Due to scarcity of available reports on effect of peppermint leaves on laying hens, comparison was done with other studiesthat used herbs of the similar family Lamiaceae. The beneficial effects of dietary inclusion of herbs on gut health, digestionof nutrients and intestinal integrity have been reported earlier (Cross et al., 2007; Brenes and Roura, 2010). These beneficialeffects might be directly associated with improvements in laying performance. In the present study, the general health statusof laying hens was good during the experimental period (64–68, 68–72, 72–76 and 64–76 weeks of age) which could berelated to the house environmental system. Generally, the birds given diets containing peppermint leaves had the greatestoverall egg production, egg mass and egg weight compared with the birds given control diet proving that peppermint hadbeneficial action in the oviposition process, imperative on the conversion of digested feed into eggs. The peppermint leavessignificantly improved feed conversion ratio and this could be related to increased efficiency of feed utilization. Moreover,the increase in productive performance of hens due to this medicinal plant could be attributed to its content of essential oils.These active components (cineole, citral, geraniol, linalool and menthol) have shown to possess antimicrobial, antifungaland antioxidant activities as well as improved digestion and absorption of dietary nutrients (Pattnaik et al., 1997; Grigoleitand Grigoleit, 2005; Bupesh et al., 2007; Radwan et al., 2008) that might have improved the performance and productionefficiency of hens in this study.Moreover, peppermint leaves has the ability to improve feed intake which was increased with the increasing levelsof supplementation. Increased feed intake was earlier reported (Al-Ankari et al., 2004) in broilers fed habek mint (Menthalongifolia) at 200 g/kg, hence palatability was not a concern as levels in our study was quite low. In the present study, additionof peppermint improved egg weight, egg production, egg mass and FCR of laying hens.The statistical analysis of the present study showed that the dietary peppermint leaves at 0.5% up to 2.0% enhanced thebird production status during the late laying period. However, most of the previous studies have been investigated in earlystages. Such as the results of Ocak et al. (2008) and Toghyani et al. (2010) demonstrated that birds given diets containingpeppermint leaves are efficacious in supporting the growth performance of broiler chicks at early stages of life. It wasreported earlier that using 2% blends of ziziphora, menta, peppermint and nettle improved egg mass and feed conversion inlaying hens (Sayedpiran et al., 2011).In this study, egg weight, egg mass and egg production significantly increased with increasing dietary peppermint leavesat all stages. In agreement with Abdel-Wareth et al. (2013) where addition of thyme or oregano leaves at 10, 20, 30 g/kg inhen diets had significantly increased (P<0.01) egg weight, egg mass and hen-day-egg production during the periods of 68–72weeks of age, are consistent with our results. Dietary supplementation with thyme leaves at the levels of 0, 0.1, 0.5 and 1%to basal diet improved the egg production rate by 6.12%, 5.16% and −2.06% compared to control, respectively (Bölükbas¸ iand Erhan, 2007). Also, addition of 0.5% thyme, oregano or rosemary leaves to laying hens diet numerically increased eggweight, egg mass, egg production and feed intake (Radwan et al., 2008). In the present study, it could be stated that dietarypeppermint leaves have positive response on production performance of laying hens attributed to the essential oils presentin it.This study showed no significant differences in yolk and albumen percentages as well as albumen height among treat-ments. However, there were significant effects on eggshell percentage, eggshell thickness and Haugh unit of laying hens at76 weeks of age. Increased shell weight and shell thickness by addition of peppermint leaves may be attributed to its mainactive components that possess antibacterial and antioxidant activities (Dorman et al., 2003; Yalc¸ in et al., 2012). It could bepostulated that peppermint may provide a healthy environment in uterus (e.g. site of calcium deposition) and consequentlyincrease shell weight and shell thickness more than the control treatment. These improvements in eggshell and Haugh unitare important for the egg-food industry, because peppermint may enhance the safety and stability of eggs. The Haugh unitscore is known as an indicator of egg freshness and is related to shelf life (Williams, 1992; Özek et al., 2011). Our findingsare in agreement with earlier study that showed supplementation of thyme improved shell weight and shell thicknesscompared to hens fed control diet (Ali et al., 2007). It is also reported that 2% blends of ziziphora, menta, peppermint andnettle improved egg Haugh unit in laying hens (Sayedpiran et al., 2011). Dietary
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