Cows with subclinical hypocalcaemia (SCH) are not easy to identify, but determining incidence and prevalence in the dairy herd is critical. The challenge: these animals do not show clinical symptoms, but have blood calcium concentrations below a still-undefined critical threshold. This level isn"t low enough to cause clinical milk fever, but is low enough to cause significant problems, often leading to a cascade of negative health effects.
Several months ago, the health reports for a 1,500-cow Midwest dairy were full of disturbing data. Despite a low incidence of clinical hypocalcaemia, or milk fever, metritis incidence was about 20% and consistently higher than desired. Days open stretched beyond 130 days for much of the herd, and cows seemed to have a difficult time efficiently transitioning to their next lactation. Although cows didn"t appear to have physical symptoms of a health disorder, peak milk also was down about 10 lbs. per cow.
The herd owners knew there was a problem. After consulting with their nutritionist and veterinarian, they determined SCH was likely at the root of the dairy"s challenge.
The dairy team evaluated the prefresh diet to ensure it was formulated for a dietary cation-anion difference (DCAD) of -8 to -12 meq/100g dry matter. This practice is proven to consistently acidify cows and helps reduce risk of clinical and SCH postpartum. As a result of this lower ration DCAD, more of the total blood calcium becomes available in ionized form – reducing the risk of SCH and milk fever.
Next, forages and byproduct commodity feeds were analyzed for sodium, potassium, chloride and sulfur – the four components of the DCAD equation – using wet chemistry analysis.
Lastly, the dairy set up a protocol to monitor urine pH. Urine pH serves as a reflection of blood pH, which assesses the effectiveness of implementing a negative DCAD diet. Urine samples were taken from cows fed the close-up diet for at least seven days and at least a week away from expected calving. These animals had acclimated to the diet, and dry matter intake levels were relatively stable. The urine samples were consistently taken within three to four hours post-feeding, the time frame urine pH would be at its lowest point.
Results from these steps offered a clearer picture of what was happening in the herd. Wet chemistry analyses of feedstuffs showed elevated levels of potassium in the prefresh diet, as well as higher-than-desired levels of dietary sodium. As a result, ration DCAD was higher than the target level for prepartum cows.
This also resulted in variable urine pH levels, with less than half of the Holstein herd falling within the target range of 5.8 to 6.5.
To correct these issues, the dairy found a new source of a lower potassium forage for the prefresh diet. Their nutritionist also decreased ration sodium levels, while increasing chloride and sulfur levels with research-proven feed ingredients. These actions lowered the prefresh diet DCAD to the desired -8 to -12 meq/100g dry matter.
Dairy personnel followed the urine pH monitoring protocol to track progress. Shortly after making these nutrition adjustments, cows were back within the urine pH target range.
Within a few weeks, metritis incidence was cut in half. Within a couple of months, days open dropped to 110 days for 75% of the herd, and peak milk climbed by 12 lbs. per cow. The dairy also reported fewer high fever incidents with fresh cows.
These significant improvements demonstrate that what you can"t see really can hurt you. In the case of SCH, the lack of physical symptoms masked the real damage the disorder caused this herd. The key to success was a deliberate, consistent monitoring program followed by a scientifically based intervention – something any herd, anywhere can implement and maintain.
To learn more about SCH monitoring and prevention, visit transition.ahdairy.com.