L-carnitine as well as lysine and methionine are amino acids of important nutritional and nutraceutical interest and are used in nutritional strategies as dietary supplements to improve feed quality characteristics in animals and broiler chicken in particular. This study investigated the effect of different levels of L-carnitine and extra levels of lysine-methionine on growth performance, carcass characteristics, and some immune system markers. Two hundred seventy male Ross 308 broilers were a fed control diet (C) and eight different diets supplemented with an excess of amino acids. In the experimental diets, identified as D1, D2, D3, D4, D5, D6, D7, and D8, extra L-carnitine, lysine, and methionine were added in excess with respect to the American National Research Council (NRC) recommendations: L-carnitine equal to NRC (D1), control diet supplemented with lysine at 30% in excess of NRC, methionine at 30% in excess of NRC, and L-carnitine equal to NRC (D2), control diet supplemented with lysine equal to NRC, methionine equal to NRC, and L-carnitine at 15% in excess of NRC (D3), control diet supplemented control diet supplemented with lysine at 15% in excess of NRC, methionine at 15% in excess of NRC, and L-carnitine at 15% in excess of NRC (D4), control diet supplemented lysine at 30% in excess of NRC, methionine at 30% in excess of NRC, and L-carnitine at 15% in excess of NRC (D5), control diet supplemented with lysine equal to NRC recommendations, methionine equal to NRC recommendations, and L-carnitine at 75% in excess of NRC (D6), control diet supplemented with lysine at 15% in excess of NRC, methionine at 15% in excess of NRC, and L-carnitine at 75% in excess of NRC (D7), and control diet supplemented with lysine at 30% in excess of NRC, methionine at 30% in excess of NRC, and L-carnitine at 75% in excess of NRC (D8). During the starter and growth phases, feed intake was not affected by dietary treatment (p > 0.05). By contrast, body weight and FCR were both affected (p < 0.001) during the starter period. During the finisher phase, feed consumption was affected (p < 0.05) by dietary treatment. Feed intake of broilers fed on C, D3, D6, and D7 were statistically similar (p > 0.05) (1851.90, 1862.00, 1945.10, and 1872.80 g/pen/day, respectively) and were higher (p < 0.05) than 1564.40 g/pen/day (D5). With the exception of drumsticks, neck, back thoracic vertebrae, and proventriculus weights, the economical carcass segments were not affected (p > 0.05) by the dietary supplementation of amino acids. Duodenum and ileum weights and lengths decreased with amino acid supplementation (p < 0.05). IgT and IgG titers against Sheep Red Blood Cells (SRBC) for both primary and secondary responses were not affected by dietary treatments (p > 0.05). Dietary amino acids supplementation did not affect IgM titer after the secondary challenge (p > 0.05) and had a significant effect (p < 0.05) on serum antibody titers in broilers vaccinated against Newcastle disease (NCD) and Gumboro ‘s disease at the 27th and 30th days, respectively.

Silybum marianum (SM) and its compounds are used as dietary supplements to improve the performance and health of chicks especially when fed broiler diets contaminated with aflatoxins. Use of SM derivatives from 0.2% to 0.8% in feed had no negative effects on the performance of broilers, but increasing SM level to 15% reduced average body weight (1620.02 g) compared to control groups (1815.04 g). Feed conversion ratio in broilers receiving SM was not significantly different and average feed intake was similar (2985.6 vs. 3145.15 g). Addition of 0.5% of SM powder in feed decreased total intestinal bacteria and coliforms. Inclusion of 4–15% of SM in feed improved sensory and qualitative characteristics of meat. SM and its derivatives (seeds, powders and extracts) improved health and quality of meat. Broiler trials showed that the highest carcass weight (1583.87 g) and breast weight (592.80) were seen in feeds containing 3% SM oil, although such findings were not consistent in other published work. Application of these compounds is recommended as a natural dietary supplement to improve performance and well-being in cases where diets may be contaminated with aflatoxin.

To investigate the effect of thyme (Thymus vulgaris L.) essential oil (TEO) or increasing inclusion of a prebiotic (TechnoMOS^®) on growth performance and carcass characteristics of Ross 308 broilers, 400 one-day-old male broilers (43.5 g, as mean of body weight) were placed in 20 pens (2.0 × 1.0 m, with a floor area of 0.10 m² per bird) in groups of 20, and each pen cage was assigned to a specific dietary treatment (four replicates per each one). The dietary treatments included basic diet (no additive; CTR), basic diet including 0.025%, 0.075%, or 0.125% of TechnoMOS^® (MOS025, MOS075, and MOS125, respectively), or basic diet including 0.075% thyme extract (TEO075). All dietary treatments were offered from the beginning of the study until the end of the trial. There were no effects of MOS or TEO on carcass characteristics. No significant effects of treatment on weight gain were obtained on a week-by-week basis; however, CTR birds gained less weight during the grower phase and overall compared with MOS birds. The same contrast for feed intake revealed that CTR birds had greater feed intake than MOS birds during both the grower phase and overall (492.18 g and 486.35 g, respectively). In conclusion, treated groups showed an improved feed conversion ratio.

Medicinal plants and their derivatives are human-friendly, nutritional supplements, and their use in the poultry industry is increasing today. Cynara scolymus is a very high-quality antioxidant medicine plant that has recently attracted the attention of poultry and nutrition researchers to supplement their rations and reduce feed costs. In the present study, the effect of powder and extract of C. scolymus on broilers has reviewed. This review shows that the impact of C. scolymus on production performance, carcass characteristics, liver enzymes activity, and meat characteristics of broiler chickens are not significant. However, the negative impact of this compound on these properties has not reported. Moreover, cholesterol levels reduced by the dietary C. scolymus supplementation. The impact of C. scolymus powder and extract on chickens’ broiler immunity was not significant in the cited literature, but dietary C. scolymus powder increases Newcastle antibody titers and lowers blood pressure. Dietary C. scolymus under heat stress increased anti-sheep red blood cell titers. No substantial studies have conducted on the effect of C. scolymus on broilers. Therefore, it is not possible to determine a single dosage for the use of C. scolymus powder or extract in broiler diets to the improvement of the broiler characteristics. More researches are needed to determining the appropriate dosage to achieve maximum performance.

The influence of dietary L-carnitine and lysine (Lys)-methionine (Met) levels on productive performance, haematology and triiodothyronine hormone levels of broilers was investigated. Dietary treatments included different L-carnitine (0, 50 and 100 mg/kg) and Lys-Met (0%, 10% and 20% over National Research Council (NRC) (1994) recommendation levels), under a 3 × 3 factorial design arrangement. From the findings, the body weight (BW) gain, feed intake and feed conversion ratio (FCR) of broilers were significantly (p < 0.05) influenced by dietary treatments in the different growing stages. Conversely, carcass yield and organs did not differ (p > 0.05) among treatments, whereas meat-cuts varied significantly when broilers were fed experimental diets. Moreover, the dietary inclusion of the highest levels of amino-acids (L-carnitine (100 mg/kg) and Lys-Met (+20%)) produced a reduction (p < 0.05) of blood uric acid, also leading to the highest triiodothyronine (T3) hormone levels. Based on the obtained results, it can be concluded that the combination of extra levels of L-carnitine associated with Lys-Met positively influenced the performance traits in broiler chickens.

To investigate the effects of adding Cynara scolymus (CS) and Silybum marianum (SM) dry extract to the diet of broiler chickens, a 2 × 2 factorial experiment was conducted using a completely randomized design with 4 treatments and 4 replicates. Ten one‐day‐old male broiler chicks of Ross 308 strain were used in each replicate. Experimental treatments included two levels of supplemental CS and MS, 250 and 500 mg/kg of dry extract of CS and SM, which were used in combination with a basal diet for 42 days. The 42‐day trial was divided into 3 periods, 1–10 days, 11–24 days, and 25–42 days of age. The data were statistically analyzed using SAS software and means differences were tested for significance using Duncan's multiple‐range test. The results showed that the effect of the experimental treatments was not significant on growth performance in the entire period (1–42 days), carcass characteristics, and weight of immunity organs. Feed cost per kilogram of live weight increased with supplemental of CS and SM (p < .01). Significant effects of CS and SM supplements were observed on antibody titer against influenza virus at 28 and 42 days and also on antibody titer against sheep red blood cells (SRBC) at 35 and 42 days. Feeding 500 mg/kg of both CS and SM in the diet of broilers resulted in the highest villus height and width, crypt depth, and percentage of oleic and linolenic acids. The results of the present study suggest that feeding 250 and 500 mg/kg of dry extract of CS and SM in the diet may have positive effects on the traits studied, but to save feed costs, only250 mg/kg is recommended.