Phosphorus feeding levels for transition cows has been a topic of discussion for some time now as our previous standards have been challenged with new research. As dairy farming progresses into a more sustainable role, the pressure is on to reduce the amount of phosphorus entering the environment from animals. At the same time, another phosphorus debate focuses on the correct requirements needed for fresh and transition cows.
Previous research states that incorrect amounts of phosphorus in a cow’s diet can present a risk to health and productivity. Too much or too little of this mineral can result in feed intake and milk depression and raises the risk of medical conditions like down cow syndrome and postpartum hemoglobinuria depending on stage of lactation. Standard recommendations range from 0.20% to 0.25% phosphorus in dry matter for dairy cows in late pregnancy, while dry cow rations should range to 0.40% phosphorus in dry matter.
“Overfeeding this mineral is sometimes intentional with the objective of preventing or at least mitigating a negative phosphorus balance in early lactation. In Europe, dry cow rations often contain 0.40% phosphorus in dry matter and above because of the use of canola as an important protein source,” cited Walter Grunberg, a professor at Justus Liebig University in Giessen, Germany, at the recent Cornell Dairy Nutrition Conference held in Syracuse, N.Y.
Recent research has exhibited that feeding high amounts of phosphorus during the dry period boosts the risk of metabolic illness for the fresh cow. “Based on current knowledge, feeding phosphorus in excess of requirements to dry cows should be avoided whenever possible,” he said. Feeding below the required amount during the dry period has resulted in many benefits for the cow, such as a positive calcium balance during early lactation. Bone mobilization is triggered by a negative phosphorus balance, resulting in metabolic calcium and phosphorus release. This research challenges the old standards that restricting phosphorus during the dry period proves harmful to the cow.
Although it may seem simple to adjust the ration and lower phosphorus levels during the dry period, it can prove to be relatively tricky. “Formulating dry cow rations with phosphorus content low enough to induce a negative phosphorus balance is at least as challenging as formulating a dry cow ration with a calcium content sufficiently low enough to induce a negative calcium balance,” noted Grunberg.
Though this research has shown remarkable results when it comes to limiting phosphorus levels during the dry cow period, there is still further research that needs to be done. The maximum intensity and duration of the phosphorus deprivation period still needs to be addressed. “Based on our current knowledge, it seems that the moderate phosphorus deprivation not exceeding three to four weeks prior to calving is innocuous while phosphorus deficiency in early lactation must be avoided to prevent negative effects on health and productivity,” explained the professor.
