Case Study: Effect of iron amino acid complex on the performance of lactating dairy cows on a commercial dairy

Lactating Holstein cows (n = 506) were used in a randomized design to determine the effect of supplemental iron on milk SCC, milk yield, and milk composition. Cows were housed in naturally ventilated freestall barns or loose housing with open lot access and milked and fed twice daily. Treatments consisted of a basal TMR (control, CTL) or CTL supplemented with 600 mg/d per cow of Fe as iron AA complex (IRN, Availa-Fe, Zinpro Corp., Eden Prairie, MN). Treatments were randomly assigned among 4 pens [average and (SD) of pen counts were 92 (24), 131 (5), 109 (19), and 17 (5)], fed for 60 d, followed by a 60-d washout phase where all cows received CTL, and fed for a second 60-d treatment period. Assignments to pen were reversed during the second treatment period. Milk yield was recorded and milk samples were collected during the morning milking at d 14, 28, 42, and 56 (+/− 3) during each period. Treatment-by-parity effects were noted for milk yield and yields of milk fat and protein; parity 1 cows fed IRN tended to produce more milk than CTL (P < 0.10), whereas parity >2 cows fed CTL yielded more milk fat and protein (P < 0.05). Treatment-by-time effects were noted (P < 0.05) for all variables except milk protein percentage. These data indicate routine supplementation of IRN in diets for lactating dairy cows cannot be supported.