What you, as nutritionist, formulate for your clients' herds is not always what the cows receive. Variability in rations is a big issue. The potential for variation, based on the mixing equipment alone, can impact cow performance.

Then, there is weather and human error. Researchers from the Veterinary Medicine Teaching and Research Center in Tulare, Calif., looked at the variation in nutrients formulated and nutrients supplied on five California dairies. The five dairies represented TMR rations formulated by four nutritionists. Overall, the most variation in nutrients was for the close-up TMR, followed by iron, copper and zinc for the high-producing-cow TMR, and niacin, copper and zinc for the fresh-cow TMR, researchers wrote in this month’s edition of Journal of Dairy Science. But it wasn't just micronutrients that were affected; there were high coefficients of variation for macronutrients such as fat and lignin.

"Lignin was high probably because rations are not generally formulated for lignin... variability in fat content may represent variability in premix nutrient content or degree of mixing of a TMR," they wrote.

Variation in lignin, fat and ash has an impact on milk yield, milkfat percentage and milk protein percentage.

"Therefore, lignin, fat and ash may be the best indices of feed management to include effects of variability on variability in milk yield, milkfat and milk protein percentages in ration formulation models," the researchers wrote.

With a better understanding of variation, computer models can be improved. "As feed management is an important factor in nutrient supply and milk production, it should be incorporated into ration formulation," the researchers concluded.

Read the abstract