At the onset of lactation, metabolic adaption mechanisms for calcium are not rapid enough; cows need a day or two to maximize calcium flows from the intestinal tract and bone to the mammary gland. Therefore, almost all cows experience some degree of calcium deficiency after calving, but calcium concentrations often return to normal within two to three days. In order to produce 22.5 pounds of colostrum on the day of calving, 23 grams of calcium is needed by the mammary gland.
Researchers initially set out to see if there was an association of subclinical hypocalcemia with milk yield, feeding, drinking, and resting behavior during the period around calving. The results were published in the February Journal of Dairy Science. Fifteen dairy cows were identified as having subclinical hypocalcemia and were paired with 15 control animals. To be classified as being subclinical, calcium concentrations were below 1.8 millimoles per liter.
Standing behavior was monitored for 14 days, from 7 days prior to calving until 7 days postfresh. In the 24 hours prior to calving, cows with subclinical hypocalcemia stood for 2.6 additional hours. The day after calving, these cows spent 2.7 hours less standing. No differences were observed in the average number of standing bouts between the two groups.
Daily milk yields were obtained for all cows up to 280 days in milk. Cows with subclinical hypocalcemia produced approximately 13 pounds more milk per day during the second, third, and fourth week after calving compared to control cows. Hypocalcemic cows in their third lactation sustained a great milk yield throughout the entire 280 days.
Despite a great milk yield, hypocalcemia cows did not consume more water after calving and tended to have a greater dry matter intake during week two. Despite the elevated intake, these animals made fewer trips to the feed and water bins. In the two weeks prior to calving, cow that would be diagnosed with subclinical hypocalcemia had an average dry matter intake 3.8 pounds per day greater than herdmates that maintained normal calcium levels.
Muscle weakness due to calcium deficiency may explain the decrease in the number of visits to feed and water bins and the drop in standing time following calving. This difference may also be attributed to social dominance or genetic potential for milk production.
The study does not refute the undesirable effect of milk fever or studies that suggest subclinical hypocalcemia may be a potential health risk for transition cows.