BEC Feed Solutions Written by:Steve Blake – BEC Feed Solutions Modified and Presented by: Ken Bruerton – Protea Park Nutrition The role of Phosphorus in Cattle Nutrition

 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)

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 WetDry

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 Weight 0.75  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

Case Study 2009 season Helen Springs The Role of Phosphorus in Cattle Growth and Reproduction

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, SO 4,PO 4 ), 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

Pasture analysis from NT property 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 Nutrient Intakes required to maintain weight These animals will lose weight on the pasture available.

 Protein Deficit = 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 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 = = 52.6g  Total ME available for growth = 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: 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: Supplements for Northern Australia

 Protein Deficit for maintenance = g  Requires (214.2/1232.7) = 174g of lick per day  Need to produce milk:  Milk requirement per litre:  Pasture required per litre to provide energy = 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 = /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. Supplements for Northern Australia