| Summary: | Supplement The AAT/PB V protein evaluation system for ruminants has now been used in Denmark, Norway and Sweden for some years and will soon be introduced in Finland and Iceland as well. The basic concepts with AAT (amino acids absorbed in the small intestine) and PB V (protein balance in the rumen) and the factors to be considered in predicting the AAT and PBV values are maintained, but the continuous development in methods and knowledge has led to changes in methods used to predict the individual factors. The inclusion of these modifications in the different countries has not taken action at the same time, but depends on the time the different countries has introduced the system and on the calendar for major changes in the feed evaluation system. It has the effect that at a given time the system may be slightly different in the different Nordic countries. but we follow the same line in the development. The following is the most important changes that has been made or arc going to be made in the system since the system was first presented. In the prediction of the AAT and PBV values of the feeds: I) changes in the nylon bag procedure to predict the protein degradability in the rumen by correcting for particle loss and for microbial N contamination of the bag residues in fibrous feeds, 2) a change from using a constant figure of 0.82 for intestinal digestibility of undegraded amino acids to an actual determination of the intestinal digestibility of the single feeds. 3) a microbial amino acid synthesis per kg of digested carbohydrates on fresh grass of 135 g is used instead of the general factor of 125 g which is maintained on all other feeds. The recommendations for AAT and PB V to different categories of ruminants will depend on the actual economical situation and feeding system and will therefore differ from place to place and probably from time to time as well. In general, it has been observed that the potential of decreasing the protein allocation is greater than the possibilities of increasing the milk ...
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