Sheep Synchronisation Tips

A high ovulation rate (O/R) is the obvious first step in achieving a high lambing percentage.

Effect of ewe live weight

Live weight has two effects:

(1)  The static (live weight) effect

·         Heavy ewes have higher ovulation rates (and more lambs) than light ewes.

·         Twinning (percentage of twin births to total births) increases by about 6% per 4.5 kg increase in ewe live weight — i.e. 1.3% per kg increase.

·         This effect operates up to at least 70 kg live weight and there is no evidence of a decline at the top end of this range. Barrenness increases markedly under average weight of 40–45 kg for Mutton-based breeds and 35–40 kg in Merinos.

High ewe live weight and live weight gain during mating causes high O/R - for each extra kg of ewe weight there will be 1.3% higher lambing percentage.

·         Comparisons of poorly reared and well-reared ewes show that while the poorly reared ewes have fewer multiple ovulations; this is probably a function of their lower adult live weight.

(2)  The dynamic (live weight gain or "flushing") effect

·         Some trials have shown ewes gaining weight quickly (e.g. 0.5–1.0 kg per week) just before mating had higher ovulation rates than ewes of similar weight with low or no weight gain.

·         However some results showed that ovulation rate was more dependent on ewe live weight at oestrus than on previous changes.

#Seasonality of ovulation rate

·         Most sheep breeds are seasonal breeders and fewer eggs are shed in the first cycles of the breeding season in early autumn.

·         The first cycle of each season features a "silent heat" — i.e. ewes ovulate but do not show oestrus.

·         Highest lambing percentage coincides with mating mid-season depending on location. Higher numbers of abnormal eggs may be shed near the beginning and end of the breeding season.

Each successive ewe oestrus during the breeding season has about 0.15 more eggs shed.

#Synchronisation

 ·         Synchronisation may be used to get ewes ovulating simultaneously (e.g. to facilitate timing of artificial insemination) and/or to induce ewes to cycle out of season.

·         The two ways of doing this are by using rams or hormonal treatment.

Use of #rams ("ram effect")

 * The introduction of rams early in the breeding season stimulates ewes to ovulate within 3–6 days (without showing oestrus if this is the first ovulation of the breeding season) and show oestrus about 17 days later.

·         Ewe flocks stimulated by the ram effect are thus likely to be synchronised.

·         Rams introduced several weeks before normal onset of oestrus may have no effect and late introduction will only stimulate those few ewes, which have not begun cycling.

Synchronisation can be used to get ewes ovulating simultaneously by using hormones or rams.

·         Rams used for synchronisation may be entire or vasectomised. Some poor results with rams vasectomised for one year or longer have been reported and this may be due to reduced libido in these rams.

·         High libido vasectomised rams are most effective and should be introduced up to a week before normal if using as teasers (i.e. to stimulate ovulation and oestrus).

Rams introduced early in the breeding season, either vasectomised or entire, will stimulate ewes to ovulate within 3-6 days.

·         Some breeds are more effective, with indigenous rams are usually superior to Merino’s.

Hormonal synchronisation can be used to:

 ·           stimulate first oestrus (e.g. first oestrus in young ewes or an early first oestrus for older ewes)

·     synchronise ewes to show oestrus at the same time (e.g. to condense lambing or for artificial insemination) during the normal breeding season

·         Controlled internal drug sponges containing progestagens (synthetic analogues of progesterone) are most commonly used.

·         Results are more heavily influenced by operator skill and timing of insemination than product type.

·         The sponge is inserted in the vagina and withdrawn after several days.

·         The ewe typically shows oestrus within three days after withdrawal within the normal breeding season.

·         This time varies depending on dose level of progestagen, type of device or sponge used and whether pregnant mare's serum gonadotropin (PMSG) is also used to stimulate greater ovulation rate.

·         Ewes not fertilised at this oestrus will return to oestrus about 16–17 days later and remain generally synchronised. This is useful when planning a return visit for an AI technician.

Synchronisation for out of season breeding usually requires PMSG also to stimulate ovulation.

·         Prostaglandin injections can also be used for synchronisation but are not common.

·         Ask a vet about synchronisation or hormonally induced oestrus if planning to use it for the first time.