Complying with Swiss farm nutrient balance regulations and fertilization planning rely on accurate reference values for phosphorus (P) excretion of livestock. This study presents the method for deriving such values considering different production scenarios, using sheep and goats as case study. The P excretion was determined through a balance approach, calculating for a defined period, the difference between dietary P intake and P retention in growth, fetal development, milk production, and wool production (only sheep). Scenarios were defined for each animal category identified as dairy ewes (n=48), suckler ewes (n=12), dairy goats (n=48), fattening lambs (n=36), and goat kids (n=1). Those according to birth season (n=3), indoor basal diet type within (grass/maize silage vs. hay), body weight (BW, n=3, 60-90 kg for ewes, 50-75 kg for goats), milk yield (MY, n=4, 350-650 kg/year for ewes, 350-950 kg/year for goats), and slaughter age (SA, n=3, 100-180 days for lambs). For each category, a reference was defined according to performance (MY, BW, SA) including a weighted average of birth season and indoor diet. Feed and milk intake were estimated using INRA (2018) and Agroscope (2021) equations, with diets optimized to cover net energy and absorbable protein requirement. Mineral phosphates contributed to 13.7 %, 12.9 %, 10.5 % and 26.9 % of total P intake for dairy ewes, suckler ewes, dairy goats, and fattening lambs, respectively. Dairy ewes, suckler ewes and dairy goats allocated respectively 92.3 %, 81.9 % and 88.4 % of retained P to MY; 3.11 %, 7.34 %, 7.02 % to first-lactation BW gain; 4.45 %, 10.5 %, 4.62 % to fetal development; 0.10 %, 0.24 % to wool (only ewes). Reference values for P excretion by dairy ewes (500 kg MY/year, 75 kg BW), suckler ewes (75 kg BW) and dairy goats (550 kg MY/year, 60 kg BW) was 2.90 kg/year (78.2 % of intake), 1.67 kg/year (83.6 % of intake), and 1.57 kg/year (73.8 % of intake), respectively. Fattening lambs (140 days SA, 45 kg BW) excreted 0.28 kg P (60.7 % of intake), while pre-weaned goat kids (56 days SA) excreted 0.04 kg P (31.4 % of intake). Based on the modelled scenarios, correction factors to the reference values were established to account for variations in farm characteristics. For dairy ewes, suckler ewes, and dairy goats P excretion varied respectively by 7.76 %, 7.89 %, 8.79 % per 10-kg BW difference and by 2.36% and 0.81% per 25-kg/year MY difference (dairy ewes and goats). For fattening lambs, P excretion varied by 17 % per 10-day SA difference. Overall, birth season and basal diet type affected the reference P excretion between -18.3 % to 13.5 %. These correction factors allow farmers to adjust the reference values to better reflect their specific production systems. The models demonstrate the impact magnitude of animal performances on P excretion in sheep and goats. The presented methodology and results provide a framework for realistic nutrient balance assessments and effective fertilization strategies, ultimately promoting optimal farm nutrient management and environmental stewardship.
