Detailed Explanation of Key Technical Points for Feeding and Management of Pregnant Sows
The process from mating and conception to farrowing is called gestation, which is the longest stage in the reproductive production of pregnant sows. The basic task of raising and managing pregnant sows well is to ensure fertilization, allow embryos and fetuses to fully grow and develop in the mother's body, prevent embryonic resorption, miscarriage, and stillbirth, and enable pregnant sows to produce large litters of piglets with good birth weight, robust constitution, and uniform size; reasonably supply full-price nutritional feed, reduce the impact of stress, ensure that sows have moderate body condition during gestation, and lay a good foundation for lactation during the nursing period. For first-litter sows, normal growth and development must also be ensured.
Metabolic Characteristics and Body Weight Changes of Pregnant Sows
The growth and development of fetuses, the development of the uterus and other organs, increase the sow's appetite and enhance feed digestibility and utilization, so feeding should meet this requirement as much as possible; however, pregnant sows should not gain as much weight as possible but should be controlled to a certain extent. Generally, lean-type first-litter sows gain 35-45 kg, and multiparous sows gain 32-40 kg.
Growth and Development of Embryos and Fetuses During Gestation
The growth and development characteristics of embryos are that organs form in the early stage and body weight increases in the later stage. Organs are formed at around 21 d. More than 60% of fetal body weight is gained after 90 d of gestation. The protein, fat, and water content of embryos increase, especially mineral content, which increases relatively quickly. From the fertilized egg to fetal maturity, embryonic growth and development go through 3 key periods.
1. The first key period, the first 30 d, is the period when the fertilized egg moves from the fertilization site, implants in different parts of the uterine horn, and gradually forms the placenta. Before the placenta is formed, it is very easily affected by environmental conditions. Incomplete feed nutrition, moldy feed, various mechanical stimuli, and high-fever diseases can all affect embryonic growth and development or cause early embryonic death. During this period, embryonic development and sow weight gain are relatively slow, and there is no need to additionally increase the amount of daily ration.
2. The second key period, 60-70 d, is when fetuses develop relatively quickly and crowd each other, which can easily cause uneven nutrient supply to fetuses located in the middle part of the uterine horn. This causes fetal death or poor development. Rough handling of sows, loud shouting, whipping, chasing, and sows crowding and biting each other will all affect uterine blood circulation. Increase fetal mortality.
3. The third key period, after 90 d, is when fetal growth and weight gain are particularly rapid. The sow's metabolic anabolic capacity is strong, body weight increases very quickly, and the required nutrients increase significantly. Fetal volume increases, the uterus expands, digestive organs are compressed, and digestive function is affected. Reduce the amount of green fodder fed. Increase concentrate feed, especially cake-type feed with more protein, to meet the needs of the sow's body weight and the rapid growth and development of fetuses.
Feeding of Pregnant Sows
1. Nutritional Requirements of Pregnant Sows
As the number of gestation days increases, the nutritional requirements of pregnant sows increase, especially in the more than 20 days before farrowing, when the requirement is greatest, among which the requirements for protein, calcium, and phosphorus are greatest; therefore, in the feeding of pregnant sows, the gestation period is generally divided into two stages. The first 80-90 days are called early gestation, and the last 20-30 days are called late gestation, so that different feeding can be applied, ensuring both maternal health and full fetal development.
(1) Nutritional requirements in early gestation. In early gestation, embryonic development is slow and nutrient requirements are not high. Feeding too much concentrate can easily cause early embryonic death. Therefore, the feeding standard for open sows is generally adopted.
(2) Nutritional requirements in late gestation. In late gestation, especially the last 30 d, fetal growth accelerates, and the mother's nutritional reserves find it difficult to meet fetal demands, so the feed nutrition level should be increased. This is greatly beneficial for fetal development, improving piglet quality, increasing the storage of nutrients in the mother's body, and meeting postpartum lactation needs. In late gestation, the volume of the maternal uterus and its contents increases, increasing abdominal pressure. In order to avoid pressure on the uterus due to feed intake while also increasing nutritional intake, the proportion of concentrate should be increased, feed volume reduced, or smaller and more frequent meals used to prevent overeating, indigestion, or constipation in sows. Feed each sow 2.5-2.8 kg per day of mixed feed at the above nutritional level.
2. Feeding Methods for Pregnant Sows
During the feeding process, because sows differ in age, development, and body condition, there are many different feeding methods. However, no matter which feeding method is adopted, feed must be given according to body condition. Pregnant sows should have moderate body condition. Multiparous sows should reach 70-80% body condition before farrowing. First-litter sows should have 80% body condition. Determine the feeding amount according to the sow's body condition and physiological characteristics.
(1) The "grasp both ends and bring along the middle" feeding method is suitable for multiparous sows with poor body condition after weaning and sows with a long lactation period. In rural areas, because the feed nutrition level is low and local-breed sows have good lactation performance and nurse many piglets, the sow's body condition is poor, so this method is chosen. Throughout gestation, a "high-low-high" nutritional level is formed.
(2) The "step-by-step increase" feeding method is suitable for first-mating sows. At mating, sows are still growing and developing, and their nutritional requirements are relatively high, so the nutritional level throughout gestation should gradually increase, reaching a peak one month before farrowing. The approaches include increasing feed nutrient concentration and increasing feeding amount, mainly focusing on increasing protein and minerals.
(3) The "rough first, fine later" method, that is, the low-first, high-later method; this method is suitable for multiparous sows with better body condition before mating, usually early-weaned sows with a better nutritional level.
(4) The "consistent" feeding method. Taking advantage of the physiological characteristics of enhanced anabolic capacity and improved nutrient utilization during gestation, while maintaining comprehensive feed nutrition, adopt a "consistent" feeding method throughout the whole process. It is worth noting that when preparing feed, feed nutrition must be well adjusted, neither too high nor too low.
3. Issues That Should Be Mainly Considered in Feeding Pregnant Sows
The feed for pregnant sows must be guaranteed in quality. Any moldy, spoiled, frozen, toxic, or strongly irritating feed (such as distillers' grains and cottonseed cake) must not be used to feed pregnant sows, otherwise miscarriage is easily caused; feeding time and frequency should be regular, that is, fixed time and fixed amount, preferably 2-3 times per day; feed should not be frequently unchanged or suddenly changed, otherwise it easily causes digestive dysfunction; the daily ration must be comprehensive, diversified, and palatable. After 3 months of gestation, the supply of green and coarse feed should be restricted, otherwise it easily presses on the fetus and causes miscarriage.
Management of Pregnant Sows
The central task of management during gestation is: do a good job in protecting the fetus, create a favorable environment, promote normal fetal development, and prevent mechanical miscarriage, especially in late gestation. Keepers should strengthen management.
1. Individual pen housing: pens are 60-70 cm wide and 2.1 m long; ensure that each pig eats evenly and there is no mutual collision. Generally, large-scale pig farms adopt this method.
2. Environmental sanitation: keep the pig house clean and sanitary, promptly clean manure and urine, and disinfect regularly; ensure the floor is dry and reduce humidity in the pen as much as possible; provide a quiet and comfortable living environment and reduce various noises as much as possible. Do a good job in cold and heat protection.
3. Appropriate exercise: for pregnant sows, appropriate exercise helps strengthen the physique, promote blood circulation, accelerate fetal development, and can also avoid dystocia. It should be noted that exercise should be stopped one week before farrowing to prevent sows from giving birth in the exercise yard; in the first month of gestation, in order to restore physical strength and body condition, exercise should be reduced.
4. Ensure feed hygiene: do not feed moldy or toxic feed. It is worth noting that if pig troughs are not cleaned or disinfected regularly and leftover feed is not removed, the feed in the trough is most likely to become moldy, and new feed will also be contaminated. Doing this for a long time is quite harmful to pig health and can easily cause miscarriage.
5. Patient and meticulous management: strengthen inspection and observe whether the sow's appetite, drinking, defecation, urination, and mental state are normal.
6. Do a good job in immunization.
Handling of Common Problems in Pregnant Sows
1. Gestational estrus (false estrus): gestational estrus means that after conception, the sow still shows slight estrous behavior within 1-2 d before or after the next expected estrus. This false estrus differs from true estrus in that the external symptoms of estrus are not obvious, generally only slight swelling of the vulva; the sow is slightly restless, but appetite does not decrease, and the response to boars is not obvious, generally refusing mating. The cause may be an imbalance in the secretion ratio of reproductive hormones, that is, insufficient progesterone secreted by the corpus luteum on the ovary and excessive estrogen secreted by the placenta. Or the nutritional status of the sow in early gestation is very poor.
[Preventive measures] Improve the nutritional status of sows before mating and in early gestation, prevent and promptly treat diseases of the sow's reproductive organs, and do a good job in cold protection and warmth preservation.
2. False pregnancy: after mating, the pig is not actually pregnant, but the abdominal circumference grows larger day by day, and the udder also develops and enlarges, until around the "expected farrowing period,"
sometimes milk can even be squeezed from the udder, but in the end no piglets are born, and the abdominal circumference and udder slowly shrink back. This phenomenon is false pregnancy. Its occurrence is due to early embryonic death and absorption, but the corpus luteum of pregnancy continues to exist and plays a role in secreting progesterone. This phenomenon is caused by endocrine dysfunction due to malnutrition, variable climate, and reproductive organ diseases.
[Preventive measures] Improve the nutritional conditions of sows before and after gestation, prevent and treat diseases of the sow's reproductive organs, feed more green and juicy feed before and after mating, or add an appropriate amount of vitamins to the ration to ensure normal development and ovulation of ovarian follicles.
3. Embryonic resorption, stillbirth, and miscarriage in sows: after early embryonic death during gestation, embryos absorbed by the uterus are called embryonic resorption (latent miscarriage). When it occurs in mid-to-late gestation, the fetus dies but is not expelled, and the water in its tissues and fetal fluids are absorbed by the mother, turning brown, like a mummy, which is called mummification; if the fetus dies shortly before farrowing and is delivered together with live piglets without changes, it is called stillbirth. Miscarriage refers to the interruption of pregnancy caused by disorder in the physiological processes of the fetus or mother, or damage to the normal relationship between them.
The causes of embryonic resorption, stillbirth, and miscarriage are quite complex and can be summarized in several aspects:
(1) Improper mating time, when sperm and eggs have already aged. Although fertilization can occur, the fertilized egg has low vitality and is prone to early death and absorption by the mother, forming embryonic resorption.
(2) Inbreeding leads to an increase in the number of stillbirths, and can also produce monster fetuses and deformed fetuses.
(3) The daily ration of pregnant sows is not comprehensive in nutrition, especially lacking high-quality protein, minerals (calcium, phosphorus), and vitamins A, E, and B group, etc., causing embryonic death.
(4) Feeding pregnant sows moldy, spoiled, toxic, or strongly irritating feed, or frozen feed, resulting in poisoning and miscarriage.
(5) Sows fed too fat or with long-term constipation are prone to stillbirth.
(6) Feeding pigs too full in late gestation, with gastrointestinal contents pressing on the fetus, can also cause premature birth, dystocia, or stillbirth.
(7) Improper management of pregnant sows, such as whipping, startling, chasing too urgently, making sows cross ditches, slip and fall, bite each other, or crowd each other when entering and leaving narrow pigpen doors, etc.
(8) In hot summer, if heat prevention and cooling work in the pig house is not done well and the temperature inside the house exceeds 32°C, the number of embryonic deaths increases.
(9) Gilts mated too early, fetuses too large, and pelvis too narrow, causing piglets to die from suffocation during farrowing.
(10) Improper clinical medication, such as laxatives, deworming drugs, dexamethasone, oxytocin, etc.
(11) Poor pig house sanitation and lax disinfection cause infection of the sow's birth canal, and disease causes embryonic death. Such diseases mainly include swine fever, parvovirus disease, Japanese encephalitis, pseudorabies, leptospirosis, toxoplasmosis, Brucella, mold, porcine reproductive and respiratory syndrome, and high-fever disease.
[Preventive measures] Carry out strict management according to the feeding and management measures for sows at each stage, and overcome the causes of the above diseases at each stage of feeding and management. For pregnant sows that show reduced feeding or no eating, abnormal behavior, red and swollen vulva with mucus discharge, and frequent straining, and may miscarry, promptly inject 10-30 mg of progesterone and administer a sedative orally to protect the fetus. For sows that have reached the expected farrowing date and show signs of farrowing, with swollen udders and milk secretion, and for which miscarriage is unavoidable or stillbirths have become mummified and remain in the uterus, artificial abortion may be adopted. The method is to first inject 4 mg of estradiol, and 6-8 h later intramuscularly inject 3-6 mg of oxytocin, or 200 mg of dexamethasone.