Did you know that a 550kg dairy cow normally has a blood calcium level of around 3 grams?
Once she calves, in lactation she requires approximately 23 grams per day!
Recent studies in NZ have shown the average herd-level prevalence of subclinical milk fever is 52%
This rate of use requires a complete blood turnover of total blood calcium every 3 hours to maintain outflow and keep her standing.
When a cow goes through the transition from being a dry to a milking cow, her body must send signals to the bone to release calcium, the intestine to absorb more calcium, and the kidneys to resorb more calcium. It takes days for her body to adjust, even with the help from pre-calving diets, and in some cases salts or ‘DCAD diets’ (for example magnesium sulphate, magnesium chloride and gypsum) to help her do this.
We have all seen and treated milk fever. But what about the cows in your herd that you don’t see down in the paddock?
Low grade or subclinical milk fever can still cause disease. In fact, it increases the risk of metritis (uterine infection after calving), ketosis and has been shown in one study to reduce pregnancy rates in affected cows by as much as 36% to their first service. Those cows with subclinical milk fever have been shown to have a 50% increased chance of being culled in the first 60 days of lactation. Not only are they at greater risk for disease, but they produce less throughout their lactation.
We know from studies where cows were artificially given something that reduced their blood calcium levels, that specific cells involved in their immune system didn’t function as well, and they had a massive drop in their dry matter intake. This is immensely important as cows have a poor appetite after calving and won’t physically eat enough to keep up with increasing energy demands.
It is important to get the pre-calving, calving and early lactation diet right, to minimise the risk of subclinical hypocalcaemia in your herd. High risk cows may require a starter drench or oral calcium bolus, to help prevent them from having problems once they calve.
The Calpro Bolus is a tool to assist with the prevention and treatment of subclinical hypocalcaemia and Milk Fever in high risk cows (those with a history of milk fever, lame cows and older cows).
The standard dose regime is one bolus given immediately after calving and another 12 hours later. This provides a sustained increase in serum calcium over 24 hours.
The boluses are given orally, via an applicator, similar to copper capsules. It’s important this is done correctly so talk to your vet about the correct technique. Cows that are being given a bolus need to be able to swallow. Clinical milk fever cows will require IV calcium initially and a bolus can be given once she is burping and swallowing. Boluses should not be used on bloated cows.
Once in the rumen they dissolve within an hour to deliver 43g of calcium (in two forms, calcium chloride and calcium sulphate). Calcium chloride is rapidly absorbed, and the calcium sulphate is absorbed over a longer period.
For more information on hypocalcaemia and whether Calpro boluses would be a useful tool for your high risk cows, speak with your lead vet.