The Ram Effect in Breeding Ewes

So how does the ram effect work? Brian Hughes, Drystock Advisor, outlines how this natural method of stimulating a ewe's reproductive system can benefit compact lambing and explains how to achieve this in practice.

THE ram effect is a natural method of bringing ewes cycling at the beginning of their natural breeding season. Ewes are seasonal breeders and as autumn approaches the shortening day length stimulates the ewe’s reproductive system into action. The start of the breeding season will vary from breed to breed but for most of the sheep breeds it will typically begin in September. This date will also vary from year to year depending on factors such as temperature, lactation status etc.

So how does the ram effect work?  Rams produce hormones known as pheromones. The ewes are sensitive to these when they have contact, sight and smell of the ram and this triggers their reproductive system to start cycling. However, if the ewes have been in contact with male sheep on a continual basis, e.g. rams or male lambs still running with the flock since spring time, then the ewes will be less sensitive to the ram effect and it will not be very effective. For the ram effect to work the ewes must be out of sight, sound and smell of male sheep (including male lambs) for at least 28 days.

Once the ram is introduced to the ewes some ewes will show heat almost immediately. This will be a silent heat that means that the ewe, while in heat will not show outwardly signs of being in heat. The remainder of the ewes will come into heat six days later. This will also be a silent heat. At this stage the ewes' reproductive system will have been kick started and the target date for joining the rams will be 14 days after the initial ram introduction. About 30-40pc of the ewes should be cycling at day 17 and the remainder should be cycling six days later. For the initial ram introduction some people use a vasectomised ram. Where this type of animal is not available a fertile ram in a well-fenced adjoining field or in a trailer in the field of ewes will do the trick. The ewes need less than 48 hours contact for the ram effect to work. If you don't mind a few early lambs you could leave a fertile ram off with the ewes for 48 hours and then remove him.

The main purpose of the ram effect is to compact lambing at the start of the natural breeding season. It does not work well where most of the ewes are already cycling. The main benefit will be in flocks lambing in early February. For some of the later lambing breeds and ewe lambs, the ram effect can be used successfully later in the season, as these will have a later natural breeding season. Farmers who breed their ewe lambs have found the ram effect works well where mating is planned for early October. When using the ram effect we would expect most of the mating to occur over an eight-day period and therefore the ram to ewe ratio should be increased from the traditional 50 ewes per ram.

Where ewes are sponged at this time of year a ratio of 10 ewes per ram would be recommended. Using the ram effect, mating will be spread out over a longer period so a ewe to ram ratio of 20:1 should be adequate.