Ten single-sire mating groups of 13 Horro ewes per ram were used to study the effects of mating on liveweight, body condition and scrotal circumference changes and their relationships with level of sexual activity at different stages of the joining period, and effects of sexual activity and pre-joining liveweight and scrotal circumference on fertility. Mating had adverse effects on liveweight, body condition and scrotal circumference. There was a tendency for mean daily liveweight loss to increase with increasing number of services during the period of peak sexual activity and over the whole joining period. Changes in scrotal circumference were non-significantly correlated with sexual activity. Pre-joining liveweight and scrotal circumference had no significant effects on the proportion of ewes served, rate of return to first service and fertility. High losses of liveweight and scrotal circumference were observed during the stage of peak sexual activity, and it could be suggested that more supplementary feed should be provided to working rams at this stage, especially if the ewe[ratio ]ram ratio is to be increased. There is no significant benefit to be gained by increasing ram mating weight and scrotal circumference from 30 kg and 27 cm to 40 kg and 31 cm respectively in Horro sheep.