DIGESTIBILITY OF NITROGEN FROM FEED WITH VARIOUS PROPORTIONS OF COD FOR MINKS

An experiment was conducted on an Experimental Farm of Fur-bearing Ani mals affiliated to the Research Institute of Animal Production in Nitr a in August to September 1995. The animals were housed in special cage s for metabolic trials. The experiments were conducted on five nonsib mink males at the age of four months. The animals were clinically heal thy and examined for plasmocytosis. The experiment consisted of three stages to determine the digestibility of nitrogen from feed ration wit h various proportions of cod fillet administered to minks and nitrogen digestibility in the rest feed (cod fillet). The animals received bas al feed ration in the first stage while in the second stage the conten t of test feed in the feed ration was 41.7% and in the third stage 62. 5% out of the original amount. Each experimental stage had two periods a preparatory period and an appropriate experimental period. The prep aratory period lasted three days, when the animals adapted themselves to a new feed ration, and the appropriate experiment lasted five days. Feed was administered twice a day (at 9 h a.m. and at 3 h p.m.). The nutritive value of feed rations was in agreement with the standard for the age category and physiologic stage concerned. Climatic conditions were observed throughout the experiments. Average air temperature was 14.2 +/- 0.6 degrees C in the first stage of experiments, 28.0 +/- 0. 4 degrees C in the second stage and 18.1 +/- 0.4 degrees C in the thir d stage. Indicators necessary to calculate digestibility coefficients for feed rations and test feed were determined during the appropriate experiment: feed intake, remaining uneaten feed and amount of excremen ts. The indicators were recorded and samples were taken twice a day, a lways an hour before feeding at 7 to 8 o'clock. A direct method was us ed to calculate nitrogen digestibility in the feed rations with variou s proportions of cod fillet, and an indirect (differential) method was used to calculate digestibility in the test feed. The results of calc ulations were processed by a mathematico-statistical method of one-fac tor analysis of variance with multivariate comparisons of differences in arithmetical means. No statistically significant intra-group differ ences were determined for the animals, it means that the set of minks was homogeneous. Tests of the effects of replications in the particula r groups revealed statistically significant differences at a significa nce level P less than or equal to 0.5 for the second stage of experime nts at administration of feed ration with 41.7% portion of cod fillet. As the biological material is homogeneous, we believe that this fact was influenced by the environment factor (climatic conditions during t he experiments). Coefficient of nitrogen digestibility in the basal fe ed ration was 67.661 +/- 1.180%, in the feed ration with 41.7% of cod fillet 72.327 +/- 0.613% and in the feed ration with 62.5% proportion of test feed 81.563 +/- 1.095%. The obtained results of nitrogen diges tibility in the test feed rations are statistically significant (P les s than or equal to 0.05). Coefficient of nitrogen digestibility in cod fillet used in feed ration with 41.7% proportion of test feed (2nd st age) was 81.240 +/- 0.864% and in the feed ration with 62.5% of test f eed it amounted to 93.020 +/- 1.033% (P < 0.05). It can be concluded f rom the results obtained that the coefficient of nitrogen digestibilit y in feed rations administered to minks is increasing in relation to t he per cent proportion of test feed. Nitrogen digestibility in test fe ed was also related to the feed proportion in feed rations (41.7% : 81 .240 +/- 0.86% and 62.5% : 93.020 +/- 1.033%). It is recommended to us e cod fillet in feed rations for minks throughout the year as it is a dietetic feed with high crude protein content (16.62%) and with low fa t content (0.60%).