How To Identify Milk Drop Syndrome in Dairy Cattle

2 October 2023

Milk drop syndrome is a common problem, and a seasonal peak is often seen during the autumn and winter, although it can occur all year round. However, identifying the root cause can be quite a challenge as it can be caused by various and combined factors.

Identifying the syndrome is the first step towards resolving the issue. It should not be confused with the problem of poor milk production across the herd. To define and identify milk drop syndrome in the herd you should be looking for a drop in milk yield in individual cows alongside a fever, with or without diarrhoea, in 5% or more of the herd in a one-week period. The drop in milk yield in individual cows will be significant - a decrease of 25% or more over one or more days.

The Causes of Milk Drop

The syndrome can be caused by multiple factors and can occur as a result of nutritional issues, infectious disease, management or environmental factors (such as heat stress) or a combination of some or all of these. Involving both your vet and nutritionist quickly will help to identify the possible nutritional and infectious disease related causes.

Nutritional Causes

Nutritional changes can make animals more prone to milk drop syndrome. For example, cows that have just moved from a grass-based diet to a housed, silage-based diet could be more predisposed to it. In addition, changing silage clamps, eating the front of silage clamps (as there are more issues with forage spoilage and keeping quality here), digestive upsets and acidosis can all be common and potentially lead to milk drop syndrome.

The symptoms of acidosis are similar to that of milk drop syndrome – reduced milk output, varying or reduced dry matter intake and diarrhoea, so it should be investigated as a possible cause in the first instance. Clinical ketosis, although quite rare, will also cause a sudden drop in milk production. Monitor the incidence of transition diseases against herd targets. If affected cows are very early in lactation, it is worth ruling out transition diseases as the cause if production is less than you expected.

Monitoring rumination rates can help with early detection of a health issue that may make cows more prone to milk drop syndrome. Rumination collars or ear tags can quickly pick up a drop in rumination time, often before clinical signs are evident. In the absence of rumination monitoring devices, manually counting cud chews (target 55 chews or more before swallowing) or assessing the percentage of cows ruminating (target 60% or more of your cows lying down should be chewing the cud) can give a good guide to rumen function and whether acidosis is present in the herd. In turn, this can help prompt a timely check on the ration being fed.

Lastly, mycotoxins should not be ruled out if there is thought to be an issue with forage quality, secondary fermentation, signs of mould on feeds or heating of forages and the TMR (Total Mixed Ration). Any presence of mycotoxins can be confirmed by carrying out TMR analysis.

Infectious Disease

There are a number of diseases that are implicated in milk drop syndrome. These include adult respiratory diseases such as Infectious Bovine Rhinotracheitis (IBR), Bovine Respiratory Syncytial Virus (RSV), although this is rare, as well as influenza viruses and husk in herds that have grazed. Both husk and IBR can cause significant milk drop and leptospirosis, Salmonella dublin and winter dysentery have also been linked with milk drop.

Winter dysentery is becoming more common in dairy herds and is thought to be a highly contagious intestinal disorder. Many believe it may be caused by a coronavirus. It affects adult cows mainly during the winter months. It has similar symptoms to milk drop syndrome, including profuse diarrhoea, a significant and sudden drop in milk yield, weight loss and depression.

In addition, there is often a seasonal autumn peak in the number of Mycoplasma wenyonii cases which also causes milk drop. This can be identified in individuals displaying swollen legs (see picture below) and swollen teats. Lethargy and poor feed intakes are also indicative of this. Exactly how this is transmitted between animals is not entirely understood but it is thought to be spread by flies. It affects red blood cells. Clinical signs will gradually disappear, though a full recovery can take up to10 days or longer. As midges are still active at this time of year, Schmallenberg should not be ruled out either when investigating the infectious causes of milk drop.

Swelling associated with Mycoplasma wenyonii infection (picture A) and an unaffected hindlimb (picture B)

Source: Strugnell, B & McAuliffe, l. 2012. Mycoplasma Wenyonii Infection in Cattle. In Practice, 34: 146-154.

What To Do If You Suspect There is Milk Drop In Your Herd

Diagnosing the root cause of milk drop syndrome can be challenging. There are many potential causes, both infectious and non-infectious. Good herd information is key to making an early and accurate diagnosis. In the majority of cases affected animals will also show symptoms other than milk drop, such as diarrhoea or respiratory distress.

If you suspect acute disease with a cluster of cases of significant milk drop you should contact your vet immediately to discuss the best means of further investigation.
It is also worth consulting your nutritionist to review the ration to rule out any nutritional causes.
In addition, bear in mind the fact that environmental stress and/or changes in management can play a significant role too.