عنوان مقاله [English]
Introduction The use of medicinal plants in poultry nutrition has been considerably increased in the recent years due to their beneficial effects, environmental compatibility and lack of adverse side effects. On the other hand, the use of antibiotic growth promoters (AGPs) in poultry production has been banned because of their residues in poultry productions and development of antibiotic resistant bacteria. The plant yucca (Yucca schidigera) belongs to agavaceae family and is native of south-western of United States and Mexico. Yucca typically grows on rocky desert slopes and creosote desert flats between 300–1,200 meters altitude, rarely up to 2,500 meters. This plant thrives in full sun and in soil with excellent drainage. It also needs no summer water. The plant is known as one of the main sources of saponins. Steroidal saponins are accounted for approximately 10% of the dry weight of Yucca stem. Saponins, the main chemical component of YS extract, exist in steroidal form, whereas they are found in a triterpenoid form in other plants, such as Quillaja saponaria. Yucca saponins have antibacterial properties. The use of Yucca schidigera extract in poultry feed is a good alternative to improve feed efficiency and increased production. Yucca extract-supplemented diets have improved growth performance, relative weight of bursa of Fabricius and reduced mortality rate, breast muscle, caecal E. coli counts in broiler chickens. In the present study, the effects of different dietary levels of a commercial product containing Yucca schidigera powder on certain variables of broiler chicks were studied.
Materials and Methods This experiment was conducted using 250 Ross 308 broiler chicks in a completely randomized design with 5 treatments and five replicates of 10 chicks each. Different dietary levels of the Yucca extract powder (0, 0.01, 0.015, 0.02, and 0.025 %) were tested in a three-stage feeding program including starter (0 to 10 days of age), grower (11 to 24 d) and finisher (25 to 42 d) phases. Blood samples were collected from one bird per replicate pen to determine the selected blood metabolites including cholesterol, triglycerides, low-density lipoprotein (LDL), and high-density lipoprotein (HDL) at the end of the experiment (42 days of age). On day 42, one chick per replicate was slaughtered and carcass characteristics were assessed. The effect of dietary yucca powder levels on cellular immune response was determined by a cutaneous basophil hypersensitivity test using phytohemagglutinin-P (PHA-P). At d 42, one bird from each replicate was selected and thickness of the interdigital skin between the third and fourth digits of both feet was measured in millimeters with a Caliper (Measurement accuracy, 0.001). Immediately after the measurement, 100 µl of the PHA-P solution and phosphate buffer saline (PBS) were injected into the interdigital skin of the left and right feet by insulin syringes, respectively. Thicknesses of the skin were measured 12h and 24h post-injection. At day 28, five chicks per treatment (1 chick/replicate) were selected and 0.5 ml of 10 % sheep red blood cell (SRBC) solution was injected into their breast muscle and after seven days (day 35) blood samples were collected from brachial vein of the birds and then, an additional injection of SRBC was performed to induce the secondary anti-SRBC humoral response. At day 42, the second series of blood samples were collected. Sera separated from blood samples and were used to evaluate anti-SRBC total (Ig T), M (Ig M) and G (Ig G) immunoglobulins.
Results and Discussion The effect of dietary Yucca powder on feed conversion ratio (FCR) was significant (P< 0.05) in the grower period (11-24 d). Chicks received 0.01% Yucca powder had the best FCR, and the highest FCR was observed in control and 0.025% Yucca powder group. There was significant difference (P< 0.05) in body weight gain (BWG) and average body weight (ABW) in the grower period (11-24 d) of broiler chickens. Broilers in 0.01% Yucca powder group, were significantly (P< 0.05) heavier than the 0.025% Yucca powder group. SRBC test showed that, IGM in first titer (35 d) was significantly (P< 0.05) more than the other groups. In the case of blood metabolites, serum LDL concentration had significant differences among the treatments (P< 0.05). The lowest LDL concentration was observed in 0.015% Yucca powder group. There was no significant difference in feed intake, CBH test and carcass traits of broiler chickens.
Conclusion According to results of this experiment, supplementation of 0.02% Yucca extract powder, improved growth performance of the broiler chickens. However, 0.01% Yucca extracts powder improved humoral immunity and decreased blood serum LDL concentration of broiler chickens.