Artificial Rearing of Lambs

Orphan lambs can be successfully raised on milk replacer, goat’s milk, and, occasionally, cow’s milk. However, cow’s milk contains less fat than ewe’s milk. Milk goats can raise several orphan lambs each. Commercial milk replacers are available for lambs. These contain 30 to 32 percent fat, 22 to 24 percent crude protein, and 22 to 25 percent lactose. Do not use calf milk replacer on lambs.

If only a few lambs are to be raised on milk replacer, they can be bottle fed, if labor is available. However, they must be fed every four hours during the first week and then every six to eight hours until they are weaned.

With newly developed systems, it is possible to feed several lambs at the same time. A milk dispensing system provides milk free-choice. In this situation, mix a new batch of milk replacer each day. Generally, milk-feeding systems use the lam-bar nipple (a rubber teat connected to a polyethylene tube). The teats are connected through a hole in a metal plate inside the lamb pen panel with tubes leading to a bucket of milk outside the pen. As the lambs stop nursing, there is no leakage from the nipple because the milk returns to the bucket by gravity flow.

Research shows that feeding cold milk is much more beneficial than feeding warm milk when the lambs are on a self-feeding system. The cold milk is not as likely to spoil and lambs do not overeat, so they have fewer digestive disorders. Keep the milk cold by placing plastic jugs full of ice in the feeding unit.

Offer creep feed to the lambs soon after they have started on liquid milk replacer. Soybean meal is an excellent feedstuff to include in creep feed for very young lambs. The starter creep should contain 17 to 20 percent protein. Ordinarily, lambs are weaned from the milk replacer in four to six weeks.

There are several methods of grafting lambs, such as using special sprays to make the ewe accept the lamb. The most successful method is as follows: locate a ewe in the process of lambing a single lamb. After her lamb is delivered, check to be sure that she is not going to have another lamb. Do not let her get up until the lamb to be grafted has been brought over and thoroughly saturated in the placental fluids the ewe has just excreted. Then rub the lamb that is being grafted together with the newborn lamb. Tie the legs of the newborn to the lamb that is being grafted. Then allow the ewe to get up and lick the lambs. If the grafted lamb is thoroughly saturated and rubbed together with the newborn lamb, the ewe usually cleans both lambs and readily accepts both.

Then place the ewe and the two lambs in a lambing pen, keeping the lambs tied together until she has thoroughly cleaned both lambs. The lambs can then be untied and allowed to nurse. It may be necessary to restrict the older grafted lamb from nursing too much until the newborn lamb has had a chance to receive its share of the colostrum.

Occasionally, ewes refuse to claim their lambs. This is more common with ewes lambing for the first time. If ewes tend to do this year after year, they should be culled. There is not a best method of getting a ewe to claim her offspring. However, one method is to put the ewe in a stanchion and tie the ewe with a halter until she allows the lamb to nurse.

Tail-Docking and Castration

Lambs should be tail-docked and castrated at about 7 to 10 days of age. There is less bleeding and lambs heal more quickly when these operations are done at an early age. Elastrator rings may be used, but they are painful and there is a greater likelihood of tetanus. A pocket knife, emasculator, or burdizzo is very effective.

Cut off tails about 1 inch from the body. A good place is at the end of the caudal folds on the underside of the tail. Push the skin on the tail toward the body before cutting to allow enough loose skin to cover the end of the stub. If tetanus is a problem, vaccinate the lambs for this disease. (Your county Extension agent has more detailed instructions for these operations.)

Shed lambing. Shed lambing requires adequate space to house lambing pens for at least 10 percent of the ewe flock. Lambing pens are usually 4 x 4 foot or 4 x 5 foot enclosures (jugs or jails). Large breeds may need 5 x 5 foot pens. Very often, machinery sheds or other existing buildings on the farm can be used during the lambing season.

Lambing pens should be in a draft-free area of the shed or barn. Prior to lambing, thoroughly prepare the lambing area. Clean the area, erect lambing pens, install necessary heat lamps, and obtain medication.

Gestation typically ranges from 147 or 152 days. However, some ewes may lamb a week early, so it pays to be ready.

Pasture lambing. Compared with shed lambing, feed costs are generally lower for pasture lambing. However, it is usually not possible to save as many lambs because it is impossible to observe all the ewes closely and frequently. However, even when lambing in the pasture, ewes not claiming their lambs or ewes that have extremely weak lambs should be placed in lambing pens. It is usually not advisable to lamb yearling ewes on pasture unattended. However, in New Mexico this is often the only practical method. When yearling ewes are lambing on pasture, graze them in a pasture where they can be observed relatively frequently, such as a trap close to the house or corrals.

Management at Lambing Time

Lambing time is probably the most critical period in the year. The higher the percentage of lambs kept alive, the higher gross and net return. Observe ewes closely during the lambing period. Many producers check their ewes frequently during the night as well as during the day. Give the ewe assistance if she is unable to deliver naturally. It is always best if the ewe is allowed to have her lamb naturally. Occasionally, pulling a lamb makes a ewe reluctant to claim the lamb.

If the ewe is having difficulty lambing, wash your hands thoroughly with soap and water and apply some lubricant before examining the ewe via the vagina. Lambing difficulties can result from the lambs being too large, the ewe having a small pelvic area, or both. Quite often, however, lambs are in an abnormal position. The normal position is with the head between and slightly above the front feet. If the lamb is coming forward with one or both legs turned back, or the head is turned back, first straighten the legs and neck. It is preferable to have both legs straight, but many lambs can be delivered with the head and one leg forward.

If the back legs are presented first, the delivery should be made in this position as rapidly as possible. Remove membranes and mucous from the lamb’s face and mouth immediately after delivery, and lift the lamb by its hind legs to clear mucous from the nose. Applying gentle pressure to the rib cage can stimulate breathing. Blowing into the lamb’s mouth may also be effective. As soon as the lamb is breathing properly, allow the ewe to lick the lamb clean. Then treat the navel with a 7 percent iodine solution; strip each teat on the ewe to remove the plug and to be sure that the ewe has colostrum available.

If it is extremely cold, a heat lamp over the lambing pen may be beneficial. Only use heat lamps long enough to dry the lamb. Prolonged use of heat lamps tends to increase a lamb’s susceptibility to pneumonia.

The first few hours of a lamb’s life are the most critical. If the lamb does not nurse shortly after birth, it will weaken rapidly. The lamb should only receive assistance to nurse if it is necessary. Best results are obtained if the lamb is allowed to nurse naturally, without assistance. Occasionally, very weak lambs may need supplemental colostrum. Colostrum must be available to provide energy, protein, minerals, vitamins, and essential antibodies that provide the lamb with vital resistance to disease. Very weak lambs may be fed with a stomach tube. Weak lambs may also be revived with a subcutaneous injection of 25 to 50 mL of a 5 percent dextrose solution.

It is essential to know that the lamb consumes colostrum soon after birth. Starvation is the major cause of death in very young lambs. Therefore, keep the ewe and lamb or lambs in a lambing pen until the lambs are strong and healthy and no problem is observed with the ewe. Often, a ewe with a single lamb can be removed from the lambing pen in 24 hours; ewes with twins usually can be removed after two days. The ewe and her lamb should be identified with corresponding numbers if possible. Overall flock production efficiency will also be enhanced if ewes with single lambs are separated from ewes with twin lambs, and fed accordingly. Ewes nursing a single lamb should receive approximately 1 to 1.25 pounds of grain concentrate daily, while ewes nursing twin lambs should receive 1.50 pounds or more of grain concentrate daily.

If the lamb does not consume all the milk produced daily, the ewe produces less milk and uses any excess energy to store fat.

Ewes suckling twin lambs normally do not deposit fat because the nutrient supply (primarily energy) does not meet the requirements of the lactating ewe. For maximum rate and efficiency of lamb gains, separate ewes nursing twin lambs from those nursing singles and feed accordingly. It is practically impossible to provide high–producing ewes nursing twin lambs enough feed during lactation to prevent loss of body weight. From a practical standpoint, these ewes must have reserves of body fat to maintain high levels of milk production. It is imperative that high–producing ewes are of acceptable body condition prior to lambing.

Daily nutrient requirements of sheep

Ram Management

It is important not to turn new rams in with the ewes as soon as they are brought to the premises. Separate the rams from the ewes for at least two weeks, treat for external parasites, and observe them carefully for contagious diseases before allowing them to breed any of the ewes.

The rams should be strong and in good condition at breeding time. If a ram is thin, or if he appears to be losing weight during the breeding season, it may be necessary to feed him separately from the ewes. Ordinarily, 1 to 1.5 pounds of oats or a grain concentrate mixture with good quality hay is sufficient. Ram lambs may need more concentrate. Also, shear rams about a month before the breeding season.

The last six weeks of gestation is the most critical period in ewe nutrition. Approximately 70 percent of the fetal growth occurs at this time. Nutrient restrictions during this period may result in lighter lambs at birth, increased postnatal lamb losses, lower levels of milk production, and possibly pregnancy disease (ketosis). In late pregnancy, ewes require approximately 50 percent more feed than they do earlier in gestation. If protein is limited during late gestation, lower birth rates and lighter ewe fleece weights can be expected. Very often inadequate phosphorus intake occurs during this period, especially with ewes on pasture or with ewes consuming hay.

Ewes in late pregnancy sometimes have difficulty consuming enough feed because of the space occupied by the fetus, particularly when they have twins or triplets. If the ewe is fed a high-roughage ration, she may not be able to consume enough to supply the necessary daily energy requirements. For ewes in late pregnancy consuming high roughage rations, it is generally advisable to feed supplemental grain.

Maintenance of the ewe is generally thought of in terms of her nutritional requirements when dry, because at that time her requirements are the lowest of the year. However, wool production is a continuous process that must be considered as part of the nutrient requirements throughout the year.

The energy requirements are a function of the animal’s basic metabolic rate. However, several factors affect maintenance requirements.

Age. Yearlings tend to have about a 20 percent higher energy requirement than adult sheep.This is probably due to the yearling’s additional requirements to support growth. This is of particular importance to producers who breed ewes to lamb first at 12 to 18 months of age.

Exercise. Grazing sheep may use from 10 to 100 percent more energy than do sheep in drylot conditions. However, the magnitude of increase depends on the distance sheep must travel to feed and water, and on the topography of the range.

Climate. Temperature, wind velocity, and humidity can jointly affect energy requirements. The length and density of the fleece also affects energy requirements. Wool plays an important role in protecting sheep from both heat and cold. The insulating properties of wool help to cool the sheep in the heat of summer and keep body temperatures warmer in winter. Without wool, a sheep’s energy requirements would be higher.

Body Condition. It takes more feed to maintain a fat sheep at a constant weight than it does a thin sheep. Keeping the sheep excessively fat is not only expensive because of the feed, but also it is detrimental to the ewe’s reproductive capabilities and overall production efficiency. A ewe should lose 5 to 7 percent of her body weight during lactation and recover this weight loss during the dry period. Additionally, the ewe should gain body weight during gestation in proportion to the weight of the fetus and accompanying fluids.

In most sheep production situations, it is most economical to increase body condition of the ewes during the nonlactation period and “milk it off” in lactation, especially when low-cost pasture is available from early to mid-gestation.

Reproduction Requirements. Reproductive efficiency depends largely upon proper nutrition before and during the breeding season. Large-bodied ewes tend to produce more lambs per ewe. Do not confuse ewes of large size and scale with ewes that look large because they are fat. Usually, excessively fat ewes have lower conception rates and higher embryonic mortality. Furthermore, extremely poor body condition is not conducive to efficient fertility and reproductive performance. Ewes that have not had a properly balanced diet, including adequate phosphorus and vitamin A, may have a poor lamb crop percentage.

Flushing. Flushing can improve the ewe’s body condition just before and during the breeding season. Generally, the practice is thought to increase ovulation rate. Flushing has more effect early in the breeding season. It is also beneficial late in the season, as it tends to increase the opportunity for all ewes to become pregnant. Flushing may be achieved by moving the ewes to a better pasture shortly before breeding. The provision of a supplemental energy source (that is, 3/4 to 1 pound of whole corn per head per day) and(or) the introduction of ewes to fresh pasture also can enhance the potential for ewes to respond to flushing. The length of the flushing period can vary, but it probably should begin 21 days before the breeding season and continue through one estrous cycle (17 days) into the breeding season if possible.

An accelerated lambing program necessitates that lambs be weaned early. The recommended hormone treatment is the same as for estrous synchronization in that progesterone should be administered for 10 to 12 days and followed immediately with an injection of 500 to 750 international units of gonadotropin, and again 16 days later. If the ewes are in an anestrous period, it is sometimes helpful to administer 2 milligrams of estradiol two days before the start of progesterone treatment.

Producers who lamb outside the natural season can expect some loss in reproductive efficiency. Only outstanding managers and those who can afford to experiment should try accelerated lambing.

Hormones, along with practical selection and management practices, are useful to:

• Synchronize estrus during the breeding season.
• Increase the ovulation rate and incidence of multiple births.
• Induce fertile mating during anestrus.
• Induce early puberty.

In general, three types of hormones are used alone or in combination to achieve these objectives.

Progestogens. 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.

During the normal breeding season, progestogens can be used to synchronize estrus when used for a 10- to 12-day period. Estrus and ovulation usually occur between the second and fifth day following the end of treatment. However, fertility is usually suboptimal on the first cycle after progestogens are administered. Higher fertility is obtained from breeding at the second estrus. When ewes have been synchronized, they generally remain well synchronized through at least the first three post-treatment estrous periods.

Estrogens. Estrogens also are female sex hormones. They are produced naturally by the ovary or they can be produced synthetically. The estrogen concentration in the blood is highest just before and during estrus. The follicles on the ovary from which eggs are developed and released are the main source of estrogens in the female. The estrogen level, therefore, drops rapidly near the end of estrus, when ovulation occurs. Estrogens are responsible for behavioral estrus (or heat). In combination with progesterone, they sensitize the animal to respond to ovulating hormones. They also influence uterine development and the preparation of the uterus for pregnancy.

Gonadotropins. Gonadotropins are hormones that cause ovulation. They are produced by the pituitary gland as well as by certain other tissues. The gonadotropin that is used most successfully in controlling reproduction in sheep is follicle stimulating hormone. Additionally, human chorionic gonadotropin (HCG) has been used to induce ovulation.

Synchronizing Estrus

Some farm-flock producers find it advantageous to plan their breeding season so that all ewes lamb at approximately the same time. This can be largely achieved by treating ewes with progesterone for 10 to 12 days to synchronize estrus. When the progesterone is removed, the ewes exhibit estrus and can be bred at this time. However, for the largest lamb crop, breed the ewes following the second estrus after progesterone treatment. An injection of gonadotropin can contribute to multiple ovulation. Therefore, pregnant mare serum gonadotropin (PMSG) can be given as the progesterone treatment is terminated, and again 16 to 18 days later.

Flushing ewes is most effective when they are mated early in the breeding season. Since ovulation rate is near a maximum during the middle of the season, flushing at this time is not as beneficial. The results of flushing are quite variable. Sometimes, when farm flock ewes are already on a high nutrition level before the breeding season, flushing may not affect ovulation or lambing percentage.

Nutrition affects total lifetime productivity of sheep by influencing mature size. Well-developed ewes consistently have higher lamb crop percentages than smaller ewes. Fat ewes, however, are typically less fertile, do not respond to flushing, and may experience more embryonic death loss.

Ewes grazed on legume pastures, such as alfalfa and clover, may at times be less fertile. Under some conditions, the estrogen content of these legumes is related to reproductive disorders. Breeding dates may be delayed and conception rate reduced when ewes are on pastures that have a high estrogen content. However, the estrogen content of legumes declines during the later stages of maturity.

Effect of Lambing and Lactation

Both lambing and lactation suppress estrous cyclicity in ewes. Generally, the postpartum anestrous phase lasts through lactation, even though the uterus typically returns to normal two to three weeks after lambing. Most ewes that lamb in late winter or spring do not exhibit estrus until the following breeding season. However, ewes that lamb in the fall usually exhibit a fertile heat four to eight weeks after lambing, or approximately two weeks after weaning.

Effect of Ram

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. If the temperature exceeds 90°F for an extended period, especially if the humidity is high, fertility of most rams is reduced. 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.

High temperatures are detrimental to fertility, embryo survival, and fetal development. This is the biggest objection to fall lamb production. High temperatures at breeding can reduce conception rate. Heat stress during gestation impairs fetal development and can cause lambs to be significantly smaller at birth.

Psychological Stimulation

The introduction of a ram near the end of the anestrous period appears to psychologically stimulate ewes. It brings about earlier ovulation and estrual activity. The ram can be either fertile or surgically sterilized. Rams should be kept with the ewes for about 10 to 14 days and removed from the flock before breeding begins. Then, at the beginning of the breeding season, rested fertile rams that are intended to sire the lamb crop can be introduced. The stimulation does not occur when rams are placed with ewes earlier, or when rams are simply left with the ewes continuously.