Professor Graeme Martin, from The University of Western Australia, has studied Merino and Suffolk rams to see whether lupins would increase testicular growth and testosterone levels in both breeds. These two breeds were chosedn because they differ in their seasonality. Suffolks are very seasonal breeders whereas Merinos can breed throughout the year.

These differences in seasonality are a result of the breeds' origins in different latitudes with different changes in the length of the day (photoperiod). Suffolks and Merinos respond differently to photoperiod, and environmental signal that acts on the reproductive system to influence the production of reproductive hormones. The secretion of reproductive hormones is also linked to nutrient supply, and increasing this supply by feeding lupins increases testicular size and testosterone production. This increases sperm production and leads to greater fertility, so the performance of rams will be increased.

Professor Martin and his team found that lupin-fed Merino rams show these changes in testicular growth and testosterone levels at all times of the year. Thus, season does not greatly modify the reproductive response of Merino rams to nutritional stimuli. However, Suffolk rams only responded during the breeding season. Suffolks are so focused on photoperiod that the feeding of additional nutrients goes unnoticed by their reproductive systems during the non-breeding season.

Until this problem is solved, Suffolk breeders can save time and money by only feeding lupins during the breeding season when an increased level of reproductive performance can be achieved. For Merino breeders, the ability of Merinos to reproduce out of season allows the extra benefits of a year-round supply of lambs.