Don’t Let Milk Fat Depression Go Undetected

Milk fat is a valuable, yet variable, component of the milk cows produce. And, while many dairies feed high-energy diets for optimal milk production, these diets can also increase the risk for milk fat depression.

What Is Milk Fat Depression?

Milk fat depression, or low-fat milk syndrome, is when a cow rapidly loses up to 50% of her milk fat yield without losing overall milk yield or other component yields.

Most cows show a significant decrease in fat within 10 hours of onset and achieve the point of lowest milk fat by day 3 or 4 in non-nutritional cases. The point of lowest milk fat takes longer to achieve in nutritional cases, typically occurring on day 7 to 18.

Milk fat depression is common in many herds, which means cows aren’t producing milk fat to their full potential and farmers are bypassing valuable component premiums. Because milk production and other components remain strong during milk fat depression, a loss in milk fat may go unnoticed. If it is noticed, pinpointing the cause can be a challenge because there are many nutritional and non-nutritional reasons for low milk fat content.

Causes of Milk Fat Depression

From a nutrition standpoint, several diet types put herds at risk for milk fat depression:

• Diets high in fermentable carbohydrates, including starch, and low in fiber
• Diets with high concentrations of unsaturated oils, typically plant-based including oilseeds and their by-products
• Pasture feeding at early growth stage and during spring and early summer
• Slug grain feeding under specific management conditions

These diets disrupt the normal biohydrogenation pathway, altering rumen fermentation and increasing trans fatty acid production. These fatty acids are intermediates in the biohydrogenation of polyunsaturated fatty acids and inhibit fat synthesis in the mammary gland.

Aside from diet, milk fat depression can also be the result of genetics, physiological state, and environment.

What To Do if You Suspect Milk Fat Depression

If milk fat depression is experienced, the first thing to do is look at the timeline of induction. This will help identify if its cause is more likely to be nutritional or non-nutritional.

Then, if dietary milk fat depression is suspected based on the longer timeline, the best approach is to systematically narrow risk factors – while maintaining milk production and energy intake.

A multi-step approach works best:

1. Evaluate diet composition and estimate the ruminal unsaturated fatty acid load (RUFAL). Minimizing unsaturated fatty acid intake may be a logical first step.
2. Evaluate if diet fermentability is higher than desirable. If it is, reducing fermentability and starch content may help minimize subclinical acidosis risk and improve rumen function, without losing milk yield. However, be cautious of shifts to reduce fermentability – especially when fermentability is within reason – because it could result in undesirable lost milk production.
3. Identify if a rumen modifier can be added to stabilize fermentation. MHA® Feed Additive is a methionine source that supports normal biohydrogenation of fatty acids. This helps reduce the risk of milk fat depression and promotes higher milk fat content.

Dietary changes should produce results within 10 to 14 days, but full recovery may take 3 weeks or more.

Minimize Milk Fat Loss to Maximize Income

Milk fat content is a key determinant of milk price and the profitability of dairy farms. Milk fat values above 4% are possible under European feeding conditions but many farms fall short of this ideal and short of their income potential.

Managing risk factors associated with milk fat depression can help cows efficiently reach milk fat goals and farmers capture the related premium for this valuable component.

Register to attend a two-part webinar series: Milk Fat Depression: What It is and Why It Matters and Is Milk Fat Depression Impacting Your Profits? to unlock additional insights on milk fat depression.

¹ Harvatine, K.J., Boisclair, Y.R., Bauman, D.E. “Recent advances in the regulation of milk fat synthesis.” Animal. 2009 Jan;3(1):40-54. doi: 10.1017/S1751731108003133. PMID: 22444171.

² Harvatine, K.J. “Managing Milk Fat Depression.” 2016.

³ Westricher-Kristen, E. “Improving rumen function with hydroxy analogue of methionine.” International Dairy Topics. 2024 (22:6).

Edwin Westreicher, Priv.-Doz. Dr. habil.

Growing up on a cattle farm started Edwin Westreicher with a lifetime of experience in the animal agriculture industry, which he is sharing with dairy customers in Europe, the Middle East, and Africa as technical services manager at NOVUS.