Complex sentence: During the war messenger pigeons could draw a special allowance of corn and seed, but as soon as the war ended this had been cancelled and anyone keeping pigeons would have to draw on their own personal rationed corn and seed to also feed the pigeons.
Split into simpler sentences: During the war messenger pigeons could draw a special allowance of corn and seed. However, as soon as the war ended this had been cancelled and anyone keeping pigeons would have to draw on their own personal rationed corn and seed to also feed the pigeons.