PHOSPHORUS NUTRITION OF DAIRY CATTLE

Dr. L. E. Chase
Department of Animal Science
Cornell University

INTRODUCTION
Saliva contains P and can be a significant
Increased environmental concerns and contributor to the endogenous P pool (Horst, 1986).
regulations have stimulated renewed interest in Any factors that depress saliva flow can shift some
phosphorus (P) in dairy cattle rations. The challenge of the endogenous P excretion to the urine. One
is to design rations with adequate P to meet the report indicated that P uptake was reduced in cows
needs of the cow while minimizing P excretion to under heat stress conditions (Sanchez et al., 1994).
the environment. Environmental regulations, which The authors suggested that decreased endogenous P
limit the quantity of P applied to land, are either in recycling via saliva could at least be a partial
place or being considered (Tamminga, 1992; Van explanation.
Horn et al., 1994). A number of papers have
examined the relationships which exist between P The primary route of P excretion is fecal
intake and excretion in dairy cattle (Brintrup et al., (Hibbs and Conrad, 1983; Morse et al., 1992b). In
1993; Chase, 1994; Dhiman et al., 1996; Harris et one study, 68.6% of the total P excreted was in the
al., 1992; Morse et al , 1992b; Satter and Dhiman, feces compared with 1% in the urine and 30.3% in
1996). Chandler (1996) indicated that P accounts milk. The total yearly P excretion of a dairy cow
for more than 50% of the cost of typical vitamin- producing 19,800 lbs of milk consuming a ration
mineral mixes used on dairy farms. Thus, there is with 0.4% P was estimated to be 40 lbs (Van Horn et
rationale from both economic and environmental al., 1994). This increased to 70 lbs/cow if ration P
considerations to minimize feeding P in excess of was increased to 0.6%. Fecal P excretion was
requirements. estimated at 30 lbs/year for cows producing 13,750
lbs of milk in a review paper (Tamminga, 1992).
METABOLISM
REQUIREMENTS
Phosphorous has a multitude of functions in The NRC (1989) requirements provide the
animals. A primary role is the integrity and base for most formulation programs in the U.S.
development of the skeletal system. Approximately, However, there is some disparity in the P
80-85% of the total P in cattle is in the bones and requirements used for dairy cows in different
teeth (Horst, 1986; NRC 1989). Phosphorus is also countries (Tamminga, 1992). Table 1 contains the P
involved with cellular energy transfer via the ADP, requirements for cows at 2 levels of milk production
ATP system. Lipid metabolism is dependent on P, calculated using current systems in 5 countries.
which is a component of phospholipids. Phosphorus There are some large differences in both the
is involved in a number of enzyme systems and is a maintenance and milk requirements. The variation
constituent of saliva. in total P requirement between countries is smaller.
It is apparent that the P requirement for high
The absorption of P in the dairy cow is producing cows needs better definition. The 1989
affected by a number of factors (Horst, 1986; NRC requirements are 10 to 22% higher than the
Miller, 1979 and NRC, 1989). The primary site of P previous NRC (1978) due to a lowering of the
absorption is the small intestine (Care, 1994). This assumed absorption efficiency. It is important to
absorption appears to be an active process which is remember that daily requirements are for grams of P
influenced by vitamin D (NRC, 1989). The total
quantity of P absorbed is related to the quantity of P
consumed, calcium to phosphorus ratio, feed source,
age and levels of other minerals such as calcium,
magnesium and potassium.

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 Table 1: Variation in P requirements of dairy cattlea
P Requirement Assumed
Milk, b Country Maintenance Milk Total Availability
(lbs) ----------------(grams)------------------ (%)
50 U.S. 17.5 44.9 62.4 50
Netherlands 25.7 34.0 59.7 60
UK 12.7 35.4 48.1 58
France 37.9 28.4 65.9 70
Germany 24.5 37.6 62.1 60
100 U.S. 17.5 89.8 107.3 50
Netherlands 25.7 68.0 93.7 60
UK 12.7 70.8 83.5 58
France 37.9 56.7 94.6 70
Germany 24.5 75.3 99.8 60
a
Adapted from Tamminga, 1992
b
4% FCM, 1350 lb cow
with diverse crop management and environmental
not P as % of the ration dry matter (DM). Rations conditions. The variation of P content of forage
should be formulated based on the grams of mineral types grown on the same farm would be
required rather than as a % of DM. considerably less. These variations in P content
indicate the importance of forage testing as a base
The P requirements for replacement heifers for ration formulation. This will be even more
are calculated using 3 equations based on body essential as we balance rations to minimize P
weight (NRC, 1989). These equations reflect the overfeeding. The median P level in total mixed
decreasing availability of ration P as calves get rations fed to dairy cattle was 1.32 times the
older. In addition, the average daily gain influences requirement at 0.49% (Spears, 1996). The range in
the P requirement. Phosphorus requirements of P content of these TMR=s was 0.36 to 0.66%.
growing heifers range from 0.23 to 0.31% of the
total ration DM. Two recent papers indicate that the AVAILABILITY
P requirement of replacement heifers gaining 2.2
lbs/day may range from 0.15 to 0.34% of total ration The availability of P in mineral sources has
DM (Bortolussi et al., 1996; Ternouth et al., 1996). been examined in a number of trials (Jackson et al.,
1988; Macrominerals, 1995; Peeler, 1972; Witt and
FEED COMPOSITION Owens, 1983). Monoammonium phosphate and
dicalcium phosphate had similar biological
The level of P found in feeds used in dairy availabilities when used in rations for growing bull
cattle rations is quite variable. Adams (1975) calves (Jackson et al., 1988). A recent summary
reported a 10.6 fold range in the P content of indicated that the biological availability of
legume-grass forage samples. Table 2 contains the monosodium phosphate, monoammonium
mean, standard deviation and normal range for P in a phosphate, sodium tripolyphosphate and
number of feeds. Note the wide normal range for diammonium phosphate were all 95-100%
these feeds, which represents about 67% of the total (Macrominerals, 1995). Similar values for
samples analyzed within feed type. The range in P monocalcium phosphate, dicalcium phosphate,
content of forages from the Southern U.S. was defluorinated phosphate, steamed bone meal, fish
previously presented at this conference (Greene, meal, and soft rock phosphate were 95-98, 93-95,
1997). The mean P content in these forages ranged 88-91, 80-82, 90-95 and 25-35%.
from 0.1 to 0.66%. The P content in bermudagrass
ranged from .02 to .51%. A range from 0.1 to 0.3%
P encompassed 91% of the bermudagrass samples.
It is important to realize that the samples in all of
these summaries are from a large number of sources

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 Table 2: Phosphorus content of feedsa
Phosphorus Normal
Feed Mean S.D.b Rangec
(%)
Legume hay .25 .05 .20 - .30
A silage .29 .05 .24 - .34
Grass hay .21 .06 .15 - .27
A silage .28 .07 .21 - .35
Sudangrass hay .19 .06 .13 - .25
A silage .26 .07 .19 - .33
Sorghum silage .21 .08 .13 - .29
Sorghum-sudan silage .25 .08 .17 - .33
Corn silage .21 .03 .18 - .24
Bakery goods .32 .20 .12 - .52
Beet pulp .09 .02 .07 - .11
Blood meal .35 .24 .10 - .59
Brewers grain, dry .59 .24 .35 - .83
Canola meal 1.13 .18 .94 - 1.31
Citrus pulp .11 .01 .10 - .12
Corn, shelled .30 .03 .27 - .33
Corn gluten feed .96 .29 .67 - 1.25
Cottonseed, whole .59 .12 .47 - .71
Cottonseed, hulls .17 .10 .07 - .27
Cottonseed meal 1.12 .14 .98 - 1.22
Distillers grains .79 .15 .64 - .94
Hominy .46 .17 .29 - .63
Peanut meal .52 .15 .37 - .67
Sorghum grain .29 .07 .22 - .36
Soy hulls .18 .08 .10 - .26
Soybean meal .67 .09 .58 - .76
Sunflower meal .84 -- --
Wheat grain .41 .15 .26 - .56
Wheat midds .89 .23 .66 - 1.12
a
Source: Dairy One Forage Testing Lab, Ithaca, NY
b
Standard deviation
c
Mean + or - 1 standard deviation

Table 3: Daily phosphorus intake as a % of the NRC requirement.a

Ration P, % of DM
Milk 0.35 0.45 0.55
(lbs/day) ---------------------------(% of NRC)------------------------------

40 110.7 142.5 174.2

60 97.3 125.2 153.0
80 89.3 114.8 140.4
100 83.6 107.5 131.4
120 79.6 102.3 125.0
a
1350 lb cow, 2nd lactation, 3.5% milk fat

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The relative bioavailability of P in canola meal and The rumen microorganisms have the ability
soybean meal was compared in Holstein bull calves to hydrolyze the phytate P. The apparent total tract
(Ingalls and Okemo, 1994). The total tract hydrolysis of phytate P in young calves and steers
disappearance of P was similar for both protein was > 99% (Nelson et al., 1976). A study using
sources at 94-96%. A second component of the trial early lactation dairy cows reported that 98% of the
compared canola meal with a mixture of phytate P was hydrolyzed (Clark et al., 1986). Eight
monocalcium phosphate and dicalcium phosphate. concentrates were used to evaluate phytate P
The authors concluded that the bioavailability of P in hydrolysis both in vitro and in vivo with dairy cows
canola meal was similar to the inorganic P source. (Morse et al., 1992a). These concentrate mixes
contained 32 to 81% of the total P in the phytate
A ruminal P release of 73% was reported form. The in vitro results indicated that > 90% of
for grass silages at a rumen outflow rate of 5%/hour the P in the phytate form was hydrolyzed. Total
(Rooke et al., 1983). The release of P in the rumen tract hydrolysis of the phytate P in this study was >
was investigated for 6 forage species (Emanuele and 94%. The results of these studies indicate that
Staples, 1990). The average P release for all forages adjustments for phytate P levels in feeds do not need
was 66% with an initial washing in water and 80% to be made when formulating rations for ruminants.
after a 72 hour incubation. The release of P was
significantly higher for alfalfa than bermudagrass REPRODUCTION
forage at both measurement times. This study did
not evaluate total tract P absorption. A primary reason indicated for feeding P in
excess of requirements in many herds is to enhance
Lactating dairy cows were used in a study reproductive performance. Research data to support
to examine mineral absorption (Khorasani et al., this is weak. Many of the early studies reported
1997). The forages used were barley, oats, triticale depressed reproduction when ration P levels were
or alfalfa silages. The absorption of P increased as <0.2% (McClure, 1994).
P intake increased. However, there were no
differences in apparent P digestibility between these Two trials were conducted with growing
forages. The average total tract P digestibility was dairy heifers to evaluate the role of added P on
30.9%. reproduction (Noller et al., 1977). These workers
reported no benefit to adding 0.1% P to basal rations
A publication from Ohio State contains the with 0.22% P. A similar result was reported with
results of a large number of trials examining calcium beef heifers fed basal rations with 0.14% P
and P utilization in dairy cows (Hibbs and Conrad, compared with supplemented rations containing
1983). These studies used a variety of forage 0.36% P (Call et al., 1978). The intensity of estrus
sources with or without grain and vitamin D was examined in another trial with dairy heifers
supplementation. In these studies, P digestion (Hurley et al., 1982). Rations containing 73, 138 or
increased when grain was added to forage based 246% of NRC phosphorus requirements were fed to
rations. 12-16 month old heifers. Ovarian function, estrous
behavior, serum progesterone or serum luteinizing
PHYTATE PHOSPHORUS hormone (LH) concentrations were not different
between these treatments.
Phytate phosphorus may account for 50 to
70% of the total P in many concentrates. In Holstein cows were fed rations containing
monogastrics, the ability to utilize P in the phytate 0.24, 0.32 and 0.42% P beginning in the 7th month of
form is limited by low intestinal phytase levels. gestation for a 12 month period (Call et al., 1987).
Rations are commonly formulated using available P Cows fed the low level (0.24%) of P produced
rather than total P content of feedstuffs to account significantly less milk than the other 2 groups.
for this. There is also considerable interest in the There were no significant differences in reproductive
addition of phytase to monogastric diets to enhance performance in this study. Milk production of these
P utilization. cows was about 15,000 lbs per lactation.
A trial was conducted at Michigan State al., 1980). This was a 2 x 2 factorial design
using 2 levels of energy and P (> 100 and 75% of conducted for the first 84 days of lactation. There
requirements) in first-lactation heifers (Carstairs et were no differences in this study on reproduction

4
related to either energy or P status of the rations. averaging 16,500 lbs of milk/year. The effect of
Actual P intakes for the 2 groups were 98 and 138% dietary P level in rations for mid to late lactation
of the NRC requirement. Milk production was 1795 cows was recently reported (Dhiman et al., 1996 and
lbs lower for cows on the high P ration (Carstairs et Satter and Dhiman, 1996). Rations contained either
al., 1981). 0.39 or 0.65% P. There were no effects on feed
intake or milk production in cows producing 53 lbs
MILK PRODUCTION of milk per day.

There have been very few research trials ENVIRONMENTAL CONCERNS

with lactating dairy cows to define the P
requirement. A trial conducted at Oklahoma State Phosphorus is the key mineral being
used rations containing 0.37, 0.55 or 0.56% P targeted in legislation currently pending in Congress.
(Steevens et al., 1971). There were no significant One proposal will limit the quantity of P applied to
differences in milk production during the first 24 land to the amount removed by crops. In a survey of
weeks of lactation. Average daily milk production 3 commercial dairy herds in New York, the mass
in this trial was 39 lbs for first-calf heifers and 45 lbs nutrient balance for P ranged between 59 and 75%
for second lactation cows. In this trial, there were no (Cornell University, 1996, and Tylutki and Fox,
differences in milk production with Ca:P ratios of 1997). The quantity of P entering the farm via
1.5:1 or 3:1. purchased feed ranged from 59 to 85%. Milk
production in these herds was between 24,000 and
A trial at Washington State used rations 28,000 lbs of milk/cow.
containing either 1 or 1.7% calcium (Kincaid et al.,
1981). Ration P levels of 0.3 an 0.54% were used One question is how much could this P
within each level of calcium. Rations were fed for mass balance potentially be lowered. We have used
the first 10 months of lactation. Milk production the Cornell Net Carbohydrate and Protein System
was about 7% lower (4.4 lbs/day) in cows fed the model on one of these herds for a number of years.
low P level in the ration. The calcium level fed did Ration formulation has decreased nitrogen excretion
not affect milk production. There was an increase in by about 30% with a similar calculated reduction in
milk production when the high level of calcium was P excretion of about 20%. During this same time,
fed to cows receiving the low P ration. The Ca:P milk production has increased from about 23,500 to
ratio in this situation was 6:1. 26,000 lbs of milk per cow. Controlled research
with high producing dairy cows is needed to verify
Rations containing either 100, 150 or 200% and better quantify these results.
of NRC requirements for P, Ca, Zn and Mn were fed
to dairy cows for 14 weeks prepartum through 22 ADDITIONAL CONSIDERATIONS
weeks of lactation (deBoer et al., 1981). Rations
were based on alfalfa silage. Ration Ca content was Phosphorus should be force fed to dairy
0.69%. There were no significant differences in cattle via TMRs or concentrate mixes rather than
milk production. Actual ration P levels were 0.34, through free choice supplements. Dairy cattle do not
0.51 and 0.69%. Average daily milk production was have the ability to balance P intake from free choice
about 61 lbs. Another trial fed rations containing supplements (Coppock et al., 1972 and 1976). One
0.24, 0.32 or 0.42% P for a full lactation (Call et al., paper with pregnant heifers indicated that feeding
1987). Milk production was significantly reduced high ration P levels (0.64%) depressed the
on the low P ration. There was no difference in milk absorption of magnesium (Schoneville et al., 1994).
production for the rations with 0.32 and 0.42% P.
Average daily milk production on these rations was The studies available also indicate that a
48 lbs. wide range of Ca:P ratios can be used as long as
dietary P is adequate (Call et al., 1987; Deitert and
Two rations providing either 68 or 60 Pfeffer, 1993; Kincaid et al., 1981; Rodehutscord et
grams of P/day were fed to dairy cows over a 2 year al. 1994 and Steevens et al., 1971). The Ca:P ratios
period (Brintrup et al., 1993). The ration P levels used in these studies ranged from 1.5:1 to 8:1. It is
were 0.39 and 0.33% on a DM basis. There were no important to remember that salivary P contributes a
significant differences in milk production for cows significant quantity of P to the animal. Thus, the

5
ration Ca:P ratio can be altered by P contributed content of dairy cattle feeds. J. Dairy Sci. 58:1538.
from saliva.
Bortolussi, G., J. H. Ternouth, and N. P. McMeniman. 1996.
Dietary nitrogen and phosphorus depletion in cattle and their
SUMMARY effects on liveweight gain, blood metabolite concentrations and
phosphorus kinetics. J. Agric. Sci. 126:493.

1. The phosphorus requirements of the high Brintrup, R., T. Mooren, U. Meyer, H. Spiekers, and E. Pfeffer.
producing dairy cow are not well defined. 1993. Effects of two levels of phosphorus intake on performance,
and fecal phosphorus excretion of dairy cows. J. Anim. Physiol.
a. Anim. Nutr. 69:29.
2. Rations should be formulated based on the
grams of P required not the % P in the Call, J. W., J. E. Butcher, J. T. Blake, R. A. Smart, and J. L.
ration. The NRC requirements for Holstein Shupe. 1978. Phosphorus influence on growth and reproduction
cows producing 60, 80 or 100 lbs of milk of beef cattle. J. Anim. Sci. 47:216.
are 68, 85 and 100 g of P per day. At
Call, J. W., J.E. Butcher, J. L. Shupe, R. C. Lamb, R. L. Boman,
normal levels of DM intake, this is and A. E. Olson. 1987. Clinical effects of low dietary
equivalent to ration levels of 0.36, 0.39 and phosphorus concentrations in feed given to lactating dairy cows.
0.42% P. If DM intake were 95% of Am. J. Vet Res. 48:133.
expected, then ration P levels would be
Care, A. D. 1994. The absorption of phosphate from the
0.38, 0.41 and 0.44% P. digestive tract of ruminant animals. Br. Vet J. 150:197.

3. There is little research data to support Carstairs, J. A., D. A. Morrow, and R. S. Emery. 1980.
feeding P in excess of requirements to Postpartum reproductive function of dairy cows as influenced by
energy and phosphorus status. J. Anim. Sci. 51:122.
enhance reproductive performance.
Carstairs, J. A., R. R. Neitzel, and R. S. Emery. 1981. Energy
4. The cow, primarily via feces, excretes and phosphorus status as factors affecting postpartum
phosphorus consumed in excess of performance and health of dairy cows. J. Dairy Sci. 64:34.
requirements.
Chandler, P. T. 1996. Environmental challenges as related to
animal agriculture-dairy. In Nutrient management of food
5. Dietary P levels will decrease as we fine animals to enhance and protect the environment. Ed: E. T.
tune protein nutrition and decrease the Kornegan. CRC Lewis Publishers, New York. p. 7.
crude protein levels in rations. This is a
Chase, L. E. 1994. Environmental considerations in developing
reflection of the high P levels in most dairy rations. Proc. Cornell Nutr. Conf., Rochester, NY. p. 56.
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Clark, W. D., Jr., J. E. Wohlt, R. L. Gilbreath, and P. K. Zajac.
6. Testing of forages for P is essential as an 1986. Phytate phosphorus intake and disappearance in the
gastrointestinal tract of high producing dairy cows. J. Dairy Sci.
input for ration formulation. 69:3151.

7. Environmental concerns will increase the Coppock, C. E., R. W. Everett, and R. L. Belyea. 1976. Effect of
need to minimize the overfeeding of P. low calcium or low phosphorus diets on free choice consumption
of dicalcium phosphate by lactating dairy cows. J. Dairy Sci.
59:571.

8. Lowering ration P levels can reduce Coppock, C. E., R. W. Everett, and W. G. Merrill. 1972. Effect
purchased feed costs. of ration on free-choice consumption of calcium-phosphorus
supplements by dairy cattle. J. Dairy Sci. 55:245.

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