Heat may affect ram fertility.
17 December 2015
Heat stress can be one factor that affects sperm production and viability if the rams cannot keep the testes cool during the eight weeks prior to joining as it takes seven to eight weeks to produce mature sperm and to reach maximum fertility, so any setbacks during this period can be disastrous.
This year, hot days in October and right through until late December with temperatures over 32 C for long periods or very high temperature over 38 C for short bursts may have affected sperm production in rams.
Mature sperm are less likely to be affected than sperm in the developing stages. A ram who has suffered heat stress before joining could successfully serve ewes with the stored mature sperm (e.g. two to three weeks), however there will be a seven week delay before new viable sperm is produced.
Good ram preparation leading up to joining is essential to ensure that ewes have the best chance to achieve optimum conception rate service in their first oestrus therefore shortening the lambing period and aiding the management at lambing and marking.
Providing the most favourable conditions and monitoring rams closely will give the best opportunity for rams to maximise their fertility at joining.
All breeding flocks will have some poor performing rams. A number of factors can affect the fertility of rams including physical abnormalities, stress, infections and high temperatures, poor nutrition and body condition. Any condition which causes a fever or rise in body temperature can cause infertility.
The ram paddock should be easily accessible with adequate shade; cool water and access to good quality feed so that rams can be regularly checked for lameness, flystrike, fighting injuries and body condition. Paddock feed quality and quantity can be regularly assessed and supplementary feed supplied to keep rams in optimum condition.
Rams should be in good condition (Condition Score 3.5) two months prior to mating. Sheep producers need to be aware of factors that can affect sperm production and may lead to temporary infertility.
All rams should be physically examined before joining to identify any abnormalities, particularly arthritis, poor feet, walking ability and swollen joints as this may affect the ram’s ability to mount. Teeth should also be checked as poor dentition may result in nutritional stress during the joining period, resulting in poor fertility.
Check the condition of the epididymis as healthy well fed and sexually rested rams may hold up to 100,000 million sperm, of which 75% is stored in the tail of the epididymis. Palpation of the tail of the epididymis can indicate the level of sperm reserves in individual rams. Epididymis tail should be large and firm, not hard and diseased. A small soft tail indicates poor reserves of sperm.
There is a close relationship between testicular size and sperm production. Rams with small testes may not produce enough sperm throughout the joining period to maintain good fertility. Research has shown that, improving the intake of protein and energy with supplementary feed, such as lupins, for two months prior to joining can increase testicle size and subsequently sperm production by up to 100 per cent. Ideally the scrotum should measure > 30cm in a 2 year or older ram.
Nutritional changes affect testicle size and sperm production much more rapidly than is reflected in live weight and body condition which highlights the importance of checking the ram’s reproductive soundness prior to joining. Over fat rams are more likely to be affected with high temperatures in hot weather and mustering.
Shearing rams just before mating is not desirable as some fleece protects the ram from heat stress. Plan shearing so that rams have three to four months wool at joining.
Temporary infertility from overheating can be caused by the lack of paddock shade, mustering, transporting. Dipping may produce a fever for a short period.
Fevers resulting from flystrike and infections from cuts and injuries from fighting will reduce the ram’s fertility.
All efforts should be made to protect rams from these conditions prior to and during joining to ensure the best lambing percentage. Of course ewe management is also extremely important.
Sustainable Agriculture Officer