OSU Sheep Team

Roger A. High, State Sheep Extension Associate

(Originally Published in Sheep Team Newsletter June 2003)

This is a difficult question to answer. There are many factors that play a function in reproduction when a sheep producer is trying to get ewes bred at the “normal” breeding season, let alone trying to get ewes bred “out-of-season”.  It almost seems as though the stars need to line up just right for breeding to occur in the ewe flock to get “fall born lambs”.

Why do we want fall born lambs?

This is a question that needs to be answered before attempting to push your ewe flock into a fall breeding scenario.  There are some very legitimate reasons why a producer would want fall born lambs in every type of operation, commercial, purebred, and any in between.  Fall lambing is simply easier than winter lambing, hypothermia is not an issue, lambs can be born outside because the weather is generally very nice and cooperative, and equally important, lambs that are born in the early fall can be targeted for the increasingly popular and many times very profitable “Christmas” or “ethnic” market.  Fall lambing also allows for more sheep to be lambed out in a facility as the fall lambs will be weaned and possibly marketed before the spring lambs are ready to arrive.  From the standpoint of the purebred producers, most fairs and exhibitions have “fall-born classes” in their shows.  Each breed has a different time line as to what is considered a fall lamb, but in general “fall born lambs” are born September 1 through December 31. In commercial operations, it is simply to market lambs to the “Christmas” ethnic market.  I am not going to go into detail in regards to the marketing of the lambs in this article because that is a completely different topic.

What are the factors that affect reproductive activity of an adult ewe?

1) Season (day length) – The principle factor affecting reproductive activity in adult ewes is season, with most ewes showing the greatest reproductive activity in the fall of the year.  As ewes undergo the transition from summer to fall, they experience a decrease in both day length and temperature.  Day length is the principal seasonal stimulus dictating reproductive activity.  Sheep are considered “short day breeders” and consequently reproductive activity increases as length of day decreases.  A ewe’s ability to perceive photoperiodic changes appears to be mediated through changes in blood levels of the hormone melatonin.  A point of importance is that when deciding to breed “out of season” (i.e. during the summer), it must be realized that the advantage of “out of season” lambs may be negated by potentially fewer lambs being born.  This may be due to fewer ewes ovulating and/or fewer ovulations per ewe.

2) Temperature - When seasons change, so does temperature.  Temperature does not appear to play a major role in dictating cyclic activity of the ewes, but it does have a major effect on embryo survival.  When ewes are housed in a hot climate vs. a cool climate, the hot environment resulted in a lower percentage of eggs fertilized, greater embryonic death, and consequently fewer dams giving birth.  It is important not to exercise sheep during conditions of elevated temperatures and high humidity.  There are problems such as ram fertility, high body condition scores (fat ewes), small lambs at birth, and a number of other problems related to high temperatures and high humidity.  Shearing will reduce heat stress under most conditions, but body temperature while in direct sunlight will be lower in sheep with one to two inches of wool than a freshly shorn sheep, because the fleece acts as an insulator.  Shearing is recommended except for sheep with no access to shade.

3) Inheritance - Another major factor that affects reproductive performance is the genetics of the ewe.  Some breeds of sheep such as the Dorset, Merino, and Rambouillet have longer breeding seasons than others.  If you want to concentrate on a natural fall lambing flock, it may be important to have the ewe base of your flock concentrated on these breeds of sheep.  There are breeds of sheep that will give you a few fall lambs each year, but if you want to concentrate your management scheme on fall lambing, it is best to have a high percentage of genetics that will allow most or all of your ewes to lamb in the fall.

4) Age - Within a breed, as a ewe matures from a yearling, length of breeding season also increases.  Ewe lambs cycling for the first time generally will start cycling for the first time about three weeks after the adults have started and stop cycling about three weeks before the adults stop cycling.  As age increases, reproductive efficiency also increases, as evaluated by greater offspring survival.  I believe the most frustrating group that you will deal with in a fall lambing scenario will be the ewe lambs, they have so many variables that come with them such as puberty, growth, nutrition and maturity.

5) Nutrition – In order for a ewe to produce, that ewe must be adequately fed and maintained in good body condition.  Undernourished ewes cannot meet their physiological needs from a nutrient standpoint and therefore can not be expected to produce.  Nutritional status of the ewe can affect reproductive rate, length of breeding season, and milking ability, as well as any other system related to production.  As in a spring breeding scenario, it is important to “flush” the ewe, and to have her on an increasing plane of nutrition in order to increase the number of ovulations and hopefully resulting offspring.  Body condition scoring can help play a major part in managing the reproductive performance of the ewe flock.

6) The “teaser” ram or the “ram” effect - One of the most interesting aspects of reproductive management of the ram is the use of a ram to stimulate breeding of ewes in anestrus (terminate anestrus). While this phenomenon has been known for many years, many producers still do not realize or capitalize on the affect that the “teaser” ram has on improving the chances of successful application of “out-of-season” breeding.   It is generally recommended that the “teaser” ram be introduced in the ewe’s flock 14 to 17 days prior to breeding the ewes.  The teaser ram will generally cause the ewes to have a silent heat 40 to 60 hours after introduction.  Estrus will not really occur with this ovulation.  After the ewes have been through one heat cycle with the “teaser” ram, they may or may not have a fully functional estrus cycle.  The chances of having a full estrus cycle for fall lambing ewes is greatly increased by the use of a “teaser” ram.  This is an area that you need to experiment with on your flock to get the greatest impact from the use of this management technique.

In summary, many of the management strategies that a sheep producer would use for winter or spring lambing are the same as those a producer would use for fall lambing.  As in winter and spring lambing scenarios, there are many variables and many stars that need to fall into line.  The use of proper genetics, a good nutrition program, and the use of  “teaser” ram seem to play major roles in helping your flock be successfully managed for a fall lambing scenario.  Adapted from the SiD Manual, Copyright 1996