Mary had a little lamb


• Spring lambs
  Mother Nature meant for sheep to mate in the fall, so that their lambs would be born in the spring when the weather is mild and the grass is plentiful. This scenario would provide the best chance for lambs to survive and thrive.
  
  Ewes are considered "seasonally, polyestrus" because their reproductive cycle is controlled by the photoperiod and they come into heat (estrus) every ~17 days (until they become pregnant) during their fertile period. Photoperiod is the relationship between light and dark in a 24-hour period.
  
  
  Short-day breeders
  Ewes are short-day breeders. When day length becomes shorter (in the fall), this triggers the ewe's brain to release hormones that jump start the reproductive system. The further away from the equator the sheep breed originated, the more likely it is to exhibit these seasonal breeding patterns. Conversely, sheep breeds developed in the tropics or nearer to the equator are less likely to display seasonal breeding patterns. Breeds in the U.S. that have less seasonal breeding patterns include the Dorset, Rambouillet, Polypay, Karakul, Merino, Finn, and hair sheep.
  
  During their fertile period, ewes will come into estrus (heat) every approximately 17 days until they are bred or their fertile period is over. Only during estrus will a ewe allow a ram to mate her. The duration of estrus is 24 to 36 hours. A ewe in heat will seek out the male. She may sniff, lick, or nuzzle him. She may fan her tail. The classic behavior response of the ram when he detects a ewe in heat is to lift his nose in the air and curl his upper lip. This is called the Flehmen response.
  
  First-time mothers
  Though it depends upon breed, nutrition, and management, ewes can become mothers by the time they reach their first birthday. This is okay if the ewe lamb has achieved approximately two-thirds of her mature size (weight) before being bred. Thus, for some producers, it is commonplace to breed well-grown ewe lambs when they are 7 to 9 months of age. Other producers wait until their ewes are 18 months old before breeding them to lamb as 2 year olds. Different breeds of sheep reach puberty (sexually maturity) at different ages.
  
  
  
• Rams
  A healthy, mature ram can probably mate 100 (or more) ewes during a breeding season, though a ratio of 1 mature ram to 30 to 50 ewes is more common to make sure lambing is not too spread out. Six to 7 month old ram lambs that have achieved approximately 50 percent of their mature size can be used for breeding. Ram lambs are usually put in with fewer ewes, 15 to 25. Some rams show a preference for ewes of their own breed or kind.
  
  
  
• Artificial insemination
  Artificial insemination (AI) is much more difficult in sheep than other livestock for several reasons. The ewe has a more complicated cervix and it is difficult to pass a standard insemination rod through the many cervical rings. Ewes show fewer visible signs of estrus, making heat detection more difficult. A teaser ram is often used to detect heat. However, high levels of conception are possible when ewes are inseminated with fresh semen deep into the vagina. Good results are achieved when frozen semen is injected into the uterine horns via a surgical procedure called laparascopy. Trans-cervical AI requires special equipment.
  
  
  
• Gestation
  A ewe is pregnant for 142 to 152 days, approximately five months or slighter shorter. Pregnancy is also called gestation. Since ewes gestate for only five months, it is possible for them to lamb more often than once per year. While annual lambing is most common, lambing intervals of 8 months are realistic, especially in the tropics and with breeds that are less seasonal in their breeding habits.
  
  Extra food
  During her last month of pregnancy, a ewe needs extra nutrition because her lambs are growing rapidly inside of her and her mammary tissue is developing. 70 percent of fetal growth occurs during the last month of pregnancy. The growth of the fetuses is also reducing her rumen capacity.
  
  If a ewe doesn't get enough feed during late pregnancy, she may get sick because her unborn lambs are taking all of her nutrient intake. Thin and fat ewes and ewes carrying multiple fetuses are most prone to pregnancy toxemia (ketosis). Thus, it is common to feed grain during late gestation. On the other hand, if a ewe eats too much during late pregnancy, she may have trouble delivering her lambs because they may get too big. Fat ewes are also more prone to problems at lambing time.
  
  Vaccinations
  On many farms, it is common to vaccinate ewes during late pregnancy for the colostridial diseases that most commonly affect sheep and lambs: clostridium perfringins type C & D (overeating disease) and tetanus. By vaccinating the pregnant ewe, the lambs will acquire immunity when they drink the colostrum, the first milk produced by the ewe after lambing. In fact, a pre-lambing vaccination is the only way to protect lambs against type C.
  
  Worms
  A ewe's immunity to internal parasites (worms) is comprised around the time of lambing. Scientisits call this phenomenon the "periparturient rise" in worm eggs. Some producers will deworm their ewes during the last month of pregnancy to prevent this from happening.
  
  Due to the widespread emergence of drug-resistant worms, a better strategy might be to increase the protein content of the ration, as the primary parasite that affects sheep is a a blood sucking worm (barber pole) that causes blood and protein loss. Higher protein rations have been shown to reduce egg counts in periparturient ewes.
  
  
  
• Lambing
  Ewes usually give birth to 1 to 3 lambs at each birthing episode. Birthing is also called parturition. Twin births (two babies) are most common in well-fed flocks and with most breeds of sheep. First-time moms, especially yearlings, are more likely to have single births, though twins are not uncommon in some breeds. Ewes produce their largest litters of lambs when they are between the ages of 3 and 6.
  
  There are some breeds of sheep that average more than two lambs per litter. In the U.S., the most prolific sheep breeds are Finnsheep and Romanov. The hair sheep breeds are also very prolific (Katahdin, St. Croix, and Barbado). The more lambs a ewe ha,s the more feed she need to produce milk for them. Oftentimes, extra lambs need to be fostered onto other ewes or artificially reared. Proflic breeds are not recommended for novice shepherds or in situations where nutrition is a limiting factor.
  
  Because some sheep are raised in difficult environments, sometimes it's more desirable for a ewe to have just one lamb. This is because there may not be enough food for the ewe to support the growth of two lambs. If the flock has to travel far for food and water, it's usually better to have one strong lamb than two or three smaller lambs that may struggle to keep up. Smaller, weaker lambs that lag behind the flock are more likely to be killed by predators.
  
  
  
• Birth weights
  The weight of newborn lambs varies by breed, sex of lamb, litter number, and ewe nutrition. The lambs from medium to small breeds are similar in size to human babies, usually between 5 and 10 pounds, with an average of 7 to 8 pounds. When birth weights get too heavy (relative to the size of the breed), difficult births can be encountered. Medium-size babies tend to have the highest survival rate.
  
  
  
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Last updated 13-Dec-2009
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