Our 4 year buffalo got pregnant a year ago but aborted at 4th month and after that she not show sign of heat again

Silent heat or a uterine problem is likely here. After an abortion, the womb may stay infected, the ovaries may not restart properly, or the buffalo may have a hidden heat that you are missing. First, keep her body condition good with enough green fodder, dry fodder, mineral mixture, and clean water. Check for any foul vaginal discharge, fever, or loss of appetite. If there is discharge or she looks weak, she needs a vet examination soon because the womb may still be infected. If she is otherwise normal, watch her closely morning and evening for heat signs like restlessness, bellowing, tail raising, mucus, and standing to be mounted. In buffalo, heat is often weak and short, so many farmers miss it. Treating this now is far cheaper than losing another breeding season and milk income. Consult a veterinarian before administering any medicine or treatment.