BEC Feed Solutions
The role of Phosphorus in Cattle Nutrition
Written by:
Steve Blake – BEC Feed Solutions
Modified and Presented by: Ken Bruerton – Protea Park Nutrition
The Role of Phosphorus in Cattle Growth and Reproduction
 Phosphorus is an essential element to life
 The chemical symbol for Phosphorus is:
P
The Role of Phosphorus in Cattle Growth and Reproduction
Nutritional Role of Phosphorus
Phosphorus (P) is present in all cells in the body
 Essential for many digestive and metabolic processes, including conversion of feed into
energy, building and repair of body tissues and cell division.
 Essential component of the bones – hydroxy apatite (dicalcium phosphoshate)
 75-85% of P is in the skeleton
 P transported in the blood stream
.
Ca & P constantly being drawn from the bone reserves and replaced.
 P deficiency results in osteomalacia (Peg Leg)
The Role of Phosphorus in Cattle Growth and Reproduction
Nutritional Role of Phosphorus
 P moves from the blood to the salivary glands. Saliva contributes more P to
the rumen than the feed eaten.
 Rumen micro organisms have a requirement for P distinct from the
requirements of the animals tissues.
 The requirement of the rumen micro-organisms is generally supplied by the
endogenous secretion into saliva.
The Role of Phosphorus in Cattle Growth and Reproduction
 Decreased P in the diet results in decreased feed intake, without an effect on Dry Matter (DM)
digestibility.
 Decreased feed intake results in: Decreased growth rate
 Decreased milk yield
 Decreased reproduction rate
 Decreased calf growth rate
 P absorbed mainly in the small intestine
 P absorption depends on: P content of the diet
 Ca: P ratio
 P bioavailability
Phosphorus Loss
 Faecal, 400kg animal looses 6 – 8g per day.
 Faecal P consists of some dietary P (feed) and some endogenous P (saliva)
 Milk – 1 litre milk contains 0.95g of P
 P deficiency leads to decreased milk volume, not decreased P content.
The Role of Phosphorus in Cattle Growth and Reproduction
Phosphorus / Energy / Protein
 Nitrogen (N), P and Energy levels in pastures generally move in parallel.
 P intakes lowest prior to spring storms. When protein and energy are also at their lowest.
 There is a misconception that P deficiency is most acute at this time.
 P deficiency is most acute in the growing season when plant P levels are at their highest. During this
time protein and energy levels are also at their highest.
 Supplementation with P, N, or Energy will only be positive, if that nutrient is the first limiting
nutrient.
The Role of Phosphorus in Cattle Growth and Reproduction
Phosphorus / Energy / Protein
 During the growing season on legume based pastures, P can be the first limiting nutrient even
though P levels are at their highest.
 N will be the first limiting nutrient on native pastures as early as mid to late summer.
 When faecal N drops below 1.3%, growth stops. However, supplementation should be started
before this. Also, never feed P when faecal N is below 1.3%.
 Necessary to address any N and/or Energy deficits before additional P supplementation is
beneficial.
 P supplementation (on its own) during the dry season leads to decreased growth rate. This is most
likely because energy is expended to metabolize the P.
The Role of Phosphorus in Cattle Growth and Reproduction
Energy
Protein
Phosphorus
Wet
Dry
The Role of Phosphorus in Cattle Growth and Reproduction
Phosphorus Requirements

Maintenance requirement for P increases with the size of the animal. It is not directly
proportionately to the body weight but rather to the Weight0.75

Increased growth leads to increased demand for P
 3.3g P / 250g/d Lwg

Lactation 0.95g P / lt milk
 @ 80% absorption = 1.2g dietary P / lt.
 @ 5lt/day = 6g/day.

With lower digestibility sources more dietary P is required.
P requirement increases during pregnancy to support growth of foetus and placenta.
 30kg calf = 210g P
 Placenta = 10 g P


90% of this 210g is needed during the last 90 days of pregnancy.
 1.5g/day until month 7
 4g/day in month 9
The Role of Phosphorus in Cattle Growth and Reproduction
Recommendations
Feed N to breeders in early autumn on native pastures
Be early rather than late with supplementation.
Ease them into supplementation with lower levels of NPN.
 Feed N to heifers and steers from late autumn on native pastures
 No P supplementation for growing stock if they are loosing weight unless protein is
supplied as well and standing dry feed is available.
 Lactating breeders feed P in late dry season at half wet season rate to match
reduced energy and protein intake
The Role of Phosphorus in Cattle Growth and Reproduction
Case Study 2009 season Helen Springs
Nutrient Intake and Growth
 Simply put: if the pasture available has enough nutrients the
cattle will grow, produce milk, reproduce.
 They need:
 Energy – drives all metabolic processes. If energy is deficient
cattle lose weight. Cows will not cycle.
 Proteins – needed to provide amino acids to make immune
proteins (antibodies), enzymes, muscle proteins (growth)
 Minerals – bones (Ca & P), electrolyte balance (Na, K, Mg, Cl,
SO4,PO4), trace minerals (Fe, Zn, Mn, Cu, Se, Co, I) for
blood, enzyme cofactors, hormones.
 Vitamins – generally produced by rumen micro-organisms. These
act as antioxidants and cofactors in enzymes.
Nutrient Intake and Growth
 If the pasture is deficient in just one nutrient growth will be
limited by the supply of that nutrient.
 If protein is deficient relative to energy DM intake will also be
suppressed. Therefore protein is a key nutrient.
 If there is enough energy and protein but P is deficient growth
will be limited.
 Mores subtle deficiencies such as trace minerals may also limit
reproduction eg Zn and Se.
 Concept of a nutrient gap:
 The forage my have energy in it but is deficient in protein


Common occurrence in northern Australia in dry Season
The forage may have enough energy and protein but is deficient
in P

Common occurrence in northern Australia in Wet Season
Supplements for Northern Australia
Pasture analysis from NT property
Growth Stage
Dry matter (DM) %
Moisture %
Crude Protein (CP) %
Ash %
Fat %
Acid Det. Fibre (ADF) %
Neutral Det. Fibre (NDF) %
Digestible DM %
Metabolisable Energy (ME) mj/kg
Dry Matter intake %
Sample 1
Mitchell
Grass
Sample 2
Mitchell
Grass
Average
Mature
90.2
9.8
2.3
10.7
2.0
44.8
71.9
43.7
6.6
1.7
Mature
91.1
8.9
2.2
8.9
1.8
46.3
72.5
43.7
6.4
1.7
Mature
90.65
9.35
2.25
6.5
1.7
Supplements for Northern Australia

DM protein levels at about 2.5% are already at a level where supplementation will
be beneficial to intake. They are also at a level where DM intake is suppressed.

From the feed analysis, predicted pasture DM intake potential is 1.7% of body
weight (4.25 kg for a 250 kg animal). As fed this = 4.7 kg

Maintenance energy and protein requirements for a beef animals are available from
NRC tables.

We know from analysis what the pasture can supply.

We have energy locked up in the pasture but the protein is limiting the intake and
therefore weight gain

We can then attempt to bridge the nutrient gap with a lick supplement.
Supplements for Northern Australia
Maintenance Requirements
Body Wt
kg
250
ADG
kg/h/d
0
ME Req
mj/h/d
34.3
Dig Protein
g/h/d
200
Nutrient Intakes required to maintain weight
Pasture Provides
Maintenance Intake
ME
Dig. Protein Kg Intake Dig Prot Intake
Protein Deficit
mj/kg
g/kg
g/h/d
g/h/d
6.5
9.9
5.3
52.2
147.8
These animals will lose weight on the pasture available.
Supplements for Northern Australia
 Protein Deficit = 147.8 g
 Supplement Crude Protein = 903 g/kg
 Supplement ME = 1.1 mj/kg
 Supplement intake required to bridge protein deficit =
147.8/0.903 = 164 g/head/day
 If lick intake is 200 g/head/day protein intake is
180.6 g and the ME intake is 0.22 mj
 This means the animal’s protein intake should allow it to
consume more dry matter and therefore exploit more
of the energy locked up in the standing dry feed.
Supplements for Northern Australia
 Consider that there is now enough protein intake to






allow an extra 2 kg/h/d of pasture intake.
That gives the animal another 18.9 g of digestible
protein and 13 mj of ME
Total protein available for gain = 19.8 + 32.8 = 52.6g
Total ME available for growth 13 + 0.22 = 13.22 mj
Extra growth possible (from NRC) 200 g/h/d
The P level in the lick is adequate to support this
weight gain
The extra protein in the lick allows the animal to
exploit the standing dry feed and continue to grow.
Supplements for Northern Australia
What About the Breeder?
 Pasture: 6.5 mj/kg ME; 9.9 g/kg dig. Protein
 400 kg cow
 ME maintenance: 49.4 mj (7.6 kg pasture)
 Digestible Protein: 290 g/d (can get 75.2 from 7.6 kg
pasture)
 Protein Deficit: 214.8 g/d – Must come from lick or
from breakdown of muscle. Cow will try to milk by
metabolising muscle and bone (for the Ca and P)
 New lick:
Plant: 1
Product: XXX
Ingr
Code
-------100
81
130
128
155
125
CNP7001
BEC FORMULATIONS
BREEDER LICK
Version: 1
Ingredient Name
Kgs
Pct
-------------------------------- --------- -----UREA
150.000 30.000
COTTON 43% Nar
100.000 20.000
AMMONIUM SULPH
100.000 20.000
KYNOFOS
70.000 14.000
SALT
50.000 10.000
LIMESTONE 38%
20.000 4.000
CAUSEWAY TRACE MINS
10.000 2.000
Formula Totals:
500.00
Totals at 100.00 Pct DM:
489.02
---------------------------------------------------------Nutrient Composition at 100.00 % DM: (Class 6)
Nutr
---11
19
20
33
38
39
60
67
88
100
101
103
105
106
107
108
Nutrient Name
Amount
-------------------- -----------RUMINANT M.E.
2.353
MOISTURE
0.000
CRUDE PROTEIN
123.27
NPN PROTEIN EQ.
114.42
R.D.P.
926.64
U.D.P.
29.855
CRUDE FAT
0.525
DRY MATTER
100.00
Total N
19.724
ASH
46.746
CALCIUM
3.744
TOTAL PHOS
3.214
SODIUM
3.996
CHLORIDE
6.249
POTASSIUM
0.276
SULPHUR
5.172
Units
-------MJ/KG
PCT
PCT
PCT
G/KG
G/KG
PCT
PCT
PCT
PCT
PCT
PCT
PCT
PCT
PCT
Supplements for Northern Australia
 Protein Deficit for maintenance = 214.2 g
 Requires (214.2/1232.7) = 174g of lick per
day
 Need to produce milk:
 Milk requirement per litre:
Fat%
3.5
ME
mj/d
4.87
Dig Prot
g/d
42
 Pasture required per litre to provide energy =
P
g/d
1.2
0.75 kg
 This also provides 7.45 g of digestible protein
Supplements for Northern Australia
 To produce 3 l of milk the extra dry matter intake
required would be 3 * 0.75 = 2.25kg
 Protein from 2.25 kg of pasture = 22.3 g
 Protein required from lick to support 3 l/day milk
output is 126 – 22.3 = 103.7g
 Required extra lick intake = 103.7 /1233.7= 84.1g
 Total lick intake required to support the extra dry
matter intake to produce 3 l of milk is about 258 g
 P intake from that is 8.3g – sufficient, considering
there is some P in the pasture (0.5 g/kg)
Supplements for Northern Australia
Summary
 Keep the better pastures for breeders
 To keep breeders milking on pastures that have
hayed off will require a lick intake of at least
250g/h/d
 This will slow the rate of weight loss in the
cows
 Start supplementing breeders while there is
still green in the pasture.