Recent changes to beef production subsidy schemes in the UK has focussed attention on the fertility and reproductive output of suckler beef systems in an attempt to ensure future financial sustainability. Adoption of modern cattle breeding technologies may be more common in the future than they have been in the past as a result of this renewed focus on commercial profitability rather than subsidy reliance. However, relatively little information is available on the biological parameters encountered when modern breeding approaches are employed within commercial crossbred suckler beef management systems in the UK. Previous work (Penny, 2005) has detailed the development of either a triple or double synchronised artificial insemination (AI) programme suitable for use with both multiparous suckler cows and first calving heifers managed as a commercial spring calving suckler herd. The objective of the current report is to detail the effects of breed type and calf sex on average gestation length (GL) in first calving crossbred suckler replacement heifers when mated using a synchronised AI programme.