There are numerous nutritional, feeding management, and milk equipment problems that can affect milk fat and milk protein. DAIReXNET has a fact sheet on troubleshooting low milk fat problems. Managing Nutrition for Optimal Milk Components

Low milk protein can reflect a low energy diet.

Some questions to answer first are:

1. Is the problem affecting the whole herd or just groups of cows?
2. How long has it been a problem?
3. Has particle size been evaluated on the total mixed rations (TMR) and refusals?
4. Have forages and the TMR been analyzed recently? (If not, this should be done.)
5. Are all high moisture ingredients being checked routinely for dry matters?
6. What is the fat level in the diet, and what are the fat sources?
7. In component-fed herds, how much grain is being fed at one feeding?
8. How often is grain being fed?
9. What is the feeding sequence?

Typically, there is more than one issue affecting milk fat and milk protein. An in-depth evaluation of the herd is usually necessary to determine the problem(s).

Mike Hutjens, Extension Dairy Specialist, University of Illinois - Illini DairyNET