For an experienced sheep farmer, there is no difficulty in keeping and breeding animals. For a beginner, pregnancy in sheep raises many questions. For the breeding of animals to be effective, it is important to know basic information about sheep estrous cycle, gestation and pregnancy.
Sheep Estrous Cycle
Most sheep breeds are seasonal polyestrous animals-they have several estrous cycles only during specific periods in a year. This is also characteristic of other polyestrous animals such as goats, cats, horses and deer. On average, the estrous cycle in sheep lasts for 17 days. In this period, the ewe (female adult sheep) exhibits active sexual behavior and allowing the ram to mount and mate with her. The ram detects the female in heat through pheromones that are released from the vagin.al discharge. The sheep is receptive to the ram only for 24-36 hours called heat period and if it is not pregnant, it will repeat the entire cycle. The ewe ovulates approximately 48 hours after the start of heat. Sheep usually reproduce when daylight hours decrease, hence, they are called short-day breeders. Other factors that influence the beginning of the estrous cycle in sheep are nutrition, breeds and the presence of males.
The estrous cycle is a set of hormonal, behavioral, anatomical and cytological events that repeat successively. It can also be defined as the time interval between two estrous. Estrus cycle in sheep is in four stages or phases: Proestrus, Estrus, Metestrus and Diestrus. Outside the reproductive season, ewes are said to be in anestrus.
- Proestrus: This is the period of preparation for oestrus. The corpus luteum returns and terminal growth of the follicles begin. Proestrus lasts for about 2 days.
- Estrus: This phase is the period in which the female is sexually receptive to the male, the clinical manifestations are less pronounced than in the cow or the mare. A ewe in heat can search for the ram but makes little effort to demonstrate its sexual desire, beyond allowing the ram to climb or mount her. The duration of estrus is about 24-36 hours, but it is shorter in sheep. The presence of the male or “intimacy” decreases the duration of estrus. Estrogens produced by rapidly growing follicles in the proestrus are responsible for the physical manifestations of estrus, such as stimulation of the vagin.al mucus, reddening of the vul.va and vagin.a, and thickening of the vagin.al epithelium. Ovulation generally occurs 14 hours after the peaking of the luteinizing hormone (24 hours after the start of heat).
- Metestrus: It is the period when the corpus luteum is formed and progesterone production begins. The metestrus lasts for 2 days.
- Diestrus: It is the period when the corpus luteum produces high levels of progesterone. If pregnancy occurs, the corpus luteum is maintained, thus preventing the next estrous cycle. If the pregnancy did not occur, the prostaglandin that is produced in the walls of the uterus causes regression or disappearance of the corpus luteum.
Signs of Heat in Sheep
Ewes that come into heat show some characteristic signs such as:
- The vul.va becomes swollen
- Clear, whitish or creamy discharge from the vul.va or vagin.a
- Frequent urination
- Frequent bleating
- Rapid movement of the tail to the sides. This movement is more precipitous when they are close to the ram
Sheep Gestation Period
How Long is a Sheep Pregnant?
The gestation period for sheep is 142 to 152 days counting from the first day of mating. Sheep have an average gestation period of 147 days. On average, old ewes carry pregnancy longer than young ewes. The gestation period also depends on the number of fetuses, breed, nutrition and environmental conditions. In order not to be confused with the date of lambing, it is highly recommended to keep records of the mating date and other information for each female. This prevents confusion and provides better care.
☛ Check This Out: Sheep Gestation Calculator and Chart
Signs of Pregnancy in Sheep
All sheep farmers need to know when a sheep is pregnant and what care should be provided. This will ensure the success of farming and will provide a good income. The signs of pregnancy in sheep are similar to the ones found in goats. These include:
- No reappearance of estrus or heat after 17 days of the last mating
- Changes in appetite or feeding pattern
- Behavioral changes being influenced by progesterone. The ewe becomes much calmer
- Swollen udder and abdomen
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Apart from the signs mentioned above, three methods could be adopted to confirm if a ewe is pregnant. They are Reflexological, Palpation and Probing methods.
- Reflexological method (using a ram): This method allows you to identify pregnancy in ewes with a high degree of accuracy. It involves allowing a ram into the pen where the ewes are. The ram quickly distinguishes pregnant ewes from those that are not-it actually shows interest in the non-pregnant ewe. For a beginner, this method may seem a bit complicated, but experts can easily understand the behavior of the animals.
- Palpation method: This method allows you to detect an increase in the size of the uterus and the presence of a fetus in it. Apply this technique only after 3 months of pregnancy. Ensure that the animal is not fed 12 hours before palpating it. For an accurate result, it is necessary to stand behind the female and on both sides of the abdomen. This allows for a smooth feel of the walls of the peritoneum of the ewe to be palpated. If the ewe is pregnant, the solid parts of the fetus will be felt, and the right side of the abdomen will become much larger than the left.
- Probing method: The determination of pregnancy in a sheep using this method is possible only from the 75th day of gestation. The finger is inserted into the rectu.m of the animal and the uterine arteries are probed. If there is vibration in them, it indicates the development of the fetus in the uterus. Before probing the sheep, contact a veterinarian. Only a specialist can detect uterine arteries and feel the vibration.
Lambing is the process of giving birth to lambs in sheep. Sheep lambing is not difficult, and ewes often deliver their lambs without being assisted. Complications during lambing are uncommon, but a pregnant sheep needs to be cared for and should be attended to when the lamb is coming out.
Signs of Labor in Sheep
When lambing is imminent, the following labor signs are seen:
- The udder becomes fuller and bigger. This occurs in 2-3 days before lambing
- Sheep begins to get anxious and milk is released from the nipples
- Sagging belly
- Loss of appetite
- Separation from the flock
- The genital organs of the sheep become swollen
- Immediately before the lambing, the sheep begins to dig a straw litter
Stages of Labor in Sheep
Lambing usually does not exceed one hour, though the duration depends on the number of lambs to be born. The interval between the birth of each lamb is 10 to 15 minutes. If the time interval is exceeded, then the ewe might be facing some complications. Hence, the ewe may need external assistance.
The stages of labor or lambing in sheep are described as follows.
- Preparation phase: In the preparation phase, the sheep gets a stuffed udder and the vul.va swells and turns redder than usual. The sheep will dig the ground with its hoofs in other to clear the space. This period lasts for about half an hour.
- Expulsion phase: This phase is characterized by the expulsion of the fetus(es). The water bag ruptures with the fluid gushing out. The amniotic sac appears at the vul.va and frequently ruptures. The reflex and voluntary contractions of the abdominal muscle and diaphragm leads to the expulsion of the fetus(es). When the lamb is out, the umbilical cord breaks off by itself. If a second lamb is on the way, it will follow after about 10 minutes.
- Afterbirth Phase: This phase should be completed within 2 hours. It involves the expulsion of all fetal membranes, majorly the afterbirth or placenta. If the afterbirth remains in the ewe or it takes longer than 2 hours, the vet must be called in.
Number of Lambs
The number of lambs that sheep can give birth to is different and depends on the breed of animals. It ranges from one to five. According to veterinarians and sheep breeders, it is optimal when a sheep gives birth to two lambs. They have good weight, gain it quickly, and are actively developing. If more than two lambs are born, the breeder has problems raising them. Typically, such offspring are characterized by low weight, weakness, and slowly gain weight.