Search

The objectives of the two studies were to determine whether the guanidination and isotope dilution methods applied both by labeling the animal ([sup.15]N-infusion method) and by diet ([sup.15]N-dilution method) give similar estimates of ileal endogenous lysine (EL) and endogenous nitrogen (EN) flows, respectively, to that of the enzyme-hydrolyzed casein (EHC) method in the growing pig and to determine whether the guandination and [sup.15]N-dilution methods give similar estimates of EL and EN flows, respectively, to that of the EHC method in the rat. For the first study, the test diet contained guanidinated and enzymatically hydrolyzed casein (molecular weight < 5,000 Da), which was also labeled with [sup.15]N. Rats (n = 30; mean BW 178 g) and pigs (n = 6; mean BW 19.2 kg) received a preliminary EHC-based diet for 7 d. The test diet was then given to the rats and pigs on d 8. Digesta were sampled from the terminal 20 cm of ileum of killed animals. The EL flows determined using the guanidination method were lower than those determined using the EHC method (means of 298 vs. 382, and 214 vs. 287 [micro]g/g of DMI, in the rat and pig, respectively; P < 0.05 for the rat and P < 0.01 for the pig). The EN flows determined with the [sup.15]N-dilution method were lower than those determined using the EHC method (means of 1,034 vs. 1,942 and 1,011 vs. 1,543 [micro]g/g of DMI, in the rat and pig, respectively, P < 0.001 for the rat and P < 0.05 for the pig). In the second study, pigs (n = 6; mean BW 27 kg) were continuously infused via the jugular vein with [sup.15]N-leucine for 11 d. The pigs received an EHC-based diet (molecular weight < 5,000 Da) during this 11-d period, after which digesta were sampled at the terminal ileum under anesthesia. The EN flow determined using the [sup.15]N-infusion method (mean of 1,971 [micro]g/g DMI) was higher (P < 0.01) than that determined using the EHC method (mean of 1,233 [micro]g/g DMI). The guanidination method gave a lower estimate of EL flow than did the EHC method in both the pig and rat. The [sup.15]N-dilution method also gave a lower estimate of EN flow than the EHC method in the pig and rat, and the [sup.15]N-infusion method gave a higher estimate of EN flow than the EHC method in the pig. Key Words: Endogenous Protein, Lysine, Nitrogen, Pigs, Rats

The mobile nylon bag technique (MNBT) may offer a simple, rapid means for assessing ileal AA digestibility of pig feed ingredients. In the present study, the effects of washing bags recovered from digesta, the amount and fineness of feeds, and feed trypsin inhibitor activity on apparent ileal digestibilities (AID) of CP and AA were determined with the MNBT. Twenty-four ileorectal anastomosed pigs (Yorkshire x Chinese Black barrows, 30 kg initial BW), of which 12 were fitted with duodenal T-cannulas, were used. Not washing the bags recovered from ileal digesta resulted in a reduction (P < 0.05) in apparent ileal digestibilities of CP and AA determined by MNBT. Washing the bags for more than 4 min overestimated (P < 0.05) the apparent ileal digestibilities of CP and AA compared with those determined with the anastomosed pigs. Sample size and fineness of grinding also affected (P < 0.05) apparent ileal digestibilities of CP determined by MNBT. The apparent ileal digestibilities of CP determined by MNBT were reduced (P < 0.05) when sample size exceeded 0.75 g and when feed was ground through screens with a mesh size of more than 1.0 mm. The closest agreement between results obtained by MNBT and a conventional ileal digestibility assay occurred when 0.75 g of feed ground through a 1.0-mm mesh screen was used per bag and bags were washed for 2 min after retrieval from digesta. Further studies are warranted to investigate the use of the mobile nylon bag technique for predicting the ileal digestibilty of AA for feeds containing antinutritional factors. Key Words: Amino Acids, Digestibility, Pigs

Three barrows, average initial BW of 35 kg, were fitted with a re-entrant cannula at the distal ileum and catheters in each of the external jugular veins. The barrows were fed twice daily a diet containing barley as the sole source of protein. A 1-d intravenous infusion of saline was followed by an 8-d continuous infusion of [15N]leucine at a rate of 30 mg/(kg BW x d). Blood samples, taken hourly for 9 d, were pooled over the 12-h period between feeding. Ileal digesta were collected hourly on d 3 and 8 of the [15N]leucine infusion and pooled over 12 and 24 h. Enrichments (atom percentage excess 15N) in nitrogen (N), leucine, isoleucine, valine, and alanine were measured in the trichloroacetic acid (TCA)-soluble and -insoluble fractions of plasma and in ileal digesta. Although the enrichments in N were similar in all pools, enrichments in amino acids in the TCA-soluble fraction of plasma were at least twice that in the TCA-insoluble fraction and in ileal digesta. The estimated contributions of endogenous N and amino acids to total N and amino acids in ileal digesta were 82.3 [+ or -] 9.38, 39.0 [+ or -] 3.83, 43.8 [+ or -] 6.50, 51.9 [+ or -] 3.24, and 51.9 [+ or -] 9.80 for N, leucine, isoleucine, valine, and alanine, respectively. The results from this study indicate that enrichments in total N in the TCA-soluble fraction of plasma may not accurately reflect enrichments in endogenous N secreted into the intestinal lumen. This factor should be considered when using the 15N-isotope dilution technique to estimate the recovery of endogenous protein in ileal digesta of pigs fed protein-containing diets. Key Words: Pigs, Isotope Dilution, Endogenous Protein, 15N, Amino Acids

Three isotope dilution techniques which detect endogenous nitrogen in pigs were compared. The 15N-isotope dilution technique was the most sensitive for determining the recovery of endogenous protein in the distal ileum digesta as compared with the 15N-leucine and 15N-isoleucine dilution techniques. This was verified by measuring the 15N-enrichment excess in total nitrogen, leucine, and isoleucine in the trichloroacetic-soluble fractioon of the blood and in ileal digesta.