FROM THE FARM REPORT: WHAT'S THE "NEW" NUMBER?

Have you noticed your milk fat numbers creeping up over the years? You’re not alone. Data from the Federal Milk Market Orders, including Order 1 (see figure) show a steady rise in both milk fat and true protein concentrations. While we still see seasonal ups and downs (peaking in winter and dipping in summer), the overall trend is clear: milk components are increasing. By improving animal genetics, feeding strategies, and herd management, we are producing milk with more value-packed components.

To keep pace with the changes in milk composition, farmers and their nutritionists are using tools to monitor and manage milk composition. One of the tools is milk fatty acid (FA) profiling. Thanks to advancements in mid-infrared (MIR) spectroscopy, we can now measure FA quickly and affordably as part of routine milk testing. The FA are grouped into:

• De novo FA (<16 carbons): made in the udder from volatile fatty acids (acetate and butyrate) produced during rumen fermentation of carbohydrates

• Mixed origin FA (16 carbons): de novo synthesis in the udder and from dietary fat

• Preformed FA (>16 carbons): from dietary fat and mobilized body fat, especially in early lactation

These FA groups tell us a lot about cow physiology, rumen health, diet composition, and management practices. For example, low de novo FA might signal a forage quality issue, subacute ruminal acidosis, or too much of the wrong type of dietary fat which are all factors that can lower milk fat synthesis. Farmers and nutritionists use FA profiles to troubleshoot low milk fat and track changes over time. Benchmarks are often based on historic within herd data or regression equations developed from other herds (Table 1). The equations were developed from datasets that represent groups of diverse herds in the US. Small changes in de novo or mixed origin FA can lead to meaningful gains in milk fat. For example, increasing de novo FA by just 0.1 g per 100 g milk can increase milk fat by 0.2 percentage units. About a decade ago, a common target for de novo FA was around 0.85 to 0.9 g/100 g milk to achieve 3.8% milk fat. But today, many herds are aiming for well over 4%. So, what’s the new number? The answer isn’t a single fixed value, it is dynamic and depends on the herd’s milk fat target.

Table 2 shows expected FA values for different milk fat targets based on regression equations developed from data from 167 Holstein herds across the US. Keep in mind that those equations were developed when average milk fat

was lower than it is today. In the Miner

Milk Lab, we’ve seen that the equations may not be as accurate for higher component-producing herds. We’re exploring a new approach of using the sum of de novo and mixed origin FA which usually make up about 65% of total milk fatty acids. For example, if your target milk fat is 4.3% then your combined de novo + mixed origin FA should be around 2.66 g/100 g of milk (4.3% milk fat x 0.95 x 0.65 where 0.95 is the proportion of milk fat that is fatty acids on average and 0.65 is the proportion of milk FA that are de novo and mixed origin). This method seems to better reflect the biology behind milk fat production and may be more reliable across a wider range of fat percentages.

We’re still testing this 65% idea and looking for more data from high component-producing herds across the US to revise the regression equations. Let me know what you think and if you’ve got data to share, we’d love to include them in our dataset.

— Heather Dann

dann@whminer.com