Milk fever: Prevention, prevention, prevention

Ask any cattle vet around the world what their least-favourite case is, and many will share a common answer: down cows.

A simple case of milk fever may be easy for the farmer to treat, but the muscle damage and nerve injury we see from cows that are down for any length of time are very difficult to manage successfully. 

About 5% of down cows do not recover, which contributes to the significant cost of milk fever on the typical New Zealand dairy farm. The average incidence of milk fever is about 2%, and the impact of both clinical and subclinical milk fever on animal health costs and production can be considerable. 

Like many areas of animal health, numerous companies promote magic cures for the downer cow, and the vet often has a boring solution which contains a number of difficult strategies to prevent the problem in the first place. 

Prevention, as is the case in a number of animal health conditions, is the main stay of milk fever and downer cow management. 

While dystocia (difficulty calving), grass staggers and toxic conditions can contribute to the prevalence of down cows on a dairy farm, the predominant cause of down cows in NZ is milk fever. 

Milk fever is an ironic name for hypocalcaemia (low blood calcium) and affected cows do not have high body temperatures – in fact, as the condition progresses, hypothermia is a common finding. 

Hypocalcaemia occurs because the metabolic demand for calcium increases about 400% on the day of calving, due to the huge draw of calcium production. Therefore, most cases occur within the first few days after calving, although it is not uncommon for cases to occur in the springer mob, or more rarely, in the milkers. 

A complex relationship occurs between many of the minerals, vitamins and hormones and their relationship with the levels of calcium within the calving cow. This has led to the widely accepted practice of feeding high levels of magnesium to springer mobs. Furthermore, calcium levels are generally restricted in springer cows, as this is risky for milk fever. 

Feeds containing high levels of phosphorus, such as palm kernel are typically avoided in the springer diet as these are precarious for milk fever – the same applies to potassium, the reason why both springer mobs and colostrum cows should not be grazed on effluent paddocks. 

Body condition scoring plays an increasingly important role in dairy cow welfare and production, and over-fat cows are predisposed to milk fever also. Certain breeds and older cows are over-represented in milk fever cases. 

Lastly, there is dietary cation-anion difference, or DCAD, to consider. This is a hugely complex topic beyond the scope of this article which relates to the levels of positively and negatively charged ions within the animals’ diet. 

Highly positive DCAD value diets – containing lots of positively charged ions like sodium and potassium – increase the risk of hypocalcaemia, while negative diets – containing chloride and sulphate – reduce the risk. This is a dramatic over-simplification, and the DCAD approach requires careful monitoring of the diet and cow performance. 

DCAD should be considered when developing a diet for your animals, but the main focus should be on getting the basics right. Keep it simple!

• Rory’s top tip: Consult a qualified, independent advisor to generate diets and management tools to reduce milk fever risk on your farm.

Treatment of milk fever seems relatively straightforward, but there many different methods utilised by farmers and vets alike in treating hypocalcaemia. 

Before the widespread use of calcium-containing metabolic solutions, numerous unusual treatment strategies were employed to tackle this frustrating condition. 

Bicycle pumps were used to inflate the udder, which was somewhat successful in managing the milk fever but contributed to the spread of mastitis and tuberculosis at the time. 

If your vet ever attends a down cow of yours and pulls out a bicycle pump from the back of their ute, ask them kindly to leave your property. 

Obviously, the focus is now on restoring the blood levels of calcium within the cow. Having a treatment protocol all staff can follow is important – develop this with your trusted vet. 

Cows suffering milk fever will require metabolic solutions delivered by injection, initially. These ‘bags’ come in a wide array of fantastic colours and every farmer and vet has their favourite – from baby pink to lime green. 

Intravenous administration for the first bag is great, but are all staff capable of this? It’s fantastic watching the immediate response as the cow becomes more alert, burps and her nose becomes moist as the solution flows in. However, if less-experienced staff attend a case, make sure there is a protocol for giving bags subcutaneously (under the skin). 

This is where I see the most common mistake. Dumping half a litre of cold metabolic solution over a cow’s ribs in one spot and walking away is a waste of time. The absorption is poor, and I see several cows that have been ‘treated’ for milk fever that have large swellings on their sides, but due to the poor absorption, haven’t got up. 

As soon as you see a milk fever case, take off the outer packaging and put the bag down your shirt to warm it, or even better, if you have time, throw it in a bucket of warm water while you get ready. Then, administer it over at least five different places under the skin before massaging each site to improve absorption. 

As soon as the cow is sitting up and can swallow, administer an oral calcium source to keep those levels up! If the cow has been down for more than 30 minutes, she may have muscle damage – inject her with an anti-inflammatory drug such as ketoprofen to manage this. 

Unresponsive cases require intensive nursing care if they are to be successful and regular assessment is essential to safeguard animal welfare.

Case study

Joe and Danielle Kehely milk 1040 spring-calving cows near Ruawai, in Northland. Their focus is on improving their herd through careful breeding and having healthy productive animals. Therefore, laboriously nursing downer cows and losing carefully bred animals is out of the question for their operation. 

In the dry period, after BCS scoring the herd was carried out, we met to discuss the diet being fed during the transition from late dry period to early lactation. We discussed magnesium supplementation in the springer mob, calcium supplementation in the colostrum mob, and management of at-risk cows as well as monitoring. 

After the couple had decided on the diet to be fed, it was decided all cows over four years of age would be drenched using a supplement containing calcium, magnesium, and an energy source. 

Blood samples would be taken periodically during calving for magnesium and NEFA levels in the springers, and calcium, magnesium, phosphorus and B-OHB in the colostrum cows. NEFA and B-OHB are useful measures of fat mobilisation in the dairy cow. 

Often, winter rain and heavy soil conditions mean there is considerable wastage of any magnesium supplementation through both dusting magnesium oxide and adding magnesium sulphate to the cows’ water supply. 

Joe and Danielle decided they would incorporate magnesium oxide into the transition cow diet to be fed on the feed pad and supplement the water with magnesium sulphate. The diet also included monensin to boost energy availability to the cows. 

The plan was adhered to religiously, and before calving, blood samples from springer cows were taken to assess magnesium status and fat mobilisation (NEFA). All of the blood results came back within normal limits, confirming that the mineral and energy status of the diet was adequate. 

Laboratory results are one thing, but practical results are often another. At the time of writing, the Kehelys have calved about 550 cows and have seen three cases of milk fever, a staggeringly low 0.57%. This compares to last season’s 6.1%. 

During calving, blood samples have been taken from cows on day four of the colostrum period to assess the success of the transition diet and management of at-risk cows. These supported the original diet in this case, but could easily have allowed for tweaks to be made if necessary. 

The Kehelys also used this routine visit as a time to catch up with the vet on animal health matters in general, and blood samples were taken for calves to measure how well the Far North team were managing the colostrum intake of their calves. 

Joe and Danielle were runners up for the share farmer of the year award, Northland. They won the DeLaval Business Performance Award and the LIC animal health and recording award 2023 too and so understand how a preventative approach can work. 

This preventive, rather than reactive approach to a relationship with the vet has worked well so far this season for the Kehelys and saved considerable time and animal health cost while boosting animal health and welfare. 

• Rory Dean is a large animal veterinarian with Kaipara Farm Vets and Dairy NZ Feed Right Adviser, as well as a member of the Australia and New Zealand College of Veterinary Scientists (Dairy Chapter).