Glycemic index of starch affects XXXX retention in grower @entity1707 .

@entity1707 @entity4336 @entity1568 @entity2247
Three studies were performed to examine the effect of starch and protein digestion rates on N retention in grower @entity1707 . In Exp. 1, the glycemic index (GI) of @entity4336 , a malting @entity2247 , and a slow-rumen-degradable @entity2247 (SRD- @entity2247 ) were measured using 6 barrows (BW = 18.0    0.5 kg). The GI of malting @entity2247 was greater (P < 0.05) than that of SRD- @entity2247 (71.1 vs. 49.4), and the GI of both @entity2247 cultivars was less (P < 0.05) than that of @entity4336 (104.8). In Exp. 2, the standardized ileal digestibility of AA and DE content of the 3 ingredients were determined using 5 ileal-cannulated barrows (BW = 20.7    2.3). The apparent total-tract energy digestibility values of @entity4336 (86.1%) and malting @entity2247 (85.7%) were greater (P < 0.05) than that of SRD- @entity2247 (82.3%). The standardized ileal digestibility of Lys was 94.0, 92.6, and 92.4% for @entity4336 , malting @entity2247 , and SRD- @entity2247 , respectively, and did not differ among grains. In Exp. 3, 6 diets were formulated to equal DE (3.40 Mcal/kg), standardized ileal digestibility of Lys (8.6 g/kg), starch (424.9 g/kg), and digestible CP (180.0 g/kg) using the values obtained in Exp. 2. Three GI [high ( @entity4336 ), medium (malting @entity2247 ), and low (SRD- @entity2247 )] and 2 rates of protein digestion [rapid (soy protein hydrolysate) and slow (soy protein isolate)] were tested in a 3   2 factorial arrangement with 36 barrows (BW = 32.2    2.5 kg). @entity1707 were fed 3.0 times the maintenance energy requirement daily in 2 meals for 2 wk and were housed in metabolic crates to collect feces and urine separately. At the end of the study, intestinal contents were collected from 4 equal-length segments of the small intestine. The percentage of unabsorbed CP in segment 1 relative to dietary CP was greater (P < 0.05) for the soy protein isolate diet than for the soy protein hydrolysate diet (170.3 vs. 116.5%). The percentages of unabsorbed starch in segments 1 and 2 were greater (P < 0.05) for the SRD- @entity2247 diet than for the malting @entity2247 or @entity4336 diet. @entity1568 intake and fecal N excretion were greater (P < 0.05) for @entity1707 fed the malting @entity2247 and SRD- @entity2247 diets than for @entity1707 fed the @entity4336 diet. Urinary N excretion was greater (P < 0.05) for @entity1707 fed the SRD- @entity2247 diet than for @entity1707 fed the @entity4336 or malting @entity2247 diet. @entity1707 fed slowly digestible starch (SRD- @entity2247 ; 46.6%) had less (P < 0.05) net N retention than @entity1707 fed @entity4336 or malting @entity2247 (54.7 and 54.1%, respectively). In conclusion, slowly digestible starch sources such as SRD- @entity2247 may not be suitable to support maximum protein deposition in restricted-fed grower @entity1707 .
