Za izboljšanje uspešnosti reje perutnine brez uporabe profilaktičnih sredstev moramo najti alternative. Med te lahko spada tanin. Cilj naloge je ugotoviti učinek vodotopne oblike kostanjevega ekstrakta (Castanea sativa Mill.) na proizvodne parametre in koncentracijo glukoze v krvi pitovnih jarkic (Ross 308). V ta namen smo uporabili dodatek Farmatan Liquid®, ki smo ga dodali vodi za pitje. Predpostavili smo, da bo dodatek pozitivno vplival na proizvodne parametre reje in znižal koncentracijo glukoze v krvi jarkic. Na osnovi koncentracije dodatka v vodi smo živali razdelili v štiri skupine (A - 0 %, B - 0,05 %, C - 0,1 %, D - 0,2 %). 720 živali provenience Ross 308 iz redne proizvodnje smo vzrejali na globokem nastilju, ločene v oddelke po 90 živali s po dvema oddelkoma na skupino. Krmljenje in napajanje je bilo ad libitum. Uporabljene popolne krmne mešanice (Bro-S, Bro-F1 in Bro-F2) so bile iz redne proizvodnje. V sedem dnevnih intervalih (7., 14., 21., 28., 35. in 42. dan) smo spremljali proizvodne parametre: povprečno maso, porabo krme, porabo vode, pogin živali in izračunavali konverzijo krme ter razmerje poraba vode:poraba krme. Na 28. in 35. dan starosti smo določili koncentracijo glukoze v krvi živali ter na 42. dan učinkovitost reje po EEF formuli. Ob koncu pitanja smo ugotovili statistično značilno razliko (p ≤ 0,05) v doseženi masi živali, kjer se je skupina D (2,578 kg) razlikovala od skupin B (2,635 kg) in C (2,654 kg). Med ostalimi proučevanimi parametri ni bilo ugotovljenih značilnih razlik. Rezultati so pokazali ugoden učinek kostanjevega ekstrakta na proizvodne parametre. In order to improve the efficiency of poultry farming without the use of prophylactics we need to find alternatives. Tannin may be one of them. The aim of this thesis is to determine the effects of a water-soluble chestnut extract (Castanea sativa Mill.) on production parameters of female broiler chicks (Ross 308) and their blood glucose levels. For this purpose we added Farmatan Liquid® to the drinking water. We hypothesized the additive will favorably influence the productivity of rearing and reduce blood glucose levels of broiler chicks. We divided the chicks into four separate groups based on the concentration of the additive (A - 0 %, B - 0,05 %, C - 0,1 %, D - 0,2 %). 720 chicks provenience Ross 308 from commercial production were reared on deep litter separated into sections of 90 animals, with two sections per group. Feeding and watering was done ad libitum. Complete feed mixtures used (Bro-S, Bro-F1 in Bro-F2) were from commercial production. We monitored the production parameters in seven day intervals (on the 7th, 14th, 21st, 28th, 35th and 42nd day): average weight, feed and water consumption, mortality rate, and we calculated the feed conversion and the ratio of water consumption to feed consumption. We checked the blood glucose levels on the 28th and 35th day, and the efficiency of breeding on the 42nd day using the EEF formula. We found a statistically significant difference (p ≤ 0,05) in chick weight at the end of the fattening period, where group D (2,578 kg) differed from groups B (2,635 kg) and C (2,654 kg). There were no significant differences in other observed parameters. Results showed a favorable effect of the chestnut extract on production parameters.