As cows are fed different rations based upon stage of life, they are also grouped according to age. But not all cows have the same amount of daily dry matter intake compared to their pen mates. Pens are fed according to number of cows present, resulting in steady intake of feed. Feeding cows in groups helps minimize the daily variability in pen intakes, which in turn helps mitigate errors involving feed availability and issues with excessive amounts left in the bunk at the end of the feeding cycle, said University of Florida researchers Jose Eduardo Santos and Mariana Nehme Marinho in a Dairy Update newsletter.

To closely manage feeding, measuring weigh backs and refusals accordingly can help calculate gross feed efficiency. This allows farmers to adjust feed mixes based upon the amount of weigh backs incorporated into the mix. “Relative to the diet offered, the weigh backs often have 1 to 2 percentage units less protein, 3 to 4 percentage units less starch, 5 to 6 percentage units more neutral detergent fiber, and longer particles,” said the researchers. Moisture content varies based upon season, particularly during the summer when sprinklers may be in use and result in wet feed.

If you are incorporating weigh backs into your daily ration, it is important to ensure you are feeding them to the correct group of cows. Because different groups receive different rations, some weigh backs deviate in nutrient content and may not be suitable for certain groups of cows. Lactating cow diets are generally high in potassium, phosphorus, and sodium, which add to the risk of hypocalcemia if this ration is used in close-up diets. Because of this, close-up cows should not receive any weigh back in their ration. Far-off diets don’t require as much protein, fat, and starch as a lactating diet. Therefore, the far-off pen should not consume weigh backs either, Santos and Nehme Marinho said.

Similar in price to a growing heifer diet, weigh backs may be used in a growing heifer diet but should not make up the entire ration due to the high protein, fat, and starch contents. “The weigh back could be an ingredient of the diet fed to heifers, but not the main ingredient, otherwise it will result in excessive weight gain and overconditioned heifers,” Santos and Nehme Marinho noted. Feeding weigh backs to heifers could also run the risk of compromising heifer development.

So, what group should you feed my weigh backs to? “Including them as part of the low-cow diet probably represents the best use of weigh backs in most farms,” the researchers cited. Feeding lactating weigh backs to low cows has been determined to be the lowest risk and most economical choice. Still, they should make up less than 20% of the total ration.