Short communication: Intestinal digestibility of amino acids in fluid- and particle-associated rumen bacteria determined using a precision-fed cecectomized rooster bioassay

Abstract

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 by differential centrifugation, including particle suspension in 0.1% Tween-80 for increased removal of PAB from ruminal digesta. Samples of FAB and PAB were fed to 9 cecectomized roosters to determine standardized digestibility of AA. Total AA digestibility was 76.8 and 75.5% for FAB and PAB, respectively, but did not differ. Differences existed in AA digestibilities within bacterial type when compared with the mean essential AA digestibility value. Compared with previous literature estimates of AA digestibility in microbes (mean = 76%; range = 57-87%) and relative to National Research Council estimates of total AA from rumen bacteria (80%), the precision-fed cecectomized rooster assay is an acceptable in vivo model to determine AA digestibility of rumen bacteria.

Invited review: Nitrogen in ruminant nutrition: A review of measurement techniques

“…Different methods have been used to estimate intestinal digestibility of microbial protein (and individual AA) including regression approaches (Storm et al, 1983a;Hvelplund and Hesselholt, 1987), in vitro procedures (Gargallo et al, 2006), and in vivo assays using cecectomized roosters (Stern et al, 1997;Fonseca et al, 2014), or mobile bags (Hvelplund et al, 1992). Single time point hydrolysis of feed or microbial protein as a routine procedure has been criticized for underestimation of AA release and minimizing the loss of acid-sensitive AA (Rutherfurd, 2009;Fessenden et al, 2017).…”

Ruminal bacteria and protozoa composition, digestibility, and amino acid profile determined by multiple hydrolysis times

“…Procedures used to detach microbes report recoveries ranging from 20 (Martín-Orúe et al, 1998) to 80% (Whitehouse et al, 1994); this might call into question the true ability of recovered bacteria to represent the particle associated bacteria (Korhonen et al, 2002). Ultimately, it is likely that differences in isolation methods are responsible for much of the reported ranges of AA composition, whereas a smaller portion of the variation can be considered a true difference in AA composition (Fonseca et al, 2014).…”

“…Heat-damaged blood meal, although relatively soluble and able to pass through pores, can have a very low digestible fraction (Ross et al, 2013). Alternative in vivo techniques, such as the precision-fed cecectomized rooster bioassay, have been used in ruminant feeds (Titgemeyer et al, 1990, Boucher et al, 2009, and Fonseca et al (2014) recently applied the technique to ruminal bacteria isolates. Total AA digestibility reported by Fonseca et al (2014) averaged 76%, with a range of 62 (Cys) to 82% (Met).…”

“…Alternative in vivo techniques, such as the precision-fed cecectomized rooster bioassay, have been used in ruminant feeds (Titgemeyer et al, 1990, Boucher et al, 2009, and Fonseca et al (2014) recently applied the technique to ruminal bacteria isolates. Total AA digestibility reported by Fonseca et al (2014) averaged 76%, with a range of 62 (Cys) to 82% (Met). The mean AA digestibility in non-formalin-treated bacteria in the current trial was 88%, with a range of 84 (Tyr) to 95% (Cys).…”

“…In vivo assays have clear advantages in providing realistic and applicable enzymatic hydrolysis conditions; however, they also require surgically altered animal models. The precision-fed cecectomized rooster bioassay was recently applied to ruminal bacteria (Fonseca et al, 2014); however, data are still lacking on protozoa AA digestibility. Additionally, avian species have different enzymes and pH conditions that might reduce the ability to make direct comparisons to ruminant digestion (Keller, 1968;Guerino and Baumrucker, 1987).…”