Phosphorus nutrition & management overcoming constraints to wider adoption

Phosphorus nutrition & management overcoming constraints to wider adoption Rob Dixon, David Coates, Bill Holmes, Bernie English & Joe Rolfe & with thanks to other members of the team preparing the new Phosphorus Manual -- Desiree Jackson, Peter Smith, Geoff Niethe, Neil MacDonald, Rebecca Matthews and Mick Sullivan QAAFI is funded by the University of Queensland and the Queensland Government

How widespread & important is phosphorus deficiency? Arguably the single most important nutritional constraint in N industry. Why is adoption of technologies to manage P nutrition so low?

Phosphorus (P) deficiency and consequences Clinical symptoms: Bone chewing, weak bones, depraved appetite, peg-leg. Sub-clinical deficiencies: Often the more difficult situations to identify. Low dietary P low pasture intake (often 10-30% decrease), Improved production with P supplements due primarily to increased intake, Reduced efficiency of rumen microbial synthesis. Reduced growth rate (often 20-40 kg liveweight /year), Reduced fertility (often 10-20 percentage units) & weaning weight, The primary limiting nutrient (P or N or energy) may not be obvious.

Outline An economic analysis A revised approach to estimating P required and P intake in grazing cattle, Storage and availability of P in body reserves of the animal, Production responses to P supplements, Constraints to adoption.

Assumptions: An analysis of the economic benefit of changing a phosphorus supplementation regime Benchmark property near Croydon, N Qld. 4,000 AE. Low soil P and acute P deficiency if no P supplements fed. Used best estimates of herd production & Breedcow/Dynama modelling. An existing management where N+P (3 g P/breeder) supplements was fed in the dry season. Principal change - to also feed P supplement in the wet season (10 g P/breeder.day for 6 months). Existing dry season supplements cost = $19 /breeder.year. Additional wet season supplement cost = $22k capital + $13/breeder.year.

An analysis of the economic benefit of changing a phosphorus supplementation regime Assumptions of changes in herd numbers and productivity: Stocking rate. Calculated to allow for higher AE of heavier animals. In addition the total AE was reduced by 10%. Breeder mortality. Reduced from 8% to 4% /year. Weaning rate. Increased from 43% to 53%. Steers. Previously sold at 42 months and 350 kg. Change to sale at 30 months and 360 kg. Cull cows. Sale weight increased from 400 kg to 420 kg.

Variable An analysis of the economic benefit of changing a phosphorus supplementation regime For a benchmark property, Croydon, N Qld. With dry season N+P supplements only With dry season N+P supplements plus wet season P supplement Animal equivalents (AE) 4,000 3,600 Total cattle 6,032 4,828 Breeders mated 2,944 2,411 Female/total turnoff 37% 46% Gross margin per AE $57 $103 Herd gross margin $228,000 $372,000 Advantage to wet season P $144,000

A revised approach to calculating whether diet P intake meets the P requirements in grazing cattle Based on: Revised CSIRO (2007) estimates of the P requirements of cattle, Availability of faecal NIRS data sets for some northern grazing systems, Revised evaluation of use of faecal P to estimate diet P.

A revised approach to calculating whether diet P intake meets the P requirements in grazing cattle Step 1. The amount of P (g/day) required by cattle can be calculated with confidence following CSIRO (2007). Estimates are a function of: Liveweight of the animal, Standard reference weight of the animal, DM intake of the animal -- used to estimate loss of P in faeces, Faecal P (0.5 g P/kg DM intake), Liveweight change (12 g P/kg gain), Lactation (1.6 g P/kg milk), Pregnancy.

A revised approach to calculating whether diet P intake meets the P requirements in grazing cattle Step 2. Estimating the diet DM digestibility, DM intake and liveweight gain for the specific situation. (i) Use faecal NIRS to measure the diet DM digestibility (DMD). (ii) Estimate the liveweight gain from diet digestibility empirically using faecal NIRS databases, e.g. In growing cattle at nil LW gain expect DMD = 52% In growing cattle at 0.6 kg/day LW gain expect DMD = 56%. (iii) Estimate the DM intake for a given LW gain & diet DMD using CSIRO (2007) & QuikIntake. e.g. 400 kg steer gaining 0.6 kg/day -- 10.3 kg DM/day.

A revised approach to calculating whether diet P intake meets the P requirements in grazing cattle Step 3. Calculating the amount of P required in the diet. From the g P required per day and the digestible DM intake -- Calculate the required mg P /MJ ME in the diet.

A revised approach to calculating whether diet P intake meets the P requirements in grazing cattle Step 4. Estimate the concentration of P in the diet selected..

Diet P concentration (g/kg) Estimating P intake by grazing cattle. Diet P concentration is closely correlated with faecal P concentration 3 2 1 Site 1 - G Site 2 - G Site 3 - G Site 1 - R Site 2 - R 1:2 line Regn 0 0 1 2 3 4 5 6 Faecal P concentration (g/kg) Measurements at Springmount, Lansdown and Narayen, and with native grass, Urochloa, buffel grass, or grass-stylo, grass-siratro pastures. G = growing, R = reproducing cattle. [Diet P] = 0.51 [Faecal P] - 0.12 R 2 = 0.81.

Diet P concentration (g/kg) Estimating P intake by grazing cattle. Diet P concentration is closely correlated with faecal P concentration 3 2 1 Site 1 - G Site 2 - G Site 3 - G Site 1 - R Site 2 - R 1:2 line Regn But 2 weaknesses in these results: (i) Only 3 sites & limited range of pastures, (ii) The relationship is not as close in cattle fed P supplements. 0 0 1 2 3 4 5 6 Faecal P concentration (g/kg) Measurements at Springmount, Lansdown and Narayen, and with native grass, Urochloa, buffel grass, or grass-stylo, grass-siratro pastures. G = growing, R = reproducing cattle. [Diet P] = 0.51 [Faecal P] - 0.12 R 2 = 0.81.

A revised approach to calculating whether diet P intake meets the P requirements in grazing cattle In summary it is possible to estimate: a) The P requirements (in g P/day) for various classes of cattle, b) The intake of DM and ME, c) The concentration of P in the diet ingested, d) Thus the intake of P (g P/day) can be calculated. e) The surplus / shortfall of diet P to meet the current P requirements for a class of animal. Faecal P concentration per MJ ME in the diet.

Amounts of diet P required grazing cattle In growing steers Liveweight gain (kg/day) Diet P required (g/day) Diet P required (g/kg diet DM) Faecal P required (g/kg faecal DM) Faecal P/diet ME (mg FP/kg DM) /(MJ ME/kg diet) -0.3 4 0.6 1.5 220 0.0 7 1.0 2.1 290 0.6 14 1.4 2.7 340 1.2 21 1.6 3.2 370

A revised approach to calculating whether diet P intake meets the P requirements in grazing cattle Extending these calculations to the breeder cow in pregnancy and lactation Differences compared to the growing animal High requirements for P for late pregnancy and lactation. Because lactation requires substantial metabolisable energy there will be a different relationship between diet DM digestibility and LW change, The voluntary intake of Bos indicus cows fed tropical forages increases by 20-30% during early and mid lactation.

Amounts of diet P required by grazing cattle In the breeder cow in early to mid lactation (Calculations assume 5 kg milk per day and 2 months pregnant) Liveweight gain (kg/day) Diet P required (g/day) Diet P required (g/kg diet DM) Faecal P required (g/kg faecal DM) Faecal P/diet ME (mg FP/kg DM) /(MJ ME/kg diet) -0.3 13 1.6 3.1 430 0.0 17 1.7 3.3 420 0.6 23 1.9 3.6 400

Availability of P in body reserves of the animal What is the potential for cattle to use body P reserves to meet a short-term dietary deficiency? There are 7-8 g P per kg LW, mostly in bones, About 3000 g P body reserves of a 400 kg breeder in replete P status, Up to 40% of P reserves can be mobilized by an animal in severe and prolonged P deficiency, A 20% mobilization in a 400 kg breeder would represent 600 g P. Each g mobilized P should be equivalent to 1.3 g diet P. Mobilization of Ca and P to provide the high demands of lactation occurs in the normal animal.

Availability of P in body reserves of the animal Growing cattle Mobilization of P in growing animals is usually low, e.g. up to 4 g P/day in a 400 kg steer, In pen experiments where young cattle have been introduced to a P deficient diet voluntary intake may not decrease for 1-3 months. Presumably due to mobilization of P. Expect some benefit from mobilization as cattle are moved from grazing a high-p pasture (a P-replete diet) to P deficient pastures. But research is lacking.

Availability of P in body reserves of the animal Breeder cow in late pregnancy and lactation Limited experimental results (e.g. Springmount & Lansdown) indicate net mobilization of up to 9 g P/day in a 400 kg cow. Studies in goats and sheep suggest 10 g P/day in a 400 kg cow. Total P mobilized a best guess that 20% of body P reserves can be mobilized would be equivalent to about 600 g P in a 400 kg breeder. A best guess for a 400 kg breeder in replete P status: o o o Mobilize up to 10 g P/day for 4 weeks, Mobilize up to 5 g P/day for 8 weeks Equal to 280 + 280 = 560 g P total mobilization.

Storage and availability of P in body reserves of the animal Some complexities likely to affect mobilization Deposition and mobilization of Ca and P are usually closely correlated, Generally it is the need of the animal for Ca which determines the extent of deposition & mobilization of both Ca and P, Thus if an animal has a high diet intake of Ca but a low diet intake of P the animal may not be able to mobilize P to alleviate the dietary deficiency. Implications for Stylo pastures, Ca in supplements.

Liveweight (kg) South African work. Demonstrated that young cows grazing P deficient pastures can mobilize of body P reserves to alleviate a P deficiency The animals were initially in replete P status (Read et al. 1986) 550 No P supplement Plus P supplement 500 450 400 350 300 250 J F M A M J J A S O N D J F M A M J J A S O N D 1978 Month 1979 Calving percentage: 1978: No P supplement = 83%, plus P supplement = 83%. [Calving Sept-Nov] 1979: No P supplement = 29%, plus P supplement = 71%. 1980: No P supplement = 55%, plus P supplement = 91%.

Storage and availability of P in body reserves of the animal If P is mobilized during late pregnancy and lactation to meet high demands then this P has to be replaced (deposition) later in lactation or post-lactation. Early weaning one consequence is to reduce the demand on the breeder for P.

Blood concentration of P as an indicator of dietary P deficiency Growing cattle The best diagnostic test, Timing is important, Practical problems for producers to obtain blood samples. Breeders Difficult to interpret during late pregnancy & lactation with expected mobilization from body P reserves, Monitor groups of young growing cattle in the breeder herd? The P-screen test Involves sampling of blood and of faeces - but protocols need to be strictly followed. Sampling kits are available

Production responses to P supplements Growing cattle Established recommendations (Winks 1990), Responses generally occur during the wet season when diet is high in energy and protein. LW gain increased up to 60 kg /year -- or more. In the dry season protein and energy will be the limiting nutrients. P supplementation during the dry season. Re-evaluation indicates that supplements of P+N have little effect (but not an adverse effect) on LW change. Research indicates that stylo pastures require special consideration o Stylos tolerate low P soils. Protein and energy in the pasture are relatively high but P concentration low, o A high Ca : P ratio (20:1) in stylo pastures exacerbates P deficiency, o Animal responses to P supplement are much greater on stylo pastures than native pastures or other grass-legume pastures.

Production responses to P supplements Breeder cattle Established recommendations (Winks 1990), Responses generally occur during the wet season when diet is high in energy and protein, Increased liveweight of the breeder for robustness, Weaning rate. Increase can range up to 30 percentage units, Weaning weight. Increase can range up to 30 kg. P supplementation during the dry season? o Established recommendation - lactating breeders need additional P, o o P supplement for a late-pregnant breeder grazing dry season pasture should avoid the need to mobilize P reserves, Key question: Can P supplements fed to breeders during the dry season be deposited into body P reserves and later mobilized?

Production responses to P supplements Breeder cattle Established recommendations (Winks 1990), Responses generally occur during the wet season when diet is high in energy and protein, Increased liveweight of the breeder for robustness, Weaning rate. Increase can range up to 30 percentage units, Weaning weight. Increase can range up to 30 kg. P supplementation during the dry season? o Established recommendation - lactating breeders need additional P, o o P supplement for a late-pregnant breeder grazing dry season pasture will avoid the need to mobilize P reserves for the conceptus, Key question: Can P supplements fed to breeders during the dry season be deposited into body P reserves and later mobilized?

P supplementation of breeder cattle during the dry season? Expect to be less effective & less efficient than P supplementation during the wet season, but may be beneficial. Springmount experiment. Breeders in late pregnancy grazing dry season pasture retained supplement P (up to 15 g P/day). South African research (de Brouwer et al. 2000). Evidence that P supplement fed through winter-spring interval ( = dry season) increased body P reserves and alleviated adverse effects of P deficient pastures. Research with breeders in the northern Australian context is needed.

Indicative estimates of P status & growth responses of young cattle to feeding P supplements Variable Acute / very deficient Deficient Marginal Soil P (P B ppm ) < 4 4-6 7-8 Forage P (g P/kg DM) < 0.5 0.5 1.0 1.0 1.5 Blood Pi (mg/l) < 25 25-35 35-45 Likely LW response (kg/year) Native pasture 40-60 20-40 0-20 Stylo pasture ------ 40-80 0-40

What are the principal constraints to wider adoption by management to address P deficiency? A consensus of the P Book cricket team: Lack of recognition of the importance of P, Lack of simple and effective diagnosis of P status of cattle, Confidence in the responses of cattle to P supplements, High cost of P supplements, Lack of recognition of the likely economic returns, Difficulties to achieve effective delivery of P supplement during the wet season (access, intakes of supplements, labour).

What should be done to improve management of P nutrition across the industry? A consensus of the P Book cricket team: Assembly of case studies of success, Better targeting of classes of cattle with greatest benefit, Need for herd records, Demonstrations of implementation & benefits, Need improved diagnostics of P status, Need improved supplement delivery systems, Need better understanding of the role of body reserves of P, Need better understanding of the dose-responses to P supplements.

Thank you