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II. Incidence, Climate, and Season
GRASS TETANY OF RUMINANTS
when the mean daily temperature was below 14°C (57°F). In addition,
there were short-term fluctuations. They indicated that 5 days after the
mean daily temperature rose above 14"C, the number of cases of grass
tetany increased. They also indicated that about 5 days after a fall in
temperature, the number of cases of tetany decreased. Figure I indicates
the distribution of tetany cases in 1952.
A v e r a y e screen temp ("C
Number of g r a s s tetany cases
FIG. I . The relationship between incidence of grass tetany and temperature and precipitation. Values for incidence of grass tetany and temperature are averages for a 5-day
period. Percipitation is the amount received daily. (From Kemp and 't Hart, 1957.)
In the Netherlands, 't Hart (1960) indicated that during cold, wet
years, tetany cases occurred during the whole summer. When incidence
during the entire year was considered, 95% of the cases occurred when
the mean temperature was between 8°C and 14°C (46OF-57"F). He
also indicated that in other parts of the world the limits were reported
as between 5°C and 15°C (4O0F-60"F). This includes "wheat pasture
poisoning" in Oklahoma, tetany on winter grazing of oats in Argentina,
and grass tetany in New Zealand. 't Hart ( 1 960) concluded .that hypomagnesemia occurred mainly when temperature was rather low, and
other conditions were favorable for grass growth. The frequency of
tetany was much higher in years with a sudden, quick growth of grass
in spring than in years with poor growth. 't Hart ( I 960) indicated that
D. L . GRUNES, P. R. STOUT, AND J . R. BROWNELL
Inglis (1960)had found a decrease in incidence of tetany when frost
't Hart (I 960) stated that the disease occurred only under conditions
of ample moisture supply, and that spring tetany was less frequent on
very dry and very wet pastures. Large numbers of cases of autumn tetany
occurred only in wet seasons.
The dry matter content of pasture herbage is often less than 15% in
wet weather. Nitrogen fertilization may decrease the dry matter content
of the forage. If grass or small grains forages are low in Mg, animals may
be unable to obtain their Mg requirenTent from damp and succulent grass.
Van der Molen (1964)reported that 2.7% of all dairy cows in the Netherlands were affected with grass tetany between May of 1960 and May
of 1961,including 7845 fatal cases. Leech et al. (1960)reported that in
Great Britain mortality was as high as 30% of clinical cases. Meyer ( 1960)
reported that heifers and cows in Germany often had hypomagnesemic
tetany, especially on being turned out in the spring, and that calves kept
on a pure milk diet beyond the fourth week often became hypomagnesemic. He found no reports of tetany in sheep in Germany.
R. Allcroft and Burns (1968)reported that 0.5% of all dairy cows in
Great Britain, 1.1% of all dairy and beef animals in Scotland, and I-2%
of dairy animals in the Netherlands had a clinical level of grass tetany
each year. In a Scottish study (E. J . Butler et al., 1963),grass tetany was
found in 25% of 103 herds surveyed, the mean incidence in the affected
herds being 4.5 -+ 0.65%. Overall incidence was 1.1 k 0.25%, and was
significantly lower when a Mg supplement was given. After clinically
normal cows were turned out to pasture, hypomagnesemia was detected
in 41% of the herds, with an overall incidence of 8.7 -+ 1%. Incidence
with clinical signs in individual herds was as high as 10.9%; mortality of
those showing clinical signs was as high as 30%.
Stewart ( I 954),using a different approach, defined three types of tetany
in Scotland: (1)spring type, a well defined seasonal disease occurring only
in cows with calves in late April or early May, within a few days of putting the animals on grass: (2) winter type, occurring in cattle being fed
winter rations in stalls, especially on grass silage or dry grass hay, usually
occurring in November or December, and characterized by sudden death
without warning: and (3)outwinter type, in cattle maintained on pastures throughout the winter, occurring most commonly in February and
March in animals on sparse forage and pastures. Many losses have occurred in herds receiving hay in addition to forage.
Herd et al. (1964)in Victoria. Australia reported that grass tetany affected beef and dairy cattle and ewes after lambing. The mortality rates
GRASS TETANY OF RUMINANTS
were estimated at I % in the beef cattle and ewe populations, and somewhat less in dairy populations. Cairney ( 1964) found in New Zealand that
incidence of presumed grass tetany averaged between 0.2% and 3.9% in
the 177 herds studied. Wet, cold, and stormy weather conditions were
associated with many animal losses. Voisin ( 1 963) discussed grass tetany
in France, Scandinavia, and Ireland.
Grass tetany has also been reported in various parts of the United
States. The publication edited by Anderson et al. (1959) contains a number of articles concerning grass tetany. Included is a report by Horvath
(1959) indicating that tetany in West Virginia occurred primarily with
mature beef cows, although some younger stock, some dairy cows,
and a few sheep were also affected. The cattle were generally fed orchard grass (Dactylis glomeruta) as pasture or hay. Attacks generally
occurred from November to January, just after calving. Some cases
occurred in February through April in cows about to calve, or which had
recently calved. Some cases occurred in late March or April on grass
which had recently turned green. Other cases occurred in April or early
May when cows were placed on “lush” pasture.
Leffel and Mason ( 1 959) indicated that hypomagnesemic tetany often
occurred in beef cattle on winter rations in western Maryland. These
animals were often fed hay composed of either timothy (Phleum prutense)
or timothy and legumes. Often the hay contained less than 0. I % Mg.
Singer et al. ( 1 958) reported on a complicated grass tetany syndrome
in Kentucky. All animals were in poor condition, and six died from apparent grass tetany. The animals were hypomagnesemic, hypocalcemic,
hypocupremic, and had high levels of K, P, nonprotein N, and urea N in
the blood serum.
Miller ( 1965) indicated that grass tetany has been a major nutritional
disease of the beef cattle industry in Georgia in recent years. The typical
problem involves a 5- to 7-year-old cow nursing a calf on a small grains
pasture. Cases generally occur during the months of December to March.
Recently, a number of cases of grass tetany have been reported with
beef cattle grazing crested wheatgrass (Agropyron desertorurn) pastures
during the spring in Nevada, Idaho, and Utah.
Hughes and Cornelius (1960) reported on grass tetany in lactating
beef cattle in California in the late 1950’s.Hjerpe ( I 964) reported a major
outbreak of grass tetany in the winter of 1963-1964 in California, with
losses estimated at 4000-6000 head. He reported that sporadic losses
from grass tetany occurred annually in California, usually during the
winter or early spring. Although deaths in affected herds were rarely as
high as 5%, they reportedly reached 20% in some herds in the 1963- 1964
GRUNES, P. R.
STOUT, A N D 1. R. BROWNELL
outbreak. R. B. Bushnell (Department of Epidemiology and Preventive
Medicine, University of California, Davis, unpublished data) reported on
738 investigated losses during this same period in California. He showed
losses increasing with the duration of cloudy, foggy, or rainy weather
which occurred following the early growth of grass during October.
Losses increased during January, following the cooler temperatures that
prevailed in December.
As reported by E. J. Butler et al. (1963), hypomagnesemia is frequently
found in apparently normal animals lacking clinical signs of grass tetany.
A California study (Brownell and Bushnell, unpublished data) of a normal
herd of 444 animals showed a mean serum Mg level of 19 ppm, with a
standard deviation of -t 0.35 ppm. The range in serum values, however,
was from 7.2 to 34.8 ppm, with 2.5% of the animals below 10 ppm, and
34.2% below 18 ppm. This herd had been subdivided into six different
management groups, the principal differences being: ( 1 ) the pasture they
had been grazing; (2) whether or not supplemental feed had been provided. In these management groups, one group of 180 animals had a mean
serum Mg level of 16 ppm and had been on dry range pasture. The group
with the highest serum Mg (mean = 24.4 ppm) was composed of 17 animals which had been receiving intensive supplemental feedings in the
form of alfalfa (Medicago sativa) hay. This herd was not sampled during
the normal grass tetany period, but a t the end of California’s long, dry
summer, when grass tetany is usually not present. Brownell and Bushnell
(unpublished data) found that independent of the time of sampling, 10%
of the animals were hypomagnesemic, but appeared normal. This is based
on sampling 18 herds ranging in size from 18 to 444 animals.
Crookshank and Sims (1955), Sims and Crookshank (1956), and R. E.
Davis and Crookshank (1956) reported on wheat pasture poisoning,
which occurs primarily in sexually mature cows in the late stages of pregnancy or with a calf. In the Texas and Oklahoma panhandles, most cases
developed sometime between 60 and 150 days after the start of grazing
on winter wheat, and in cows with calves under 60 days old.
111. Symptoms of Animals
Underwood ( 1966) gave the following description of the clinical signs
of grass tetany: “The initial signs are those of nervous apprehension,
with ears pricked, head held high and staring eyes. At this stage the animal’s movements are stiff and stilted, it staggers when walking and there
is a twitching of the muscles, especially of the face and ears. Within a
few hours or days of the initial signs, extreme excitement and violent
GRASS TETANY OF RUMINANTS
convulsions develop; the animal lies flat on its side; the forelegs ‘pedal’
periodically and the jaws work, making the teeth grate. If treatment is
not given at this stage death usually occurs during or after one of the convulsions or the animal may pass into a coma and die. Mortality is high in
clinical cases without treatment.
“A chronic form of hypomagnesemia, characterized by a stiff gait and
gradual loss of condition, can occur for several weeks without affecting
appetite or milk yield. This disturbance is followed either by recovery or
by the acute form of tetany, as just described. Preconvulsive clinical
signs in sheep are less clearly defined than in cattle and can easily be
confused with those of hypocalcaemia or pregnancy toxaemia.”
Barker (see R. Allcroft and Burns, 1968) subdivided cases into two
groups: hypomagnesemia accompanied by hypocalcemia; and hypomagnesemia accompanied by normal serum Ca. R. Allcroft and Burns ( 1968)
concluded that 76% of those with hypomagnesemia also had hypocalcemia, and that 36% of these cases developed within 4 days of calving.
This syndrome, with both serum Mg and Ca low, was called preconvulsive tetany by Barker (1939). The related symptoms include tetany of
forelegs and hind legs, hyperesthesia (unusual sensitivity), of which one
symptom is fluttering of the eyelids, and convulsions that may be very
sudden in onset. Type two (hypomagnesemia accompanied by normal
serum Ca) is further subdivided into two distinct clinical categories:
slight symptoms (only slightly nervous, some twitching, but not convulsions); and acute severe symptoms (including the most dramatic examples
of hypomagnesemic tetany, with tetanic convulsive cases often occurring
suddenly and the animal dying within minutes). Swan and Jamieson ( 1956)
reported twelve such acute cases of grass tetany. Rook (1 963) described
such a case in an experimental cow which developed very acute tetany
and convulsions and died in about 10 minutes.
R. E. Davis ( 1 959) indicated that the symptoms of “wheat pasture
poisoning” observed in the Texas and Oklahoma panhandles are almost
identical with those of grass tetany in the Netherlands, Great Britain,
and New Zealand. He wrote: “The first symptoms are usually excitement,
incoordination, and loss of appetite. Viciousness, staggering, and falling
come later. Nervousness becomes more apparent with muscular twitching, which is particularly noticeable in the extremities. The animal often
grinds its teeth and salivates profusely. The third eyelid will protrude or
flicker as in tetanus.
“General tetanic contractions of the muscles follow until the animal
nears a state of prostration. A sudden noise or touching the animal causes
a reflex response often resulting in clonic-tonic convulsions. Some muscles are in tetanic contraction.
GRUNES, P. R. STOUT, A N D J. R. BROWNELL
“The next symptoms are labored breathing and a pounding heart. Convulsions with periods of relaxation occur. During these periods of relaxation the animal attempts to get up and if successful will run into obstructions without attempting to avoid them. Following the period of extreme
excitement the animal goes into a comatose condition. The animal usually
becomes comatose 6 to 10 hours after the onset of the initial symptoms.
If treatment is started before the coma stage begins the chances of recovery are good. Very few animals survive if treatment is started when
the animal is in the comatose state.”
The diagnosis of grass tetany by clinical symptoms alone is difficult.
A more positive diagnosis can be made when the level of Mg in the blood
is also known.
Sjollema ( 1930), in a series of papers, described grass tetany as a hypomagnesemic disorder. Normal animals in his study had 13-20 ppm of
Mg in blood serum, whereas animals with tetany had serum Mg contents
of 5-10 ppm. He also observed that the serum Ca:Mg ratio varied considerably, normal animals having a ratio of 5.6; tetany animals a ratio of
14.6; and animals with “milk disease,” probably what is now known as
milk fever, a ratio of 2. Meyer (1960) classified animals as hypermagnesemic if they had greater than 32 ppm of Mg in their serum; normal
from 18-32; slightly hypomagnesemic 12- 18; severely hypomagnesemic
less than 12. Storry and Rook (1963) in an experimental feeding trial
showed that animals with a Mg-sufficient diet had serum Mg levels of
20-27 ppm, and that animals approaching tetany had Mg levels of 10- I5
ppm. In the same study, urine losses of Mg ranged from I to 2 g per day
on the sufficient diet, and decreased to 0 when the blood serum Mg fell
below 20 pprn. At the same time, Mg lost in the feces was about 2 g
per day on the sufficient diet and fell steadily to 1 g per day when the animals were placed on a deficient diet.
Crookshank and Sims ( I 9 5 9 , in a study of wheat pasture poisoning in
Texas, established normal serum levels for 185 Hereford cows as being
20.5 k 2.5 ppm for Mg; 1 10.8 f6.7 ppm for Ca. Sixty animals with wheat
pasture poisoning had an average serum Mg level of 13.5 ? 7.5 ppm, and
Ca levels of 66.8 & 11.2 ppm. Potassium levels appeared to be elevated
but quite variable, the normal mean being 197 -1- 22 ppm K, and affected
animals being 234 ? 83 ppm K. The affected animals were much more
variable than the normals, 10% being greater than 400 ppm K. Serum
albumin was slightly depressed and serum globulin greatly increased in
GRASS TETANY OF RUMINANTS
the affected animals as compared to the normals, giving a very significant
depression in the a1bumin:globulin ratio. They concluded that the wide
range of values observed in many of the constituents measured indicated
effects of the wheat pasture poisoning rather than the cause.
W. M. Allcroft and Green ( 1938) indicated that, under certain conditions, cattle may tolerate extremely low blood serum Mg levels without
showing the clinical symptoms of grass tetany.
Cow’s milk normally contains approximately 120 ppm Mg (Meyer,
1960). Rook and Storry (1962) quote a normal range of 70-180 ppm.
They and others (Cunningham, 1933; de Groot, 1959) present evidence
that the Mg content of milk does not decline if feed or Mg intake is reduced or if hypomagnesemia occurs. T. H. Arkley (unpublished data,
1964) found in California that regardless of whether samples were taken
under good or poor conditions, the Mg concentration of the milk of range
animals was always between 100 and 120 ppm and seemed unrelated to
serum Mg content.
As noted above, urine Mg concentrations dropped very low for Mgdeficient animals (Storry and Rook, 1963). The kidneys function to eliminate Mg whenever serum levels are above the renal threshold of about 18
ppm Mg. Above the renal threshold, the concentrations of Mg in the
blood plasma and Mg excreted in the urine are linearly related. When
the plasma Mg level falls below the renal threshold, reabsorption in the
kidney exceeds excretion and essentially no Mg is lost in the urine.
In the past, it has been a problem to study grass tetany, because of the
difficulty of artificially inducing the disease in animals. However, recently
there appears to be progress in this direction.
Bohman et al. ( I 969) induced symptoms, resembling field cases of grass
tetany, in cattle by administering KCI and either trans-aconitic acid or
citric acid. The materials were suspended in water and administered by
rumen tube within a 5-minute period. When one of the acids or KCl was
administered alone, the symptoms of tetany were not induced. Administration of both citric acid and KCl reduced the concentration of Mg
measured in the blood plasma 24 hours later. Further work, Scotto et al.
(1969), indicated that the level of citric acid in the blood increased as
the amount of KCI added with the citric acid was increased. It is possible
that the citric and trans-aconitic acid were complexing Mg, thus reducing
the availability to the cattle.
Suttle and Field (1969) induced grass tetany symptoms in sheep by
D. L. GRUNES, P. R. STOUT,AND J. R. BROWNELL
decreasing the dietary intake of Mg, while increasing the intake of K.
The Mg concentrations in the blood plasma were reduced by increasing
the K intake, as well as by reducing the Mg intake.
Ward ( 1 966) added a high rate of KCl to a cow by means of a stomach
pump; although the cow died, no tetany symptoms were observed. Geelen et al. (1966) induced tetany in an animal with a previous history of
tetany by intravenous administration of histamine. Montgomerie et al.
(1929) reported a case of tetany in Welsh mountain ponies .just after a
long railway journey. The ponies were found to be both hypocalcemic and
hypomagnesemic. Hjerpe and Brownell (1966) reported on four animals,
which were selected from a herd of 12 because of their low concentration
of Mg in the blood serum. When they were trucked 38 miles, all four animals were lower in serum Mg than was measured on the ranch 4 days
previously. The two animals with the lowest serum Mg levels developed
tetany symptoms during the trip, and serum Ca was also considerably
below that measured 4 days earlier.
Magnesium in soils has been reviewed by Beeson (1959), Salmon
(1963), and Metson (1968). The relation between soil Mg and plant nutrition has been reviewed by Bould (1964). Thompson (1960) reviewed
the relationship between soil Mg and plant and animal nutrition.
Beeson ( 1 959) indicated that rocks average about 2% Mg, but the range
is extremely wide. Since soils are developed from parent rocks, soils exhibit a wide range in total Mg content. As soil development increases
under strong weathering and leaching conditions, the Mg content may
decrease. In general, acidic igneous rocks are low in Mg and more basic
rocks are high. Sedimentary rocks, especially sandstones and shales,
are generally low in Mg.
Beeson (1959) indicated that Mg deficiency in plants occurs frequently
on coarse-textured soils of the Atlantic and Gulf Coastal Plains of the
United States. However, Mg deficiency of crop plants also occurs on
finer-textured soils of the somewhat less humid Middle West (Beeson,
1959). He indicated that it is likely that continued cropping and heavy
applications of K and other non-Mg fertilizers may be responsible. Beeson (1959) also indicated that the Mg content of waters in the United
States correlates well with the occurrence of deficiencies of this element
in the soil.
Attempts to relate Mg in the soil to Mg in plants have been only moderately successful. In the United States, an extraction technique is common-
GRASS TETANY OF RUMINANTS
ly used to obtain exchangeable Ca and Mg (Heald, 1965). This technique
involves displacing the adsorbed ions with a concentrated salt solution
such as NH4Cl, NH4 acetate, NaCI, Na acetate, or BaClz. Some investigators have also used dilute acids such as 0.4 N HCl or 0.5 N acetic acid
(Heald, 1965). Heald recommended against determining exchangeable
Ca or Mg on soils containing free carbonates, gypsum, or excess soluble
Salmon ( 1964: Fig. 2) obtained correlations of 0.99 between the concentration of Mg in ryegrass grown in a greenhouse and a ratio involving
ion activities of Mg, Ca, and K in equilibrium soil solutions. The Mg concentrations in the plants were directly related to Mg activities in soil extracts, but inversely related to K and Ca activities in these extracts.
Magnesium concentrations in plants were also inversely related to soil
pH. A further discussion of this concept is presented by Arnold ( 1967).
In New Zealand, Metson ( I 968) indicated that consideration is being
given to assessing Mg status of the soil by including both exchangeable
Mg and Mg present after boiling the soil with normal HCl. The acidsoluble Mg is used as a measure of Mg reserves.
In England, Salmon and Arnold ( I 963) exhaustively cropped soils for
up to 1 I months in a greenhouse. Although the “exhaustion” Mg (Mg
taken up by crops plus residual exchangeable Mg) was greater than the
initial exchangeable Mg, the two measurements were highly correlated
(r = 0.99). In some of these intensively cropped soils, the exchangeable
Mg was increased by wetting and drying. If this occurs in the field, Mg
lost in cropping could be replenished by only small releases of nonexchangeable Mg.
In North Carolina, Rice and Kamprath ( 1 968) found that Mg uptake
by corn (Zea mays L.) from exchangeable Mg was closely related to the
initial exchangeable Mg in sandy coastal plain soils. However, a large
part of the Mg absorbed by plants also came from nonexchangeable
forms. They suggested that H ions exchanged from the roots may have
been effective in releasing nonexchangeable Mg.
Embleton (1966) reviewed the literature relating analyses of Mg in
soil extracts to Mg deficiency in plants. Several investigators found that
when the exchangeable Mg was less than 6% of the cation exchange capacity, a plant growth response to added Mg was likely. Embleton (1966)
indicated that Prince et al. (1947) had found in New Jersey that an ideal
amount of Mg would be up to 10% of the exchange capacity of the soil.
The Mg status of New Jersey soils is further discussed by Bear et al.
Felbeck (1959) suggested that Mg fertilization be recommended when
D. L. GRUNEJ, P. R. STOUT, AND J . R. BROWNELL
the exchangeable Mg is less than 10% of the cation exchange capacity,
or less than 100 Ib of exchangeable Mg per acre. The latter figure is about
0.41 meq per 100 g of soil, assuming 2,000,000 lb per acre 6 inches of soil.
This would equal 0.5 mg of Mg per 100 g of soil.
In West Virginia, the recommendation for good plant growth is that
Mg sould equal lO-15% of the exchange capacity, or not less than twice
the exchangeable K percentage (Horvath and Todd, 1968). They also
recommended that the Ca: Mg ratio in the soil should be about 5 : I .
(Wider ratios would be expected to tend to induce Mg deficiency of plants.)
In Scotland, Reith ( 1 967) indicated that plant growth response to Mg
can be expected when there is less than 3 mg of readily soluble Mg per
100 g of soil. He extracted soils with either 2.5% acetic acid or neutral
normal ammonium acetate, the values being similar for both extractants.
For red clover growing on slightly acid, mineral soils, he recommended
a value of not less than 16 mg of Mg per 100 g of soil as a level to ensure
that the herbage content of Mg is as high as possible under practical
All in all, it appears that much research needs to be done before soil
analyses can be used to accurately predict Mg availability to plants. As
will be discussed later, the situation is complicated by the fact that, for
some plants, low temperatures result in low concentrations of Mg in the
Tetany occurs most frequently on grasses accomplishing most of their
growth during cool weather, such as occurs during the spring. It often
occurs on perennial grasses such as ryegrass (Lolium perenne) in the
British Isles, the Netherlands, and New Zealand; crested wheatgrass
(Agropyron desertorurn and Agropyron cristatum) in Nevada and Idaho;
and orchardgrass (Dactylis glomerata) in West Virginia. In California,
tetany often occurs on annual grasses such as soft chess (Bromus mollis)
and mouse barley (Hordeurn leporinum).
In the Southern United States, tetany is often observed on wheat (Triticum aestivurn) (“wheat pasture poisoning”), rye (Secale cereale), and
oat (Avena sativa) forage used as green pastures.
Legumes and herbs contain higher concentrations of Mg and Ca than
grasses (see Table I). Todd (1966) also indicated that clovers have higher
concentrations of Mg than pasture grasses. However, the clovers do not
grow as early in the spring as the ryegrasses. Todd (1966) indicated that
timothy (Phleum pratense) has lower Mg concentrations than the various
GRASS TETANY OF RUMINANTS
Mineral Content of Swards in the Netherlands”
Dry matter composition
“Data presented by van der Molen (1964) were obtained from an investigation by P. F. J .
van Burg and G . H. Arnold in 1961.
ryegrasses (Loliumspp.) or cocksfoot (orchardgrass, Dactylis glomerata).
Nitrogen fertilization reduces the clover content of pastures and would
thus reduce the Mg concentration in the pasture forage. Todd ( 1 966) also
indicated that while herbaceous weeds have higher concentrations of Mg
than grasses, they reduce the productivity of the sward.
One way of avoiding grass tetany might be to breed or select legumes
that would start to grow as early in the spring as the grasses.
The incidence of hypomagnesemia is related to low Mg concentrations
in forage. However, grass tetany is sometimes not observed even when
Mg concentrations in the forage are low. Kemp (1960) plotted values for
Mg in blood serum against the corresponding values for Mg in herbage
for 822 dairy cows in the Netherlands. He indicated that no cases of
clinical tetany occurred at blood serum Mg values above 9 ppm or at
herbage Mg levels above 0.19%.This established 0.20%Mg as the “safe”
level for Mg in forage.
Kernp’s data also indicated that for each level of Mg in the forage, increasing the concentration of K and crude protein in the forage decreased
the level of Mg in the blood serum, and increased the likelihood of tetany.
Kemp indicated that low concentrations of Mg in the blood, as well as
frequent cases of tetany, were obtained when Mg in the herbage varied
between 0.175 and 0.200%, while K and total N averaged 3.88 and
Metson et al. ( 1966) indicated that on New Zealand pastures associated
with outbreaks of grass tetany in beef cattle, K concentrations in forage
averaged 3.29% (ranging from 2.0 to 4.0%), while N concentrations
averaged 5.28% (ranging from 4.2 to 6.3%). The Mg concentration in
these forages averaged 0.19% (ranging from 0.14 to 0.25%).They sug-