A research study published in the May Journal of Dairy Science looked at the effect of supplementing cows from 60 days pre-partum through 60 days postpartum with 0 or 30 milligrams per kilogram of supplemental iron from iron amino acid complex.
In the study, all animals were changed to pre-fresh diets at 14 days before anticipated calving and then to lactating diets following calving; iron supplementation rates remained constant.
Hematocrit, hemoglobin, serum iron, unsaturated iron binding capacity and percentage iron binding saturation were measured at the start of the experiment, seven days before calving, seven days after calving and at 60 days in milk.
Iron supplementation did not affect any measure of iron status and values did not change greatly over time. Milk production, milk composition and dry matter intake were not affected by treatment. However, somatic cell count was reduced when cows were fed supplemental iron (114,000 cells/ml vs. 94,000 cells/ml).
The limited response to supplemental iron may have been because basal diets were adequate in iron (ranging from 282 to 336 milligrams of iron per kilogram of dry matter) even though most of the basal dietary iron was provided by forages, which are generally considered poor sources of available iron.
There may be additional benefits to supplementing rations with iron. At the recent California Animal Nutrition Conference, Mike Socha, research nutritionist with Zinpro Corp., said, anecdotally, several nutritionists throughout the U.S. have also reported improvements in cow performance and fertility when supplementing cows with approximately 30 parts per million of supplemental iron or giving cows iron injections.
Generally, herds responding to the supplemental iron are fed no animal by-products, and dairy personnel report cows craving dirt. "I would not recommend supplementing iron across the board, but in some feeding situations," notes Socha. More research on iron supplementation is needed.
Socha goes into more detail in his paper here.