Providing adequate mineral supplementation is an important topic to consider in a stocker operation. However, on irrigated pastures excess levels of certain nutrients can create other challenges. Soil phosphorus concentrations that are too high can increase the risk of sediment runoff too high in phosphorus that can potentially contaminate surface waters, according to University of Wisconsin researchers.

To avoid those issues, these researchers conducted a two-year study to determine if managed pastures could provide sufficient levels of nutrients without additional supplementation. They provided either a trace mineralized salt or a 67:33 mixture of trace mineralized salt and dicalcium phosphate to Holstein steers that were rotationally grazed on pastures consisting of cool-season grasses and legumes. In the first year of the study, the steers were grazed for 137 days, and in the second year, a different group of steers was grazed for 126 days. According to the researchers, phosphorus concentrations in the pastures averaged 0.25 percent, which is greater than the suggested P requirement for steers gaining 2.2 pounds per day. 

The results indicated no significant differences between the steers that received the phosphorus supplementation versus those that did not. There were no significant differences in body weight, average daily gain or free-choice supplemental mineral intake between the two treatment groups. As a result, the authors concluded that phosphorus supplementation is generally not necessary for grazing stocker cattle in Wisconsin or in several regions across the Midwest, as the forage alone contains adequate phosphorus concentrations.