Pig farming plays a vital role in converting human inedible protein sources into edible animal protein. A significant portion of ingested nitrogen (N) and phosphorus (P) is excreted in the manure
however
this poses environmental challenges, particularly in regions with intensive pig production. Accurate estimation of nutrient excretion is crucial when assessing the environmental impact of pig production and management strategies. To this end, understanding how management influences BW composition is important. In the current study, the influence of sex and slaughter weight on body composition and nutrient efficiency in Piétrain crossbreds was examined in two experiments. Four sex categories were tested: entire male pigs (EM), barrows (BA), immunocastrates (IC), and gilts (GI). Experiment 1 occurred under experimental conditions (individual housing, nutrient-rich diet) while experiment 2 represented controlled farm circumstances (group housing, commercial diet). Slaughter weight in experiments 1 and 2 were 110-148 kg and 99-138 kg, respectively. Body composition was analysed at the beginning and end of the growing-finishing phase. Nitrogen efficiency, based on the conversion of ingested N into body N, was calculated. In general, slaughter weight had a clear effect on body composition and nutrient excretions in BA and a lesser effect in GI. In contrast, no effect of slaughter weight on body composition and N excretions was observed in EM and IC within the tested weight range. As slaughter weight increased in BA, CP and water content decreased while fat content increased. This resulted in increasing N excretion and decreasing N efficiency at higher slaughter weights. Only weak correlations between estimated lean meat content and N content in the body were observed. No significant effect of BW on whole-body P content or P excretion was observed. The measured body composition values can be used for future research and modelling of nutrient excretions in pig production.