The effect of Vitex agnus castus fruit powder on performance, egg quality, blood biochemical parameters, immune response, reproductive system and tibial characteristics of laying hens in the second cycle of production

Introduction: For millenniums, aromatic plants have been used for the treatment of many diseases worldwide. These plants contain a wide variety of active phytochemicals including flavonoids, terpeniods, lignans, sulfides, polyphenolics, carotenoids, coumarins, saponins, plant sterols and phthalides (Craig 1999). Among all, Vitex agnus-castus (VAC) fruit extract, known as a phytoestrogenic herb, has been used for the treatment of menstrual disorders (amenorrhoea, dysmenorrhoea), premenstrual syndrome (PMS), corpus luteum insufficiency, hyperprolactinaemia, infertility, acne, menopause, and disrupted lactation (Daniele et al. 2005). Previous studies have reported the efficacy of VAC in PMS, cycle disorders, hyperprolactinaemia and mastalgia in human and other animals. However, no study has yet been published on the effect of VAC on laying hens' performance in second cycle of production. Therefore, the aim of present study was to investigate the effect of dietary supplementation of VAC fruit powder on performance, egg quality, immune responses, blood biochemical parameters, tibial characteristics, and reproductive traits of laying hens in second cycle of production. Material and methods: This experiment was conducted to determine the nutritional value of VAC and to investigate its effects on performance and egg quality of laying hens in the second cycle of production. In the first step, AOAC methods were used for determination of the nutritional value of VAC. In the second step, 150 Leghorn Hy-Line (W-36) laying hens (80 to 90 weeks of age) were used based on a completely randomized design with 5 treatments, 5 replicates and 6 hens per each replicate. Treatment diets included 0 (control), 0.5, 1, 1.5, and 2% of VAC fruit powder. The birds received basal diet (corn- and soybean-based diet with 15.05% crude protein and 2802 kcal/kg metabolizable energy) in a mash form and formulized according to the Hy-Line W-36 (2016) nutrient requirements. The diet did not have any antibiotics and coccidiostats. Water and feed were provided ad-libitum during the experiment. Lighting program was 16 hours light and 8 hours darkness during the experiment. Egg weight (EW, gr), egg production (EP, %) and egg mass (EM, gr/hen/day) were recorded daily. Feed intake (FI, gr) was measured weekly and feed conversion ratio (FCR, grams of feed: grams of egg mass) was calculated weekly. In the present study, all performance parameters were presented in three periods (first 4 weeks, second 4 weeks, and entire 8 weeks). At the end of 2, 4, 6, and 8 weeks of the experiment, two eggs from each replicate were randomly selected for measurement of the egg qualitative traits and presented for each period. For determination of immune response, at 6 and 8 weeks of experiment, 0.5 mL of 20% sheep red blood cells (SRBC) were injected to the breast muscle of 2 hens per replicate. Then blood samples were taken from brachial vein 7 days after each injection (Nelson et al. 1995). At the end of experiment, one bird per each replicate was slaughtered for evaluating tibial characteristics (Zhang and Coon 1997) and reproductive traits (Renema et al. 2010). Results and discussion: The results showed that crude protein (CP), ether extract (EE), crude fiber (CF), and crude ash were 10.5%, 5.6%, 56.0% and 12.6% of dry matter, respectively. Performance parameters such as FI, EP, EM, EW and FCR were not significantly affected by various levels of VAC fruit powder (P>0.05). Egg quality factors such as Haugh unit, shell strength, shell percentage, shell thickness, and egg yolk color were not affected significantly by dietary treatments (P>0.05). However, albumin percentage was increased, but yolk percentage was decreased significantly during the first 4 weeks of experiment (P<0.05). In this regard, Karacollokcu et al. (2016) reported the insignificant effect of myrtus and vitex essential oil supplementation (alone or in combination) on production performance and internal and external quality traits of the eggs (except for egg specific gravity and yolk color) during the peak of egg production period in laying hen. Vakili (2011) indicated that, adding essential oils of thyme and fennel into the diet of the laying hens significantly improved Haugh unit scores. Vakili (2011) suggested that bird’s age and production cycle are the effective factors on eggs' internal and external quality. Nonetheless, addition of 40 mg of thyme extracts per kg of diet had insignificant effect on eggshell quality parameters of laying hens (Vakili 2011). Immune responses, tibia characteristics and reproductive traits of laying hens were not significantly affected by various levels of VAC powder (P>0.05). Also, blood concentration of glucose, high density lipoprotein, alanine aminotransferase and aspartate aminotransferase enzymes were not affected by dietary treatments (P>0.05), but triglyceride and cholesterol were decreased (P<0.05). A decrease in serum cholesterol concentration could be related to hypocholesterolemic activity of herbal essential oils via the inhibition of hepatic 3-hydroxyl-3-methyl-glutaryl-coenzyme A reductase, the rate-limiting enzyme of cholesterol biosynthesis in smooth endoplasmic reticulum (Srinivasan 2004), and also high levels of VAC fiber. Moreover, steroid like compounds (phytoestrogens and ecdysteroids), capable of binding to estrogen receptors, have been previously isolated from VAC (Bahrebar et al. 2010). It is concluded that these compounds can affect lipid metabolism in a dose dependent manner (Bahrebar et al. 2010). Furthermore, the existence of antioxidant compounds such as flavonoids and iridoids, were beneficial in the normalizing of serum lipid levels (Bahrebar et al. 2010). Conclusion: The results of this experiment indicated that feeding VAC at 0.5-2% had insignificant effect on performance, but could improve lipid metabolism via decreasing the blood concentrations of triglyceride and cholesterol in laying hens.