Hot topic: Fat, from fatty acid nutrition to milk fat
By: John Goeser, PhD, PAS & Dipl. ACAN, Rock River Laboratory Animal Nutrition, Research, and Innovation Director
Over a portion of the summer season, milk components declined (both milk protein and fat content) and butterfat value rose to a premium level, accounting for nearly 60 percent of the Class III milk price (John Geuss, July 2017; Accessed online at http://milkprice.blogspot.com/2017/07/june-class-and-component-prices-rise.html). This seasonal milk fat decline, coupled with the fact that fat accounts for a majority of producers’ milk payments and marginal milk prices, has put fatty acid nutrition and fat tests in the focused crosshairs of nearly all producers and their nutritionists.
We (the dairy industry) have come to understand that specific long-chain fatty acids can impact diet metabolism and energy partitioning, beyond just calories. I have not historically focused on fatty acid nutrition, nor do I consider myself an expert. Yet, I’m finding myself concentrating on this area more due to advancing research (from Prof. Adam Lock of Michigan State University, and others), nutrition technologies, and dairy economics. I’ve gone back to my human nutrition (biochemistry) notes from grad school to revisit the impact fatty acids may have on metabolism, beyond calories, as I see the dairy industry moving in this direction. Similar to how nutritionists now formulate for specific amino acids (i.e. Lysine and Methionine), the dairy nutrition industry is transitioning towards better recognizing and feeding specific fatty acids.
Long-chain fatty acids
The focal point of all this recent interest in fatty acids is long-chain fatty acids, meaning 16 to 22 carbons in length. The 16 and 18 carbon fatty acids are predominant in dairy diets (Lock and de Souza, 2017). You may recognize a few:
Palmitic (C16:0) fat has become much more prevalent in diets, with some recognizing increased butterfat in part to the addition of this fat. However, this fat supplement may alter energy partitioning in the cow.
Stearic acid (C18:0) is the major fatty acid in tallow, and likely leads to poor fat digestibility (Lock et al., 2005; Dr. Neil Michael, personal communication).
Oleic acid (cis-9 C18:1) is a fat within supplements that likely improves total fat digestion by creating a more digestible fatty acid profile, which is better absorbed than some others (Lock and de Souza, 2017; Dr. Kevin Murphy, personal communication).
18-carbon fatty acids
The 18-carbon fatty acids with double bonds (Oleic, Linoleic, and Linolenic) can positively or negatively affect animal performance. The C18:2 (two double bonds) and C18:3 (three double bonds) fatty acids are biohydrogenated into C18:0 (no double bonds) by rumen bacteria. If all goes well, the C18:0 is used by the dairy cow. Yet when undergoing milk fat depression, we now understand that an inadequate rumen fat breakdown creates a negative intermediate fatty acid (trans-10, cis-12 C18:2, Conjugated Linoleic Acid (CLA)) that decimates milk fat content and dairy profitability.
More comprehensive routine NIR tools are now available to investigate nutrition (Total Mixed Ration (TMR)) contributors to milk fat depression, such as TMR fatty acid content and profile, and extensive in situ rumen starch digestion measures. These TMR measures can help nutritionists better quantify the Rumen Unsaturated Fatty Acid Load ((RUFAL); Oleic + linoleic + linolenic acid contents; Dr. Tom Jenkins, personal communication).
Recently, several nutritionists with whom I work in support of have found both excessive rumen starch digestion, and RUFAL, as contributing factors towards less-than-ideal milk fat content within their client herds. In one example, despite the TMR being only 23 percent (of Dry Matter (DM)) starch, the rumen starch digestion was nearly immediate, leading to over 22 percent rumen degradable starch (% of DM; well beyond the 85th percentile for TMR, which is about 19.4% of DM). In this case, faster digesting starch was not hurting the cows, but likely slightly altering rumen pH and fatty acid biohydrogenation, creating more CLA and milk fat depression.
In another situation, the starch digestion was moderate, however the RUFAL was well beyond what the rumen could process due to oilseeds in the diet. In this situation, the overload in RUFAL meant more CLA passing out of the rumen, and depressed milk fat levels.
These situations fascinate us for two reasons: 1) Our fatty acid nutrition understanding continues to evolve at a rapid pace, better explaining animal performance and, 2) We are better able to advise dairies now than even two years ago, incorporating hard data (i.e. rapid TMR fatty acid and nutrition detail), as well as economics, into our decision-making strategies. This evolution of industry progress and research will continue. I’m confident that as it does we can in turn improve our nutritional abilities to counteract and proactively avoid milk fat depression on-farm – helping bring more to the bottom line of the farmer.
References
Lock, A.L. and J. de Souza. 2017. Update on fatty acid digestion and metabolism and impacts on milk production. Proc. Tri-State Dairy Nutrition Conf. Apr 17-19, 2017. Fort Wayne, IN.
Lock, A.L., K.J. Harvatine, I.R. Ipharraguerre, M.E. Van Amburgh, J.K. Drackley and D.E.
Bauman. 2005. The dynamics of fat digestion in lactating dairy cows: what does the literature tell us? Proc. Cornell Nutrition Conf. pp. 83-94.
