Manipulating the onset of lambing season in communal ewes through hormonal intervention

The study was conducted to evaluate the effectiveness of using long-acting medroxyprogesterone acetate (MPA) to delay the lambing season in communal wool sheep ewes. The study was conducted in three phases. In phase 1, a random assessment was made to determine whether the hormone had any effect on delaying the onset of the lambing season. In the second phase, the administration of the hormone at different times during the perceived mating season was assessed. In the third phase, it was investigated whether the use of the hormone had residual effects in the subsequent lambing season after the treatment was discontinued. From the results it is evident that the administration of 150 mg MPA before conception could delay lambing between two and three months. November seems to be the optimum month for hormone administration. However, administration of the hormone did not guarantee effective prevention of conception in all treated ewes and discontinuation of treatment resulted in ewes reverting to pre-treatment lambing patterns. In conclusion, long-acting MPA can be used selectively as an effective method to delay the lambing season in communal ewes and to manipulate it towards more favourable environmental conditions for ewes and lambs. There can be a seasonal effect on time of conception in communal ewes and this should be considered when timing a hormonal treatment protocol. Keywords: communal sheep farming, lambing season, manipulation, medroxyprogesterone acetate