A FORAGE FACTS Publication of the KANSAS FORAGE TASK FORCE
Kansas State University Agricultural Experiment Station and Cooperative Extension Service
FOAMY PASTURE BLOAT
INTRODUCTION
An important factor affecting animal performance of cattle grazing high-quality legume and cereal grain
pastures is frothy bloat. Bloat can have potentially devastating effects on animal health, if cattle are not monitored
closely, especially when cattle are first introduced to bloat-susceptible pastures and/or during certain climatic
conditions and plant growth stages when the nutrient composition of the grazed forage changes rapidly. For example,
average death losses attributed to wheat pasture bloat have been estimated at 2 to 3 percent, but can occasionally
reach 20 percent. In addition to increased death loss, other consequences of bloat that reduce profitability
of grazing enterprises include reduced weight gains, lower milk production, reduced feed efficiency, increased labor
costs and added treatment costs. Understanding the causes of bloat and using practices that reduce and/or
prevent pasture bloat will help to reduce losses and improve performance of cattle grazing lush forages.
DEFINITION
Foamy bloat occurs when cattle consume feeds
that are readily digestible, such as finely ground grains
and high-quality alfalfas, clovers and cereal grain forages.
Once consumed, these feeds provide readily
available nutrients that are immediately utilized by ruminal
microbes, leading to a very rapid production of
gas in the rumen. In the case of foamy, or frothy bloat,
these gasses are then "trapped" in a thick, proteinaceous
foam. The presence of the thick foam prevents
the animal from expelling the gas, leading to excessive
pressure and creating the characteristic distended abdomen.
If severe cases are left untreated, pressure can
continue to build, resulting in severe discomfort and
eventual death.
CAUSES OF BLOAT
Bloat is thought to occur when highly digestible
feeds are degraded and fermented rapidly. Rapid fermentation
can occur when rapidly growing, succulent
forages are consumed. This includes alfalfas and clovers
grazed during the pre-bloom and early-bloom
stages and cool-season annual and perennial forages
during periods of rapid growth. Factors influencing the
incidence of frothy bloat in grazing animals can be categorized
into three areas: animal, plant and ruminal
factors.
Animal Factors. Variation in incidence and severity
of bloat between animals grazing the same pasture
may be partially related to animal factors such as
differences in diet selection, forage intake and saliva
production. Increased saliva production may reduce
formation and stability of frothy bloat through its potential
anti-foaming characteristics, buffering capabilities
and effects on rate of passage. Animals highly susceptible
to bloat may secrete less saliva and/or have
unique ruminal populations of bacteria and protozoa
compared with less susceptible animals. Although forage
intake would appear to affect an animal's susceptibility
to wheat pasture bloat, research remains unclear
on the role of forage intake patterns on occurrence of
bloat.
Plant factors. In general, bloat provocative forages
are actively growing, highly digestible species
with high protein and low fiber contents. These include
temperate legumes such as red clover, white clover,
Persian clover and alfalfa, as well as small grains and
FORAGE FACTS Publication Series
Research and Extension
annual and perennial grasses such as winter wheat.
Foamy bloat has been associated with increases in
soluble proteins and/or carbohydrates associated with
the rapidly growing forage, as well as a more rapid release
of plant cell contents in the rumen that leads to a
high rate of ruminal gas production. In addition to
soluble proteins, mineral content of the grazed forage
also has been related to metabolic disorders of animals
grazing winter wheat. Research indicates that increased
occurrence of bloat is associated with increases in calcium
(Ca) and magnesium (Mg) concentrations of legumes,
as well as increased potassium (K) and/or
potassium:sodium ratios of winter wheat.
Ruminal factors. Perhaps even more important
than the mineral composition of the grazed forage are
the relative ratios of cations ingested by the animal and
present in the rumen. While ruminal concentrations of
soluble proteins and minerals may not initiate bloat,
they are believed to increase the stability of foam in the
rumen, potentially increasing the incidence and severity
of bloat. Attraction between soluble proteins, which
are negatively charged, and positively-charged mineral
ions present in rumen fluid can increase the stability
and strength of foams. Similar to colloidal suspensions
of soils, divalent (Ca and Mg) and trivalent ions can
form bonds with two or three negatively charged protein
particles, thereby creating a more stable foam compared
with sodium, a monovalent ion. Several trials
evaluating legume bloat indicated that ruminal Ca, Mg
and K concentrations were significantly higher and Na
levels significantly lower in bloating animals, suggesting
Na supplementation may reduce the incidence of
bloat. Additional wheat pasture bloat research also indicates
an increase in occurrence of bloat concurrent
with increases in forage potassium levels.
PREVENTION OF BLOAT
Cattle and pasture management, as well as the
use of surfactants and additives will help to reduce the
incidence of pasture bloat. Occurrence of bloat is affected
by a combination of climatic conditions, soil fertility,
forage maturity and grazing management factors.
Reducing the incidence of bloat may require changes in
several management practices, as well as close management
of grazing animals.
Grazing Management. Possible pasture management
techniques include managing interseeded, or
"mixed" pastures to maintain no more than 50 percent
alfalfa or clover, and selecting alfalfa and clover varieties
with less potential for causing bloat.
Cattle Management. Fill cattle on dry roughage
before introducing them to bloat-susceptible pastures.
If possible, delay initial turnout until midday, when
pastures are dry. Where facilities and labor management
permit, identify animals with greater susceptibility
to bloat and manage them separately.
Use of Surfactants. Surfactants, or anti-foaming
agents, have been used successfully in some grazing
situations. Spraying surfactants on bloat-provoking
pastures when conditions are conducive to bloating
works well, especially in highly controlled grazing systems
with small paddocks. An alternative to pasture
spraying is to add the agent to drinking water; however,
addition to drinking water may be less effective
because of variation in water consumption.
Poloxalene. Several studies indicate that feeding
poloxalene (Bloat Guard) at levels of 1 to 2 grams/100
pounds of body weight per day dramatically reduces
bloat. Poloxalene is a mild detergent that reduces the
surface tension of the foam, resulting in decreased formation
of foam and release of gasses entrapped in the
foam. There are several products available for use in
grazing programs, including mineral supplements,
blocks, liquid feeds and top dresses. It is important to
remember that in order to be effective, adequate
amounts of poloxalene must be consumed on a regular
basis. Guaranteed consumption of a sufficient amount
of poloxalene may mean hand-feeding 1 to 2 pounds of
a highly palatable supplement containing poloxalene
each day.
Ionophores. Although not as effective as
poloxalene, Rumensin and Bovatec have been shown to
reduce the incidence and severity of frothy bloat while
also improving animal performance. Research with
winter wheat pasture indicates that ionophores may reduce
the incidence of bloat by reducing the amount of
gas produced by microbes in the rumen. Ionophores
work well when included in supplementation programs,
providing a level of bloat protection while improving
daily gains throughout the grazing season.
SUMMARY
The occurrence of frothy bloat in grazing livestock
is initiated primarily by a rapid release of plant
cell contents that are quickly degraded and fermented
in the rumen. The gasses produced in the rumen are
then trapped in a thick foam that prevents the animal
from expelling the produced gasses. While actual death
loss due to bloat may be small, subclinical bloat can reduce
animal performance and increase labor and medical
costs. Evaluating your pasture management techniques,
watching cattle closely, and providing
bloat-reducing products can reduce the occurrence of
bloat and improve animal performance when grazing
lush, high-quality forages.
Kansas State University Agricultural Experiment Station and Cooperative Extension Service
It is the policy of Kansas State University Agricultural Experiment Station and Cooperative Extension Service that all persons shall have equal opportunit y and
access to its educational programs, services, activities, and materials without regard to race, color, religion, national origin, sex, age or disability. Kansas State
Universit y is an equal opportunity organization. Issued in furtherance of Cooperative Extension Work, Acts of May 8 and June 30, 1914, as amended. Kansas
State University, County Extension Councils, Extension Districts, and United States Department of Agriculture Cooperating, Marc A. Johnson, Director.
Contact: Steve Paisley
Extension Specialist
Livestock Production, South Central
Telephone: 316-663-5491
FAX: 316-662-9197
E-mail: spaisley@oznet.ksu.edu