Research Note
Milk Protein:
Target Yield Over Concentration
Beginning around 2010, the combination of genetics and nutrition accelerated the concentration of milk fat in U.S. milk. The protein-to-fat ratio plummeted, which was not problematic for the next decade-and-a-half given the high market value for milk fat. However, today’s milk markets put a much higher value on protein.
Even with advanced genomic selection, it’s going to take many bovine generations to increase milk protein concentration without impeding the gains made in milk yield.
Meanwhile — short term — what can nutritionists do to increase the protein:fat ratio?
First, do no harm, says Penn State’s Dr. Kevin Harvatine, particularly do no harm to milk yield.
“Keep in mind that the milk check rewards the yield of components, not their concentration. So the ‘rising tide’ of increasing milk yield ‘lifts all boats’, including milk protein. As others have pointed out, dietary changes that increase the concentration of milk protein but decrease milk yield are going to hurt the bottom line.
“Unlike for milk fat, at present we do not have as many nutrition tools to generate large changes in milk protein.”
Most of the recent work, Harvatine says, has been done around amino acid supplements, which are a useful tool that often will increase milk protein yield through increased milk flow rather than just increasing milk protein.
He notes that we can gain some insight into understanding the sources of variation: “The 10th and 90th percentile of test days in the DHIA database is 3.0% and 3.5%, respectively. The seasonal rhythm and herd genetic potential are the two biggest contributors and should be considered first to set accurate goals.”
Are there other dietary opportunities in the offing?
Harvatine points out that the mammary gland employs multiple distinct but coordinated “assembly lines” — fat, protein, and lactose — to synthesize milk. In this “factory”, regulation of lactose and protein are tightly connected. For example, the whey protein alpha lactalbumin is the rate limiting component of lactose synthesis. Selecting for higher milk protein disconnects lactose synthesis from casein synthesis, the major milk protein.
“In order to increase milk protein independent of fat and lactose, we need to understand how to tell the mammary gland to specifically make more casein and whey. We do not have a good understanding, but work 25 years ago showed important roles for energy signals, like insulin.
“However,” Harvatine adds, “while we’re trying to realize the potential to increase mammary protein synthesis, we may find that the rumen becomes the limiting factor.”
Meanwhile, before cow’s milk gets back to the “ideal” 0.79 protein:fat ratio, milk processors may re-engineer existing plants to add cream separators, co-locate separate cheese and butter processing, or make other changes to deal with the current 0.76-75 ratio.
Learn more at the upcoming Dairy Cattle Nutrition Workshop.
Questions?
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