Mating, How many rams are needed?
By Dr Mackie Hobson BSc(Agric),BVSc

1. Reproduction

As a generalisation most producers use about 4 rams per 100 ewes (depending on their mating system). However, should we not be thinking testicular size (mass) rather than the number of rams? The reason is that testicular size varies between rams and nutrition has a major impact on testicular size.

Testosterone production is also correlated to testicle volume so has impact on a number of factors including:

• Sperm production
• Time for find ewe in heat

The testosterone link between sperm production, higher levels of mate-seeking behaviour and increased copulation rates is nature’s way of regulating their copulation rate according to the sperm supply that they have available to them

Each gram of testicle will produce on average 20-25 million sperm a day

An ejaculate of >0.5ml (motility of 3) will contain approximately 1500 million sperm

• A ram with a large testicle (just under 1kg) will produce about 15 effective mating’s a day
• A ram with a small testicle  (300g) will produce only produce about 4 effective mating’s a day

Remember on average each ewe is mated 3 times while in heat.

Considering that the seminiferous tubules occupy 67–83% of the rams’ testes and that most of the cells forming the seminiferous tubules are sperm cells in their different stages of development the Testicular volume can be the prediction of sperm production.

Under drought conditions, unless rams have been intensively fed, their testicles will be smaller than normal. 

We know that Angora goat ewes have more synchronised heat periods than sheep and after the ram is introduced may come into heat over a 3-4 days period so the rams may be under more pressure to cover the ewes than sheep.

So as producers, we need to consider increasing the number of rams (especially in poorer nutritional conditions) but more importantly we need to be thinking testicular volume more than just the number of rams required.

How often is it just the ewe (weight and body condition) that gets the blame when low conception rates occur post mating occur in dry conditions rather than considering testicular size.

Possibly a ratio of ram ratio of 5:100 ewes (1:20) should be considered in Angora goats mating under extensive conditions.

How does nutrition impact on testicle size in Angora goat rams?

Looking at data we collected from veld rams compared to ‘fed’ rams it is clear the impact that nutrition has on testicle size. See the ‘bell shaped’ graph below of 4 years of different veld ram testicle sizes (to the left) compared to the light blue line of the fed rams (to the right).

Testicular Volume

Scrotal circumference was measured at final selection of stud rams (veld) over a 4 year period.

Testicle traits are highly heritable. Therefore selection for scrotal circumference may over many decades lead to ‘round testicles’ where ultimately it is volume of testicle that we need to be selecting for.

For this reason Dr Johan Van Rooyen at Grootfontein Agricultural College worked out the most accurate way of determining testicular volume (using cylinder and sphere calculations). It is easy enough to measure the scrotal circumference and length and plug these values into the formula to get the testicular volume.

Example below comparing 2 rams for testicular volume.

• Ram with a circumference of 30cm and length of 11cm: Volume =507 cubic cm
• Ram                                            22cm                            8cm                 = 199

References:

• Does Size Matter? Testicular Volume and Its Predictive Ability of Sperm Production in Rams

by Rafael Montes-Garrido, Luis Anel-Lopez, Marta F. Riesco,Marta Neila-Montero,Cristina Palacin-Martinez,Cristina Soriano-Úbeda,,Juan Carlos,Paulino de Paz,Luis Anel,andMercedes Alvarez

• Dr Johan Van Rooyen, Grootfontein Agricultural College
• Journal of Animal Ecology, Testes size, testosterone production and reproductive behaviour in a natural mammalian mating system

Brian T. Preston, Ian R. Stevenson, Gerald A. Lincoln, Steven L. Monfort, Jill G. Pilkington, Kenneth Wilson