Breeding work and constant development make a difference
Since the end of the 1980s, it has become common practice to mix individual amino acids in pig feed in order to achieve a more balanced feed composition. Specifically, feed today has a much lower content of soybean meal than previously. Feed for finishers, for example, contains approximately 148 grams of protein per feed unit whereas at the end of the 1980s, feed contained as much as 185 grams of protein.
If the effect of amino acids is calculated in isolation, one pig (a 2019 pig in breeding terms) fed on 2019 feed will excrete 31 percentage points less nitrogen than if the same pig were to be fed typical feed from the end of the 1980s. The corresponding figure for ammonia evaporation is 36 percentage points lower for a pig on 2019 feed compared to the same pig and feed from the end of the 1980s.