Some of you attended our fall producer meeting last year, when we had a good discussion with Dr. Murray Gillies from Vetoquinol on milk fever and calcium therapy. Although that may seem like a lifetime ago with all that has happened in 2020 (need we say more!), one of the major take home messages, was that our understanding of milk fever, both clinical and subclinical hypocalcemia, is constantly evolving, and subsequently so do our therapies for treatment and prevention. A full recap of the meeting, or milk fever in general, is beyond the scope of this newsletter, but current and ongoing research is starting to classify hypocalcemic cows into different groups, and relate those to the well-known negative health effects of increased dystocias or calving difficulities, retained placentas, DAs, mastitis, ketosis and reduced milk production. Interestingly, new research has grouped cows into 4 groups post calving, in relation to calcium status
Normocalcemic – blood calcium remains in normal range all 3 days post calving
Transient subclinical hypocalcemia ( tSCH) – where calcium is below normal at calving, but within normal range on day 3 or 4
Delayed subclinical hypocalcemia ( dSCH) – where calcium is normal at calving, but below normal range on day 4
Persistent subclinical hypocalcemia ( pSCH) – where calcium is below normal range at calving and day 4
For simplicity and for consistency with a few other newer studies, let us combine groups 3 and 4 into chronic hypocalcemic cows (cSCH). The important message is that different research groups have shown that it is not necessarily how low serum calcium drops, but the persistency of the subclinical hypocalcemia that increases the risk of an adverse health condition and decreased production. McCart et al 2020 showed that transient SCH had little negative association with health, production or reproduction, but chronic SCH had more health problems, delayed reproductive success, lower production and increased removal from the herd. In short, the common strategy of giving supplemental calcium at calving plus or minus 12 hours later, may only be beneficial in a subgroup of cows and perhaps missing the most clinically important group. Ongoing research is also looking at the potential benefits of giving 2 boluses at the initial dose with regards to increasing serum calcium and milk fever prevention.
You may also recall that another take home message was that calcium boluses, commonly used to help prevent clinical milk fever or treat subclinical hypocalcemia, are not all created equal. In general , calcium boluses should supply a safe, non-irritating rapidly available calcium source, have rapid bolus dissolution, and supply a sufficient amount of calcium. It should also create a mild systemic acidosis so that parathyroid hormone has increased activity for bone and kidney resorption of calcium, as well as active absorption of calcium through the gut.
So which is the best bolus to use Doc?
While most of the boluses available today are similar, there are a few differences of note. Dr Register boluses, although the highest in Calcium chloride which is the source most of the rapidly available calcium, are a non-coated bolus. Therefore the calcium chloride, which is quite acidic, can be very irritating to the esophagus. This is especially true if the bolus breaks upon administration, a drawback not associated with all the other boluses which have a gelatin coating for protection. Rumilife24, another common OTC calcium bolus available, contains the lowest calcium chloride concentration and thereby the lowest rapidly available calcium. In addition to that, a study out of a Alberta by Solvet, the pharmaceutical company who makes the Cal-Boost bolus measured the dissolution time of 3 boluses ; Cal-Boost, Transition and Rumilife 24 in a rumen fistulated cow (a permanent hole in the side of a cow giving direct access to the inside of the rumen) by measuring weight of the bolus over time by pulling the remnants of the bolus directly from the rumen at various time increments. They showed that their boluses was completely dissolved by 90 minutes, Transition bolus was completely dissolved by 180 min, and even by 240 minutes, the Rumilife24 bolus was still mostly undissolved. Corresponding blood calcium levels at these same time increments seemed to correlate with the dissolution times for each different bolus.
Talk to your herd vet or trusted advisor about whetheryou are getting the most out of your calcium bolus therapy.