Fernando Díaz-Royón, DVM, and Álvaro García, DVM, PhD, South Dakota State University, say there is agreement between dairy producers and their nutritionists that the high fat concentration in distillers grains (DG) can result in milk fat depression.
Due to the high fiber content in DG, dairy nutritionists could be tempted to replace part of the forage neutral detergent fiber (NDF) with NDF from distillers grains. However, due to its small particle size, this fiber in DG is not “effective”, having a reduced capacity to stimulate cud chewing and rumination which would help maintain milk fat.
These factors can lead to rumen acidosis, which can compound the negative effects caused by the rumen load of polyunsaturated fatty acids. These effects have been reported in trials conducted by the Dairy Science Department at South Dakota State University.
From these studies, some practical recommendations can be drawn in order to maximize distillers grains inclusion without significant negative effects on milk fat yield or concentration:
1. Although formulating diets for adequate NDF concentrations is important, it needs to be accompanied by particle size assessment of the ration in cows fed a total mixed ration.
2. Although adding buffers to the diet (e.g. bicarbonate) can ameliorate the effects of low rumen pH, their effect is transitory and is not a substitute for adequate particle sized rations.
3. The amounts and fat composition of other feedstuffs included in the diet will dictate how much distillers grains can be safely included.
4. Even with adequate particle size, avoid the inclusion of more than 10% wet distillers grains products when fermented corn feedstuffs (e.g corn silage, high-moisture corn, etc.) constitute already 50% or more of the diet dry matter.
Read the full report and a synopsis of the South Dakota State University research on distillers grains and milk fat depression at http://igrow.org/up/resources/02-2012-2012.pdf.