Minimize milk fat depression in the heat of summer

By Barry Visser
Enhancing milk fat is beneficial to animal performance and farm profitability. Today, butterfat accounts for more than half of your milk check. Production goals are often based on combined milk fat and protein yields. Although the dog days of summer may not be an ideal time to improve milk fat, several factors may help you minimize your decline.

I recently had an opportunity to participate in a couple roundtable discussions with Dr. Kevin Harvatine, associate professor of nutritional physiology at Penn State University, to discuss the dynamics of milk fat synthesis. Much of his research focuses on the risk factors for milk fat depression.

Summer is tough
Most dairy producers and nutritionists recognize a seasonal pattern to milk components.

“Expect the seasonal rhythm of milk fat concentration to be about 0.25 [percentage] units lower in July than it was in January,” Harvatine said.

Butterfat will vary by stage of lactation and breed. Genetics plays a key role in herd butterfat levels. Most genetic indexes place an emphasis on higher component milk.

Inconsistent feeding time or variation in feed distribution can impact meal patterns and promote slug feeding. Cow comfort and stocking density can negatively impact resting time, resulting in lower butterfat. Heat abatement strategies are critical to success this time of year and can promote more consistent intakes and cow comfort.

Vegetable oils
Too much vegetable oil has been shown to negatively impact milk fat. Ingredients we typically see in the upper Midwest that contain high levels of readily available vegetable oil include distillers grains, hominy feed, whole soybean, and some bakery and candy byproducts. Wet corn sources contain moderate levels of vegetable oil, but we generally feed higher levels as part of a greater dietary or agronomic strategy. The corn grain contribution in corn silage, high moisture corn, earlage or snaplage can attribute a significant level of readily available oil. This becomes an even greater risk factor to milk fat depression months after harvest when starch availability reaches its peak, potentially impacting rumen pH.

When the unsaturated (liquid) fatty acids contained in the vegetable oil in these ingredients enter the rumen, rumen bacteria try to convert them to saturated (solid) fatty acids found in tallow and butter. This process of fatty acid conversion is called biohydrogenation and it occurs via two pathways.

The normal pathway of fatty acid conversion has no negative effects on milk fat production. The altered pathway produces some intermediate fatty acid compounds that have a very dramatic and powerful negative effect on milk fat production if they escape the rumen and are absorbed in the gut. In fact, just a few grams of these intermediates can decrease milk fat by more than 0.5 percentage units.

Milk fat depression occurs when the preferred (normal) pathway is overwhelmed with more vegetable oil than it can metabolize and/or when cow’s rumen pH is lowered.

Healthy rumens and feeding for milk fat
Certain levels of effective fiber are necessary to promote cud chewing and rumination. Particle size and digestibility of forage fiber impact total intake of neutral detergent fiber. Adequate forage NDF intake relates directly to rumen pH, and rumen pH is linked to milk fat.

A healthy rumen environment minimizes wide fluctuations in rumen pH through balanced carbohydrate nutrition, which leads to the formation of more acetate and butyrate. Acetate and butyrate are volatile fatty acids that serve as precursors to de novo milk fat. This process is good for the cow.

When addressing a milk fat depression challenge, the first steps generally involve minimizing or removing feed ingredients containing the high levels of readily available vegetable oil. Reducing the amount of vegetable oil reduces the potential amounts of the intermediate fatty acid compounds. In some cases, it may be necessary to reduce or replace some of the corn sources.

Feeding elevated levels of sodium and potassium or rumen modifiers, such as yeast and direct-fed microbials, can be beneficial to improving milk fat. Work with your feed team and nutritionist to evaluate feed ingredients and management factors that may contribute to greater stability in rumen pH.

Taking steps to support rumen health and beneficial microbial balance will help improve dairy efficiency and optimize dairy cattle performance, including milk fat concentration, during hot summer months. Do not forget the power of cow comfort in promoting consistent intakes and adequate lying time.

This article was originally written for Barry Visser’s July column in Dairy Star.  Click here for the original article.

About the author:  Barry Visser is a dairy technical specialist based in Minnesota.  He grew up on his family’s dairy farm in northwest Minnesota.  Visser received his bachelor’s degree in animal science from the University of Minnesota in 1994.  He worked as a dairy nutritionist for four years before returning to graduate school to earn his master’s degree in dairy cattle nutrition.  His research focused primarily on transition cows and minimizing pre- and post-calving metabolic challenges.  While a graduate student, Visser also worked as an assistant herdsman for the University of Minneosta St. Paul dairy herd.  At Vita Plus, Visser works with fellow employee owners to troubleshoot farm nutrition, forage quality and management challenges.