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Virginia Cooperative Extension - Knowledge for the CommonWealth

Grouping lactating dairy cows into two or more feeding groups can reduce output of nitrogen and phosphorus

Dairy Pipeline: June 2003

Charles C. Stallings
Extension Dairy Scientist, Nutrition
(540) 231-4758

The trend over the last 10 to 15 years is for feeding one group of lactating dairy cows. The reasons are many but center around keeping feeding simple, cheap feeds, and herd size. Interestingly the recent trend has been for grouping of dry cows into two groups, far-off and close-up. When feeding one group of lactating dairy cows we tend to balance the ration for the higher producers in the group. This is with limitations because it is difficult to balance energy in rations for more than 100 lbs. of milk per cow per day. The high producing dairy cow will use body fat deposits to make up any shortage. This is not the case with protein, so we sometimes feed high amounts for high producers resulting in overfeeding of lower producers. This directly results in more nitrogen being excreted in the urine and feces. The same is true for phosphorus except most is excreted in the feces. Phosphorus is many times over supplemented according to a recent Virginia survey and the 2001 NRC publication. Both nitrogen and phosphorus can be problems in the environment. Feeding two or more rations to lactating dairy cows will result in a better match of ration nutrient concentration and the cows' requirement resulting in less nitrogen and phosphorus being excreted. A cow will many times drop in production when switched from a high group ration to a low group ration. One suggestion is to not change nutrient density by more than 15%. This translates to 15.7% protein when a high group ration of 18.5% protein is fed. Early lactation cows should be kept on the high group ration for at least one to two months to achieve milk production potential. After this time they should be grouped by production considering reproductive status in some cases. Another way to consider ration formulation is to balance rations for 30% above average for one-group herds, 20% for each group of a two-group herd, and 10% for each group of a three-group herd. These numbers are based on lead factors we developed in the 1980's for computerized ration formulation. The more groups we have the more similar the production within each group and the more similar the nutrient requirements. As we develop nutrient management plans for dairy farms it may be advantageous to consider grouping the lactating cows in order to reduce nutrient excretion.

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