Residual effect of narasin on ruminal fermentation characteristics in lambs

ABSTRACT This study aimed to evaluate the effect of narasin withdrawal on wethers ruminal fermentation characteristics. Four wethers cannulated at the rumen were subjected to a 4 × 4 Latin Square experimental design. The trial lasted 144 days, divided into 4 periods of 36 days each. The diet was composed by 950 g/kg of coastcross hay and 50 g/kg of ground corn, used as a carrier for the narasin. The experimental diets were defined by frequency of narasin offer: 1) no feed additives (N0); 2) 13 mg of narasin/kg of DM every 24 hours (N13); 3) 26 mg of narasin/kg of DM every 48 hours (N26), and 4) 39 mg of narasin/kg of DM every 72 hours (N39). The narasin was offered for 25 days, and at the last 11 days of each period, all the animals received the same proportion of forage and concentrate, but without narasin inclusion (withdrawal period). Last day of narasin offering was denominated day 0 and the first day of withdrawal day 1. The fed offer and orts were daily recorded to determine de DMI and nutrient intake. Ruminal fluid was collected 6 hours after concentrate offering from d0 to d11 to determine ruminal pH, SCFA and ammonia nitrogen. There was no difference for dry matter intake among treatments after narasin withdrawal. There was no treatment and day interaction for total SCFA concentration, molar proportion of acetate, butyrate, isobutyrate, valerate, isovalerate and rumen pH. Treatment and day interaction after narasin withdrawal interactions was observed for molar proportion of propionate (P