REGULAR ARTICLES Dietary supplementation of milk thistle (Silybum marianum): growth performance, oxidative stress, and immune response in natural summer stressed broilers Munib Ahmad 1 & Naila Chand 1 & Rifat Ullah Khan 2 & Nazir Ahmad 3 & Irfan Khattak 4 & Shabana Naz 5 Received: 14 June 2019 /Accepted: 29 August 2019 # Springer Nature B.V. 2019 Abstract The aim of the study was to investigate the influence of dietary supplementation of various levels of milk thistle (MT) on growth performance, oxidative stress, and immune response of natural summer stressed broilers. A total of 120 1-day old broiler chicks were distributed into 4 treatments: MT-0 (control), MT-5 (5 g/kg of MT), MT-10 (10 g/kg of MT), and MT-15 (15 g/kg of MT), each with 3 replicates having 10 birds per replicate. Results showed that overall feed intake, body weight, feed conversion ratio (FCR), and dressing percentage were significantly (P < 0.5) higher with MT-15 as compared with the other experimental treatments. Unlikely, significantly lower level of malondialdehyde (MDA) was observed with MT-15. Dietary supplementation of MT had no significant effect on paraoxonase activity in broiler. Antibody titer was significantly (P < 0.05) higher with MT-15 while it was lower with the control treatment. It was concluded that dietary supplementation of MT at the rate of 15 g/kg can significantly lower the negative effects of natural summer stressed broilers. Keywords Growth performance . Oxidative stress . Milk thistle . Immune response Introduction Heat stress is one of the major issues of the poultry industry in the tropical region. Along with high ambient temperature, humid waves have an adverse effect on poultry health and productivity (Khan et al. 2011). Temperature above 30 °C is considered as summer stress and ultimately, body temperature increases (Rehman et al. 2018). Poultry, particularly broilers, are sensitive to summer stress which exerts incalculable neg- ative impact on their productivity (Khan et al. 2014). Summer stress also causes adverse effects on immune system and lipid peroxidation (Chand et al. 2016, 2017; Rahman et al. 2017a). Generally, the growth rate is very high in broiler but their adaptation to the change in external environmental tempera- ture is very poor which lead to oxidative stress (Rahman et al. 2017b). When the limit of free radicals is greater than their requirement, they affect various organelles and cell membrane (Khan 2011). Ventilation, bird density, nutritional, and hus- bandry practices are important methods for reducing heat stress in poultry. Among these methods, nutritional strategies are the most suitable mean of reducing heat stress by keeping balance in the water, electrolytes, vitamins, and antioxidants (Khan et al. 2012). Milk thistle (Silybum marianum), a phytogenic plant, is a valuable source of antioxidants (Alhidary et al. 2017). This plant contains biologically active compounds such as silymarin, silydianin, and silychristine (Wu et al. 2009). Silymarin occurs in the highest concentration in fruit portion of the milk thistle plant. It is an active component, which * Shabana Naz drshabananaz@gcuf.edu.pk 1 Department of Poultry Science, Faculty of Animal Husbandry & Veterinary Sciences, The University of Agriculture, Peshawar, Pakistan 2 Department of Animal Health, Faculty of Animal Husbandry & Veterinary Sciences, The University of Agriculture, Peshawar, Pakistan 3 Department of Animal Nutrition, Faculty of Animal Husbandry & Veterinary Sciences, The University of Agriculture, Peshawar, Pakistan 4 College of Veterinary Science and Animal Husbandry, Abdul Wali Khan University, Mardan, Pakistan 5 Department of Zoology, Faculty of Animal Husbandry & Veterinary Sciences, GC University, Faisalabad, Pakistan Tropical Animal Health and Production https://doi.org/10.1007/s11250-019-02060-4