LAUSR

Thirty six crossbred (predominantly English with some Bos indicus influence) beef steers (initial BW 264.8 + 35.8 kg) were blocked by BW and used in a completely random design to examine the effects of mineral supplementation on performance and serum mineral status in beef cattle grazing annual ryegrass pastures for 84 d. All cattle were withheld from mineral for approximately 60 d prior to the initiation of the study and were allowed to graze dormant bahiagrass pastures (Paspalum notatum), and also had access to bahiagrass hay. On d -1, cattle were weighed and stratified by BW into Light (n = 6 pastures) and Heavy (n = 4 pastures) blocks and returned to their dormant warm season pasture. On d 0, cattle were weighed, a 10 mL blood sample was collected for serum mineral status and cattle were moved to their respective 1.2 ha annual ryegrass treatment pastures. Treatments were randomly assigned to pasture and consisted of CON (no complete mineral supplementation), or MIN (free choice access to a complete beef mineral.) Cattle grazed annual ryegrass for 84 d, after which a final BW was collected as well as a second 10 mL blood sample. Data were analyzed as a mixed model with weight block a random effect and treatment a fixed effect and pasture was the experimental unit. Supplementing MIN tended (P = 0.06) to increase total weight gain at d 84 and increased (P = 0.01) ADG (1.61 vs. 1.67 kg/d for CON and MIN, respectively). Additionally, feeding MIN resulted in increased serum Co, Zn, and Se (P = 0.01) but resulted in no differences in serum Fe and Cu (P > 0.10). Feeding MIN resulted in greater performance and increased some serum mineral levels, however the lack of response in serum Cu to MIN bears further examination.