Effects of diets with different protein and DL-methionine levels on the growth performance and N-balance of growing minks

This study was performed to evaluate the effects of diets with different protein and dl-methionine (Met) levels on nitrogen (N) retention, nutrient digestibility, growth performance, and some blood parameters in growing minks. Eighty healthy male minks were selected and randomly divided into five groups with different types of diet. The dietary protein levels, expressed as percentage of dry matter (DM), were 36% (HP) and 28% (LP), corresponding to average 363g and 295g protein/kg DM, respectively. LP was supplemented with Met (0.3%, 0.6% and 0.9% DM); the codes were LP+M1, LP+M2 and LP+M3, respectively. From July to middle of September, the average daily gain and feed: gain ratio (F/G) of the minks that received the diet with 0.6% Met added to the low protein diet was better than feeding HP and other groups. Fecal N and Urinary N of group LP+M2 were the lowest one, in contrast, the daily retention of N was the highest one. Digestibility of DM and CP were not affected by different diets, but digestibility of fat declined with dietary protein level decreasing. Serum urea nitrogen (SUN) was affected by different protein and Met levels. Considering all factors the best performance could be observed offering LP+M2, the prime level of Met was 13.87 g/kg DM in dietary, and 258.5 g digestible protein kg(-1) DM was enough for mink in growing period. Furthermore, addition of Met in low protein diets for minks would be beneficial in terms of reduced feed expenses and lower nitrogen emissions to the environment.