The wider impacts of hypocalcaemia

Farmers are often very good at identifying classical cases of clinical hypocalcaemia; however, subclinical hypocalcaemia (SH) can often rumble on unnoticed, causing multiple early lactation problems.

SH is defined by a blood calcium of between 1.4mmol/L and 2.1mmol/L, although this range is still much debated and often confined to zero to three days in milk.

Non‑lactating cows have a daily maintenance requirement of 21g of calcium, which can almost triple to 55g during the first week of lactation in high‑yielding Holsteins. This sudden increase in calcium demand occurs concurrently with a 30% decrease in feed intake around parturition, restricting calcium intake during this critical period¹.

It is not the nadir of calcium concentration, but rather the persistency of SH that increases the risk of disease^2,3.

SH occurs in at least 25% of first lactation heifers and 50% of cows in their third or later lactation⁴, and costs a minimum of £92 per case⁵.

A gateway disease

Like other metabolic diseases, such as ketosis, SH can be described as a gateway disease as low calcium post‑calving can be the starting point for many problems – including decreased fertility, retained cleansings, uterine prolapses, left displaced abomasum, metritis, endometritis, mastitis, reduced dry matter intake (DMI), reduced milk production, ketosis and an increased risk of culling.

For this reason, vets play an important role in checking for signs of subclinical disease and initiating investigations.

Primiparous cows are three to four times more likely to experience a postparturient disease or removal event during the first 60 days in milk (DIM), compared to a normocalcaemic cow, and multiparous cows are almost twice as likely¹.

Prevalence of persistent SH (low calcium one to four DIM) is about 22.9% in primiparous cows and only 12.5% in multiparous cows, but this reverses with delayed SH (normal calcium at one DIM, then low calcium two to four DIM) where 25% of multiparous cows are affected compared to 13.2% of primiparous. These same multiparous cows with a delayed SH have a lower milk yield throughout at least the first 10 weeks of lactation¹.

In total, 76% of SH cows have an excessive energy deficit compared to normocalcaemic cows – and this rises to 85% if the condition is prolonged past three days in milk¹.

Additionally, cows that developed metritis had prolonged SH (from 1 to 12 DIM) compared to herd mates that did not develop metritis.

SH can also impact fertility. A 2018 study found cows from grazing herds diagnosed with SH at calving took 32 days longer to get pregnant again, compared to cows that had a normal level of calcium at calving⁶. In addition, housed cows with SH at one, two and three DIM had a 70% reduced odds of pregnancy to first service².

Use of data to diagnose SH

Typically, SH is identified when a farm client sees an increase in postparturient diseases and suspects a problem exists in his or her fresh cows, so reaches out to his or her vet for help.

However, other opportunities exist for vets to identify SH, such as during an annual herd health review. The upcoming inclusion of Government funding for an annual herd health review, as part of the sustainable farming incentive, presents an opportunity for vets to further engage with farm clients.

Providing accurate data is recorded throughout the year and presented at the herd health review, problem trends can be identified and investigated. Additionally, more widespread local data collection will aid our understanding of SH at a national level.

Acquiring good data about disease cases can be conducted in many ways – from running the appropriate report on a herd’s management software to manually flicking through the farm diary or medicine book and adding them up. Practice antibiotic sales will also identify trends and can be broken down into likely numbers of treatments.

It can be helpful to investigate data by lactation group to see whether differences exist. For example, heifers may be struggling to access feed or cubicle space to lie down due to bullying or overstocking, leading to the problem occurring more frequently in that group. Similarly, it may be that the problems are occurring more frequently in the older cows or the highest yielders, which are using a lot of calcium early in the lactation – so checking tag numbers will help identify any patterns.

The author’s practice is trialling a data management system that helps vets and farmers to collate all data into meaningful, easy-to-use formats. This includes everything from body condition and rumen fill scores, to stocking density and feed access.

The data can be analysed in a succinct manner and specific reports can be created. For example, a transition check report looks at all the factors that may increase the risk of getting clinical hypocalcaemia or SH.

A regular report is shared with farmers, which identifies how their management practices are impacting disease risk and provides improvement advice.

Identify at-risk cows

By using records and data, it is then possible to identify cows that may be at a higher risk of SH and, therefore, implement an alternative management approach to reduce risk in these animals.

Multiparous, high‑yielding cows, and cows with low DMIs (such as lame cows) will benefit from supplemental calcium post‑calving⁷.

A 2018 study with Jersey cows found higher parity cows, those with a male calves and those with a lower 305‑day milk yield were associated with a higher risk of SH⁸.

Collaboration with nutritionists

Room for improvement generally exists in terms of the extent to which vets provide feedback to nutritionists regarding how any diet changes are affecting the cows.

A collaborative approach between a farm’s vet and nutritionist will achieve the best outcomes for farmers. Joint visits can efficiently investigate transition diet‑related health problems, such as SH. Dairy nutrition can be a daunting topic, so these are also excellent CPD and relationship-building opportunities.

Beware of bolus choice

As more calcium bolus products become available, it is important for vets and farmers to be savvy, and choose a product that meets their needs. Not all calcium treatments are the same and farms that switch to a cheaper bolus may find it is less effective, allowing subclinical disease to quietly occur.

This is especially the case where low calcium after calving is resulting in fertility problems. The amount of money saved by using a cheaper bolus can be soon lost when it takes longer for cows to get back in calf. However, by the time a problem is noticed, the consequences cannot be easily rectified – so the focus has to be on prevention.

Conclusion

Vets need to keep SH in mind, as it is generally a bigger problem than we give it credit for in our day-to-day vetting and even seemingly well‑managed herds can be easily caught out.

Being mindful of how small changes to transition cow management, fostering a collaborative approach to nutrition, analysing farm data and mineral products will allow vets to proactively prevent SH from occurring.