Farmnote 17/96 [Reviewed, content current August 2006]
By Keith Croker, Senior Research Officer, Animal Research and Development Services, South Perth
Often farmers underestimate the importance of ram preparation. To avoid poor lambing percentages, it is vital to pay attention to ram management leading up to joining.
An infertile or inactive ram can reduce conception rates during joining or broaden the spread of conception and therefore, lambing. The basis of good ram management is careful preparation for mating. This requires:
- an understanding of sperm production;
- a health examination of the ram;
- adjusting nutrition levels if necessary; and
- an understanding of the ram's effect on flock fertility.
Recommendations
- To improve a ram's production of sperm, treatments must begin eight weeks before joining.
- For late summer-autumn joining periods, feed the rams 500 g lupin seed per head per day for eight weeks before they are joined with ewes, unless they are in body condition score 3 to 4.
- Use a minimum of 1.5 per cent rams.
- Maximise the chances of ewes receiving more than one service during an oestrus.
- Use a higher proportion of young rams (two-tooth) being joined with ewes for the first time (up to 4 per cent).
- Use at least five rams per flock.
- Flocks grazing highly oestrogenic subterranean clover pastures require a higher percentage of rams (at least 2 per cent of mature rams).
- Use more four-tooth rams being joined for the first time than the recommended number of experienced four-tooth rams.
Sperm production
It takes about seven weeks from their initiation for sperm to be available for ejaculation, so the critical pre-joining period for rams is seven to eight weeks. If the joining period is six weeks long, then all the sperm used by rams during joining will have already begun their development by the first day of joining. Treatments to the rams after that day can influence only the proportion of developing sperm which degenerate and the successful delivery of the sperm at mating. To improve a ram's production of sperm, treatments must begin eight weeks before joining.
The number of sperm produced per gram of testes per day is constant (about 20 million per gram per day), regardless of the size of the testes. This means that the larger the testes, the more sperm produced purely on a weight ratio. Therefore, the size of the testes is a good index of a ram's sperm production.
Both the circumference and the volume of the two testes are closely correlated with the weight of the testes. The relationship between the circumference of the scrotum and the weight of the testes of Merino rams is shown in Figure 1, which shows that these measures can indicate potential sperm production.
Figure 1. The relationship between the circumference of the scrotum and the weight of the testes of Merino rams
(from Foster, Hoffman and Briggs, Australian Veterinary Journal 66, 20-22)
Research has been unable to identify the minimum testicle size below which lambing percentages are reduced. This is because usually more than one ram is joined with a flock, making it difficult to gauge the influence of individual rams on the flock performance. However, it is desirable for rams to have as much testicular tissue as possible at the start of joining.
Physical examination of rams
Examine rams about eight weeks before the start of joining. Check their teeth, horns (for flystrike) and feet to make sure that there are no problems. Treating the horn area with a long-acting residual fly treatment should reduce the chances of this area being struck before the start of joining. Continue regular checks for flystrike until the start of joining.
Examine the pizzle and penis and palpate the testes and epididymides (the long tubes which run up the sides of the testicles). The testes should feel firm and springy with no lumps or other abnormalities in either the testes or the epididymides - lumps may indicate physical damage or infection. Test all rams with unexplained lumps or swellings in the epididymides for Brucella ovis, which is a bacterium that can drastically reduce ram fertility.
Soft or very hard testes indicate degeneration or scar tissue and rams with these defects should not be used for breeding. Old rams which have a low sperm producing capacity (smaller and degenerative soft testes) will often be culled through this palpation test, or for poor teeth condition.
Supplementary feeding
The testes are very sensitive to nutrition and respond rapidly to changes in the diet. Testes are smallest in autumn, when the quality and quantity of feed in paddocks are invariably at their poorest.
Feeding supplements to rams grazing poor pastures before the start of joining can increase the size of the testes. Rams joined with the ewes in spring probably do not need supplementary feeding because the paddock feed is usually good at this time and the rams should be in adequate condition (body condition score 3 to 4). For late summer - autumn joining periods, feed the rams 500 g lupin seed per head per day for eight weeks before they are joined with ewes, unless they are in body condition score 3 to 4.
Ram to ewe ratio
A ewe must receive between 50 and 100 million sperm deposited in her vagina to have a good chance of conception. Rams are very active at the start of joining and mate frequently. There is a marked drop in the number of sperm in each ejaculate soon after the start of joining. Ewes which receive more than one service during an oestrus have a better chance of conceiving than ewes which receive only one service, because they will be inseminated with more sperm.
Rams have a large capacity to produce sperm and a strong desire to mate continually with ewes. Recent reports indicate that it is possible to reduce the number of mature rams joined without adverse effects provided that:
- a minimum of 1.5 per cent rams are used;
- rams have large and firm testes, that is, there are large reservoirs of sperm; and
- flocks are large enough to have at least five rams, for example, five rams to 350 ewes.
Young rams (two-tooth) being joined with ewes for the first time require a higher flock proportion (up to 4 per cent) than do the older rams - the minimum number joined should be five.
With flocks grazing highly oestrogenic subterranean clover pastures, it is suggested that a higher percentage of rams be joined with the ewes, that is, at least 2 per cent of mature rams.
Mating efficiency
In the agricultural areas, mature rams often dominate younger rams and prevent them from mating ewes. Therefore, do not join two-tooth rams with the same flock as older rams.
In the pastoral areas, large paddocks and low stocking rates reduce the opportunity for mature rams to dominate inexperienced rams and young rams need not be segregated during joining.
Previous mating experience improves the efficiency of rams. Use a higher proportion of four-tooth rams being joined for the first time than would be used with four-tooth rams.
Further reading
- Farmnote No. 11/89 'Causes and control of ram infertility'(Agdex 432/652).