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Rumen escape protein and diet quality of cattle grazing smooth bromegrass, switchgrass, and big bluestem
Abstract
Warm-season grasses often provide higher levels of performance for beef production than forage quality parameters predict. A 2-yr pasture study near Mead, NE was conducted to characterize and quantify escape protein and diet quality of cattle grazing a cool-season grass, smooth bromegrass (Bromus inermis Leyss.), and two warm-season grasses, switchgrass (Panicum virgatum L.) and big bluestem (Andropogon gerardii Vitman) at vegetative, elongation, early reproductive, and regrowth stages of plant development. Each paddock was strip grazed daily by three ruminally-fistulated steers with minimum forage allowance of 40 kg hd$\sp{-1}$ d$\sp{-1}$. Following total rumen evacuations, the omasum was sampled to represent post-ruminally degraded forage. After a 45-min post-evacuation grazing period, diet samples were collected from the rumen. Five 0.1-m$\sp2$ quadrats were clipped to estimate forage on offer. Proteins escaping degradation were characterized by SDS-PAGE and immunoblotting. Total crude protein was highest for smooth bromegrass across all grass maturities. Escape protein calculated on a protein basis in switchgrass and big bluestem (43.2%) was higher than smooth bromegrass (24.1%). Escape protein calculated on a dry matter basis was 5.0% for all three grasses. Ruminally degraded protein was highest in smooth bromegrass. In warm-season grasses, escape protein (%DM) decreased from vegetative to early reproductive stages. Dietary crude protein was 3 to 4 percentage points higher than forage on offer for warm-season grasses and up to 8 percentage points greater in smooth bromegrass. Dietary in vitro dry matter disappearance was higher and fiber components were lower than forage on offer in all grasses. Dietary lignin generally did not exceed 4%. Diet quality of regrowth was similar to elongation stage diets. The molecular weights of escaping proteins were 24 to 26 kDa and may originate from chloroplast membranes. The lack of bundle sheath cell bound ribulose 1,5-bisphosphate carboxylase/oxygenase passing from the rumen may indicate that in grazing animals, it does not escape ruminal degradation and that anatomical barriers may not solely protect proteins from ruminal degradation.
Subject Area
Livestock|Botany|Agriculture
Recommended Citation
Kirch, Brett H, "Rumen escape protein and diet quality of cattle grazing smooth bromegrass, switchgrass, and big bluestem" (1995). ETD collection for University of Nebraska-Lincoln. AAI9536619.
https://digitalcommons.unl.edu/dissertations/AAI9536619