how can I increase the cow milk

Low milk yield is usually from feed shortage, poor water, or udder trouble. First, give more green fodder, enough dry fodder, and a balanced concentrate mix. Keep clean water in front of her all day. Milk her at fixed times, fully and gently, and keep the udder clean. If she is thin, add mineral mixture and good quality protein feed. If milk has dropped suddenly, check for mastitis, fever, or heat stress. Treating this now costs far less than the permanent milk loss if left untreated. If you want, I can help you plan the exact ration for your cow.