Phosphorus is one of the most expensive nutrients in swine diets. Use of standardized total tract digestibility (STTD) of P, instead of apparent total tract digestibility (ATTD), may reduce the cost of diets because STTD values, unlike ATTD values, are additive in mixed diets. Values for STTD of P can be determined by correcting ATTD of P for the basal endogenous loss of P. The basal endogenous loss of P is estimated by using a P-free diet. Gelatin has been widely used in P-free diets because it does not contain any P and is a good source of protein. However, gelatin products can make diets dusty and sticky which can reduce the palatability of these diets and make them hard to work with. In addition, feeding pigs with diets containing no P may cause health issues in pigs. Blood plasma, casein, and potato protein concentrate are possible protein alternatives to gelatin because the P in blood plasma and casein is close to 100% digestible and potato protein concentrate provides very little P. Therefore, the objective of this experiment was to test the hypothesis that the basal endogenous loss of P from pigs fed a diet containing blood plasma, casein, or potato protein concentrate are not different from that of pigs fed a diet containing gelatin.
Experimental design
Forty pigs (body weight: 19.34 kg; SD = 0.80) were allotted to 4 low-P diets using a randomized complete block design with two blocks of 20 pigs for a total of 10 replicate pigs per diet. Pigs were housed individually in metabolism crates. Diets were based on cornstarch and sucrose and also contained 20% gelatin, 20% blood plasma, 18.5% casein, or 20% potato protein concentrate
Pigs were fed experimental diets for 12 days with the initial 5 days considered the adaptation period. Feces and urine samples were collected separately for 4 d following the adaptation period. Fecal and urine samples were stored at – 20 °C immediately after collection.
Data were analyzed using a model that included diet as fixed effect and block as random effect.
Results
Feed intake and fecal excretion were greater (P < 0.05) for pigs fed diets containing blood plasma, casein, and potato protein concentrate compared with pigs fed the gelatin diet, but pigs fed the diet containing potato protein concentrate had the greatest (P < 0.05) fecal excretion compared with pigs fed the other protein sources. The ATTD of dry matter (DM) was lower (P < 0.05) in the diet containing potato protein concentrate compared with diets containing gelatin, blood plasma, or casein. Phosphorus intake was different (P < 0.05) between all diets, with pigs fed the diet containing gelatin having the lowest and pigs fed the diet containing blood plasma having the greatest P intake. There was no difference in concentration of fecal P (%) from pigs fed the gelatin diet compared with pigs fed the casein diet, but pigs fed the gelatin diet had less (P < 0.05) fecal P output (g/d) compared with pigs fed diets containing the other protein sources. Basal endogenous loss of P was not different between the gelatin and casein diets, but pigs fed diets containing blood plasma or potato protein concentrate had greater (P < 0.05) basal endogenous P loss than pigs fed the other diets. Therefore, it was concluded that a diet containing casein may be used to determine endogenous losses of P in growing pigs.
Key points
- Pigs fed diets containing blood plasma and potato protein concentrate had greater basal endogenous loss of P compared with pigs fed the gelatin diet, indicating that not all of the P provided by these ingredients is 100% absorbed by pigs. Therefore, these ingredients would not be good alternatives to gelatin to determine the basal endogenous loss of P.
- Basal endogenous loss of P was not different between pigs fed the gelatin and casein diets and, therefore, casein may be used as an alternative to gelatin.
Table 1. Basal endogenous loss of P by pigs fed low-P diets1
a,b,c,dMeans within a row without a common superscript letter are different (P < 0.05).
1BEL = basal endogenous loss; DMI = dry matter intake.