Abstract The determination of the standardized total tract digestibility (STTD) of phosphorus (P) in feed ingredients for pigs involves quantifying the basal endogenous losses (BEL) of phosphorus, which originate from digestive secretions such as enzymes and mucoproteins, as well as from desquamated intestinal epithelial cells, and can be influenced by the age or category of the pigs. Thus, the objective of this study was to evaluate the BEL of P in female pigs from four different age categories: Initial (28 days and 7.80 ± 0.55 kg body weight – BW), Growing (78 days and 33.99 ± 3.02 kg BW), Finishing (125 days and 79.82 ± 4.05 kg BW), and Adult (243 days and 169.03 ± 6.50 kg BW). Twenty-four female pigs, six animals per category, were fed a phosphorus-free (P free) diet, containing starch, sugar, gelatin, cellulose, oil, minerals, vitamins, limestone and 0.5% titanium dioxide as an indigestible marker. The animals were fed at 2.8 × maintenance ME requirement for nine days, seven days for adaptation and two days for fecal collection, to determine BEL of P (g/kg of dry matter intake). A randomized complete block design was used, with four treatments (animal categories), six replicates per treatment, and one animal per experimental unit. Data were evaluated using quadratic polynomial (QP), linear broken-line (LBL), quadratic broken-line (QBL), and asymptotic exponential models. Model selection was based on the lowest Akaike Information Criterion (AIC) value and/or the highest coefficient of determination (R²). The average BEL of P were 0.414, 0.457, 0.459, and 0.624 g/kg of DM intake for the initial, growing, finishing, and adult phases, respectively (Table 1). The LBL model had the best fit to the data (P 0.001; AIC = -123,2; R² = 0.573; eq = −0.0019 × (67.7333 − X) × (X 67.7333) + 0.4357). This result indicates stability of BEL of P during early development, with an increase beginning at 67.7 kg BW. Therefore, it can be concluded that phosphorus BEL in pigs increases with age, highlighting that this factor should be considered in the determination of STTD of P in pigs.
Barbosa et al. (2026) studied this question.