Sires from British breeds are less likely to cause calving difficulties than sires from Continental breeds. Consequently, heifers have usually been mated to Aberdeen-Angus, Beef Shorthorn or Hereford sires although Continental sires produce bigger, faster growing calves which mature at heavier weights. However, information is available on calving difficulties for sires used in AI and this enables easy calving Continental sires to be selected.
A group of 70 Hereford x British Friesian heifers were allocated at random to be mated, using AI, to a progeny tested high performance easy calving Aberdeen-Angus or to an easy calving sire of the Blonde d'Aquitaine, Limousin and Simmental breeds.
Only one sire from each breed was involved. The heifers were mated to commence calving in mid August 1985. A combined PRID/PG (PRID, CEVA; prostaglandin ICI Estrumate) technique was used to synchronise oestrus in the heifers and they were served by AI at 72 and 96 hours after the PG injection.