The national cow herd consists of 1.64m dairy and 0.43m beef cows. They produce a total of 1.76m reared calves annually. Of these 0.42m heifers go as herd replacements, leaving 0.46m heifers and 0.88m males available for beef production. There is a 2:l ratio of males to femaies in the population of calves available for beef production. Also, there are few straightbred dairy heifer calves available and the mean birth date of heifer calves for beef production is later than that cf males. The objectives of the present experiment were (i) to compare the performance and carcass composition of non-implanted and implanted heifers and steers and (ii) to compare the carcass composition of serially slaughtered non-implanted and implanted heifers.

Sixty tour (48 female and 16 male) Spring born Hereford x Friesian calves (initial live-weight 45 kg) were purchased and reared on milk replacer and concentrates. After 81 days they were blocked on weight and assigned from within sex type to 8 treatment groups.