Monitoring your DCAD Program - Taking Urine Samples

Adapted by Rosalía López-López, DVM & Noelia Silva-del-Río, UCCE Dairy Herd Health Specialist

When calcium demand for colostrum and milk production exceeds the calcium available in plasma, cows might suffer milk fever or hypocalcemia. This peripartum metabolic disorder affects mostly high producing cows in their third or greater lactation. Jersey cows show greater predisposition to hypocalcemia than Holstein cows. The prevalence of clinical hypocalcemia has been reported to be 5% whereas subclinical hypocalcemia affects approximately 50% of all multiparous cows.

One of the strategies used to prevent clinical and subclinical hypocalcemia in dairy cows is to feed anionic salts in close-up diets [dietary cation anion difference (DCAD)]. Increasing dietary anions (Cl^- and SO₄^2-) induces a compensated metabolic acidosis which increases tissue responsiveness to paratohormone (PTH). This hormone enhances bone resorption and intestinal absorption of calcium.

Using total mixed rations (TMR) ad libitum is the best method of delivering anionic salts without depressing feed intake. However, correctly mixing anionic salts into the close-up TMR can be challenging. Urine pH is a good indicator of blood pH. Thus, in order to asses if the DCAD program is working, we can monitor urine pH of close-up cows. Urine pH should be monitored on 8 to 10 cows from the close-up pen, and preferably, it would be done twice a week. If cows are fed TMR, changes in urine pH relative to time of feeding will be negligible. Urine samples should be collected midstream to avoid alkalinity from vaginal secretions or contamination with manure. Below are some tips to quickly obtain urine samples:

Avoid sampling when farm personnel is working with close-up cows (pen moves, checking ear tags, giving vaccines, etc.).
Approach cows slowly without scaring them.
Do not hold the tail while stimulating urination
Massage the vulva by stroking from the rear udder attachment to the lower vulva. Use one hand and avoid placing your second hand on the cow.
To reduce friction during the stroking, wear plastic sleeves instead of latex gloves or bare hands.

The success of a DCAD program can be easily evaluated by monitoring urine pH. In Holstein cows, urine pH values should be between 6.2 and 6.8, and for Jersey cows between 5.8 and 6.3 (with DCAD supplementation). If the urine fails to be acidified, evaluate if the inclusion rate of anionic salts in the diet is adequate, and that the preparation and delivery of the ration is done properly.

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