Most sheep are seasonally polyestrus and short-day breeders. They start their estrus when the length of the day begins to decrease. The cycles of estrous will continue every 16 to 17 days until the ewe is bred or returns to anestrus Schoenian. Therefore most breeding in ovine occurs in the months between October and November. Estrus lasts approximately 24 to 36 hours, and is where the ewe will stand to be mounted by the male.
Detecting estrus in sheep is much harder than that is cattle especially dairy cattle, it is almost required to have a ram present Schoenian. Animals that are seasonally anestrus is believed to have come from preventing the ewes from conceiving during a time when the survival rate of the embryo would not be high. Anestrus is a state where a female is not exhibiting normal estrous cycles. The ovaries are relatively inactive. There are no follicles of corpus lutea present on the ovaries either.
The embryo survival rate is reduced a lot by the temperature and the humidity in the environment Pathways to Pregnancy and Parturition. Which is why fall becomes the ideal time for conception, because the embryo is at an ideal temperature and then the lamb goes through parturition during a moderate temperature also. There are certain breeds of sheep that are less affected by the season and can have longer breeding seasons or practically breed year-round. The location of the sheep relative to the equator will also have some changing effects on the ewe.
Photoperiod: the period of time during the day when there is daylight. Photoperiod regulates reproductive cyclicity in seasonal breeders. Pathways to Pregnancy and Parturition. Sheep are seasonal breeders that enter into the breeding season during shorter photoperiods; thus, they are short-day breeders.
In the mid and high latitudes of temperate regions, breeding begins in autumn, when the daylight becomes shorter. The Mechanism behind the effects of photoperiod involves the secretion of melatonin, which stimulates GnRH release.
The retina of the eye is stimulated by the presence of light. When light is abundant, an excitatory pathway is active inhibiting melatonin release. Because of genetic differences, different breeds of sheep maintain different levels of photoresponsiveness.
Melatonin is a modified amino acid secreted by the pineal gland that communicates information about environmental lighting to various parts of the body. Melatonin has important effects on maintaining biological rhythms, and has important effects on reproductive function. Light that is exposed to the retina is first relayed to the suprachiasmatic nucleus of the hypothalamus, an area of the brain well known for coordinating biological clock signals Fibers from the hypothalamus descend to the spinal cord and project back to the pineal gland.
Thus it converts signals from the sympathetic nervous system into hormonal signals Bowen. Seasonal changes in day length have profound effects on reproduction in sheep, and melatonin is a key player in controlling such events. During the non-breeding season, the gonads become inactive, but as breed season approaches, the gonads must be rejuvenated.
Photoperiod is the most important cue to allow animals to determine what season it is. The joining period should cover two complete estrous cycles 35 days. Exogenous melatonin is more successful toward the end of the seasonal anestrous period. This product is not commercially available in many countries.
A similar effect can be obtained by manipulating the photoperiod under management programs in which the ewes and rams are in confinement housing. This may require darkening windows to reduce exogenous light sources and completing barn chores during only those 8 hours to avoid using lights during the dark period. After 6—8 weeks, ewes will start to cycle.
If the rams are housed under similar conditions, scrotal circumference and breeding capacity will increase. Estrus induction in acyclic ewes requires exposure to exogenous progestagen for a minimum of 5 days; most programs use 7 days.
The progestagen used may be either natural progesterone delivered intravaginally in a controlled intravaginal drug-releasing device CIDR , or melengestrol acetate fed at hour intervals at a dose of 0.
Ovulation and subsequent fertility is usually poor unless eCG is given at removal of the progestagen; usually, IU is administered. If ewes are cycling, progestagen exposure needs to be sufficiently long ie, 11—14 days to outlast any CLs present on the ovaries.
Use of eCG at progestagen removal time is optional — IU and is generally not necessary during the ovulatory season if artificial insemination is not being used. Shorter exposures in cycling ewes can be used if prostaglandin PG F 2alpha or one of its analogues is administered either at, or 12—24 hours before, pessary or CIDR removal.
Estrous cyclic ewes can also be synchronized by two injections of PGF 2alpha or one of its analogues 8—11 days apart, although fertility is poorer than with progestagen programs.
Estrus commonly is seen 1—3 days after progestagen removal, with a shorter interval during the fall or with the use of CIDRs, or within 3 days of the second PGF 2alpha injection.
Before a program is set up, the attending veterinarian should be sure a sufficient number of rams is available for the program and that the rams are fertile. During the normal ovulatory season and without synchronization, a ram to ewe ratio of is usually sufficient, although if the rams are young, or the environment is rough, then the number of ewes per ram should be lowered.
From developing new therapies that treat and prevent disease to helping people in need, we are committed to improving health and well-being around the world. The Veterinary Manual was first published in as a service to the community.
The legacy of this great resource continues in the online and mobile app versions today. This site complies with the HONcode standard for trustworthy health information: verify here. Common Veterinary Topics. This is because the overhead of maintaining ewes can be supported by the sale of many lambs. However, some marketing schemes may be profitable with lower reproductive rates because of the advantages of timing sales and specialty markets. Genetics across and within breed also play a part in the seasonality of the estrous cycle.
Some breeds are capable of out of season breeding for example, the Dorset breed. And, some animals within a breed are more able to express those characteristics than others. Choose a breed of sheep that matches your season of choice and then monitor your own flock for the animals that best represent that breed. Keep and use ranch records to pick replacement ewes and rams that help meet your objectives.
Interestingly, ranch location also influences the percentage of ewes in estrus and ovulating and the ovulation rate. Here in the Pacific NW we are further north compared to Texas, and so our ewes are more seasonal in their breeding than the same ewes would be there See Table 1.
Use caution when choosing replacements from other locations. Flushing improving plane of nutrition and body condition score fatness or body energy reserves both influence the reproductive system.
Temperature, ewe age, and presence of ram also influence reproduction. Table 1. You can find more information on reproduction, nutrition, and genetics of sheep on the OSU website.
Good luck with your breeding plans this season and the following ones. I would be glad to discuss any of this information with you and help develop flock management plans. This file contains spreadsheets with contact information for all federal and state licensed slaughtering facilities in the state of Oregon.
These are arranged by business name, facility type, and county location. Species-specific information is also included. Some of these facilities do meat processing too. Non-slaughter, meat processing facilities will be added in the future. Minerals are critically important for the health and well-being of livestock. Cattle, sheep, and goats are frequently pastured together, but sheep are vulnerable to copper toxicity which cattle and goats need. Learn methods for managing this. This collection contains publications and information on selecting, purchasing, and preparing a meat animal for home slaughter.
It includes resources for beef, goat meat, lamb, pork, poultry, and rabbit. Outlines management practices to help sheep producers achieve greater productivity. Includes a sheep management calendar. Discusses flock management, lamb management and nutrition, how to calculate adjusted weaning weight, how to address
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