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Aspects contributing to the butterfat depression

Author: Dr. Adam Lock, Michigan State University

It is not uncommon to see a butterfat drop of up to 0.5% over the spring–summer period in grazing dairy cows. This can occur in the absence of significant signs of acidosis and lameness, so, over the last number of years, we have begun to examine the relationship between the cow's diet, how it reacts in the rumen and its effect on butterfat depression. Understanding this relationship has allowed us to troubleshoot low butterfat and minimise the initial risk. While many factors affect butterfat percentage, one such issue is the oil or fat content of grazed grass.

More oil, more effect

Most fats/oils contained within plants are unsaturated, while the fats contained in milk and butter are saturated. Unsaturated fats are toxic to the rumen bacteria, and in order for them to survive, they go through a process called ‘biohydrogenation.’ This process creates by-products, which, in effect, stop the udder from producing butterfat. Grass, which can have especially high oil content in that late spring/summer period, can cause this butterfat depression. The degree of butterfat drop is “dose” dependent, so the more oil in the grass, the larger the effect. Research has shown that the more leaf, or the ‘lusher’ grass is, the higher the fat content. Also, the more nitrogen we use in our pastures, the higher the fat content, creating an even larger effect.

Maintain rumen health

While we cannot eliminate these issues in full, we can minimise their effect by allowing the rumen to do what it does best: creating a good rumen environment. This is achieved through maintaining a good rumen pH, maintaining adequate fibre levels in the diet and avoiding the over-feeding of starch-based ingredients. This will allow the cow to handle higher levels of fats/oils.