FRESH COWS EXPERIENCE LOW BLOOD CALCIUM MORE THAN PREVIOUSLY THOUGHT
Clinical hypocalcemia, also known as milk fever, in fresh cows is an economically important metabolic disorder that increases the risk of mastitis, retained placenta, displaced abomasum, and ketosis, which affects lactational performance. The incidence of clinical hypocalcemia in the U.S. ranges between 4-7% and can be reduced with proper nutritional management. Until recently the prevalence of subclinical hypocalcemia in fresh cows was unknown. Blood was collected from 1462 cows (480 herds in 21 states) within 48 hours of calving and analyzed for calcium. Surprisingly, 47% of cows had subclinical hypocalcemia, which was defined as serum calcium < 2.0 mM or < 8 mg/dL. Cows did not have clinical signs of milk fever. Subclinical hypocalcemia increased with age and was present in 25%, 41%, 49%, 51%, 54% and 42% of 1st through 6th lactation cows, respectively. The normal homeostatic response to hypocalcemia may have limits with a cow’s age and may contribute to greater or prolonged hypocalcemia in older cows.
Subclinical hypocalcemia should be viewed as a threat to transition cow health! Blood calcium is important for several physiological and immune functions. Hypocalcemia reduces the ability of immune cells to respond to stimuli and contributes to infections, like mastitis and metritis. Also, hypocalcemia reduces smooth muscle contraction which reduces rumen, abomasal, and intestine motility leading to displaced abomasum and lower feed intake. In a recent study in Florida, researchers found that cows with subclinical hypocalcemia, as defined by a serum calcium ≤ 8.59 mg/dL between 0 and 3 days in milk, had reduced concentrations of neutrophils in blood, impaired neutrophil function, and increased incidence of metritis (78 vs. 20%) compared to cows with normal calcium concentrations. Subclinical hypocalcemia also increased lipid mobilization and therefore concentrations of NEFA (705 vs. 427 uM) and BHBA (9.9 vs. 7.7 mg/dL) in blood during the first 12 days in milk.
Identification of cows with subclinical hypocalcemia is impractical because the cows do not display obvious clinical signs. At Miner Institute we have been measuring blood calcium of fresh cows within 12 hours of calving for several years now, and treat cows with subclinical hypocalcemia. However, most herds do not have equipment for real-time calcium analysis, so prevention is the only option for managing subclinical hypocalcemia. In a recent Wisconsin study using two commercial herds with effective programs of feeding anionic salts, supplementing 2nd or greater lactation cows with two oral calcium boluses (1st bolus at 0 to 2 h and a 2nd bolus at 8 to 35 h after calving) neither harmed nor benefited early-lactation health or milk yield. However, lame cows supplemented with oral calcium boluses averaged 0.34 fewer health events in the 1st 30 days in milk compared with lame cows that were not supplemented with oral calcium boluses. Also, cows with a higher previous lactation mature-equivalent milk production (> 105% of herd rank) and supplemented with oral calcium boluses produced six pounds more milk at the first test than similar high-producing cows that were not supplemented. It appears that supplementing targeted subpopulations with oral calcium may be beneficial for herds with a low incidence of milk fever.
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