Read the Progressive Dairy Canada digital edition

Dairy calcium metabolism and supplementation: An ever-changing science

Murray Gillies for Progressive Dairy Published on 12 June 2020
Cow with her calf

Recent research from dairy universities (such as Cornell University) suggests we’re still unsure of the “best” protocols for supplementing fresh dairy cows with calcium.

Although research is evolving, veterinarians understand the current scientific literature and how to best manage calcium supplementation.



What we know:

  • Many cows enter into a low blood calcium status within hours of calving, regardless of diet.

  • Calcium is of extreme importance to the fresh dairy cow, and supplementing these cows with calcium is of great value.

  • Oral treatments should be heavily favoured over intravenous treatments as long as a cow is able to stand.

  • Dairy operations benefit greatly by having on-farm standard operating procedures (SOPs) developed in conjunction with their veterinarians to determine which cows get treated, when and how, and when IV therapy is required.

What we don’t know:

  • The long-term negative effects of acute subclinical hypocalcemia versus chronic subclinical hypocalcemia

  • How to strategically use oral calcium to maximize effectiveness and minimize potential long-term effects of hypocalcemia

Dairy cows typically become hypocalcemic in the hours that follow calving. Recent research suggests cows that are successful at quickly overcoming hypocalcemia by mobilizing calcium from their bones and diet have favourable outcomes – not just in the transition period but through their entire lactation.

Hypocalcemia that lasts for about 24 hours after calving is now referred to as “acute subclinical milk fever.” Hypocalcemia that persists for 48 to 72 hours is called “chronic subclinical milk fever,” and these cows can have many health and reproduction challenges throughout their lactation. Certain cows are at higher risk of chronic hypocalcemia (old cows, lame cows, sick cows, certain breeds, etc.); however, some “normal-looking” cows may also enter into this chronic low calcium state, unbeknownst to even the most astute dairy farmer.

It is important to supplement cows with oral calcium in the acute phase to help them overcome their calcium shortfalls. Most dairy producers are doing this by administering a calcium bolus at calving and again 12 to 24 hours later. Calcium boluses will cause a noticeable rise in blood calcium that lasts approximately six hours. No bolus currently on the Canadian market is likely to elevate blood calcium measurably beyond six hours, regardless of what might be claimed.


Research is finding current calcium bolus protocols do not adequately address the needs of the chronically affected hypocalcemic cows. The three protocols below are an example of how cows may be grouped and considered for prospective calcium supplementation at calving. More is not necessarily better – for example, research that looked into giving two boluses at the same time at calving and then again 24 hours later (four boluses in two days) had a negative effect on health and reproduction in heifers. Talk with your veterinarian to determine a protocol and a strategy to minimize the impact of hypocalcemia in your herd.

Fresh cow calcium bolus protocol suggestions:

  • Normal fresh cow on an effective DCAD transition diet: One bolus after calving and one bolus 12 to 24 hours later (two boluses in total)

  • Normal fresh cow not on any form of transition diet: One bolus after calving, one bolus repeated in 12 to 24 hours followed by one bolus in another 24 hours (three boluses in total)

  • High-risk cow (old, lame, ill, etc.): One bolus after calving and repeated every 12 hours for three days (for a total of six boluses)

Currently, cowside calcium tests are being developed to inexpensively and conveniently test the calcium status of a fresh cow. These tests are not currently available; however, they are expected in the near future. Ideally, they would monitor blood calcium in cows just as they do with management of ketosis via cowside BHBA testing, allowing to repeatedly check a cow’s calcium status after calving and supplement according to her individual needs.

We still have plenty to learn about maintaining adequate blood calcium status in recently fresh cows. We can say for certain that an appropriate calcium bolus program for your cows at calving will reduce the duration and incidence of clinical and subclinical hypocalcemia in your herd. Consult your veterinarian to determine the best plan for you. end mark

PHOTO: Fresh cow calcium bolus protocols that help reduce the duration and incidence of hypocalcemia. Staff photo.

Dr. Murray Gillies grew up on a dairy farm in Sussex, New Brunswick. He is a board member of the Canadian Association of Bovine Veterinarians (former president), American Association of Bovine Practitioners board member and director for District 12, and a member of the Canadian Animal Health Surveillance System. He is an expert recognized by the Canadian Veterinary Medical Association on dairy antimicrobial use. 


References omitted but are available upon request. Click here to email an editor.

Murray Gillies is a technical services veterinarian at Vetoquinol. Email Murray Gillies.