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Intestinal digestibility of amino acids in fluid- and particle-associated rumen bacteria determined using a precision-fed cecectomized rooster bioassay
Microbial protein represents the majority of metabolizable protein absorbed by ruminant animals. Enhanced understanding of the AA digestibility of rumen microbes will improve estimates of metabolizable protein. The objective of this experiment was to determine the digestibility of AA in fluid- (FAB) and particle-associated bacteria (PAB) using the precision-fed cecectomized rooster bioassay. Bacteria were isolated from 4 ruminally-cannulated lactating Holstein cows fed an 89% forage diet (DM basis). Samples of FAB and PAB were fed to nine cecectomized roosters to determine standardized digestibility of AA. Data were analyzed using PROC MIXED (SAS, 2004). Bacterial N composition (average = 8.3%) was similar to previous literature values. Total AA digestibility was (mean ± SE) 76.8 ± 2.4 and 75.5 ± 2.2 percent for FAB and PAB, respectively. Amino acid digestibility did not differ between FAB and PAB (P > 0.05). There were differences in essential (EAA) and non-essential AA digestibility within bacterial type when compared with mean essential or non-essential AA digestibility values (P < 0.05). Arginine, His, and Met were greater than the mean EAA digestibility in FAB, whereas Trp and Val were lower. Arginine and Lys were greater than the mean EAA digestibility in PAB, whereas Phe and Val were lower. Compared with previous literature and relative to NRC (2001) estimates of AA digestibility in microbes, the precision-fed cecectomized rooster assay is an acceptable in vivo model to determine AA digestibility of rumen bacteria.
Keywords: amino acid, digestibility, rumen bacteria