty acids is very sensitive to lipid oxidation [
42]. Some of the oxidized lipid products may adversely affect the health of chickens and can display mutagenic, cytotoxic, or carcinogenic properties [
43]. The effects of milk thistle infusion on groups E1 and E2 reduced the risk of undesirable oxidation. The lack of changes in DPPH in the breast muscles indicated the maintenance of a similar level of oxidative stress for all groups, which translated into being able to obtain a greater amount of valuable raw material from groups E1 and E2. In addition, there was a decrease in DPPH in the blood serum of 5.58 percentage points for the E1 group and 0.38 percentage points for the E2 group. Milk thistle meal used by other authors also positively influenced the tested parameter [
13].
An increase in the glutathione levels [
44] and vitamin C in the blood serum of the E1 and E2 groups testifies to the better oxidative stability of the organism. It has been shown that both of these antioxidants can synergistically interact [
18]. In addition, a greater proportion of ascorbic acid in the blood serum caused by the addition of milk thistle has an anti-stress effect that directly affects the welfare of chickens and the quality of the raw material obtained [
45].