What drug can be used to induce estrus by lysing a large corpus luteum (CL) of 230 days in a cow?

The correct choice is prostaglandin, as prostaglandins are effective medications used to induce estrus by causing the lysis of the corpus luteum (CL). In the case of a large CL, such as one that has persisted for 230 days, administering prostaglandin causes the CL to regress, which then leads to a decline in progesterone levels. This decrease in progesterone enables the cow to resume estrus cycles, thus facilitating breeding opportunities.

Prostaglandin F2α is particularly noteworthy in this context because it specifically targets the luteal tissue to induce luteolysis. Following the regression of the CL, the cow can exhibit estrus behavior, making prostaglandins a valuable tool in reproductive management in cattle.

Other options are not suited for inducing estrus through lysis of a large CL. Estrogen is more commonly used to synchronize estrus rather than to induce it through luteal regression. Oxytocin is primarily involved in uterine contractions and does not have a direct role in lysing a CL. Progesterone, on the other hand, helps maintain pregnancy and does not facilitate the onset of estrus by lysis of the CL.