This story occurred in 2014. The black calf had a large 7 on its forehead. It represented 7 years of plenty, which are nearly over.
The next one, born on Rosh HaShanah 25 Sept 2014, had a small white 7 on its forehead. Many assume it is the large 7 represented 7 years of plenty and the small 7 on a red calf represents 7 years of scarcity ("in the red").