Fructan catabolism by rumen microbiota of cattle and sheep

Authors: Weinert-Nelson, Jennifer; Kagan, Isabelle; ELY, DONALD - University Of Kentucky; Flythe, Michael; Harlow, Brittany

Submitted to: Fermentation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/19/2023
Publication Date: N/A
Citation: N/A

Interpretive Summary: Fructans are fructose chains of varying lengths. In cool-season grasses, they provide energy reserves. When ruminants ferment cool-season grasses in the rumen, the fermented fructans provide energy to make protein. Little information exists on differences in the fermentation of fructans by cattle and sheep, which could be useful in understanding how these species differ in utilizing nutrients. To gain more understanding about possible differences, freeze-dried ground orchardgrass was incubated with rumen fluid (containing microbes) from steers or ram lambs (4 of each species). Samples were analyzed at the start of the incubation and 2, 4, and 8 hours later to examine changes in the fructan profile. In the first 2 hours, the longer fructans (more than 8 fructose units long) began to disappear in both sheep and cattle incubations, while shorter fructans (4 to 8 fructose units long) increased before beginning to disappear. The results suggest that rumen microbes utilize long fructans first and break them down into shorter chains. Fructans disappeared more rapidly in cattle than in sheep fermentations, especially between 2 and 4 hours of incubation. Shorter fructans disappeared more slowly in sheep fermentations, with most of the disappearance occurring between 4 and 8 hours of incubation. The results suggest that cattle may be able to utilize fructans more rapidly or more efficiently than sheep, and suggest that different enzymes are active in the rumen cattle and sheep.

Technical Abstract: Fructans serve as the primary form of storage carbohydrate in cool-season grasses, but little is known about potential differences in ruminal fermentation of fructans between cattle and sheep. An ex vivo study was conducted to evaluate species differences in fructan catabolism. Buffered media containing ground orchardgrass (Dactylis glomerata L.) substrate was inoculated with uncultivated rumen microbiota obtained from cattle and sheep (n = 4 species-1). Fructan profiles were monitored over the incubation period (8 h; 39°C) using high-performance anion-exchange chromatography coupled to pulsed amperometric detection (HPAEC-PAD). In both species, disappearance of long-chain fructans (degree of polymerization [DP] > 8) was evident by 2 h of incubation (p < 0.01), whereas short-chain fructans (DP 4 – 8) increased from 0 to 2 h prior to subsequent degradation (p < 0.01). However, the overall rate of long-chain fructan ca-tabolism was greater in bovine versus ovine fermentations, particularly between 2 and 4 h (p < 0.01). Additionally, rapid utilization of short-chain fructans occurred from 2 – 4 h in bovine fer-mentations, but was delayed in ovine fermentations, with substantial degradation occurring on-ly after 4 h of incubation (p < 0.01). These results indicate that cattle may have a greater capacity for ruminal fructan utilization.