Managing blood pH pre-calving ‘can be a gamechanger’

Her metabolism is under pressure as she prepares to calve, initiate milk production, and shift to a higher-energy diet. At the same time, her liver, rumen, and immune system are all adjusting to new demands. How well she copes during this period depends on more than just calcium— it’s about supporting the full range of metabolic processes with the right mineral balance, good body condition, and consistent feeding. Getting these factors right pre-calving sets the foundation for health, performance, and fertility across the whole season.

What is DCAD, and why does it matter during transition?

DCAD refers to the balance between positively charged ions (mainly sodium and potassium) and negatively charged ions (mainly chloride and sulphur) in the diet. High DCAD diets, common with lush spring pasture, make the cow’s blood slightly alkaline, which is a problem during transition. It blunts the hormonal signals that allow the cow to release calcium from her bones and absorb it from her diet.

Switching to a negative DCAD diet just before calving slightly acidifies the blood. This stimulates the parathyroid hormone response, effectively priming the cow’s system to mobilise calcium as soon as lactation begins.

Without this preemptive adjustment, cows are at much greater risk of both clinical and subclinical milk fever. Subclinical cases are especially common and often go undetected, but they have a direct impact on uterine tone, retained placenta rates, appetite, mastitis incidence, and conception success.

Mobilising calcium is only the beginning

Feeding a negative DCAD diet during the final three weeks of the dry period helps kickstart calcium metabolism before calving. But calcium is only part of the transition equation. Magnesium is another critical factor as it’s essential for activating the enzymes that regulate calcium metabolism. Without sufficient magnesium, the DCAD effect is blunted.

Combining magnesium with appropriate chloride and sulphur sources supports the acidifying effect needed to prompt a metabolic shift. But this needs to be done carefully. Excess sulphur, for example, can interfere with copper and selenium uptake.

Don't guess - test

Guesswork doesn’t work when it comes to transition diets. A transition cow needs a well-balanced, negative DCAD formulation designed to deliver a reliable response, without suppressing appetite or triggering acidosis.

Urine pH is the best on-farm tool to track whether your pre-calving diet is doing the job. The target range is 5.5 to 6.0 for Jerseys, and 6.0 to 6.5 for Holstein Friesians. Collect urine samples from a handful of cows four to six hours after feeding, and adjust accordingly.

Consistency matters too. If the transition mineral mix isn’t evenly distributed through the ration, or if cows can sort through their feed, intake will vary, and so will outcomes.

The all-important liver

One of the key insights from recent research is just how much work the liver does during transition. As feed intake drops and energy demand spikes post-calving, the liver becomes the centre of activity – mobilising fat, metabolising toxins, producing glucose, and processing nutrients.

To handle this, the liver needs the right building blocks. Trace minerals such as selenium, zinc, copper, and manganese all support liver detoxification and antioxidant capacity. Choline, niacin, vitamin E, and methionine also play roles in liver regeneration and energy metabolism. These nutrients aren’t just nice to have, they help reduce the risk of ketosis, fatty liver, and sluggish recovery post-calving.

Condition, fibre, and rumen function

Maintaining adequate neutral detergent fibre (NDF) intake – ideally over 45% of the diet – with high-quality, palatable forage keeps the rumen full and working. This helps preserve rumen muscle tone and volume, both of which are essential for appetite and energy intake post-calving.

Body condition scoring (BCS) is another useful tool. Cows should calve down at a BCS of 4.8 to 5.2, with no more than 0.25 to 0.5 of a score gained over the dry period. Over-conditioned cows are more prone to metabolic issues, while under-conditioned cows struggle to reach peak milk or cycle effectively.

Newer technologies, such as 2D/3D imaging and automated BCS systems, can provide accurate condition tracking during the dry and transition periods, helping farmers fine-tune feeding and management decisions before issues arise.

What success looks like

A successful transition is marked by less than 2% clinical metabolic disease, strong appetite close to calving, good liver function, steady energy levels, optimal rumination, and rapid recovery within 48 hours post-calving. When done well, the benefits extend beyond calving with fewer down cows, better early lactation intake, stronger immune response, fewer retained placentas, and quicker return to cycling with higher conception rates.

Chris Balemi is the founder of Agvance Nutrition