Effects of different protein sources in low-phosphorus diets on calculated basal endogenous loss of phosphorus by growing pigs

The objective of this experiment was to test the hypothesis that the basal endogenous loss (BEL) of P from pigs fed a diet containing spray dried plasma, casein, or potato protein concentrate is not different from that of pigs fed a diet containing gelatin. Forty pigs (body weight: 19.34 kg; SD = 0.80) were housed individually in metabolism crates and allotted to four low-P diets using a completely randomized block design with two blocks of 20 pigs and five pigs per diet in each block. Diets were based on cornstarch and sucrose and contained 200 g/kg gelatin, 200 g/kg spray dried plasma, 185 g/kg casein, or 200 g/kg potato protein concentrate. With the exception of Ca and P, diets were formulated to meet requirements of all nutrients. Feces and urine samples were collected for 4 d following a 5-d adaptation period. Fecal samples were dried and ground, and fecal and urine samples were analyzed for P. Data were analyzed using a model that included diet as fixed effect and block as random effect. Results indicated that feed intake and fecal excretion of dry matter were greater (P < 0.05) in pigs fed diets containing spray dried plasma, casein, or potato protein concentrate compared with pigs fed the gelatin diet, with pigs fed potato protein concentrate having the greatest (P < 0.05) excretion. The apparent total tract digestibility (ATTD) of dry matter was least (P < 0.001) in pigs fed the diet containing potato protein concentrate, but there were no differences among gelatin, spray dried plasma, and casein diets. The ATTD of P was greater (P < 0.001) in pigs fed diets containing spray dried plasma or casein compared with pigs fed gelatin or potato protein concentrate diets. The BEL of P was not different between the gelatin and casein diets (i.e., 176 and 234 mg/kg dry matter intake), but pigs fed diets containing spray dried plasma or potato protein concentrate had greater (P < 0.001) BEL of P (i.e., 338 and 374 mg/kg dry matter intake) compared with pigs fed gelatin or casein diets. In conclusion, the BEL of P was greater if calculated from diets containing spray dried plasma or potato protein concentrate compared with gelatin. However, casein may be an alternative to gelatin to estimate the BEL of P because casein provides a greater amount of P compared with gelatin, which compensates for the deficient level of P in gelatin, but does not affect the BEL of P.