Updated: October 20, Former Extension Educator Mike Fournier explained to the Sheep Management class that shepherds can heavily influence whether their ewes lamb singles or twins each year. Single births - or none at all - cannot always be blamed on the ram. How can you ensure your ewe weans healthy lambs?
Some breeds, like Finn sheep, have multiple births - more like litters. Black-faced breeds tend to have less multiple births than white-faced breeds. It may look silly, but a breeding harness can save you from a lambless season. A crayon is inserted in a pocket, and when a ram mounts the ewe to breed, the crayon leaves the color on the ewe so you know she is bred. Change the color of the crayon every 2 weeks. If the ram doesn't mount any ewes, or if a ram continues to mount the same ewes throughout the breeding season, you know there is a problem with your ram.
Most breeds of sheep only come into season once every 12 months, so each animal is only likely to produce one to two lambs during each year. By the time they are weaned at a few months old in the spring, pastures are richer and food is more plentiful. The average gestation period for sheep is around five months, although this may be a little shorter in some cases. This will give a good indication of when to expect the lambs to arrive.
During the autumn breeding season, ewes come into oestrus on heat approximately every 17 days, with the window of fertility lasting for somewhere around 24 to 36 hours.
The season itself will vary in length from four to eight months depending on the breed but is usually concentrated during the three to four months of autumn. Thin and fat ewes and ewes carrying multiple fetuses are most prone to a metabolic disorder called pregnancy toxemia or ketosis , caused by an inadequate intake of energy calories during late pregnancy. For this reason, it is common to feed some grain during late gestation.
On the other hand, if a ewe eats too much feed, especially grain, during late pregnancy, she may have trouble delivering her lambs because they may get too big to fit through her pelvic cavity. Fat ewes are also more prone to having problems at lambing time. By vaccinating the pregnant ewe, the lambs acquire temporary, passive 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 enterotoxemia and to provide protection for early docking and castration, though anti-toxins can be administered to provide immediate, short-term immunity. Scientists call this phenomenon the "periparturient egg rise. Thus, it is a common practice to deworm ewes during their last month of pregnancy. A dewormer that is effective against hypobiotic larvae should be used. Due to the widespread emergence of drug-resistant worms, another strategy is to increase the protein content of the late-gestation ration, as the primary parasite that affects sheep is a blood sucking worm barber pole that causes blood and protein loss.
Higher protein rations have been shown to reduce fecal egg counts in periparturient ewes. If deworming is done, it is recommended that treatment be applied selectively to ewes that need treatment or would benefit from it.
For example, if ewes are scanned for fetal numbers, those carrying multiple births can be selected for deworming, while those with single births can be left untreated. Lambing Ewes usually give birth to 1 to 3 lambs at each birthing event.
Birthing is called lambing. The technical term for all species is parturition. Twin births two babies is most common in well-managed flocks and with many 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. The hair sheep breeds Katahdin, St. Croix, and Barbados Blackbelly also tend to be quite prolific, with mature ewes averaging more than two lambs per lambing.
Infertile, diseased, or disinterested rams often cause poor lambing rates. The average number of ewes that can be mated to a ram are as follows: well-matured ram lambs, 15 to 30 ewes; yearlings to five-year-old rams, 25 to 50 ewes. However, in many of the low-rainfall areas of New Mexico, the average number of ewes per ram may be 30 to 40 percent lower than these values. These rates depend upon season, temperature, sex drive, and body condition.
Rams six years and older that are in good physical condition may still be suitable for pasture or hand breeding. Rams vary in their sexual behavior. Some rams mate repeatedly with the same ewes, even though several other ewes in heat are present. Some rams prefer black-faced or white-faced ewes when both groups are in the same flock. Temperature has a pronounced effect on the ram's semen quality. Rams may be completely sterile or show lower fertility during late summer as a result of the heat.
Rams must be in good physical condition for successful reproduction. Malnutrition, internal parasites, or disease can cause sterility or depress the ram's desire to mate. Common diseases, such as those affecting the feet or any of the external breeding organs, can make it impossible for a ram to breed ewes. The formation and development of sperm requires six to seven weeks. Therefore, after recovery from sickness or heat stress, it takes six to seven weeks for a ram to produce sperm capable of fertilization.
An infertile ram in a one-sire flock can cause complete lambing failure. Also, a single dominant infertile ram in a large flock incorporating several rams can prevent fertile rams from mating and result in a lower lambing rate. It is important to fertility test rams, particularly in one-sire flocks.
Semen testing by qualified veterinarians is recommended to farm-flock producers, especially when only one or two rams are being used. If semen testing is not possible, the use of a marking harness can be beneficial. If several of the ewes return to heat, it may be necessary to substitute another ram.
Reproduction in sheep can be controlled by artificially inducing estrus, ovulation, and fertilization. The use of hormones is effective if management, genetic selection of breeds, and strains of breeds allow for out-of-season breeding. For accelerated lamb production or out-of-season breeding, use sheep that most normally fit the desired reproductive pattern. To further alter the reproductive process, regulate conditions such as light, temperature, nutrition, association with the ram, and other environmental factors that affect reproduction.
In general, three types of hormones are used alone or in combination to achieve these objectives. These are female sex hormones. They include those produced naturally as well as artificially. Progesterone is produced after ovulation by the corpus luteum, which forms on the ovary. Exogenous progestogens are used during the breeding season to synchronize estrus and ovulation. They also may be used during the anestrous period to help prepare the uterus for pregnancy and to sensitize the animal to be more responsive to hormones that cause estrus and ovulation.
They can be administered by ear implant, daily injection, daily feeding, or by insertion of an impregnated sponge pessary placed in the vagina.
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