Ram desire, ability and stamina
Your rams' productivity will also be affected by how they want to mate, and their physical ability to perform during joining.
Ram desire and mating
Desire, or libido, refers to a ram's urge to mate. The onset of libido coincides with puberty and the start of sperm production, the timing of which is determined by body weight rather than age.
Rams generally reach puberty between the weight range of 23-27kg. Almost all rams heavier than 27kg, regardless of age, will have reached puberty and developed a desire to mate. Maximum reproductive capacity is generally attained when a ram is 1-2 years old.
Libido is regulated by the release of testosterone. Merino rams show libido almost continuously once they reach puberty, though nutrition and age can have a marked effect on a ram's desire to mate. In British breeds, there is a marked decline in testis size, semen volume and libido during the non-breeding season.
Ram nutrition and mating
You must ensure your rams receive good nutrition, as poor nutrition will affect sperm production and reduce libido. Rams that are losing weight rapidly or are below store condition are most likely to be affected. On the other hand, overweight rams may also show reduced libido, particularly in hot weather.
Ram age and desire to mate
Age also affects a ram's desire to mate. From 6 years of age, their fertility and libido start to decline, generally due to disease-related conditions such as brucellosis and arthritis. You should ensure about a third of Merino rams are turned over annually to keep the ram flock young and vigorous.
A ram's success rate in inseminating ewes is known as its mating ability.
Young rams, at their first joining (18-24 months), generally have a poorer mating ability than mature rams. You should avoid joining young rams with maiden ewes, and allow young rams to mix with mature rams for joining to older ewes.
Old rams may mount but not serve ewes because of physical problems such as lameness or arthritis. Other rams may fail to inseminate the ewe because of abnormalities or injury to the penis (e.g. bent or short penis, or damage from shearing cuts). You should physically examine your rams annually to detect any problems. It's also important to do this prior to purchasing replacements and joining.
Stamina, or serving capacity, is a combination of libido and mating ability, and refers to the paddock mating performance of a ram. Rams that have a high serving capacity will successfully serve a large number of ewes over a short period of time.
Although it's possible to measure serving capacity in pen or yard tests, the results may not relate to ram fertility in the paddock. Some rams produce a lot of lambs while others produce very few. In any group of rams there will always be a wide variation in the serving capacity of individual animals, ranging from very high to very low.
To promote higher serving capacity in your rams, you should:
- keep the ram flock young, and physically and reproductively healthy
- ensure a realistic percentage of rams are joined (2-3%)
- allow for a joining period of at least 6 weeks.