Rory Lewandowski, OSU Extension Educator, Athens County
Reproductive performance is an important factor in determining profitability in the sheep flock. Most breeds of sheep have seasonal breeding patterns and the majority of flocks in Ohio are spring lambing. In this scenario, the peak fertility of the ewe is from late September through November. The breeding season will extend somewhat beyond peak fertility for the late spring lambing system and begin somewhat before peak fertility for the late winter lambing system. Some management attention given to the ewes and rams prior to the breeding season can pay dividends in terms of increased conception and lambing rate.
A primary consideration regardless of the lambing production system and timing used is nutrition of the flock. The nutritional status of the ewe and ram at breeding is probably the primary factor that influences reproductive performance. The nutritional status of the flock is also a factor that a flock manager has a lot of control over. Evaluation of the body condition of the ram and ewe before breeding can tell the manager whether nutrient consumption should be increased or decreased. Based on a scale of 1 to 5, with 1 being very thin and 5 being fat, the goal should be to have the ram and ewe enter the breeding season somewhere around a 3.5 body condition score.
One practice that is helpful with ewes that are below the target body condition score is to provide them with a diet high in energy that allows them to gain weight. This practice is termed flushing and should be done 2-4 weeks before breeding. The high energy diet can be provided by supplementing a high energy grain such as corn at a rate of one-half to one pound per ewe per day, or by providing a high quality pasture. Flushing can result in an increased lambing rate and a decreased number of open ewes.
One caution that is generally given if ewes are to be flushed using a high quality pasture is to keep them off pastures with a high content of legumes (clovers and alfalfa) and use grass pastures. The reason given is that these legumes contain estrogen that leads to infertility and decreases the conception rate and pregnancy of the ewes. Does this caution mean that ewes must graze pure grass pastures? Legumes typically help to boost the energy content of a pasture sward and generally are considered as a positive to improve pasture quality. What does high content of legumes mean?
Clovers and alfalfa contain compounds known as phytoestrogens. In clover species the specific compounds are isoflavones. These isoflavones exhibit estrogen like behavior in sheep, while cattle do not seem to be affected by them to the same degree. I reviewed some of the scientific literature about this topic and it appears that sheep are more susceptible to the effects of isoflavones because as they are metabolized in cattle they are rapidly excreted in the urine, whereas in sheep they are not rapidly excreted and remain in their system longer. In addition, the estrogen receptors in sheep appear to be more sensitive to these compounds as compared to cattle.
There are also other factors that influence the level or concentration of phytoestrogens in legumes. The specific variety is one such factor. Improved cultivars have been found to have lower phytoestrogen contents. Environmental factors such as drought can increase the phytoestrogen content. Finally, soil phosphorus levels can influence the amount of phytoestrogens in legumes. Legumes grown in soil phosphorus deficient conditions have contained higher phytoestrogen concentrations as compared to legumes grown in non-deficient soil phosphorus conditions.
Still, the question remains, what is considered a high level of legumes with regard to this condition? In the literature that I reviewed, the legume stands that produced a negative effect upon reproductive performance were either pure stands or predominantly legume stands. I had a sheep farmer raise this question with me back in 2008 as he wondered about including clover in a grass pasture. I wrote an email to Dr. Shulaw asking him about this issue. He sent me some of the literature that I reviewed and summarized in this article and he also wrote, in part, “At this point in time, unless ewes are grazing pure stands of clover near breeding season I don’t have much evidence to make me concerned about infertility.” As I am out and about on sheep farms and looking at pastures it is rare that I ever see a pasture that contains more than 35-40% clover. The bottom line is that unless you have a pasture that is well over 50% clover, it should be fine to use in a flushing pass before the breeding season.
Some attention should also be given to the ram(s). In addition to making sure that they are in good body condition, it is recommended that a breeding soundness exam (BSE) be conducted prior to breeding season. The BSE consists of a physical examination, a reproductive tract examination and a semen evaluation. Waiting until after the breeding season to discover a problem with your ram that shows up in the form of an extended lambing season or open ewes is costly. Contact your veterinarian to schedule a BSE. It is money well spent.
Finally, I need to close with a word about internal parasites. One practice that use to be recommended was to de-worm all the ewes and rams in the flock before the breeding season. This practice is no longer recommended due to the resistance that parasites have developed to chemical de-wormers. De-worming all ewes and rams at one time is a method that will select for resistance. Instead, de-worm with a chemical de-wormer based upon individual animal need. This can be determined by using the FAMACHA scoring system. Those animals scoring a 3 or higher on this 1 to 5 scale should be de-wormed with a chemical de-wormer. Animals scoring a 1 or a 2 should not be dosed with a chemical de-wormer. For more information about parasite control and use of the FAMACHA eye scoring system, contact a member of the OSU Sheep Team.
The breeding season is upon the majority of flock owners in Ohio. Some pro-active management action can insure that it is a successful and profitable breeding season.