Effect of dietary crude protein level on basal ileal endogenous losses and standardized ileal digestibilities of crude protein and amino acids in newly weaned pigs

The study was carried out to estimate basal ileal endogenous crude protein and amino acid losses (IAAL(B)) and standardized ileal digestibilities (SID) of crude protein (CP) and amino acids (AA) originating from casein in newly weaned pigs from linear relationships between ileal recoveries and dietary intakes of graded levels of CP and AA. A total of 14 (12 + 2 for replacement) 3-week-old barrows weighing 5.7 kg was fitted with simple T cannulas at the distal ileum. At 28 days of age, the pigs were randomly allocated to the six experimental diets with two pigs per diet in four weekly repeated measurements. Corn starch-based diets, containing six graded levels of CP from casein (90, 155, 220, 285, 350, 415 g/kg CP as-fed basis respectively), were formulated. Titanium dioxide (TiO2) was included as a digestibility marker. Each experimental period consisted of 7 days. Ileal digesta were collected for a total of 24 h during day 6 and 8. Splitting the total range of 90 to 415 g/kg CP into smaller ranges, i.e. from 90 to 220, 220 to 350 or 285 to 415 g/kg CP, provides estimates for CP and AA recoveries which are not significantly different from zero. As a result, dietary CP and AA originating from casein are completely digested and absorbed until the end of the small intestine. In addition, the use of large ranges of dietary CP levels showed that IAAL(B) were affected (p < 0.050) by the dietary CP content. Accepting that ileal recoveries of CP and AA are exclusively of endogenous origin when purified corn starch casein-based diets are fed, IAAL(B) were estimated as a function of the dietary CP level. There were linear increases (p < 0.050) in IAAL(B) when the dietary CP content was increased from 90 to 415 g/kg. Average IAAL(B) expressed in g/kg dry matter intake (DMI) were 16.3, 0.7, 0.2, 0.9 and 0.2 for CP, lysine, methionine, threonine and tryptophan respectively. These values are in close agreement with IAAL(B) obtained in grower-finisher pigs.