To lyse a large corpus luteum around day 230 in a cow and induce estrus, which pharmacologic combination is used?

• A. Prostaglandin alone
• B. Corticosteroids alone
• C. Prostaglandin & corticosteroids
• D. Oxytocin

Answer: (C)

To end the function of the corpus luteum and bring the cow back into estrus, you need to stop progesterone production. Prostaglandin F2α is the primary luteolytic agent that induces regression of the CL, leading to a drop in progesterone and a new luteolytic cascade. However, a very large corpus luteum, especially late in diestrus or near term, can be more resistant to prostaglandin alone. Adding a corticosteroid helps enhance luteolysis by further suppressing progesterone synthesis and promoting the luteolytic response, making the regression more reliable and faster. So combining prostaglandin with a corticosteroid provides a stronger, more consistent way to lyse a large CL and trigger estrus. Prostaglandin alone can be less effective in this situation, corticosteroids alone don’t cause luteolysis, and oxytocin does not lyse the CL.