FAT content has been a casualty of the bias towards high protein levels in current milk pricing schedules, Dr Bob Elliot, DSM Nutritional Products, said.
Added to this was a greater incidence in cows of liver dysfunction, laminitis, elevated somatic cell counts and poor fertility rates.
"If you want to feed cows more protein, the three things are good cow condition, very good intakes and a lot of starch in the diet," Dr Elliot said.
"But essentially those three things, especially the last one, are not conducive to maintaining a healthy paunch in the animal, which is good for butterfat."
He said maximum fat concentrations occurred when a cow's rumen was alkaline, at about pH 6.7, while maximum protein concentrations occurred in an acidic environment, or pH 5.8.
"The modern cow doesn't possess more efficient biochemical pathways for producing milk - what the modern cow does is simply direct more of her energy towards milk production and less towards effort or maintaining her body reserves," Dr Elliot said.
He said increased rumen acidity produced trans-fatty acids, which inhibited the synthesis of fat in the udder.
The solution was feeding saturated fats, which unlike polyunsaturated fats, did not produce trans-fatty acids.
"We have a perfect source of saturated fat in palm kernel meal," Dr Elliot said. "When substituted into a protein-based ration, it routinely gives us a 0.5 or 0.8pc fat."
Palm kernel meal can substitute for lupins or barley, which do not contain saturated fats.
It is in limited supply in WA but will become more available as demand increases.
"If you want to get more fat, use palm kernel meal, it's as simple as that," Dr Elliot said.
He said farmers should bear this in mind when told to feed more grass.
"We actually need to get to more of a feedlot situation, especially when the energy deficit is greatest," he said.
He said wet by-products like finely chopped sileages and lush, wet grasses led to insufficient saliva production in cows, while increasing rumen acidity.
Even in pasture-fed animals without grain supplements, rumen pH could be well below pH 5.8 for a good part of the day.