When you think of milk fever, you think of calcium. We treat milk fever with calcium and the cow typically responds quickly and successfully. Even though milk fever is easy to treat, the disease is costly with an estimated cost of $350/case. Hypocalcemia typically leads to or is a forewarning of transitional disease. The clinically weaker and immuno-suppressed cow is at greater risk for injury, mastitis, retained placenta, and metritis. Therefore, we need to strive for a low herd incidence. A herd level milk fever incidence should be less than 3%. This article will analyze the impact of nutrition on the incidence of milk fever.
To achieve a low incidence rate, we need to focus on prevention. An obvious strategy to decrease milk fever is to maintain pre-fresh dry matter intakes and to lessen the degree of dry matter intake decline prior to calving through adequate bunk space (30” per head) and cow comfort. Additionally, the dry cow should consume a ration with excellent forage quality and adequate metabolizable protein (>1200g/day) without exceeding the NEl requirement of 14-15 Mcal per head per day (0.64 Mcal NEl per pound of DM). Another milk fever control strategy that has been incorporated in pre-fresh rations and extensively analyzed is the DCAD (Dietary Cation Anion Difference) Theory which focuses on Calcium, Magnesium, Potassium, Sulfur, Sodium, and Chloride dietary levels.
Lean et al analyzed 137 trials with 2545 calvings to determine which minerals had the greatest influence on the development of milk fever. The results will surprise you! First, picture a bell curve.
Milk fever incidence in response to varying dietary calcium concentrations as predicted by Model 1.
(Lean et al Journal of Dairy Science 89:669–684 2006)
When analyzing the influence of calcium as a % of dry matter intake on milk fever incidence, the highest incidence of milk fever occurred at calcium levels between 1.1-1.5% dry matter with decreasing incidence below 1.1%DM and above 1.5%DM. Lean saw a greater benefit to lowering pre-fresh calcium levels to <0.5% dry matter.
Second, the meta-analysis revealed a significant influence of magnesium on the incidence of milk fever. In fact, the influence of magnesium was significantly more important than potassium! The study showed a greater benefit to formulating pre-fresh rations with magnesium levels >0.4% dry matter. We understand many farms have seen a higher milk fever incidence with high potassium forages. The greater incidence was likely a result of insufficient dietary magnesium levels! Low potassium levels are often recommended, but the agronomic negatives are more significant to the dairy’s bottom-line than the metabolic benefit to the cow. Lowering grass potassium levels significantly reduces yields (correspondence with Dr. Ferguson, University of Pennsylvania).
With the information presented in the meta-analysis, we recommend keeping pre-fresh calcium levels low, <0.5% dry matter, potassium levels as low as physically possible for the farm, and, more importantly, magnesium levels >0.4% dry matter.
Please work closely with your nutritionist and veterinarian, ensuring excellent communication between all team members, to optimize the health and productivity of your transition cows.