Effects of Pennyroyal (Mentha pulegium L.) Supplementation on production performance, egg quality traits, and biochemical parameters of blood and egg in laying hens at later stages of the production period

BACKGROUND: According to the promising outcomes acquired in recent studies that focused on using natural feed additives in animal nutrition, poultry nutritionists have also been interested in investigating these medicinal herbs' effects on poultry performance and egg characteristics. Pennyroyal (Mentha pulegium L.), a natural source of antioxidant, antimicrobial, anti‐inflammatory, etc. compounds, is recommended as a potential alternative for antibiotics, with similar benefits and no adverse effects on animal health or their products. Considerable effects have been reported on laying hens’ performance and their eggs’ internal and external traits by pennyroyal inclusion in their diets. OBJECTIVES: Due to the different results reported by pennyroyal inclusion in laying hens’ diets in recent limited studies, this study was designed to reinvestigate the impacts of pennyroyal (Mentha pulegium L.) supplementation (PS) on productive performance, egg quality traits, and biochemical compounds in blood and egg yolk in aged laying hens. The findings of this experiment may help for a better understanding of PS impacts on desired parameters, along with improving aged laying hens’ performance. MATERIALS AND METHODS: A total of 144 Leghorn (Hyline‐W36 strain) laying hens (53 weeks old) were used to investigate the effects of PS on performance, egg quality, and biochemical parameters of blood and egg yolk in old laying hens. The animals were distributed into three treatment groups; including a control diet (without PS), 0.5%, and 1% PS diets with six replicates and eight birds per replicate. RESULTS: The results indicated that the egg production rate (except for week eight) and egg mass were significantly reduced by PS in the laying hens’ diet during the first four weeks and the total period of the experiment (P<0.05). However, the feed conversion ratio increased by PS (P<0.05). Based on the egg quality trait evaluations (week 4), the yolk percentage, yolk height, and yolk index reduced, while shell‐breaking strength represented a significant increase in PS groups (P<0.05). However, shell thickness and albumen percentage reduced and increased by 1% PS, respectively (P<0.05). At week eight, the Haugh unit reduced while the albumen pH increased by PS (P<0.05). The findings revealed a decline in the egg density in 1% PS groups (P<0.05). In the case of serum biochemical parameters, alanine aminotransferase increased, whereas malondialdehyde (MDA) levels reduced in the PS groups (P<0.05). Moreover, the triglyceride levels of both serum and egg yolk (accompanied by the very low‐density lipoprotein level of serum) decreased by PS (P<0.05). CONCLUSIONS: In conclusion, PS reduced serum and egg yolk triglyceride levels, accompanied by serum MDA, along with reducing production performance.