## 2 Materials and Methods
### Scientific Background of Data Requirement and Modules of AGEM-S
#### 2.2.2 Nutrition Module  
The starting point for ammonia emissions is the N excretion (N output) of pigs, calculated as the difference between N input and N retention. The rate of N excretion is determined by the digestion and efficiency of protein utilization of the animals. In this respect, the different utilization types differ considerably. Moreover, the N retention of animals varies over time. Available research findings show that the N retention of pigs is 31-45%. The proportion of unutilized urinary N is 49-51% of the intake, while the proportion of fecal N is around 15-20% [33]. The vast majority of urinary N, i.e., 65-85%, is present in the form of urea and other easily mineralized compounds [34]. In contrast, the majority of fecal N is protein, which is why it is decomposed and converted to ammonia more slowly [35]. For this reason, TAN can be considered as the amount of N excreted via urine [36]. The N retention of pigs differs significantly by genotype and age category, according to our own findings [37]. In the model, average live weight data are considered in each group, which is, of course, a source of smaller or larger errors. While calculating the N retention of the animals in the model, our own results were used. For weaned piglets and for fattening pigs, we distinguished the genotypes (\"A\" or \"B\") based on our own previous results, while for the other pig categories (sows, boars, breeding animals), the retention values from the national inventory calculation were used [38]. There are no large variations in the TAN proportion of excreted nitrogen in these age categories; the proportion of TAN in total excreted nitrogen varies between 55 and 59%. Literature data for intensive pig breeds are close to our measured N-flow values [33; 39]. Regarding the TAN content of excreted nitrogen, the most common TAN value used in the available literature is 70% [34]; thus, this was used in the AGEM calculation. In the integrated approach to calculate ammonia emission reduction in the feeding module, all influencing factors that may modify the amount of N incorporated and excreted by pigs were taken into account in AGEM-S, with the inclusion of correction factors (CFs) accepted in the international literature. Reduced protein feeding strategy: The amount of nitrogen excreted by pigs is influenced by dietary factors, the most important of which is the protein and amino acid supply. Research results have shown that it is possible to reduce the protein content of pig diets by up to 3-4% without compromising the production results when limited essential amino acids are supplemented [40]. Experiments show that a 1% reduction in dietary protein content reduces the TAN content of manure by 8.6-10% [40; 41; 42; 43; 44]. In the AGEM-S, a 10% reduction in TAN was applied, while reducing the protein content of the diet by 1%. Using more nutritional phases: The protein and amino acid requirements of pigs change daily with age, which is related to the different ratio of weight gain and maintenance. This change of requirements can be followed by different feeding phases. The effect of multiphase feeding is most applicable in the fattening phase. During fattening, the use of a 3-phase feeding reduces N excretion by 16% compared to fattening on a single phase feeding [45], and 5 phases instead of 2 phases results in a reduction of 0.45 kg N/N excretion per animal per year [44]. In the AGEM-S model, the number of feeding phases as an emission influencing factor was used only in the case of fattening, where 3-phase fattening was the reference, and one more phase meant \(-\)0.15 kg N/year correction and one less phase meant \(+\)0.15 kg N/year correction, respectively. A maximum of 4 fattening, 3 piglet, 2 suckling or pregnant sow, 2 gilt, and 1 boar feeding phases can be chosen. In practice, the reduced protein feeding strategy can be combined with the increase of nutritional phases.