Editor’s note: The following case study was handled by Milos Haas, ruminant nutritionist from Kitchener, Ontario, Canada. He writes about his experiences here.
Typical milk fever, when a cow goes down right after calving, is rarer than it used be years ago. Adjustments in close-up dry cow diets, such as lowering potassium and balancing for DCAD content, has helped to prevent clinical cases.
Unfortunately, the problem has not been solved. And, based on blood work from dairy farms, almost 50 percent of fresh cows experience subclinical hypocalcemia.
This was the case at one of my client’s farms. Fresh cows were expressing signs related to potential problems with the immune system, such as a higher percentage of retained placentas, high rate of metritis and increased mastitis infections right after calving, even though the whole herd somatic cell count was low. There had been no clinical milk fever in this herd for years.
Energy and fiber content of the diet before or after calving did not indicate any problems. Potassium content of the diet before calving was between 1.1 to 1.2 percent, phosphorus at 0.4 percent, magnesium at 0.37 percent, vitamin E at 2,000 IU per head per day, selenium at 8 mg per day (80 percent organic), and vitamin D at 25,000 IU/head/day.
The DCAD of the pre-fresh diet was +100 mEq/kg.
Urine pH of pre-fresh cows was in the 8.1-8.3 range, on average. Mycotoxin levels in the tested feed samples were very low.
Despite this, there was more than a 15 percent incidence of retained placenta, along with many cases of metritis, which had a negative impact on conception rate at first breeding. The pregnancy rate fell to 13 percent.
I asked a veterinary clinic to start collecting blood samples between the first and second milking after calving. We had more than 80 percent of samples showing signs of subclinical hypocalcemia.
Based on this information, I adjusted the close-up dry cow ration DCAD level to -100 mEq/kg by using a product with hydrochloric acid. Palatability of this product was good, and it actually increased dry matter intake in pre-fresh group from 10.2 kg to almost 11 kg. Vitamin D levels have been increased to 36,000 IU/day, as well. Urine pH in close-up group has been lowered to a range of 6.5 to 7.0. Two weeks later, we noticed a significantly lower incidence of retained placenta, better intakes after calving, and less ketosis. The levels of blood calcium after calving were normal again.
Urine pH monitoring is an important part of this program.
Every time we encounter an increase in retained placentas, there is close relationship with an increase in urine pH in the close-up group. My experience shows that it is important to prevent subclinical hypocalcemia by lowering DCAD of the ration and lowering urine pH.
Lowering potassium might not be sufficient in prevention of subclinical hypocalcemia; it seems that there is a need to actively lower close-up diet DCAD and lower urine pH to 6.5 -7.0.
Meanwhile, my client’s herd (350 cows) is getting good milk production; the pregnancy rate now exceeds 20 percent and the incidence of retained placenta is well below 5 percent.