In suckler beef production it is estimated that 55% of the total cost is required to maintain and replace the breeding females while only 1095 of total feed energy intake is stored in the tissue of the calves and cows. The low reproductive rate of the cow is primarily responsible for this low efficiency. Even in a well managed herd, weaning rate Is about 0.95 calves per cow per annum or less. It Is frequently hypothesised that increasing litter size by inducing twin calving would increase output, biological and economic efficiency provided few extra Inputs were required. Although twinning may increase the efficiency of beef production, spontaneous twin-calving is frequently associated with an Increased incidence of calving problems, poor calf survival, retained placentae and longer rebreeding intervals. Such problems related to twin-calving cannot be studied unless the frequency of twinning is increased above the levels that occur spontaneously. Embryo transfer can be used to Increase the frequency of twin calving thus allowing a better assessment of the potential to Increase output. A suckler herd, with a high level of twinning, was established to determine the effects of litter size on calving performance and calf survival rates.