A typical Heck bull should be at least 1.6 m (5'3") high and a cow 1.4 m (4'7"), with weight 600 to 900 kg (1,300 to 2,000 lb). Heck cattle are twenty to thirty centimeters shorter than the aurochs they were bred to resemble. However, cross-breeding efforts continue to increase the size and weight of the breed, particularly in Germany.
The Heck bulls were not much larger than the bull of most breeds of domestic cattle, while wild aurochs bulls are believed to have often exceeded 1000 kilograms (2,200 lb), half the size of a rhinoceros. So the African Watusi cattle were then brought into the herd. The result was a somewhat larger animal, but it also caused infertility among the cows, a sign of the genetic divergence that had occurred between these populations of Bos over the millennia. Heck cattle were first bred outside of a zoo in 1980. There were 88 registered at that time. Continued crossbreeding with these animals resolved the infertility in the cows.
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