Editor's note: The following case was handled by Carl Old an independent nutritionist from LeGrand, Calif.

One of the herds that Carl Old works with wanted to reduce the amount of whole cottonseed fed in the ration to reduce feed cost. This particular herd decided to try an allocation of the whole cottonseed so the ration change would have minimal affect on overall herd performance. The cottonseed was dropped from the ration of cows that were 150 days in milk that averaged 110 pounds of milk.

However, once the ration changes were implemented, the overall butterfat content of the herd dropped significantly. On paper, the two rations were very similar (before and after the changes), but the cows said the rations weren’t. (It’s important to note that butterfat depression wasn’t noticed in pens where cottonseed remained the same.)

Old explains that the new rations were isonitrogenous, but carbohydrates replaced some, but not all of the fat. Differences in net energy intake, using NRC values, were 2.04 megacalorie (Mcal), which only explained 90 percent of the reduction in milk energy content. Current models assume an efficiency of metabolizable energy (ME) use for net energy of .62. Using this estimate indicated that ME intakes dropped by 3.29 Mcal. The normal pathway for fat synthesis from acetate has a maximum efficiency of .70. For a reduced ME intake of 3.29 Mcal and an efficiency of .69, predicted energy reduction is 2.26 Mcal, explaining all of the observed variation in milkfat.

Here are the two points that Old took away from this:

  • Models based on efficiencies published in various editions of the NRC publication “Nutrient Requirements of Dairy Cattle” may not accurately estimate feeds required for maintenance, milk production, tissue repletion and growth of the gravid uterus.
  • The best replacement for whole cottonseed is whole cottonseed. “Even at currents prices, whole cottonseed is worth it for the highest-producing cows,” he says.

Rations were readjusted and butterfat levels recovered.