A meta-analysis was conducted to quantify production responses to chromium (Cr) supplementation and better understand variables that affect this response. Multivariate random and mixed effects models were used to develop and fit all models. The response variable was described by the mean difference of milk yield, ECM, DMI, and milk fat and protein yields between cows that received Cr supplementation and cows in the control group. Treatment means from 28 studies were used to assemble a database of studies designed specifically to investigate the effects of supplementing Cr on dairy cows. Of the 93 treatment means, 38 means fed the Cr starting in the dry period. Overall, Cr supplementation increased production, and the mean difference is affected by stage of lactation (characterized by DIM in our analysis), Cr source (Cr-methionine, Cr-propionate, Cr-chelate, Cr-picolinate, Cr-yeast), and dose (0-19 mg/d). The models for milk yield, milk fat, and milk protein suggest the greatest response for Cr supplementation between a 6 to 7 mg/d supplementation rate. However, the greatest response for DMI was predicted to be at a supplementation rate of 9 mg/d. The models suggest peak mean differences in yields of milk, ECM, fat, and protein at approximately 100 DIM with supplementation of Cr starting at pre- or postcalving. Although the production of ECM maximizes at approximately 100 DIM there is still a benefit in production to feeding Cr up to 168 to 186 DIM, depending on the Cr source.
Roman-Garcia et al. (Sun,) studied this question.