By: Emily DeKlein, M.Sc. (in progress)
GVF Ruminant Summer Student
Grand Valley Fortifiers
Butterfat levels in dairy production are influenced by a complex set of factors, posing numerous challenges, particularly during the summer when butterfat values tend to decrease. Understanding butterfat composition is crucial for dairy producers aiming to maximize their milk cheque returns and maintain herd productivity/health.
In the context of dairy cow rumen health, biohydrogenation—a process conducted by rumen microbes—plays a central role in producing various fatty acids. Under normal conditions, biohydrogenation proceeds without disrupting milk fat synthesis in the mammary gland. However, certain risk factors can trigger an alternative biohydrogenation pathway, resulting in altered fatty acid intermediates that may inhibit milk fat synthesis. This can lead to milk fat depression (MFD), a common challenge in dairy herds. Factors such as genetics, season, physiological state, and especially diet impact milk fat concentration, contributing to its variability within and across farms.
Today, varying degrees of MFD are frequently observed in dairy herds, both in intensive and extensive systems. These levels are often below the cow’s genetic potential for milk fat production, indicating a dietary or environmental influence. Onset of diet-induced MFD typically signals a shift in ruminal fermentation and, in more severe cases, may be associated with ruminal acidosis and reduced efficiency in the rumen. Although increasing energy intake through concentrates can boost milk production, it may inadvertently harm rumen microbial balance, thus lowering butterfat levels. Addressing MFD requires careful management of risk factors, which are not the same across farms.
In this study, data collection involved both on- and off-farm evaluations. Onfarm assessments, for both core-farms and single-visit farms included analysis of feed particle size with the Penn State particle separator, corn silage quality, manure sieve evaluations, temperature/humidity monitoring, milk fatty acid analysis and an overall management questionnaire. Off-farm evaluations looked at ration composition, nutrient content, forage tests, and feed formulations. Key parameters such as genetics, herd health, and mammary health were not measured in this study but play significant roles in butterfat concentration.
Given the diversity of risk factors influencing butterfat, it’s essential to approach each farm individually. For instance, farms with high butterfat levels may exhibit strong feed management practices with minimal sorting, but the same may hold true for farms with lower butterfat levels. As a nutritionist, it is crucial to identify the unique risk factors for each operation and determine realistic butterfat targets.
Seasonal fluctuations also naturally reduce butterfat as a response to longer daylight hours and higher temperatures. Even in temperate climates with minimal temperature or humidity variation, milk fat synthesis in dairy cattle declines in the summer months. The extent of this decline is influenced by factors such as genetics, environmental stressors, and seasonal forage quality changes.
Results and Insights from Data Collection
Following the data collection process, approximately 200 parameters were analyzed to identify those most closely correlated with butterfat. To refine the analysis, herds were divided into the top and bottom 25% based on butterfat values, highlighting key factors with meaningful correlations.
Across the 77 farm visits, average butterfat was 4.07 kilograms per hectolitre, with an average milk yield of 38.75 litres per cow per day. Milk fatty acid analysis was conducted with core farms, collecting samples over five days prior to each farm visit. Strong correlations emerged between butterfat and specific milk fatty acid levels, suggesting a close relationship between fatty acid composition and butterfat.

Understanding the Role of Fatty Acids in Butterfat Composition
The study underscored that higher fatty acid levels correspond to higher butterfat, though understanding how these fatty acids interact offers deeper insights into cow health and productivity.
De Novo Fatty Acids: These fatty acids are not derived directly from the cow’s diet but are synthesized in the mammary gland using precursors produced by rumen microbes. High levels of de novo fatty acids are associated with effective rumen fermentation, supported by a diet rich in effective fiber and fermentable carbohydrates. Elevated de novo fatty acid synthesis generally indicates a healthier rumen environment and improved milk quality.
Mixed Fatty Acids: Originating from both dietary sources and endogenous production, mixed fatty acids contribute to milk fat’s fluidity and firmness. They essentially serve as a bridge between de novo and preformed fatty acids, adding stability and energy density to milk.
Preformed Fatty Acids: These fatty acids come from dietary fats or body fat mobilization, particularly during times of negative energy balance, such as early lactation. To support butterfat concentration, cows should receive adequate energy to minimize unnecessary fat mobilization. Controlled inclusion of dietary fats can also balance milk fat composition without causing MFD or metabolic issues.
On-Farm Trends and Best Practices for Butterfat Management
Analysis revealed key trends among herds with higher butterfat scores. Farms with higher butterfat typically experienced less feed bunk sorting, lower feed bunk temperatures, higher airflow at cow resting levels, more consistent manure scores, and a greater percentage of cows with an ideal manure score of 3.
For effective butterfat management, it’s beneficial to use these indicators as tools rather than strict standards. Regularly monitoring of various factors— such as feed management, rumen health, and cow comfort—can help identify areas for improvement. Milk fatty acid analysis is a strong tool, offering concrete insights into the sources of butterfat within the cow.
It was a great opportunity to work with an amazing group of people at Grand Valley Fortifiers. Special thank-you to the specialists and producers that assisted us with this project!
This article was written for the Winter 2024 Dairy Grist. To read the whole Dairy Grist, click the button below.