Chemical composition and nutrient accretion of intact male pigs growing from 28 kg to 125 kg body weight

Knowledge of the body’s nutrient content and nutrient accretion during growth is crucial for deriving nutrient requirements, developing feeding strategies, and estimating nutrient excretion in pigs. However, data on the chemical composition of contemporary fattening boar breeds are scarce. Most available data on the body composition of fattening pigs originated from studies with castrates or female pigs. Therefore, this study aimed to evaluate the chemical composition of BW gain in fattening boars growing from 28 to 125 kg BW. Seventy-five pigs were slaughtered at four stages: 28 kg BW (n = 20), 60 kg BW (n = 20), 90 kg BW (n = 16), and 125 kg BW (n = 19). Previously, the animals were kept individually in pens and nutrient-adequate pelleted feed was offered for ad libitum consumption in three feeding phases. Individual feed consumption and BW development were determined. After euthanisation, representative whole body samples, including the emptied gastrointestinal tract, were obtained and chemically analysed for total N, ether extract ( EE ), ash, P, Ca, and amino acids. The concentration of these nutrients in the BW gain was calculated by fitting regression models to nutrient mass as a function of BW. A quadratic regression was employed for EE, and linear regressions for the other nutrients. The mean feed conversion ratio in the entire fattening period was 2.1 kg feed/kg BW gain (n = 19), and the average BW gain was 1.23 kg/d (n = 19). Per 1 kg of BW gain, 29.2 g N was accreted. The accretion of EE followed a quadratic function and was markedly lower when compared with published values for castrates and females. Ash, Ca, and P accretions were 29.5 g, 7.8 g, and 5.1 g per kg BW gain. The results indicate that nutrient accretion in contemporary fattening boars, particularly protein and ether extract, differs from that of castrates and females reported in the literature. This suggests a need to re-evaluate the chemical composition of currently used breeds, including systematic comparisons of boars, castrates, and females.