*Rick Grant is president of the William H. Miner Agricultural Research Institute in Chazy, N.Y.

PRODUCING milk with greater fat and protein content enhances herd profitability. In fact, the amount of milk components produced daily explains more than 50% of the variation in net income over feed costs among dairy farms (Bailey et al., 2005; Karszes and Howland, 2015).

Nutrition and feeding management that optimize rumen function help boost milk production and milk component percentages and yield (Stokes et al., 2000). A group of scientists led by Dr. Dave Barbano at Cornell University has been studying the link between nutrition and on-farm management, rumen function and milk composition with an initial focus on bulk tank milk sampling.

De novo fatty acids

The percentage of milk de novo fatty acids — those synthesized in the mammary gland — is positively correlated with the percentage of fat and true protein in the milk (Barbano et al., 2014). De novo fatty acids explain nearly one-half of the variation in milk fat percentage and about 68% of the variation in milk true protein.

These short-chain fatty acids (C4 to C14) comprise about 20-30% of total milk fatty acids. De novo fatty acids reflect rumen functioning — especially fiber fermentation that produces acetate and butyrate, which are the building blocks of these short-chain fatty acids. The relative amount of de novo fatty acids in milk fat is a barometer of how well the cow is being fed and managed for optimal rumen fermentation.

There are also preformed, long-chain fatty acids (C18:0, C18:1 and C18:3) that make up about 35-40% of total fatty acids and the mixed group of fatty acids (C16) that comprise about 35%. Recent innovations allow the rapid measurement of these milk fatty acid groups using mid-infrared technology (Barbano and Melilli, 2016).

Ongoing research is attempting to define the optimal relationship among these three fatty acid groups that results in the highest milk component output. At the most recent Cornell Nutrition Conference, Barbano and Melilli (2016) proposed that Holstein herds need to achieve a concentration of de novo fatty acids greater than 0.85 g/100 g of milk to maintain a fat test greater than 3.75% and true protein greater than 3.10%. Likewise, mixed fatty acids should exceed 1.40 g/100 g of milk.

Rumen pH, milk composition

Several nutritional factors play well-known roles in altering milk fat composition, such as dietary fat content and its composition, fermentable carbohydrates and forage particle size (summarized in Woolpert et al., 2016a).

However, the role of management has been much less clear. Many factors influence rumen fiber digestion and microbial protein production. Rumen pH has a large impact on fiber fermentation and nutritional factors such that too much rumen fermentable starch will lower pH and decrease both the rate and extent of fiber digestion. Additionally, poor feeding management can negatively influence rumen pH if it results in slug feeding and other unnatural feeding behaviors.

What has become evident recently is that feeding or management practices that degrade the rumen environment — notably, anything that reduces pH — result in a shift in rumen biohydrogenation to an alternate pathway, and trans-10, cis-12 conjugated linoleic acid (CLA) accumulates. Small amounts of this CLA isomer have a powerful milk fat-depressing effect (Harvatine and Bauman, 2011).

Even small changes in rumen pH can influence milk fat. As little as a 0.10 reduction in rumen pH can translate into a 0.10 decrease in milk fat associated with the shift in CLA isomer production (Jenkins and Prokop, 2013).

So, a critical question becomes: What management practices enhance rumen conditions, as reflected by the de novo fatty acid content of the milk?

Nutrition, farm management

Woolpert et al. (2016b) visited more than 70 farms in northern New York and Vermont, assessed their management and feeding practices and compared this information with their bulk tank milk compositions. Herds were categorized as either high or low in de novo fatty acids.

Nutritional and management factors that were consistently associated with greater de novo milk fatty acids and higher milk fat and true protein content included:

* Stocking density. Herds with higher de novo synthesis were 10 times more likely to have feed bunk space of at least 18 in. per cow and five times more likely to have a stall stocking density of less than 110%.

The relationship between stocking density and de novo fatty acid content in milk makes sense, given that overstocking increases the feeding rate and aggression at the feed bunk, depresses rumination and increases the risk for lower rumen pH.

In fact, recent work from The Miner Institute (Campbell and Grant, 2016) found that overstocking has a greater negative effect on rumen pH than lower dietary physically effective neutral detergent fiber (peNDF).

* Feeding frequency. High de novo freestall farms were five times more likely to feed twice a day, which presumably resulted in better rumen conditions for microbial fermentation. For tie-stall farms, high de novo farms were 11 times more likely to feed at least five times per day (many were component-fed herds).

* Dietary fiber. High de novo herds were 10 times more likely to feed a total mixed ration with greater than or equal to 21% peNDF (as a percentage of dry matter). This is not surprising, given the long-established relationship among dietary effective fiber, rumen pH and microbial fiber fermentation.

The Bottom Line

The de novo fatty acid content of bulk tank milk is positively correlated to milk fat and true protein output on commercial dairy farms. In the future, mid-infrared technology will be used to routinely monitor milk for the proportions of de novo, mixed and preformed fatty acids.

Overcrowded freestalls, limited bunk space, reduced feeding frequency and insufficient dietary fiber are associated with reduced de novo fatty acid synthesis and overall lower milk fat and true protein content.

References

Bailey, K.E., C.M. Jones and A.J. Heinrichs. 2005. Economic returns to Holstein and Jersey farms under multiple component pricing. J. Dairy Sci. 88:2269-2280.

Barbano, D.M., and C. Melilli. 2016. New milk analysis technologies to improve dairy cattle performance. In: Proceedings of Cornell Nutrition Conference for Feed Manufacturers. Oct. 18-20. Syracuse, N.Y. p. 61-71.

Barbano, D.M., C. Melilli and T.R. Overton. 2014. Advanced use of FTIR spectra of milk for feeding and health management. In: Proceedings of Cornell Nutrition Conference for Feed Manufacturers. Oct. 20-22. Syracuse, N.Y. p. 105-113.

Campbell, M.A., and R.J. Grant. 2016. Interactions between the feed and feeding environment. In: Proceedings of Cornell Nutrition Conference for Feed Manufacturers. Oct. 18-20. Syracuse, N.Y. p. 49-60.

Harvatine, K.J., and D.E. Bauman. 2011. Characterization of the acute lactational response to trans-10, cis-12 conjugated linoleic acid. J. Dairy Sci. 94:6047-6056.

Jenkins, T., and W. Prokop. 2013. You control milk fat depression — Don't let it control you. In: Proceedings of Western Dairy Management Conference. March 6-8. Reno, Nev. p. 238-248.

Karszes, J.K., and B.L. Howland. 2015. Understanding net milk income over feed costs and its impact on profitability. Dairy Business East. 7:22-24.

Stokes, S.R., D.N. Waldner, E.R. Jordan and M.L. Looper. 2000. Managing milk composition: Maximizing rumen function. Publ. L-5389. Texas Agricultural Extension Service, Texas A&M University System.

Woolpert, M.E., H.M. Dann, K.W. Cotanch, C. Melilli, L.E. Chase, R.J. Grant and D.M. Barbano. 2016a. Management, nutrition and lactation performance are related to bulk tank milk de novo fatty acid concentration on northeastern U.S. dairy farms. J. Dairy Sci. 99:8486-8497.

Woolpert, M.E., H.M. Dann, K.W. Cotanch, C. Melilli, L.E. Chase, R.J. Grant and D.M. Barbano. 2016b. Management practices and dietary physically effective fiber are related to bulk tank milk de novo fatty acid concentration on Holstein dairy farms. J. Dairy Sci. 99 (E-Suppl. 1):592 (Abstr.).

Volume:88 Issue:12