、。
Once I give the cows some hay, my afternoon work is done.
Literal
Cows [to-に] hay [object-を] give-and, midday-[genitive-の] work [topic-は] ending is.
A rural/farm vignette. The やる here is not the colloquial 'do' but the verb やる meaning 'to give (to an inferior or to animals/plants)' — one of the Japanese 'giving' verbs that are sensitive to the social position of the recipient. The hierarchy is: 差し上げる (give to superior) > あげる (neutral give) > やる (give to inferior/animal/plant). Feeding the cows takes やる because cows are animals. 昼の仕事 ('midday work') is the afternoon's tasks on the farm. The sentence-final ~はおわりです is a casual statement of completion.