Achieving high system throughput for limitedfeedback communications against the time-varying channel effect is rather crucial in modern mobile system designs. Within the beamforming setup, this paper derives analytic throughput results for both the "more feedback less often" and "less feedback more often" scenarios. More specifically, under the assumptions that (i) the channels over two consecutive time slots follow the first-order Markov model and (ii) in each time slot, reliable feedback of a fixed amount of bits is allowed, the achievable system throughput over two consecutive time slots in both scenarios are characterized. In particular, while the exact throughput is in an integral form, we derive the associated closed-form approximate formulae which facilitate throughput evaluation without resorting to numerical integration. The analytic results also lead to a very low-complexity throughput-based mode selection scheme. Simulation study shows that: (1) the derived closed-form approximation is quite accurate; (2) with the aid of the proposed mode selection method, the throughput performance is robust against the channel temporal variation.