Dr Vlok Ferreira
National Technical Manager of Ruminants, RCL Foods
Success of your sheep herd starts with the ram, since the ram is responsible for about 70% of the genetic progress in the herd.
“The ram makes up half of the herd, and the ewe makes up half of the lamb.”
What are the requirements posed to the ram under natural circumstances?
Three rams should be able to cover 100 ewes for a 5 week period. Every day 1/17 of the herd should be in estrus, which is about 6 ewes. Every ram therefore has 2 ewes to cover.
Requirements of the ram
Nutrition has a large impact on fertility and, especially in the first year, rams should be fed so that their genetic potential for maximum mature weight is reached. The level of nutrition and especially energy, protein, vitamins and minerals have an influence on fertility.
Semen quality is determined by volume, concentration, motility (movement), and abnormalities and mortalities of the sperm. All of these characteristics are influenced by nutrition, as it is harmful when the ram’s level of nutrition is lower than that of its maintenance. It is also harmful when the level of nutrition is much higher than its maintenance, as there will be fat deposits around the testes.
One infertile ram has a much bigger impact on the herd than one infertile ewe.
Relationship between size of testes, nutrition and ram fertility
Semen quality, the volume of semen produced, and mating ability are linked and cannot be separated. It is difficult to accurately measure semen production, but a good estimation can be made by measuring the size of the ram’s testes.
Sperm is produced at a daily rate of 20 million spermatozoa per gram of testes tissue. There is an 85% correlation between sperm production and the size of the testes, as weight, volume and diameter therefore serves as an indication of semen volume.
Size of the testes
The size of a ram’s testes is determined through means of scrotum volume, scrotal circumference, testes diameter and the length of the testes. If possible, testes diameter should be measured with testes length, as the form of testes differs.
Results from an experiment done at the University of Pretoria found a 35% correlation between body weight and testes size. Rams that were adapted to veld conditions were placed on high concentrate rations, and it was found that over an 8 month period, their body weight increased with 59% and their testes volume increased with 116%.
The ability of the testes to produce semen more than doubled.
Important to remember
The presence of twins is only experienced during the first week of the lambing season confirms this relationship. The selection for testes volume resulted in a dramatic increase of weaning percentage, due to increased twins and triplets being born.
It takes 49 days for sperm to reach maturity, and another 14 to 21 days to move through the epididymis, which is a total of about 70 days.
Supplementation of the ram
Results show that a period of about 3 months is necessary for the testes to reach “maximum capacity”. It is therefore suggested that rams are brought into good condition 3 months before the mating season.
The feed of the ram should be adapted roughly two weeks before mating, so that it is on the same level as that of the ewe. If the ram’s feed intake is not high enough, it will result in a decrease in testes volume during mating season. This effect is increased if the supplementary feeding was inadequate before the mating season.
There is an 80% correlation between ovulation rate and testes size on a constant body composition, and the advancement of a ewe’s breeding season may also take place.
The heritability of testes volume is 40%, which means that increased fertility may be found in both male and female animals.