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Publication Date
1981
Description
Studies were conducted to provide the basic knowledge for breeding a bloat-safe alfalfa cultivar. Two working hypotheses of pasture bloat were tested. The cell-rupture theory proposed that leaf mesophyll cell rupture is an important event in the occurrence of pasture bloat. The initial-rate-of-digestion (IRD) theory proposed that susceptibility to rapid initial digestion by ruminal bacteria is a characteristic of bloat-causing forages. The studies involved comparisons of bloat-causing and bloat-safe legumes: alfalfa (Medicago sativa L. ), red clover (Trifolium pratense L.), arrowleaf clover (Trifolium vesiculosum Savi), birdsfoot trefoil (Lotus comiculatus L.), deer milkvetch (Astragalus cicer L.), and sainfoin (Onobrychis viciifolia Scop.). IRD was measured in vitro and, with the nylon-bag technique, in fistulated sheep or cattle. Daily bloat incidence and rumen-fluid composition were recorded in fistulated cattle fed fresh alfalfa. Bloat-causing legumes were digested more rapidly than bloat-safe legumes. Concentrations of plant cell constituents were higher in rumen fluid of sheep fed alfalfa than in sheep fed three bloat-safe legumes. Daily measurements of IRD by the nylonbag technique were moderately correlated with daily bloat incidence, and the concentration of chlorophyll in rumen fluid was higher in bloated cattle than in nonbloated cattle. Important events in IRD are (1) mechanical disruption prior to microbial digestion, (2) bacterial colonization and invasion of plant tissues, (3) maceration of plant tissues by pectinolytic enzymes, and ( 4) disruption of plant cell walls. Differences between bloat-causing and bloat-safe legumes have been identified in each of these events, but at this level of comparison the several bloat-safe legumes have different characteristics. These studies have provided the basis for breeding a bloat-safe alfalfa cultivar by selecting for low !RD.
Citation
Howarth, R E.; Cheng, K J.; Fay, J P.; Majak, W; Lees, G L.; Goplen, B P.; and Costerton, J W., "Initial Rate of Digestion and Legume Pasture Bloat" (1981). IGC Proceedings (1977-2023). 20.
(URL: https://uknowledge.uky.edu/igc/1981/section11/20)
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Initial Rate of Digestion and Legume Pasture Bloat
Studies were conducted to provide the basic knowledge for breeding a bloat-safe alfalfa cultivar. Two working hypotheses of pasture bloat were tested. The cell-rupture theory proposed that leaf mesophyll cell rupture is an important event in the occurrence of pasture bloat. The initial-rate-of-digestion (IRD) theory proposed that susceptibility to rapid initial digestion by ruminal bacteria is a characteristic of bloat-causing forages. The studies involved comparisons of bloat-causing and bloat-safe legumes: alfalfa (Medicago sativa L. ), red clover (Trifolium pratense L.), arrowleaf clover (Trifolium vesiculosum Savi), birdsfoot trefoil (Lotus comiculatus L.), deer milkvetch (Astragalus cicer L.), and sainfoin (Onobrychis viciifolia Scop.). IRD was measured in vitro and, with the nylon-bag technique, in fistulated sheep or cattle. Daily bloat incidence and rumen-fluid composition were recorded in fistulated cattle fed fresh alfalfa. Bloat-causing legumes were digested more rapidly than bloat-safe legumes. Concentrations of plant cell constituents were higher in rumen fluid of sheep fed alfalfa than in sheep fed three bloat-safe legumes. Daily measurements of IRD by the nylonbag technique were moderately correlated with daily bloat incidence, and the concentration of chlorophyll in rumen fluid was higher in bloated cattle than in nonbloated cattle. Important events in IRD are (1) mechanical disruption prior to microbial digestion, (2) bacterial colonization and invasion of plant tissues, (3) maceration of plant tissues by pectinolytic enzymes, and ( 4) disruption of plant cell walls. Differences between bloat-causing and bloat-safe legumes have been identified in each of these events, but at this level of comparison the several bloat-safe legumes have different characteristics. These studies have provided the basis for breeding a bloat-safe alfalfa cultivar by selecting for low !RD.
