Reducing phosphorus leaching in soil
Phosphorus (P) is critical for healthy plants to grow in New Zealand’s naturally P deficient soil, says Hamilton-based Soil Scientist Dr Gordon Rajendram.
Phosphorus accounts for 30% of the mineral component of the animal and is essential for growth, energy, bone development, blood formation and nutrient metabolism. Phosphorus leaves the farm ‘on the tanker’ every day, so it needs to be replaced effectively.
Deficiency has negative effects on animal performance, fertility and bone mineralisation, causing reduced feed intake, poor growth and milk production, reduced fertility and impaired digestion. And it causes ‘creeper cows’ – cows down but alert (unlike milk fever where they are sleepy) and perhaps showing red urine if post parturient haemoglobinuria (PPH) develops. These cows won’t respond completely to intravenous calcium/magnesium injections; phosphorus seems to be the only way to get them up and stay up.
Phosphorus is a hot topic. Farmers seem to be encountering more metabolic issues than ever, and ‘creeper cows’ is a common condition. There’s an obvious trend emerging in various regions and feeding systems. Clinical symptoms also appear to be ‘sudden’, between one year and the next.
Phosphorus ‘awareness’ is rapidly spreading, although diagnosis, prevention and treatment options have been limited until now. To save a lot of stress, unproductive time and treatment costs, and to avoid unproductive animals, the focus now needs to move quickly to prevention from cure.
Fodder beet
Traditionally, phosphorus has been taken up from the soil into the grass, but changing fertiliser and feeding practices mean farmers can no longer rely on adequate phosphorus levels being fed.
Depending on the proportion of the diet, whole crop cereal silages (maize, barley, cereal straw) may not provide adequate phosphorus levels. In particular, the sharp rise in the use of fodder beet as a winter feed crop (and increasingly through milking) is cause for concern.
On the positive side, fodder beet has high yields, high energy content and low cost ($/kg DM), yet it offers one of the lowest concentrations of phosphorus in any feed delivered in NZ; so mineral deficiencies must be identified to avoid serious metabolic issues.
Spotting deficiency
Cows deficient in phosphorus may try to get it by eating soil and rocks (known as pica). Diagnosing phosphorus deficiency can be problematic because of the animal’s ability to regulate minerals from the bones. A low phosphorus blood level is often the last stop before the deficiency is critical. It’s the hard-to-diagnose sub-clinical symptoms that are often missed, which is why our company encourages farmers to be aware and ask questions where phosphorus is concerned.
Prevention
Until recently, the only practical way to supplement phosphorus for dairy cows grazing fodder beet has been DCP (di calcium phosphate). This is high in calcium (24%) yet offers a lower level of phosphorus (18%) compared to calcium. But the availability of phosphorus from DCP is variable, and highly dependent on the quality, manufacturing process and source of the product. Another downside of feeding DCP is its high cost as a source of calcium (often problematic pre-calving), especially where limestone is readily available and used post-calving.
In Australia and Europe, phosphorus supplementation is well-understood and widely practiced. Fortunately, products developed and proven in these countries are now available for the first time in New Zealand.
BEC Feed Solutions’ products Bolifor MGP+ (magnesium phosphate), in lick blocks, provides a rich and available phosphorus source for grazing cattle, and this is the easiest way to supplement herds while they are on crops.
Unlike DCP, Bolifor MGP+ boosts the phosphorus in cows’ diets without added calcium pre-calving (which needs to be managed carefully), and it contains significant levels of magnesium. These products are formulated to mix into daily feed rations, or basic feed blends, making them suited to many systems including mineral dispensers.
• Trina Parker is country manager for BEC Feed Solutions.
