Perspectives and Commentary: Fat nutrition and metabolism of early-lactation dairy cows

Abstract

Purpose

My objective was to review key factors involved in identifying and characterizing how dairy cows metabolize fat sources and their resultant effects on DMI, milk fat depression, and body condition, with emphasis on early lactation. Thus, short-term, mid-lactation studies were not included.

Sources

The main sources of information were peer-reviewed journal articles, some dairy nutrition conference proceedings, a monograph, several abstracts, a still pertinent periodical article (Lock and Bauman, 2007), and 50 yr of research and field experiences in this area.

Synthesis

Forms of fat, such as triglycerides or free fatty acids whether unsaturated or saturated, affect DMI, milk fat depression, and body condition. The more unsaturated that fatty acids (FA) are, especially the amount of linoleic acid, the more negatively these facets are affected.

Conclusions and Applications

Know what kinds of fat sources are being fed. What is the FA composition of feedstuffs fed and fat sources, especially the UFA and their levels? The more UFA sources there are, the more DMI and milk fat percentage may be negatively affected. Linoleic FA is a key marker for these negative effects, which may ensue if daily intake of linoleic acid is 300 to 400 g or more. This can be exacerbated by other factors such as low dietary forage levels, greater starch, wet forages, and finely chopped forages, which all contribute to lower rumen pH, which facilitates milk fat depression. Reduction in DMI is the major consideration when fat supplementation occurs, with digestibility of fat supplements being a secondary consideration. Either palmitic or stearic acid above 80%, but especially above 90%, in a fat supplement is of concern and may be less digestible because they can become more crystalline. This can also be a factor when physically blending these single sources together. However, if these 2 FA sources are melted and then prilled, this crystalline formation is not likely to occur. Palmitic and stearic acids melted together and then prilled incorporate the complementary benefits of both, potentially in ratios of 1:1 to 2:1, palmitic to stearic acid.